Source file src/cmd/go/internal/modload/load.go

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package modload
     6  
     7  // This file contains the module-mode package loader, as well as some accessory
     8  // functions pertaining to the package import graph.
     9  //
    10  // There are two exported entry points into package loading — LoadPackages and
    11  // ImportFromFiles — both implemented in terms of loadFromRoots, which itself
    12  // manipulates an instance of the loader struct.
    13  //
    14  // Although most of the loading state is maintained in the loader struct,
    15  // one key piece - the build list - is a global, so that it can be modified
    16  // separate from the loading operation, such as during "go get"
    17  // upgrades/downgrades or in "go mod" operations.
    18  // TODO(#40775): It might be nice to make the loader take and return
    19  // a buildList rather than hard-coding use of the global.
    20  //
    21  // Loading is an iterative process. On each iteration, we try to load the
    22  // requested packages and their transitive imports, then try to resolve modules
    23  // for any imported packages that are still missing.
    24  //
    25  // The first step of each iteration identifies a set of “root” packages.
    26  // Normally the root packages are exactly those matching the named pattern
    27  // arguments. However, for the "all" meta-pattern, the final set of packages is
    28  // computed from the package import graph, and therefore cannot be an initial
    29  // input to loading that graph. Instead, the root packages for the "all" pattern
    30  // are those contained in the main module, and allPatternIsRoot parameter to the
    31  // loader instructs it to dynamically expand those roots to the full "all"
    32  // pattern as loading progresses.
    33  //
    34  // The pkgInAll flag on each loadPkg instance tracks whether that
    35  // package is known to match the "all" meta-pattern.
    36  // A package matches the "all" pattern if:
    37  // 	- it is in the main module, or
    38  // 	- it is imported by any test in the main module, or
    39  // 	- it is imported by a tool of the main module, or
    40  // 	- it is imported by another package in "all", or
    41  // 	- the main module specifies a go version ≤ 1.15, and the package is imported
    42  // 	  by a *test of* another package in "all".
    43  //
    44  // When graph pruning is in effect, we want to spot-check the graph-pruning
    45  // invariants — which depend on which packages are known to be in "all" — even
    46  // when we are only loading individual packages, so we set the pkgInAll flag
    47  // regardless of the whether the "all" pattern is a root.
    48  // (This is necessary to maintain the “import invariant” described in
    49  // https://golang.org/design/36460-lazy-module-loading.)
    50  //
    51  // Because "go mod vendor" prunes out the tests of vendored packages, the
    52  // behavior of the "all" pattern with -mod=vendor in Go 1.11–1.15 is the same
    53  // as the "all" pattern (regardless of the -mod flag) in 1.16+.
    54  // The loader uses the GoVersion parameter to determine whether the "all"
    55  // pattern should close over tests (as in Go 1.11–1.15) or stop at only those
    56  // packages transitively imported by the packages and tests in the main module
    57  // ("all" in Go 1.16+ and "go mod vendor" in Go 1.11+).
    58  //
    59  // Note that it is possible for a loaded package NOT to be in "all" even when we
    60  // are loading the "all" pattern. For example, packages that are transitive
    61  // dependencies of other roots named on the command line must be loaded, but are
    62  // not in "all". (The mod_notall test illustrates this behavior.)
    63  // Similarly, if the LoadTests flag is set but the "all" pattern does not close
    64  // over test dependencies, then when we load the test of a package that is in
    65  // "all" but outside the main module, the dependencies of that test will not
    66  // necessarily themselves be in "all". (That configuration does not arise in Go
    67  // 1.11–1.15, but it will be possible in Go 1.16+.)
    68  //
    69  // Loading proceeds from the roots, using a parallel work-queue with a limit on
    70  // the amount of active work (to avoid saturating disks, CPU cores, and/or
    71  // network connections). Each package is added to the queue the first time it is
    72  // imported by another package. When we have finished identifying the imports of
    73  // a package, we add the test for that package if it is needed. A test may be
    74  // needed if:
    75  // 	- the package matches a root pattern and tests of the roots were requested, or
    76  // 	- the package is in the main module and the "all" pattern is requested
    77  // 	  (because the "all" pattern includes the dependencies of tests in the main
    78  // 	  module), or
    79  // 	- the package is in "all" and the definition of "all" we are using includes
    80  // 	  dependencies of tests (as is the case in Go ≤1.15).
    81  //
    82  // After all available packages have been loaded, we examine the results to
    83  // identify any requested or imported packages that are still missing, and if
    84  // so, which modules we could add to the module graph in order to make the
    85  // missing packages available. We add those to the module graph and iterate,
    86  // until either all packages resolve successfully or we cannot identify any
    87  // module that would resolve any remaining missing package.
    88  //
    89  // If the main module is “tidy” (that is, if "go mod tidy" is a no-op for it)
    90  // and all requested packages are in "all", then loading completes in a single
    91  // iteration.
    92  // TODO(bcmills): We should also be able to load in a single iteration if the
    93  // requested packages all come from modules that are themselves tidy, regardless
    94  // of whether those packages are in "all". Today, that requires two iterations
    95  // if those packages are not found in existing dependencies of the main module.
    96  
    97  import (
    98  	"context"
    99  	"errors"
   100  	"fmt"
   101  	"go/build"
   102  	"internal/diff"
   103  	"io/fs"
   104  	"maps"
   105  	"os"
   106  	pathpkg "path"
   107  	"path/filepath"
   108  	"runtime"
   109  	"slices"
   110  	"sort"
   111  	"strings"
   112  	"sync"
   113  	"sync/atomic"
   114  
   115  	"cmd/go/internal/base"
   116  	"cmd/go/internal/cfg"
   117  	"cmd/go/internal/fips140"
   118  	"cmd/go/internal/fsys"
   119  	"cmd/go/internal/gover"
   120  	"cmd/go/internal/imports"
   121  	"cmd/go/internal/modfetch"
   122  	"cmd/go/internal/modindex"
   123  	"cmd/go/internal/mvs"
   124  	"cmd/go/internal/search"
   125  	"cmd/go/internal/str"
   126  	"cmd/internal/par"
   127  
   128  	"golang.org/x/mod/module"
   129  )
   130  
   131  // PackageOpts control the behavior of the LoadPackages function.
   132  type PackageOpts struct {
   133  	// TidyGoVersion is the Go version to which the go.mod file should be updated
   134  	// after packages have been loaded.
   135  	//
   136  	// An empty TidyGoVersion means to use the Go version already specified in the
   137  	// main module's go.mod file, or the latest Go version if there is no main
   138  	// module.
   139  	TidyGoVersion string
   140  
   141  	// Tags are the build tags in effect (as interpreted by the
   142  	// cmd/go/internal/imports package).
   143  	// If nil, treated as equivalent to imports.Tags().
   144  	Tags map[string]bool
   145  
   146  	// Tidy, if true, requests that the build list and go.sum file be reduced to
   147  	// the minimal dependencies needed to reproducibly reload the requested
   148  	// packages.
   149  	Tidy bool
   150  
   151  	// TidyDiff, if true, causes tidy not to modify go.mod or go.sum but
   152  	// instead print the necessary changes as a unified diff. It exits
   153  	// with a non-zero code if the diff is not empty.
   154  	TidyDiff bool
   155  
   156  	// TidyCompatibleVersion is the oldest Go version that must be able to
   157  	// reproducibly reload the requested packages.
   158  	//
   159  	// If empty, the compatible version is the Go version immediately prior to the
   160  	// 'go' version listed in the go.mod file.
   161  	TidyCompatibleVersion string
   162  
   163  	// VendorModulesInGOROOTSrc indicates that if we are within a module in
   164  	// GOROOT/src, packages in the module's vendor directory should be resolved as
   165  	// actual module dependencies (instead of standard-library packages).
   166  	VendorModulesInGOROOTSrc bool
   167  
   168  	// ResolveMissingImports indicates that we should attempt to add module
   169  	// dependencies as needed to resolve imports of packages that are not found.
   170  	//
   171  	// For commands that support the -mod flag, resolving imports may still fail
   172  	// if the flag is set to "readonly" (the default) or "vendor".
   173  	ResolveMissingImports bool
   174  
   175  	// AssumeRootsImported indicates that the transitive dependencies of the root
   176  	// packages should be treated as if those roots will be imported by the main
   177  	// module.
   178  	AssumeRootsImported bool
   179  
   180  	// AllowPackage, if non-nil, is called after identifying the module providing
   181  	// each package. If AllowPackage returns a non-nil error, that error is set
   182  	// for the package, and the imports and test of that package will not be
   183  	// loaded.
   184  	//
   185  	// AllowPackage may be invoked concurrently by multiple goroutines,
   186  	// and may be invoked multiple times for a given package path.
   187  	AllowPackage func(ctx context.Context, path string, mod module.Version) error
   188  
   189  	// LoadTests loads the test dependencies of each package matching a requested
   190  	// pattern. If ResolveMissingImports is also true, test dependencies will be
   191  	// resolved if missing.
   192  	LoadTests bool
   193  
   194  	// UseVendorAll causes the "all" package pattern to be interpreted as if
   195  	// running "go mod vendor" (or building with "-mod=vendor").
   196  	//
   197  	// This is a no-op for modules that declare 'go 1.16' or higher, for which this
   198  	// is the default (and only) interpretation of the "all" pattern in module mode.
   199  	UseVendorAll bool
   200  
   201  	// AllowErrors indicates that LoadPackages should not terminate the process if
   202  	// an error occurs.
   203  	AllowErrors bool
   204  
   205  	// SilencePackageErrors indicates that LoadPackages should not print errors
   206  	// that occur while matching or loading packages, and should not terminate the
   207  	// process if such an error occurs.
   208  	//
   209  	// Errors encountered in the module graph will still be reported.
   210  	//
   211  	// The caller may retrieve the silenced package errors using the Lookup
   212  	// function, and matching errors are still populated in the Errs field of the
   213  	// associated search.Match.)
   214  	SilencePackageErrors bool
   215  
   216  	// SilenceMissingStdImports indicates that LoadPackages should not print
   217  	// errors or terminate the process if an imported package is missing, and the
   218  	// import path looks like it might be in the standard library (perhaps in a
   219  	// future version).
   220  	SilenceMissingStdImports bool
   221  
   222  	// SilenceNoGoErrors indicates that LoadPackages should not print
   223  	// imports.ErrNoGo errors.
   224  	// This allows the caller to invoke LoadPackages (and report other errors)
   225  	// without knowing whether the requested packages exist for the given tags.
   226  	//
   227  	// Note that if a requested package does not exist *at all*, it will fail
   228  	// during module resolution and the error will not be suppressed.
   229  	SilenceNoGoErrors bool
   230  
   231  	// SilenceUnmatchedWarnings suppresses the warnings normally emitted for
   232  	// patterns that did not match any packages.
   233  	SilenceUnmatchedWarnings bool
   234  
   235  	// Resolve the query against this module.
   236  	MainModule module.Version
   237  
   238  	// If Switcher is non-nil, then LoadPackages passes all encountered errors
   239  	// to Switcher.Error and tries Switcher.Switch before base.ExitIfErrors.
   240  	Switcher gover.Switcher
   241  }
   242  
   243  // LoadPackages identifies the set of packages matching the given patterns and
   244  // loads the packages in the import graph rooted at that set.
   245  func LoadPackages(ld *Loader, ctx context.Context, opts PackageOpts, patterns ...string) (matches []*search.Match, loadedPackages []string) {
   246  	if opts.Tags == nil {
   247  		opts.Tags = imports.Tags()
   248  	}
   249  
   250  	patterns = search.CleanPatterns(patterns)
   251  	matches = make([]*search.Match, 0, len(patterns))
   252  	allPatternIsRoot := false
   253  	for _, pattern := range patterns {
   254  		matches = append(matches, search.NewMatch(pattern))
   255  		if pattern == "all" {
   256  			allPatternIsRoot = true
   257  		}
   258  	}
   259  
   260  	updateMatches := func(rs *Requirements, pld *packageLoader) {
   261  		for _, m := range matches {
   262  			switch {
   263  			case m.IsLocal():
   264  				// Evaluate list of file system directories on first iteration.
   265  				if m.Dirs == nil {
   266  					matchModRoots := ld.modRoots
   267  					if opts.MainModule != (module.Version{}) {
   268  						matchModRoots = []string{ld.MainModules.ModRoot(opts.MainModule)}
   269  					}
   270  					matchLocalDirs(ld, ctx, matchModRoots, m, rs)
   271  				}
   272  
   273  				// Make a copy of the directory list and translate to import paths.
   274  				// Note that whether a directory corresponds to an import path
   275  				// changes as the build list is updated, and a directory can change
   276  				// from not being in the build list to being in it and back as
   277  				// the exact version of a particular module increases during
   278  				// the loader iterations.
   279  				m.Pkgs = m.Pkgs[:0]
   280  				for _, dir := range m.Dirs {
   281  					pkg, err := resolveLocalPackage(ld, ctx, dir, rs)
   282  					if err != nil {
   283  						if !m.IsLiteral() && (err == errPkgIsBuiltin || err == errPkgIsGorootSrc) {
   284  							continue // Don't include "builtin" or GOROOT/src in wildcard patterns.
   285  						}
   286  
   287  						// If we're outside of a module, ensure that the failure mode
   288  						// indicates that.
   289  						if !ld.HasModRoot() {
   290  							die(ld)
   291  						}
   292  
   293  						if pld != nil {
   294  							m.AddError(err)
   295  						}
   296  						continue
   297  					}
   298  					m.Pkgs = append(m.Pkgs, pkg)
   299  				}
   300  
   301  			case m.IsLiteral():
   302  				m.Pkgs = []string{m.Pattern()}
   303  
   304  			case strings.Contains(m.Pattern(), "..."):
   305  				m.Errs = m.Errs[:0]
   306  				mg, err := rs.Graph(ld, ctx)
   307  				if err != nil {
   308  					// The module graph is (or may be) incomplete — perhaps we failed to
   309  					// load the requirements of some module. This is an error in matching
   310  					// the patterns to packages, because we may be missing some packages
   311  					// or we may erroneously match packages in the wrong versions of
   312  					// modules. However, for cases like 'go list -e', the error should not
   313  					// necessarily prevent us from loading the packages we could find.
   314  					m.Errs = append(m.Errs, err)
   315  				}
   316  				matchPackages(ld, ctx, m, opts.Tags, includeStd, mg.BuildList())
   317  
   318  			case m.Pattern() == "work":
   319  				matchModules := ld.MainModules.Versions()
   320  				if opts.MainModule != (module.Version{}) {
   321  					matchModules = []module.Version{opts.MainModule}
   322  				}
   323  				matchPackages(ld, ctx, m, opts.Tags, omitStd, matchModules)
   324  
   325  			case m.Pattern() == "all":
   326  				if pld == nil {
   327  					// The initial roots are the packages and tools in the main module.
   328  					// loadFromRoots will expand that to "all".
   329  					m.Errs = m.Errs[:0]
   330  					matchModules := ld.MainModules.Versions()
   331  					if opts.MainModule != (module.Version{}) {
   332  						matchModules = []module.Version{opts.MainModule}
   333  					}
   334  					matchPackages(ld, ctx, m, opts.Tags, omitStd, matchModules)
   335  					for tool := range ld.MainModules.Tools() {
   336  						m.Pkgs = append(m.Pkgs, tool)
   337  					}
   338  				} else {
   339  					// Starting with the packages in the main module,
   340  					// enumerate the full list of "all".
   341  					m.Pkgs = pld.computePatternAll()
   342  				}
   343  
   344  			case m.Pattern() == "std" || m.Pattern() == "cmd":
   345  				if m.Pkgs == nil {
   346  					m.MatchPackages() // Locate the packages within GOROOT/src.
   347  				}
   348  
   349  			case m.Pattern() == "tool":
   350  				for tool := range ld.MainModules.Tools() {
   351  					m.Pkgs = append(m.Pkgs, tool)
   352  				}
   353  			default:
   354  				panic(fmt.Sprintf("internal error: modload missing case for pattern %s", m.Pattern()))
   355  			}
   356  		}
   357  	}
   358  
   359  	initialRS, err := loadModFile(ld, ctx, &opts)
   360  	if err != nil {
   361  		base.Fatal(err)
   362  	}
   363  
   364  	pld := loadFromRoots(ld, ctx, loaderParams{
   365  		PackageOpts:  opts,
   366  		requirements: initialRS,
   367  
   368  		allPatternIsRoot: allPatternIsRoot,
   369  
   370  		listRoots: func(rs *Requirements) (roots []string) {
   371  			updateMatches(rs, nil)
   372  			for _, m := range matches {
   373  				roots = append(roots, m.Pkgs...)
   374  			}
   375  			return roots
   376  		},
   377  	})
   378  
   379  	// One last pass to finalize wildcards.
   380  	updateMatches(pld.requirements, pld)
   381  
   382  	// List errors in matching patterns (such as directory permission
   383  	// errors for wildcard patterns).
   384  	if !pld.SilencePackageErrors {
   385  		for _, match := range matches {
   386  			for _, err := range match.Errs {
   387  				pld.error(err)
   388  			}
   389  		}
   390  	}
   391  	pld.exitIfErrors(ctx)
   392  
   393  	if !opts.SilenceUnmatchedWarnings {
   394  		search.WarnUnmatched(matches)
   395  	}
   396  
   397  	if opts.Tidy {
   398  		if cfg.BuildV {
   399  			mg, _ := pld.requirements.Graph(ld, ctx)
   400  			for _, m := range initialRS.rootModules {
   401  				var unused bool
   402  				if pld.requirements.pruning == unpruned {
   403  					// m is unused if it was dropped from the module graph entirely. If it
   404  					// was only demoted from direct to indirect, it may still be in use via
   405  					// a transitive import.
   406  					unused = mg.Selected(m.Path) == "none"
   407  				} else {
   408  					// m is unused if it was dropped from the roots. If it is still present
   409  					// as a transitive dependency, that transitive dependency is not needed
   410  					// by any package or test in the main module.
   411  					_, ok := pld.requirements.rootSelected(ld, m.Path)
   412  					unused = !ok
   413  				}
   414  				if unused {
   415  					fmt.Fprintf(os.Stderr, "unused %s\n", m.Path)
   416  				}
   417  			}
   418  		}
   419  
   420  		keep := keepSums(ld, ctx, pld, pld.requirements, loadedZipSumsOnly)
   421  		compatVersion := pld.TidyCompatibleVersion
   422  		goVersion := pld.requirements.GoVersion(ld)
   423  		if compatVersion == "" {
   424  			if gover.Compare(goVersion, gover.GoStrictVersion) < 0 {
   425  				compatVersion = gover.Prev(goVersion)
   426  			} else {
   427  				// Starting at GoStrictVersion, we no longer maintain compatibility with
   428  				// versions older than what is listed in the go.mod file.
   429  				compatVersion = goVersion
   430  			}
   431  		}
   432  		if gover.Compare(compatVersion, goVersion) > 0 {
   433  			// Each version of the Go toolchain knows how to interpret go.mod and
   434  			// go.sum files produced by all previous versions, so a compatibility
   435  			// version higher than the go.mod version adds nothing.
   436  			compatVersion = goVersion
   437  		}
   438  		if compatPruning := pruningForGoVersion(compatVersion); compatPruning != pld.requirements.pruning {
   439  			compatRS := newRequirements(ld, compatPruning, pld.requirements.rootModules, pld.requirements.direct)
   440  			pld.checkTidyCompatibility(ld, ctx, compatRS, compatVersion)
   441  
   442  			for m := range keepSums(ld, ctx, pld, compatRS, loadedZipSumsOnly) {
   443  				keep[m] = true
   444  			}
   445  		}
   446  
   447  		if opts.TidyDiff {
   448  			cfg.BuildMod = "readonly"
   449  			ld.pkgLoader = pld
   450  			ld.requirements = ld.pkgLoader.requirements
   451  			currentGoMod, updatedGoMod, _, err := UpdateGoModFromReqs(ld, ctx, WriteOpts{})
   452  			if err != nil {
   453  				base.Fatal(err)
   454  			}
   455  			goModDiff := diff.Diff("current/go.mod", currentGoMod, "tidy/go.mod", updatedGoMod)
   456  
   457  			ld.Fetcher().TrimGoSum(keep)
   458  			// Dropping compatibility for 1.16 may result in a strictly smaller go.sum.
   459  			// Update the keep map with only the loaded.requirements.
   460  			if gover.Compare(compatVersion, "1.16") > 0 {
   461  				keep = keepSums(ld, ctx, ld.pkgLoader, ld.requirements, addBuildListZipSums)
   462  			}
   463  			currentGoSum, tidyGoSum := ld.fetcher.TidyGoSum(keep)
   464  			goSumDiff := diff.Diff("current/go.sum", currentGoSum, "tidy/go.sum", tidyGoSum)
   465  
   466  			if len(goModDiff) > 0 {
   467  				fmt.Println(string(goModDiff))
   468  				base.SetExitStatus(1)
   469  			}
   470  			if len(goSumDiff) > 0 {
   471  				fmt.Println(string(goSumDiff))
   472  				base.SetExitStatus(1)
   473  			}
   474  			base.Exit()
   475  		}
   476  
   477  		if !ExplicitWriteGoMod {
   478  			ld.Fetcher().TrimGoSum(keep)
   479  
   480  			// commitRequirements below will also call WriteGoSum, but the "keep" map
   481  			// we have here could be strictly larger: commitRequirements only commits
   482  			// loaded.requirements, but here we may have also loaded (and want to
   483  			// preserve checksums for) additional entities from compatRS, which are
   484  			// only needed for compatibility with ld.TidyCompatibleVersion.
   485  			if err := ld.Fetcher().WriteGoSum(ctx, keep, mustHaveCompleteRequirements(ld)); err != nil {
   486  				base.Fatal(err)
   487  			}
   488  		}
   489  	}
   490  
   491  	if opts.TidyDiff && !opts.Tidy {
   492  		panic("TidyDiff is set but Tidy is not.")
   493  	}
   494  
   495  	// Success! Update go.mod and go.sum (if needed) and return the results.
   496  	// We'll skip updating if ExplicitWriteGoMod is true (the caller has opted
   497  	// to call WriteGoMod itself) or if ResolveMissingImports is false (the
   498  	// command wants to examine the package graph as-is).
   499  	ld.pkgLoader = pld
   500  	ld.requirements = ld.pkgLoader.requirements
   501  
   502  	for _, pkg := range pld.pkgs {
   503  		if !pkg.isTest() {
   504  			loadedPackages = append(loadedPackages, pkg.path)
   505  		}
   506  	}
   507  	sort.Strings(loadedPackages)
   508  
   509  	if !ExplicitWriteGoMod && opts.ResolveMissingImports {
   510  		if err := commitRequirements(ld, ctx, WriteOpts{}); err != nil {
   511  			base.Fatal(err)
   512  		}
   513  	}
   514  
   515  	return matches, loadedPackages
   516  }
   517  
   518  // matchLocalDirs is like m.MatchDirs, but tries to avoid scanning directories
   519  // outside of the standard library and active modules.
   520  func matchLocalDirs(ld *Loader, ctx context.Context, modRoots []string, m *search.Match, rs *Requirements) {
   521  	if !m.IsLocal() {
   522  		panic(fmt.Sprintf("internal error: resolveLocalDirs on non-local pattern %s", m.Pattern()))
   523  	}
   524  
   525  	if i := strings.Index(m.Pattern(), "..."); i >= 0 {
   526  		// The pattern is local, but it is a wildcard. Its packages will
   527  		// only resolve to paths if they are inside of the standard
   528  		// library, the main module, or some dependency of the main
   529  		// module. Verify that before we walk the filesystem: a filesystem
   530  		// walk in a directory like /var or /etc can be very expensive!
   531  		dir := filepath.Dir(filepath.Clean(m.Pattern()[:i+3]))
   532  		absDir := dir
   533  		if !filepath.IsAbs(dir) {
   534  			absDir = filepath.Join(base.Cwd(), dir)
   535  		}
   536  
   537  		modRoot := findModuleRoot(absDir)
   538  		if !slices.Contains(modRoots, modRoot) && search.InDir(absDir, cfg.GOROOTsrc) == "" && pathInModuleCache(ld, ctx, absDir, rs) == "" {
   539  			m.Dirs = []string{}
   540  			scope := "main module or its selected dependencies"
   541  			if ld.inWorkspaceMode() {
   542  				scope = "modules listed in go.work or their selected dependencies"
   543  			}
   544  			m.AddError(fmt.Errorf("directory prefix %s does not contain %s", base.ShortPath(absDir), scope))
   545  			return
   546  		}
   547  	}
   548  
   549  	m.MatchDirs(modRoots)
   550  }
   551  
   552  // resolveLocalPackage resolves a filesystem path to a package path.
   553  func resolveLocalPackage(ld *Loader, ctx context.Context, dir string, rs *Requirements) (string, error) {
   554  	var absDir string
   555  	if filepath.IsAbs(dir) {
   556  		absDir = filepath.Clean(dir)
   557  	} else {
   558  		absDir = filepath.Join(base.Cwd(), dir)
   559  	}
   560  
   561  	bp, err := cfg.BuildContext.ImportDir(absDir, 0)
   562  	if err != nil && (bp == nil || len(bp.IgnoredGoFiles) == 0) {
   563  		// golang.org/issue/32917: We should resolve a relative path to a
   564  		// package path only if the relative path actually contains the code
   565  		// for that package.
   566  		//
   567  		// If the named directory does not exist or contains no Go files,
   568  		// the package does not exist.
   569  		// Other errors may affect package loading, but not resolution.
   570  		if _, err := fsys.Stat(absDir); err != nil {
   571  			if os.IsNotExist(err) {
   572  				// Canonicalize OS-specific errors to errDirectoryNotFound so that error
   573  				// messages will be easier for users to search for.
   574  				return "", &fs.PathError{Op: "stat", Path: absDir, Err: errDirectoryNotFound}
   575  			}
   576  			return "", err
   577  		}
   578  		if _, noGo := err.(*build.NoGoError); noGo {
   579  			// A directory that does not contain any Go source files — even ignored
   580  			// ones! — is not a Go package, and we can't resolve it to a package
   581  			// path because that path could plausibly be provided by some other
   582  			// module.
   583  			//
   584  			// Any other error indicates that the package “exists” (at least in the
   585  			// sense that it cannot exist in any other module), but has some other
   586  			// problem (such as a syntax error).
   587  			return "", err
   588  		}
   589  	}
   590  
   591  	for _, mod := range ld.MainModules.Versions() {
   592  		modRoot := ld.MainModules.ModRoot(mod)
   593  		if modRoot != "" && absDir == modRoot {
   594  			if absDir == cfg.GOROOTsrc {
   595  				return "", errPkgIsGorootSrc
   596  			}
   597  			return ld.MainModules.PathPrefix(mod), nil
   598  		}
   599  	}
   600  
   601  	// Note: The checks for @ here are just to avoid misinterpreting
   602  	// the module cache directories (formerly GOPATH/src/mod/foo@v1.5.2/bar).
   603  	// It's not strictly necessary but helpful to keep the checks.
   604  	var pkgNotFoundErr error
   605  	pkgNotFoundLongestPrefix := ""
   606  	for _, mainModule := range ld.MainModules.Versions() {
   607  		modRoot := ld.MainModules.ModRoot(mainModule)
   608  		if modRoot != "" && str.HasFilePathPrefix(absDir, modRoot) && !strings.Contains(absDir[len(modRoot):], "@") {
   609  			suffix := filepath.ToSlash(str.TrimFilePathPrefix(absDir, modRoot))
   610  			if pkg, found := strings.CutPrefix(suffix, "vendor/"); found {
   611  				if cfg.BuildMod != "vendor" {
   612  					return "", fmt.Errorf("without -mod=vendor, directory %s has no package path", absDir)
   613  				}
   614  
   615  				readVendorList(VendorDir(ld))
   616  				if _, ok := vendorPkgModule[pkg]; !ok {
   617  					return "", fmt.Errorf("directory %s is not a package listed in vendor/modules.txt", absDir)
   618  				}
   619  				return pkg, nil
   620  			}
   621  
   622  			mainModulePrefix := ld.MainModules.PathPrefix(mainModule)
   623  			if mainModulePrefix == "" {
   624  				pkg := suffix
   625  				if pkg == "builtin" {
   626  					// "builtin" is a pseudo-package with a real source file.
   627  					// It's not included in "std", so it shouldn't resolve from "."
   628  					// within module "std" either.
   629  					return "", errPkgIsBuiltin
   630  				}
   631  				return pkg, nil
   632  			}
   633  
   634  			pkg := pathpkg.Join(mainModulePrefix, suffix)
   635  			if _, ok, err := dirInModule(pkg, mainModulePrefix, modRoot, true); err != nil {
   636  				return "", err
   637  			} else if !ok {
   638  				// This main module could contain the directory but doesn't. Other main
   639  				// modules might contain the directory, so wait till we finish the loop
   640  				// to see if another main module contains directory. But if not,
   641  				// return an error.
   642  				if len(mainModulePrefix) > len(pkgNotFoundLongestPrefix) {
   643  					pkgNotFoundLongestPrefix = mainModulePrefix
   644  					pkgNotFoundErr = &PackageNotInModuleError{MainModules: []module.Version{mainModule}, Pattern: pkg}
   645  				}
   646  				continue
   647  			}
   648  			return pkg, nil
   649  		}
   650  	}
   651  	if pkgNotFoundErr != nil {
   652  		return "", pkgNotFoundErr
   653  	}
   654  
   655  	if sub := search.InDir(absDir, cfg.GOROOTsrc); sub != "" && sub != "." && !strings.Contains(sub, "@") {
   656  		pkg := filepath.ToSlash(sub)
   657  		if pkg == "builtin" {
   658  			return "", errPkgIsBuiltin
   659  		}
   660  		return pkg, nil
   661  	}
   662  
   663  	pkg := pathInModuleCache(ld, ctx, absDir, rs)
   664  	if pkg == "" {
   665  		dirstr := fmt.Sprintf("directory %s", base.ShortPath(absDir))
   666  		if dirstr == "directory ." {
   667  			dirstr = "current directory"
   668  		}
   669  		if ld.inWorkspaceMode() {
   670  			if mr := findModuleRoot(absDir); mr != "" {
   671  				return "", fmt.Errorf("%s is contained in a module that is not one of the workspace modules listed in go.work. You can add the module to the workspace using:\n\tgo work use %s", dirstr, base.ShortPath(mr))
   672  			}
   673  			return "", fmt.Errorf("%s outside modules listed in go.work or their selected dependencies", dirstr)
   674  		}
   675  		return "", fmt.Errorf("%s outside main module or its selected dependencies", dirstr)
   676  	}
   677  	return pkg, nil
   678  }
   679  
   680  var (
   681  	errDirectoryNotFound = errors.New("directory not found")
   682  	errPkgIsGorootSrc    = errors.New("GOROOT/src is not an importable package")
   683  	errPkgIsBuiltin      = errors.New(`"builtin" is a pseudo-package, not an importable package`)
   684  )
   685  
   686  // pathInModuleCache returns the import path of the directory dir,
   687  // if dir is in the module cache copy of a module in our build list.
   688  func pathInModuleCache(ld *Loader, ctx context.Context, dir string, rs *Requirements) string {
   689  	tryMod := func(m module.Version) (string, bool) {
   690  		if gover.IsToolchain(m.Path) {
   691  			return "", false
   692  		}
   693  		var root string
   694  		var err error
   695  		if repl := Replacement(ld, m); repl.Path != "" && repl.Version == "" {
   696  			root = repl.Path
   697  			if !filepath.IsAbs(root) {
   698  				root = filepath.Join(replaceRelativeTo(ld), root)
   699  			}
   700  		} else if repl.Path != "" {
   701  			root, err = modfetch.DownloadDir(ctx, repl)
   702  		} else {
   703  			root, err = modfetch.DownloadDir(ctx, m)
   704  		}
   705  		if err != nil {
   706  			return "", false
   707  		}
   708  
   709  		sub := search.InDir(dir, root)
   710  		if sub == "" {
   711  			return "", false
   712  		}
   713  		sub = filepath.ToSlash(sub)
   714  		if strings.Contains(sub, "/vendor/") || strings.HasPrefix(sub, "vendor/") || strings.Contains(sub, "@") {
   715  			return "", false
   716  		}
   717  
   718  		return pathpkg.Join(m.Path, filepath.ToSlash(sub)), true
   719  	}
   720  
   721  	if rs.pruning == pruned {
   722  		for _, m := range rs.rootModules {
   723  			if v, _ := rs.rootSelected(ld, m.Path); v != m.Version {
   724  				continue // m is a root, but we have a higher root for the same path.
   725  			}
   726  			if importPath, ok := tryMod(m); ok {
   727  				// checkMultiplePaths ensures that a module can be used for at most one
   728  				// requirement, so this must be it.
   729  				return importPath
   730  			}
   731  		}
   732  	}
   733  
   734  	// None of the roots contained dir, or the graph is unpruned (so we don't want
   735  	// to distinguish between roots and transitive dependencies). Either way,
   736  	// check the full graph to see if the directory is a non-root dependency.
   737  	//
   738  	// If the roots are not consistent with the full module graph, the selected
   739  	// versions of root modules may differ from what we already checked above.
   740  	// Re-check those paths too.
   741  
   742  	mg, _ := rs.Graph(ld, ctx)
   743  	var importPath string
   744  	for _, m := range mg.BuildList() {
   745  		var found bool
   746  		importPath, found = tryMod(m)
   747  		if found {
   748  			break
   749  		}
   750  	}
   751  	return importPath
   752  }
   753  
   754  // ImportFromFiles adds modules to the build list as needed
   755  // to satisfy the imports in the named Go source files.
   756  //
   757  // Errors in missing dependencies are silenced.
   758  //
   759  // TODO(bcmills): Silencing errors seems off. Take a closer look at this and
   760  // figure out what the error-reporting actually ought to be.
   761  func ImportFromFiles(ld *Loader, ctx context.Context, gofiles []string) {
   762  	rs := LoadModFile(ld, ctx)
   763  
   764  	tags := imports.Tags()
   765  	imports, testImports, err := imports.ScanFiles(gofiles, tags)
   766  	if err != nil {
   767  		base.Fatal(err)
   768  	}
   769  
   770  	ld.pkgLoader = loadFromRoots(ld, ctx, loaderParams{
   771  		PackageOpts: PackageOpts{
   772  			Tags:                  tags,
   773  			ResolveMissingImports: true,
   774  			SilencePackageErrors:  true,
   775  		},
   776  		requirements: rs,
   777  		listRoots: func(*Requirements) (roots []string) {
   778  			roots = append(roots, imports...)
   779  			roots = append(roots, testImports...)
   780  			return roots
   781  		},
   782  	})
   783  	ld.requirements = ld.pkgLoader.requirements
   784  
   785  	if !ExplicitWriteGoMod {
   786  		if err := commitRequirements(ld, ctx, WriteOpts{}); err != nil {
   787  			base.Fatal(err)
   788  		}
   789  	}
   790  }
   791  
   792  // DirImportPath returns the effective import path for dir,
   793  // provided it is within a main module, or else returns ".".
   794  func (mms *MainModuleSet) DirImportPath(ld *Loader, ctx context.Context, dir string) (path string, m module.Version) {
   795  	if !ld.HasModRoot() {
   796  		return ".", module.Version{}
   797  	}
   798  	LoadModFile(ld, ctx) // Sets targetPrefix.
   799  
   800  	if !filepath.IsAbs(dir) {
   801  		dir = filepath.Join(base.Cwd(), dir)
   802  	} else {
   803  		dir = filepath.Clean(dir)
   804  	}
   805  
   806  	var longestPrefix string
   807  	var longestPrefixPath string
   808  	var longestPrefixVersion module.Version
   809  	for _, v := range mms.Versions() {
   810  		modRoot := mms.ModRoot(v)
   811  		if dir == modRoot {
   812  			return mms.PathPrefix(v), v
   813  		}
   814  		if str.HasFilePathPrefix(dir, modRoot) {
   815  			pathPrefix := ld.MainModules.PathPrefix(v)
   816  			if pathPrefix > longestPrefix {
   817  				longestPrefix = pathPrefix
   818  				longestPrefixVersion = v
   819  				suffix := filepath.ToSlash(str.TrimFilePathPrefix(dir, modRoot))
   820  				if strings.HasPrefix(suffix, "vendor/") {
   821  					longestPrefixPath = suffix[len("vendor/"):]
   822  					continue
   823  				}
   824  				longestPrefixPath = pathpkg.Join(mms.PathPrefix(v), suffix)
   825  			}
   826  		}
   827  	}
   828  	if len(longestPrefix) > 0 {
   829  		return longestPrefixPath, longestPrefixVersion
   830  	}
   831  
   832  	return ".", module.Version{}
   833  }
   834  
   835  // PackageModule returns the module providing the package named by the import path.
   836  func (ld *Loader) PackageModule(path string) module.Version {
   837  	pkg, ok := ld.pkgLoader.pkgCache.Get(path)
   838  	if !ok {
   839  		return module.Version{}
   840  	}
   841  	return pkg.mod
   842  }
   843  
   844  // Lookup returns the source directory, import path, and any loading error for
   845  // the package at path as imported from the package in parentDir.
   846  // Lookup requires that one of the Load functions in this package has already
   847  // been called.
   848  func Lookup(ld *Loader, parentPath string, parentIsStd bool, path string) (dir, realPath string, err error) {
   849  	if path == "" {
   850  		panic("Lookup called with empty package path")
   851  	}
   852  
   853  	if parentIsStd {
   854  		path = ld.pkgLoader.stdVendor(ld, parentPath, path)
   855  	}
   856  	pkg, ok := ld.pkgLoader.pkgCache.Get(path)
   857  	if !ok {
   858  		// The loader should have found all the relevant paths.
   859  		// There are a few exceptions, though:
   860  		//	- during go list without -test, the p.Resolve calls to process p.TestImports and p.XTestImports
   861  		//	  end up here to canonicalize the import paths.
   862  		//	- during any load, non-loaded packages like "unsafe" end up here.
   863  		//	- during any load, build-injected dependencies like "runtime/cgo" end up here.
   864  		//	- because we ignore appengine/* in the module loader,
   865  		//	  the dependencies of any actual appengine/* library end up here.
   866  		dir := findStandardImportPath(path)
   867  		if dir != "" {
   868  			return dir, path, nil
   869  		}
   870  		return "", "", errMissing
   871  	}
   872  	return pkg.dir, pkg.path, pkg.err
   873  }
   874  
   875  // A packageLoader manages the process of loading information about
   876  // the required packages for a particular build,
   877  // checking that the packages are available in the module set,
   878  // and updating the module set if needed.
   879  type packageLoader struct {
   880  	loaderParams
   881  
   882  	// allClosesOverTests indicates whether the "all" pattern includes
   883  	// dependencies of tests outside the main module (as in Go 1.11–1.15).
   884  	// (Otherwise — as in Go 1.16+ — the "all" pattern includes only the packages
   885  	// transitively *imported by* the packages and tests in the main module.)
   886  	allClosesOverTests bool
   887  
   888  	// skipImportModFiles indicates whether we may skip loading go.mod files
   889  	// for imported packages (as in 'go mod tidy' in Go 1.17–1.20).
   890  	skipImportModFiles bool
   891  
   892  	work *par.Queue
   893  
   894  	// reset on each iteration
   895  	roots    []*loadPkg
   896  	pkgCache *par.Cache[string, *loadPkg]
   897  	pkgs     []*loadPkg // transitive closure of loaded packages and tests; populated in buildStacks
   898  }
   899  
   900  // loaderParams configure the packages loaded by, and the properties reported
   901  // by, a loader instance.
   902  type loaderParams struct {
   903  	PackageOpts
   904  	requirements *Requirements
   905  
   906  	allPatternIsRoot bool // Is the "all" pattern an additional root?
   907  
   908  	listRoots func(rs *Requirements) []string
   909  }
   910  
   911  func (pld *packageLoader) reset() {
   912  	select {
   913  	case <-pld.work.Idle():
   914  	default:
   915  		panic("loader.reset when not idle")
   916  	}
   917  
   918  	pld.roots = nil
   919  	pld.pkgCache = new(par.Cache[string, *loadPkg])
   920  	pld.pkgs = nil
   921  }
   922  
   923  // error reports an error via either os.Stderr or base.Error,
   924  // according to whether ld.AllowErrors is set.
   925  func (pld *packageLoader) error(err error) {
   926  	if pld.AllowErrors {
   927  		fmt.Fprintf(os.Stderr, "go: %v\n", err)
   928  	} else if pld.Switcher != nil {
   929  		pld.Switcher.Error(err)
   930  	} else {
   931  		base.Error(err)
   932  	}
   933  }
   934  
   935  // switchIfErrors switches toolchains if a switch is needed.
   936  func (pld *packageLoader) switchIfErrors(ctx context.Context) {
   937  	if pld.Switcher != nil {
   938  		pld.Switcher.Switch(ctx)
   939  	}
   940  }
   941  
   942  // exitIfErrors switches toolchains if a switch is needed
   943  // or else exits if any errors have been reported.
   944  func (pld *packageLoader) exitIfErrors(ctx context.Context) {
   945  	pld.switchIfErrors(ctx)
   946  	base.ExitIfErrors()
   947  }
   948  
   949  // goVersion reports the Go version that should be used for the loader's
   950  // requirements: ld.TidyGoVersion if set, or ld.requirements.GoVersion()
   951  // otherwise.
   952  func (pld *packageLoader) goVersion(ld *Loader) string {
   953  	if pld.TidyGoVersion != "" {
   954  		return pld.TidyGoVersion
   955  	}
   956  	return pld.requirements.GoVersion(ld)
   957  }
   958  
   959  // A loadPkg records information about a single loaded package.
   960  type loadPkg struct {
   961  	// Populated at construction time:
   962  	path   string // import path
   963  	testOf *loadPkg
   964  
   965  	// Populated at construction time and updated by (*packageLoader).applyPkgFlags:
   966  	flags atomicLoadPkgFlags
   967  
   968  	// Populated by (*packageLoader).load:
   969  	mod         module.Version // module providing package
   970  	dir         string         // directory containing source code
   971  	err         error          // error loading package
   972  	imports     []*loadPkg     // packages imported by this one
   973  	testImports []string       // test-only imports, saved for use by pkg.test.
   974  	inStd       bool
   975  	altMods     []module.Version // modules that could have contained the package but did not
   976  
   977  	// Populated by (*packageLoader).pkgTest:
   978  	testOnce sync.Once
   979  	test     *loadPkg
   980  
   981  	// Populated by postprocessing in (*packageLoader).buildStacks:
   982  	stack *loadPkg // package importing this one in minimal import stack for this pkg
   983  }
   984  
   985  // loadPkgFlags is a set of flags tracking metadata about a package.
   986  type loadPkgFlags int8
   987  
   988  const (
   989  	// pkgInAll indicates that the package is in the "all" package pattern,
   990  	// regardless of whether we are loading the "all" package pattern.
   991  	//
   992  	// When the pkgInAll flag and pkgImportsLoaded flags are both set, the caller
   993  	// who set the last of those flags must propagate the pkgInAll marking to all
   994  	// of the imports of the marked package.
   995  	//
   996  	// A test is marked with pkgInAll if that test would promote the packages it
   997  	// imports to be in "all" (such as when the test is itself within the main
   998  	// module, or when ld.allClosesOverTests is true).
   999  	pkgInAll loadPkgFlags = 1 << iota
  1000  
  1001  	// pkgIsRoot indicates that the package matches one of the root package
  1002  	// patterns requested by the caller.
  1003  	//
  1004  	// If LoadTests is set, then when pkgIsRoot and pkgImportsLoaded are both set,
  1005  	// the caller who set the last of those flags must populate a test for the
  1006  	// package (in the pkg.test field).
  1007  	//
  1008  	// If the "all" pattern is included as a root, then non-test packages in "all"
  1009  	// are also roots (and must be marked pkgIsRoot).
  1010  	pkgIsRoot
  1011  
  1012  	// pkgFromRoot indicates that the package is in the transitive closure of
  1013  	// imports starting at the roots. (Note that every package marked as pkgIsRoot
  1014  	// is also trivially marked pkgFromRoot.)
  1015  	pkgFromRoot
  1016  
  1017  	// pkgImportsLoaded indicates that the imports and testImports fields of a
  1018  	// loadPkg have been populated.
  1019  	pkgImportsLoaded
  1020  )
  1021  
  1022  // has reports whether all of the flags in cond are set in f.
  1023  func (f loadPkgFlags) has(cond loadPkgFlags) bool {
  1024  	return f&cond == cond
  1025  }
  1026  
  1027  // An atomicLoadPkgFlags stores a loadPkgFlags for which individual flags can be
  1028  // added atomically.
  1029  type atomicLoadPkgFlags struct {
  1030  	bits atomic.Int32
  1031  }
  1032  
  1033  // update sets the given flags in af (in addition to any flags already set).
  1034  //
  1035  // update returns the previous flag state so that the caller may determine which
  1036  // flags were newly-set.
  1037  func (af *atomicLoadPkgFlags) update(flags loadPkgFlags) (old loadPkgFlags) {
  1038  	for {
  1039  		old := af.bits.Load()
  1040  		new := old | int32(flags)
  1041  		if new == old || af.bits.CompareAndSwap(old, new) {
  1042  			return loadPkgFlags(old)
  1043  		}
  1044  	}
  1045  }
  1046  
  1047  // has reports whether all of the flags in cond are set in af.
  1048  func (af *atomicLoadPkgFlags) has(cond loadPkgFlags) bool {
  1049  	return loadPkgFlags(af.bits.Load())&cond == cond
  1050  }
  1051  
  1052  // isTest reports whether pkg is a test of another package.
  1053  func (pkg *loadPkg) isTest() bool {
  1054  	return pkg.testOf != nil
  1055  }
  1056  
  1057  // fromExternalModule reports whether pkg was loaded from a module other than
  1058  // the main module.
  1059  func (pkg *loadPkg) fromExternalModule(ld *Loader) bool {
  1060  	if pkg.mod.Path == "" {
  1061  		return false // loaded from the standard library, not a module
  1062  	}
  1063  	return !ld.MainModules.Contains(pkg.mod.Path)
  1064  }
  1065  
  1066  var errMissing = errors.New("cannot find package")
  1067  
  1068  // loadFromRoots attempts to load the build graph needed to process a set of
  1069  // root packages and their dependencies.
  1070  //
  1071  // The set of root packages is returned by the params.listRoots function, and
  1072  // expanded to the full set of packages by tracing imports (and possibly tests)
  1073  // as needed.
  1074  func loadFromRoots(ld *Loader, ctx context.Context, params loaderParams) *packageLoader {
  1075  	pld := &packageLoader{
  1076  		loaderParams: params,
  1077  		work:         par.NewQueue(runtime.GOMAXPROCS(0)),
  1078  	}
  1079  
  1080  	if pld.requirements.pruning == unpruned {
  1081  		// If the module graph does not support pruning, we assume that we will need
  1082  		// the full module graph in order to load package dependencies.
  1083  		//
  1084  		// This might not be strictly necessary, but it matches the historical
  1085  		// behavior of the 'go' command and keeps the go.mod file more consistent in
  1086  		// case of erroneous hand-edits — which are less likely to be detected by
  1087  		// spot-checks in modules that do not maintain the expanded go.mod
  1088  		// requirements needed for graph pruning.
  1089  		var err error
  1090  		pld.requirements, _, err = expandGraph(ld, ctx, pld.requirements)
  1091  		if err != nil {
  1092  			pld.error(err)
  1093  		}
  1094  	}
  1095  	pld.exitIfErrors(ctx)
  1096  
  1097  	updateGoVersion := func() {
  1098  		goVersion := pld.goVersion(ld)
  1099  
  1100  		if pld.requirements.pruning != workspace {
  1101  			var err error
  1102  			pld.requirements, err = convertPruning(ld, ctx, pld.requirements, pruningForGoVersion(goVersion))
  1103  			if err != nil {
  1104  				pld.error(err)
  1105  				pld.exitIfErrors(ctx)
  1106  			}
  1107  		}
  1108  
  1109  		// If the module's Go version omits go.sum entries for go.mod files for test
  1110  		// dependencies of external packages, avoid loading those files in the first
  1111  		// place.
  1112  		pld.skipImportModFiles = pld.Tidy && gover.Compare(goVersion, gover.TidyGoModSumVersion) < 0
  1113  
  1114  		// If the module's go version explicitly predates the change in "all" for
  1115  		// graph pruning, continue to use the older interpretation.
  1116  		pld.allClosesOverTests = gover.Compare(goVersion, gover.NarrowAllVersion) < 0 && !pld.UseVendorAll
  1117  	}
  1118  
  1119  	for {
  1120  		pld.reset()
  1121  		updateGoVersion()
  1122  
  1123  		// Load the root packages and their imports.
  1124  		// Note: the returned roots can change on each iteration,
  1125  		// since the expansion of package patterns depends on the
  1126  		// build list we're using.
  1127  		rootPkgs := pld.listRoots(pld.requirements)
  1128  
  1129  		if pld.requirements.pruning == pruned && cfg.BuildMod == "mod" {
  1130  			// Before we start loading transitive imports of packages, locate all of
  1131  			// the root packages and promote their containing modules to root modules
  1132  			// dependencies. If their go.mod files are tidy (the common case) and the
  1133  			// set of root packages does not change then we can select the correct
  1134  			// versions of all transitive imports on the first try and complete
  1135  			// loading in a single iteration.
  1136  			changedBuildList := pld.preloadRootModules(ld, ctx, rootPkgs)
  1137  			if changedBuildList {
  1138  				// The build list has changed, so the set of root packages may have also
  1139  				// changed. Start over to pick up the changes. (Preloading roots is much
  1140  				// cheaper than loading the full import graph, so we would rather pay
  1141  				// for an extra iteration of preloading than potentially end up
  1142  				// discarding the result of a full iteration of loading.)
  1143  				continue
  1144  			}
  1145  		}
  1146  
  1147  		inRoots := map[*loadPkg]bool{}
  1148  		for _, path := range rootPkgs {
  1149  			root := pld.pkg(ld, ctx, path, pkgIsRoot)
  1150  			if !inRoots[root] {
  1151  				pld.roots = append(pld.roots, root)
  1152  				inRoots[root] = true
  1153  			}
  1154  		}
  1155  
  1156  		// ld.pkg adds imported packages to the work queue and calls applyPkgFlags,
  1157  		// which adds tests (and test dependencies) as needed.
  1158  		//
  1159  		// When all of the work in the queue has completed, we'll know that the
  1160  		// transitive closure of dependencies has been loaded.
  1161  		<-pld.work.Idle()
  1162  
  1163  		pld.buildStacks()
  1164  
  1165  		changed, err := pld.updateRequirements(ld, ctx)
  1166  		if err != nil {
  1167  			pld.error(err)
  1168  			break
  1169  		}
  1170  		if changed {
  1171  			// Don't resolve missing imports until the module graph has stabilized.
  1172  			// If the roots are still changing, they may turn out to specify a
  1173  			// requirement on the missing package(s), and we would rather use a
  1174  			// version specified by a new root than add a new dependency on an
  1175  			// unrelated version.
  1176  			continue
  1177  		}
  1178  
  1179  		if !pld.ResolveMissingImports || (!ld.HasModRoot() && !ld.allowMissingModuleImports) {
  1180  			// We've loaded as much as we can without resolving missing imports.
  1181  			break
  1182  		}
  1183  
  1184  		modAddedBy, err := pld.resolveMissingImports(ld, ctx)
  1185  		if err != nil {
  1186  			pld.error(err)
  1187  			break
  1188  		}
  1189  		if len(modAddedBy) == 0 {
  1190  			// The roots are stable, and we've resolved all of the missing packages
  1191  			// that we can.
  1192  			break
  1193  		}
  1194  
  1195  		toAdd := make([]module.Version, 0, len(modAddedBy))
  1196  		for m := range modAddedBy {
  1197  			toAdd = append(toAdd, m)
  1198  		}
  1199  		gover.ModSort(toAdd) // to make errors deterministic
  1200  
  1201  		// We ran updateRequirements before resolving missing imports and it didn't
  1202  		// make any changes, so we know that the requirement graph is already
  1203  		// consistent with ld.pkgs: we don't need to pass ld.pkgs to updateRoots
  1204  		// again. (That would waste time looking for changes that we have already
  1205  		// applied.)
  1206  		var noPkgs []*loadPkg
  1207  		// We also know that we're going to call updateRequirements again next
  1208  		// iteration so we don't need to also update it here. (That would waste time
  1209  		// computing a "direct" map that we'll have to recompute later anyway.)
  1210  		direct := pld.requirements.direct
  1211  		rs, err := updateRoots(ld, ctx, direct, pld.requirements, noPkgs, toAdd, pld.AssumeRootsImported)
  1212  		if err != nil {
  1213  			// If an error was found in a newly added module, report the package
  1214  			// import stack instead of the module requirement stack. Packages
  1215  			// are more descriptive.
  1216  			if err, ok := err.(*mvs.BuildListError); ok {
  1217  				if pkg := modAddedBy[err.Module()]; pkg != nil {
  1218  					pld.error(fmt.Errorf("%s: %w", pkg.stackText(), err.Err))
  1219  					break
  1220  				}
  1221  			}
  1222  			pld.error(err)
  1223  			break
  1224  		}
  1225  		if slices.Equal(rs.rootModules, pld.requirements.rootModules) {
  1226  			// Something is deeply wrong. resolveMissingImports gave us a non-empty
  1227  			// set of modules to add to the graph, but adding those modules had no
  1228  			// effect — either they were already in the graph, or updateRoots did not
  1229  			// add them as requested.
  1230  			panic(fmt.Sprintf("internal error: adding %v to module graph had no effect on root requirements (%v)", toAdd, rs.rootModules))
  1231  		}
  1232  		pld.requirements = rs
  1233  	}
  1234  	pld.exitIfErrors(ctx)
  1235  
  1236  	// Tidy the build list, if applicable, before we report errors.
  1237  	// (The process of tidying may remove errors from irrelevant dependencies.)
  1238  	if pld.Tidy {
  1239  		rs, err := tidyRoots(ld, ctx, pld.requirements, pld.pkgs)
  1240  		if err != nil {
  1241  			pld.error(err)
  1242  		} else {
  1243  			if pld.TidyGoVersion != "" {
  1244  				// Attempt to switch to the requested Go version. We have been using its
  1245  				// pruning and semantics all along, but there may have been — and may
  1246  				// still be — requirements on higher versions in the graph.
  1247  				tidy := overrideRoots(ld, ctx, rs, []module.Version{{Path: "go", Version: pld.TidyGoVersion}})
  1248  				mg, err := tidy.Graph(ld, ctx)
  1249  				if err != nil {
  1250  					pld.error(err)
  1251  				}
  1252  				if v := mg.Selected("go"); v == pld.TidyGoVersion {
  1253  					rs = tidy
  1254  				} else {
  1255  					conflict := Conflict{
  1256  						Path: mg.g.FindPath(func(m module.Version) bool {
  1257  							return m.Path == "go" && m.Version == v
  1258  						})[1:],
  1259  						Constraint: module.Version{Path: "go", Version: pld.TidyGoVersion},
  1260  					}
  1261  					msg := conflict.Summary()
  1262  					if cfg.BuildV {
  1263  						msg = conflict.String()
  1264  					}
  1265  					pld.error(errors.New(msg))
  1266  				}
  1267  			}
  1268  
  1269  			if pld.requirements.pruning == pruned {
  1270  				// We continuously add tidy roots to ld.requirements during loading, so
  1271  				// at this point the tidy roots (other than possibly the "go" version
  1272  				// edited above) should be a subset of the roots of ld.requirements,
  1273  				// ensuring that no new dependencies are brought inside the
  1274  				// graph-pruning horizon.
  1275  				// If that is not the case, there is a bug in the loading loop above.
  1276  				for _, m := range rs.rootModules {
  1277  					if m.Path == "go" && pld.TidyGoVersion != "" {
  1278  						continue
  1279  					}
  1280  					if v, ok := pld.requirements.rootSelected(ld, m.Path); !ok || v != m.Version {
  1281  						pld.error(fmt.Errorf("internal error: a requirement on %v is needed but was not added during package loading (selected %s)", m, v))
  1282  					}
  1283  				}
  1284  			}
  1285  
  1286  			pld.requirements = rs
  1287  		}
  1288  
  1289  		pld.exitIfErrors(ctx)
  1290  	}
  1291  
  1292  	// Report errors, if any.
  1293  	for _, pkg := range pld.pkgs {
  1294  		if pkg.err == nil {
  1295  			continue
  1296  		}
  1297  
  1298  		// Add importer information to checksum errors.
  1299  		if sumErr, ok := errors.AsType[*ImportMissingSumError](pkg.err); ok {
  1300  			if importer := pkg.stack; importer != nil {
  1301  				sumErr.importer = importer.path
  1302  				sumErr.importerVersion = importer.mod.Version
  1303  				sumErr.importerIsTest = importer.testOf != nil
  1304  			}
  1305  		}
  1306  
  1307  		if stdErr, ok := errors.AsType[*ImportMissingError](pkg.err); ok && stdErr.isStd {
  1308  			// Add importer go version information to import errors of standard
  1309  			// library packages arising from newer releases.
  1310  			if importer := pkg.stack; importer != nil {
  1311  				if v, ok := rawGoVersion.Load(importer.mod); ok && gover.Compare(gover.Local(), v.(string)) < 0 {
  1312  					stdErr.importerGoVersion = v.(string)
  1313  				}
  1314  			}
  1315  			if pld.SilenceMissingStdImports {
  1316  				continue
  1317  			}
  1318  		}
  1319  		if pld.SilencePackageErrors {
  1320  			continue
  1321  		}
  1322  		if pld.SilenceNoGoErrors && errors.Is(pkg.err, imports.ErrNoGo) {
  1323  			continue
  1324  		}
  1325  
  1326  		pld.error(fmt.Errorf("%s: %w", pkg.stackText(), pkg.err))
  1327  	}
  1328  
  1329  	pld.checkMultiplePaths(ld)
  1330  	return pld
  1331  }
  1332  
  1333  // updateRequirements ensures that ld.requirements is consistent with the
  1334  // information gained from ld.pkgs.
  1335  //
  1336  // In particular:
  1337  //
  1338  //   - Modules that provide packages directly imported from the main module are
  1339  //     marked as direct, and are promoted to explicit roots. If a needed root
  1340  //     cannot be promoted due to -mod=readonly or -mod=vendor, the importing
  1341  //     package is marked with an error.
  1342  //
  1343  //   - If ld scanned the "all" pattern independent of build constraints, it is
  1344  //     guaranteed to have seen every direct import. Module dependencies that did
  1345  //     not provide any directly-imported package are then marked as indirect.
  1346  //
  1347  //   - Root dependencies are updated to their selected versions.
  1348  //
  1349  // The "changed" return value reports whether the update changed the selected
  1350  // version of any module that either provided a loaded package or may now
  1351  // provide a package that was previously unresolved.
  1352  func (pld *packageLoader) updateRequirements(ld *Loader, ctx context.Context) (changed bool, err error) {
  1353  	rs := pld.requirements
  1354  
  1355  	// direct contains the set of modules believed to provide packages directly
  1356  	// imported by the main module.
  1357  	var direct map[string]bool
  1358  
  1359  	// If we didn't scan all of the imports from the main module, or didn't use
  1360  	// imports.AnyTags, then we didn't necessarily load every package that
  1361  	// contributes “direct” imports — so we can't safely mark existing direct
  1362  	// dependencies in ld.requirements as indirect-only. Propagate them as direct.
  1363  	loadedDirect := pld.allPatternIsRoot && maps.Equal(pld.Tags, imports.AnyTags())
  1364  	if loadedDirect {
  1365  		direct = make(map[string]bool)
  1366  	} else {
  1367  		// TODO(bcmills): It seems like a shame to allocate and copy a map here when
  1368  		// it will only rarely actually vary from rs.direct. Measure this cost and
  1369  		// maybe avoid the copy.
  1370  		direct = make(map[string]bool, len(rs.direct))
  1371  		for mPath := range rs.direct {
  1372  			direct[mPath] = true
  1373  		}
  1374  	}
  1375  
  1376  	var maxTooNew *gover.TooNewError
  1377  	for _, pkg := range pld.pkgs {
  1378  		if pkg.err != nil {
  1379  			if tooNew, ok := errors.AsType[*gover.TooNewError](pkg.err); ok {
  1380  				if maxTooNew == nil || gover.Compare(tooNew.GoVersion, maxTooNew.GoVersion) > 0 {
  1381  					maxTooNew = tooNew
  1382  				}
  1383  			}
  1384  		}
  1385  		if pkg.mod.Version != "" || !ld.MainModules.Contains(pkg.mod.Path) {
  1386  			continue
  1387  		}
  1388  
  1389  		for _, dep := range pkg.imports {
  1390  			if !dep.fromExternalModule(ld) {
  1391  				continue
  1392  			}
  1393  
  1394  			if ld.inWorkspaceMode() {
  1395  				// In workspace mode / workspace pruning mode, the roots are the main modules
  1396  				// rather than the main module's direct dependencies. The check below on the selected
  1397  				// roots does not apply.
  1398  				if cfg.BuildMod == "vendor" {
  1399  					// In workspace vendor mode, we don't need to load the requirements of the workspace
  1400  					// modules' dependencies so the check below doesn't work. But that's okay, because
  1401  					// checking whether modules are required directly for the purposes of pruning is
  1402  					// less important in vendor mode: if we were able to load the package, we have
  1403  					// everything we need  to build the package, and dependencies' tests are pruned out
  1404  					// of the vendor directory anyway.
  1405  					continue
  1406  				}
  1407  				if mg, err := rs.Graph(ld, ctx); err != nil {
  1408  					return false, err
  1409  				} else if _, ok := mg.RequiredBy(dep.mod); !ok {
  1410  					// dep.mod is not an explicit dependency, but needs to be.
  1411  					// See comment on error returned below.
  1412  					pkg.err = &DirectImportFromImplicitDependencyError{
  1413  						ImporterPath: pkg.path,
  1414  						ImportedPath: dep.path,
  1415  						Module:       dep.mod,
  1416  					}
  1417  				}
  1418  			} else if pkg.err == nil && cfg.BuildMod != "mod" {
  1419  				if v, ok := rs.rootSelected(ld, dep.mod.Path); !ok || v != dep.mod.Version {
  1420  					// dep.mod is not an explicit dependency, but needs to be.
  1421  					// Because we are not in "mod" mode, we will not be able to update it.
  1422  					// Instead, mark the importing package with an error.
  1423  					//
  1424  					// TODO(#41688): The resulting error message fails to include the file
  1425  					// position of the import statement (because that information is not
  1426  					// tracked by the module loader). Figure out how to plumb the import
  1427  					// position through.
  1428  					pkg.err = &DirectImportFromImplicitDependencyError{
  1429  						ImporterPath: pkg.path,
  1430  						ImportedPath: dep.path,
  1431  						Module:       dep.mod,
  1432  					}
  1433  					// cfg.BuildMod does not allow us to change dep.mod to be a direct
  1434  					// dependency, so don't mark it as such.
  1435  					continue
  1436  				}
  1437  			}
  1438  
  1439  			// dep is a package directly imported by a package or test in the main
  1440  			// module and loaded from some other module (not the standard library).
  1441  			// Mark its module as a direct dependency.
  1442  			direct[dep.mod.Path] = true
  1443  		}
  1444  	}
  1445  	if maxTooNew != nil {
  1446  		return false, maxTooNew
  1447  	}
  1448  
  1449  	var addRoots []module.Version
  1450  	if pld.Tidy {
  1451  		// When we are tidying a module with a pruned dependency graph, we may need
  1452  		// to add roots to preserve the versions of indirect, test-only dependencies
  1453  		// that are upgraded above or otherwise missing from the go.mod files of
  1454  		// direct dependencies. (For example, the direct dependency might be a very
  1455  		// stable codebase that predates modules and thus lacks a go.mod file, or
  1456  		// the author of the direct dependency may have forgotten to commit a change
  1457  		// to the go.mod file, or may have made an erroneous hand-edit that causes
  1458  		// it to be untidy.)
  1459  		//
  1460  		// Promoting an indirect dependency to a root adds the next layer of its
  1461  		// dependencies to the module graph, which may increase the selected
  1462  		// versions of other modules from which we have already loaded packages.
  1463  		// So after we promote an indirect dependency to a root, we need to reload
  1464  		// packages, which means another iteration of loading.
  1465  		//
  1466  		// As an extra wrinkle, the upgrades due to promoting a root can cause
  1467  		// previously-resolved packages to become unresolved. For example, the
  1468  		// module providing an unstable package might be upgraded to a version
  1469  		// that no longer contains that package. If we then resolve the missing
  1470  		// package, we might add yet another root that upgrades away some other
  1471  		// dependency. (The tests in mod_tidy_convergence*.txt illustrate some
  1472  		// particularly worrisome cases.)
  1473  		//
  1474  		// To ensure that this process of promoting, adding, and upgrading roots
  1475  		// eventually terminates, during iteration we only ever add modules to the
  1476  		// root set — we only remove irrelevant roots at the very end of
  1477  		// iteration, after we have already added every root that we plan to need
  1478  		// in the (eventual) tidy root set.
  1479  		//
  1480  		// Since we do not remove any roots during iteration, even if they no
  1481  		// longer provide any imported packages, the selected versions of the
  1482  		// roots can only increase and the set of roots can only expand. The set
  1483  		// of extant root paths is finite and the set of versions of each path is
  1484  		// finite, so the iteration *must* reach a stable fixed-point.
  1485  		tidy, err := tidyRoots(ld, ctx, rs, pld.pkgs)
  1486  		if err != nil {
  1487  			return false, err
  1488  		}
  1489  		addRoots = tidy.rootModules
  1490  	}
  1491  
  1492  	rs, err = updateRoots(ld, ctx, direct, rs, pld.pkgs, addRoots, pld.AssumeRootsImported)
  1493  	if err != nil {
  1494  		// We don't actually know what even the root requirements are supposed to be,
  1495  		// so we can't proceed with loading. Return the error to the caller
  1496  		return false, err
  1497  	}
  1498  
  1499  	if rs.GoVersion(ld) != pld.requirements.GoVersion(ld) {
  1500  		// A change in the selected Go version may or may not affect the set of
  1501  		// loaded packages, but in some cases it can change the meaning of the "all"
  1502  		// pattern, the level of pruning in the module graph, and even the set of
  1503  		// packages present in the standard library. If it has changed, it's best to
  1504  		// reload packages once more to be sure everything is stable.
  1505  		changed = true
  1506  	} else if rs != pld.requirements && !slices.Equal(rs.rootModules, pld.requirements.rootModules) {
  1507  		// The roots of the module graph have changed in some way (not just the
  1508  		// "direct" markings). Check whether the changes affected any of the loaded
  1509  		// packages.
  1510  		mg, err := rs.Graph(ld, ctx)
  1511  		if err != nil {
  1512  			return false, err
  1513  		}
  1514  		for _, pkg := range pld.pkgs {
  1515  			if pkg.fromExternalModule(ld) && mg.Selected(pkg.mod.Path) != pkg.mod.Version {
  1516  				changed = true
  1517  				break
  1518  			}
  1519  			if pkg.err != nil {
  1520  				// Promoting a module to a root may resolve an import that was
  1521  				// previously missing (by pulling in a previously-prune dependency that
  1522  				// provides it) or ambiguous (by promoting exactly one of the
  1523  				// alternatives to a root and ignoring the second-level alternatives) or
  1524  				// otherwise errored out (by upgrading from a version that cannot be
  1525  				// fetched to one that can be).
  1526  				//
  1527  				// Instead of enumerating all of the possible errors, we'll just check
  1528  				// whether importFromModules returns nil for the package.
  1529  				// False-positives are ok: if we have a false-positive here, we'll do an
  1530  				// extra iteration of package loading this time, but we'll still
  1531  				// converge when the root set stops changing.
  1532  				//
  1533  				// In some sense, we can think of this as ‘upgraded the module providing
  1534  				// pkg.path from "none" to a version higher than "none"’.
  1535  				if _, _, _, _, err = importFromModules(ld, ctx, pkg.path, rs, nil, pld.skipImportModFiles); err == nil {
  1536  					changed = true
  1537  					break
  1538  				}
  1539  			}
  1540  		}
  1541  	}
  1542  
  1543  	pld.requirements = rs
  1544  	return changed, nil
  1545  }
  1546  
  1547  // resolveMissingImports returns a set of modules that could be added as
  1548  // dependencies in order to resolve missing packages from pkgs.
  1549  //
  1550  // The newly-resolved packages are added to the addedModuleFor map, and
  1551  // resolveMissingImports returns a map from each new module version to
  1552  // the first missing package that module would resolve.
  1553  func (pld *packageLoader) resolveMissingImports(ld *Loader, ctx context.Context) (modAddedBy map[module.Version]*loadPkg, err error) {
  1554  	type pkgMod struct {
  1555  		pkg *loadPkg
  1556  		mod *module.Version
  1557  	}
  1558  	var pkgMods []pkgMod
  1559  	for _, pkg := range pld.pkgs {
  1560  		if pkg.err == nil {
  1561  			continue
  1562  		}
  1563  		if pkg.isTest() {
  1564  			// If we are missing a test, we are also missing its non-test version, and
  1565  			// we should only add the missing import once.
  1566  			continue
  1567  		}
  1568  		if _, ok := errors.AsType[*ImportMissingError](pkg.err); !ok {
  1569  			// Leave other errors for Import or load.Packages to report.
  1570  			continue
  1571  		}
  1572  
  1573  		pkg := pkg
  1574  		var mod module.Version
  1575  		pld.work.Add(func() {
  1576  			var err error
  1577  			mod, err = queryImport(ld, ctx, pkg.path, pld.requirements)
  1578  			if err != nil {
  1579  				if ime, ok := errors.AsType[*ImportMissingError](err); ok {
  1580  					for curstack := pkg.stack; curstack != nil; curstack = curstack.stack {
  1581  						if ld.MainModules.Contains(curstack.mod.Path) {
  1582  							ime.ImportingMainModule = curstack.mod
  1583  							ime.modRoot = ld.MainModules.ModRoot(ime.ImportingMainModule)
  1584  							break
  1585  						}
  1586  					}
  1587  				}
  1588  				// pkg.err was already non-nil, so we can reasonably attribute the error
  1589  				// for pkg to either the original error or the one returned by
  1590  				// queryImport. The existing error indicates only that we couldn't find
  1591  				// the package, whereas the query error also explains why we didn't fix
  1592  				// the problem — so we prefer the latter.
  1593  				pkg.err = err
  1594  			}
  1595  
  1596  			// err is nil, but we intentionally leave pkg.err non-nil and pkg.mod
  1597  			// unset: we still haven't satisfied other invariants of a
  1598  			// successfully-loaded package, such as scanning and loading the imports
  1599  			// of that package. If we succeed in resolving the new dependency graph,
  1600  			// the caller can reload pkg and update the error at that point.
  1601  			//
  1602  			// Even then, the package might not be loaded from the version we've
  1603  			// identified here. The module may be upgraded by some other dependency,
  1604  			// or by a transitive dependency of mod itself, or — less likely — the
  1605  			// package may be rejected by an AllowPackage hook or rendered ambiguous
  1606  			// by some other newly-added or newly-upgraded dependency.
  1607  		})
  1608  
  1609  		pkgMods = append(pkgMods, pkgMod{pkg: pkg, mod: &mod})
  1610  	}
  1611  	<-pld.work.Idle()
  1612  
  1613  	modAddedBy = map[module.Version]*loadPkg{}
  1614  
  1615  	var (
  1616  		maxTooNew    *gover.TooNewError
  1617  		maxTooNewPkg *loadPkg
  1618  	)
  1619  	for _, pm := range pkgMods {
  1620  		if tooNew, ok := errors.AsType[*gover.TooNewError](pm.pkg.err); ok {
  1621  			if maxTooNew == nil || gover.Compare(tooNew.GoVersion, maxTooNew.GoVersion) > 0 {
  1622  				maxTooNew = tooNew
  1623  				maxTooNewPkg = pm.pkg
  1624  			}
  1625  		}
  1626  	}
  1627  	if maxTooNew != nil {
  1628  		fmt.Fprintf(os.Stderr, "go: toolchain upgrade needed to resolve %s\n", maxTooNewPkg.path)
  1629  		return nil, maxTooNew
  1630  	}
  1631  
  1632  	for _, pm := range pkgMods {
  1633  		pkg, mod := pm.pkg, *pm.mod
  1634  		if mod.Path == "" {
  1635  			continue
  1636  		}
  1637  
  1638  		fmt.Fprintf(os.Stderr, "go: found %s in %s %s\n", pkg.path, mod.Path, mod.Version)
  1639  		if modAddedBy[mod] == nil {
  1640  			modAddedBy[mod] = pkg
  1641  		}
  1642  	}
  1643  
  1644  	return modAddedBy, nil
  1645  }
  1646  
  1647  // pkg locates the *loadPkg for path, creating and queuing it for loading if
  1648  // needed, and updates its state to reflect the given flags.
  1649  //
  1650  // The imports of the returned *loadPkg will be loaded asynchronously in the
  1651  // ld.work queue, and its test (if requested) will also be populated once
  1652  // imports have been resolved. When ld.work goes idle, all transitive imports of
  1653  // the requested package (and its test, if requested) will have been loaded.
  1654  func (pld *packageLoader) pkg(ld *Loader, ctx context.Context, path string, flags loadPkgFlags) *loadPkg {
  1655  	if flags.has(pkgImportsLoaded) {
  1656  		panic("internal error: (*packageLoader).pkg called with pkgImportsLoaded flag set")
  1657  	}
  1658  
  1659  	pkg := pld.pkgCache.Do(path, func() *loadPkg {
  1660  		pkg := &loadPkg{
  1661  			path: path,
  1662  		}
  1663  		pld.applyPkgFlags(ld, ctx, pkg, flags)
  1664  
  1665  		pld.work.Add(func() { pld.load(ld, ctx, pkg) })
  1666  		return pkg
  1667  	})
  1668  
  1669  	pld.applyPkgFlags(ld, ctx, pkg, flags)
  1670  	return pkg
  1671  }
  1672  
  1673  // applyPkgFlags updates pkg.flags to set the given flags and propagate the
  1674  // (transitive) effects of those flags, possibly loading or enqueueing further
  1675  // packages as a result.
  1676  func (pld *packageLoader) applyPkgFlags(ld *Loader, ctx context.Context, pkg *loadPkg, flags loadPkgFlags) {
  1677  	if flags == 0 {
  1678  		return
  1679  	}
  1680  
  1681  	if flags.has(pkgInAll) && pld.allPatternIsRoot && !pkg.isTest() {
  1682  		// This package matches a root pattern by virtue of being in "all".
  1683  		flags |= pkgIsRoot
  1684  	}
  1685  	if flags.has(pkgIsRoot) {
  1686  		flags |= pkgFromRoot
  1687  	}
  1688  
  1689  	old := pkg.flags.update(flags)
  1690  	new := old | flags
  1691  	if new == old || !new.has(pkgImportsLoaded) {
  1692  		// We either didn't change the state of pkg, or we don't know anything about
  1693  		// its dependencies yet. Either way, we can't usefully load its test or
  1694  		// update its dependencies.
  1695  		return
  1696  	}
  1697  
  1698  	if !pkg.isTest() {
  1699  		// Check whether we should add (or update the flags for) a test for pkg.
  1700  		// ld.pkgTest is idempotent and extra invocations are inexpensive,
  1701  		// so it's ok if we call it more than is strictly necessary.
  1702  		wantTest := false
  1703  		switch {
  1704  		case pld.allPatternIsRoot && ld.MainModules.Contains(pkg.mod.Path):
  1705  			// We are loading the "all" pattern, which includes packages imported by
  1706  			// tests in the main module. This package is in the main module, so we
  1707  			// need to identify the imports of its test even if LoadTests is not set.
  1708  			//
  1709  			// (We will filter out the extra tests explicitly in computePatternAll.)
  1710  			wantTest = true
  1711  
  1712  		case pld.allPatternIsRoot && pld.allClosesOverTests && new.has(pkgInAll):
  1713  			// This variant of the "all" pattern includes imports of tests of every
  1714  			// package that is itself in "all", and pkg is in "all", so its test is
  1715  			// also in "all" (as above).
  1716  			wantTest = true
  1717  
  1718  		case pld.LoadTests && new.has(pkgIsRoot):
  1719  			// LoadTest explicitly requests tests of “the root packages”.
  1720  			wantTest = true
  1721  		}
  1722  
  1723  		if wantTest {
  1724  			var testFlags loadPkgFlags
  1725  			if ld.MainModules.Contains(pkg.mod.Path) || (pld.allClosesOverTests && new.has(pkgInAll)) {
  1726  				// Tests of packages in the main module are in "all", in the sense that
  1727  				// they cause the packages they import to also be in "all". So are tests
  1728  				// of packages in "all" if "all" closes over test dependencies.
  1729  				testFlags |= pkgInAll
  1730  			}
  1731  			pld.pkgTest(ld, ctx, pkg, testFlags)
  1732  		}
  1733  	}
  1734  
  1735  	if new.has(pkgInAll) && !old.has(pkgInAll|pkgImportsLoaded) {
  1736  		// We have just marked pkg with pkgInAll, or we have just loaded its
  1737  		// imports, or both. Now is the time to propagate pkgInAll to the imports.
  1738  		for _, dep := range pkg.imports {
  1739  			pld.applyPkgFlags(ld, ctx, dep, pkgInAll)
  1740  		}
  1741  	}
  1742  
  1743  	if new.has(pkgFromRoot) && !old.has(pkgFromRoot|pkgImportsLoaded) {
  1744  		for _, dep := range pkg.imports {
  1745  			pld.applyPkgFlags(ld, ctx, dep, pkgFromRoot)
  1746  		}
  1747  	}
  1748  }
  1749  
  1750  // preloadRootModules loads the module requirements needed to identify the
  1751  // selected version of each module providing a package in rootPkgs,
  1752  // adding new root modules to the module graph if needed.
  1753  func (pld *packageLoader) preloadRootModules(ld *Loader, ctx context.Context, rootPkgs []string) (changedBuildList bool) {
  1754  	needc := make(chan map[module.Version]bool, 1)
  1755  	needc <- map[module.Version]bool{}
  1756  	for _, path := range rootPkgs {
  1757  		path := path
  1758  		pld.work.Add(func() {
  1759  			// First, try to identify the module containing the package using only roots.
  1760  			//
  1761  			// If the main module is tidy and the package is in "all" — or if we're
  1762  			// lucky — we can identify all of its imports without actually loading the
  1763  			// full module graph.
  1764  			m, _, _, _, err := importFromModules(ld, ctx, path, pld.requirements, nil, pld.skipImportModFiles)
  1765  			if err != nil {
  1766  				if _, ok := errors.AsType[*ImportMissingError](err); ok && pld.ResolveMissingImports {
  1767  					// This package isn't provided by any selected module.
  1768  					// If we can find it, it will be a new root dependency.
  1769  					m, err = queryImport(ld, ctx, path, pld.requirements)
  1770  				}
  1771  				if err != nil {
  1772  					// We couldn't identify the root module containing this package.
  1773  					// Leave it unresolved; we will report it during loading.
  1774  					return
  1775  				}
  1776  			}
  1777  			if m.Path == "" {
  1778  				// The package is in std or cmd. We don't need to change the root set.
  1779  				return
  1780  			}
  1781  
  1782  			v, ok := pld.requirements.rootSelected(ld, m.Path)
  1783  			if !ok || v != m.Version {
  1784  				// We found the requested package in m, but m is not a root, so
  1785  				// loadModGraph will not load its requirements. We need to promote the
  1786  				// module to a root to ensure that any other packages this package
  1787  				// imports are resolved from correct dependency versions.
  1788  				//
  1789  				// (This is the “argument invariant” from
  1790  				// https://golang.org/design/36460-lazy-module-loading.)
  1791  				need := <-needc
  1792  				need[m] = true
  1793  				needc <- need
  1794  			}
  1795  		})
  1796  	}
  1797  	<-pld.work.Idle()
  1798  
  1799  	need := <-needc
  1800  	if len(need) == 0 {
  1801  		return false // No roots to add.
  1802  	}
  1803  
  1804  	toAdd := make([]module.Version, 0, len(need))
  1805  	for m := range need {
  1806  		toAdd = append(toAdd, m)
  1807  	}
  1808  	gover.ModSort(toAdd)
  1809  
  1810  	rs, err := updateRoots(ld, ctx, pld.requirements.direct, pld.requirements, nil, toAdd, pld.AssumeRootsImported)
  1811  	if err != nil {
  1812  		// We are missing some root dependency, and for some reason we can't load
  1813  		// enough of the module dependency graph to add the missing root. Package
  1814  		// loading is doomed to fail, so fail quickly.
  1815  		pld.error(err)
  1816  		pld.exitIfErrors(ctx)
  1817  		return false
  1818  	}
  1819  	if slices.Equal(rs.rootModules, pld.requirements.rootModules) {
  1820  		// Something is deeply wrong. resolveMissingImports gave us a non-empty
  1821  		// set of modules to add to the graph, but adding those modules had no
  1822  		// effect — either they were already in the graph, or updateRoots did not
  1823  		// add them as requested.
  1824  		panic(fmt.Sprintf("internal error: adding %v to module graph had no effect on root requirements (%v)", toAdd, rs.rootModules))
  1825  	}
  1826  
  1827  	pld.requirements = rs
  1828  	return true
  1829  }
  1830  
  1831  // load loads an individual package.
  1832  func (pld *packageLoader) load(ld *Loader, ctx context.Context, pkg *loadPkg) {
  1833  	var mg *ModuleGraph
  1834  	if pld.requirements.pruning == unpruned {
  1835  		var err error
  1836  		mg, err = pld.requirements.Graph(ld, ctx)
  1837  		if err != nil {
  1838  			// We already checked the error from Graph in loadFromRoots and/or
  1839  			// updateRequirements, so we ignored the error on purpose and we should
  1840  			// keep trying to push past it.
  1841  			//
  1842  			// However, because mg may be incomplete (and thus may select inaccurate
  1843  			// versions), we shouldn't use it to load packages. Instead, we pass a nil
  1844  			// *ModuleGraph, which will cause mg to first try loading from only the
  1845  			// main module and root dependencies.
  1846  			mg = nil
  1847  		}
  1848  	}
  1849  
  1850  	var modroot string
  1851  	pkg.mod, modroot, pkg.dir, pkg.altMods, pkg.err = importFromModules(ld, ctx, pkg.path, pld.requirements, mg, pld.skipImportModFiles)
  1852  	if ld.MainModules.Tools()[pkg.path] {
  1853  		// Tools declared by main modules are always in "all".
  1854  		// We apply the package flags before returning so that missing
  1855  		// tool dependencies report an error https://go.dev/issue/70582
  1856  		pld.applyPkgFlags(ld, ctx, pkg, pkgInAll)
  1857  	}
  1858  	if pkg.dir == "" {
  1859  		return
  1860  	}
  1861  	if ld.MainModules.Contains(pkg.mod.Path) {
  1862  		// Go ahead and mark pkg as in "all". This provides the invariant that a
  1863  		// package that is *only* imported by other packages in "all" is always
  1864  		// marked as such before loading its imports.
  1865  		//
  1866  		// We don't actually rely on that invariant at the moment, but it may
  1867  		// improve efficiency somewhat and makes the behavior a bit easier to reason
  1868  		// about (by reducing churn on the flag bits of dependencies), and costs
  1869  		// essentially nothing (these atomic flag ops are essentially free compared
  1870  		// to scanning source code for imports).
  1871  		pld.applyPkgFlags(ld, ctx, pkg, pkgInAll)
  1872  	}
  1873  	if pld.AllowPackage != nil {
  1874  		if err := pld.AllowPackage(ctx, pkg.path, pkg.mod); err != nil {
  1875  			pkg.err = err
  1876  		}
  1877  	}
  1878  
  1879  	pkg.inStd = (search.IsStandardImportPath(pkg.path) && search.InDir(pkg.dir, cfg.GOROOTsrc) != "")
  1880  
  1881  	var imports, testImports []string
  1882  
  1883  	if cfg.BuildContext.Compiler == "gccgo" && pkg.inStd {
  1884  		// We can't scan standard packages for gccgo.
  1885  	} else {
  1886  		var err error
  1887  		imports, testImports, err = scanDir(modroot, pkg.dir, pld.Tags)
  1888  		if err != nil {
  1889  			pkg.err = err
  1890  			return
  1891  		}
  1892  	}
  1893  
  1894  	pkg.imports = make([]*loadPkg, 0, len(imports))
  1895  	var importFlags loadPkgFlags
  1896  	if pkg.flags.has(pkgInAll) {
  1897  		importFlags = pkgInAll
  1898  	}
  1899  	for _, path := range imports {
  1900  		if pkg.inStd {
  1901  			// Imports from packages in "std" and "cmd" should resolve using
  1902  			// GOROOT/src/vendor even when "std" is not the main module.
  1903  			path = pld.stdVendor(ld, pkg.path, path)
  1904  		}
  1905  		pkg.imports = append(pkg.imports, pld.pkg(ld, ctx, path, importFlags))
  1906  	}
  1907  	pkg.testImports = testImports
  1908  
  1909  	pld.applyPkgFlags(ld, ctx, pkg, pkgImportsLoaded)
  1910  }
  1911  
  1912  // pkgTest locates the test of pkg, creating it if needed, and updates its state
  1913  // to reflect the given flags.
  1914  //
  1915  // pkgTest requires that the imports of pkg have already been loaded (flagged
  1916  // with pkgImportsLoaded).
  1917  func (pld *packageLoader) pkgTest(ld *Loader, ctx context.Context, pkg *loadPkg, testFlags loadPkgFlags) *loadPkg {
  1918  	if pkg.isTest() {
  1919  		panic("pkgTest called on a test package")
  1920  	}
  1921  
  1922  	createdTest := false
  1923  	pkg.testOnce.Do(func() {
  1924  		pkg.test = &loadPkg{
  1925  			path:   pkg.path,
  1926  			testOf: pkg,
  1927  			mod:    pkg.mod,
  1928  			dir:    pkg.dir,
  1929  			err:    pkg.err,
  1930  			inStd:  pkg.inStd,
  1931  		}
  1932  		pld.applyPkgFlags(ld, ctx, pkg.test, testFlags)
  1933  		createdTest = true
  1934  	})
  1935  
  1936  	test := pkg.test
  1937  	if createdTest {
  1938  		test.imports = make([]*loadPkg, 0, len(pkg.testImports))
  1939  		var importFlags loadPkgFlags
  1940  		if test.flags.has(pkgInAll) {
  1941  			importFlags = pkgInAll
  1942  		}
  1943  		for _, path := range pkg.testImports {
  1944  			if pkg.inStd {
  1945  				path = pld.stdVendor(ld, test.path, path)
  1946  			}
  1947  			test.imports = append(test.imports, pld.pkg(ld, ctx, path, importFlags))
  1948  		}
  1949  		pkg.testImports = nil
  1950  		pld.applyPkgFlags(ld, ctx, test, pkgImportsLoaded)
  1951  	} else {
  1952  		pld.applyPkgFlags(ld, ctx, test, testFlags)
  1953  	}
  1954  
  1955  	return test
  1956  }
  1957  
  1958  // stdVendor returns the canonical import path for the package with the given
  1959  // path when imported from the standard-library package at parentPath.
  1960  func (pld *packageLoader) stdVendor(ld *Loader, parentPath, path string) string {
  1961  	if p, _, ok := fips140.ResolveImport(path); ok {
  1962  		return p
  1963  	}
  1964  	if search.IsStandardImportPath(path) {
  1965  		return path
  1966  	}
  1967  
  1968  	if str.HasPathPrefix(parentPath, "cmd") {
  1969  		if !pld.VendorModulesInGOROOTSrc || !ld.MainModules.Contains("cmd") {
  1970  			vendorPath := pathpkg.Join("cmd", "vendor", path)
  1971  
  1972  			if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
  1973  				return vendorPath
  1974  			}
  1975  		}
  1976  	} else if !pld.VendorModulesInGOROOTSrc || !ld.MainModules.Contains("std") || str.HasPathPrefix(parentPath, "vendor") {
  1977  		// If we are outside of the 'std' module, resolve imports from within 'std'
  1978  		// to the vendor directory.
  1979  		//
  1980  		// Do the same for importers beginning with the prefix 'vendor/' even if we
  1981  		// are *inside* of the 'std' module: the 'vendor/' packages that resolve
  1982  		// globally from GOROOT/src/vendor (and are listed as part of 'go list std')
  1983  		// are distinct from the real module dependencies, and cannot import
  1984  		// internal packages from the real module.
  1985  		//
  1986  		// (Note that although the 'vendor/' packages match the 'std' *package*
  1987  		// pattern, they are not part of the std *module*, and do not affect
  1988  		// 'go mod tidy' and similar module commands when working within std.)
  1989  		vendorPath := pathpkg.Join("vendor", path)
  1990  		if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
  1991  			return vendorPath
  1992  		}
  1993  	}
  1994  
  1995  	// Not vendored: resolve from modules.
  1996  	return path
  1997  }
  1998  
  1999  // computePatternAll returns the list of packages matching pattern "all",
  2000  // starting with a list of the import paths for the packages in the main module.
  2001  func (pld *packageLoader) computePatternAll() (all []string) {
  2002  	for _, pkg := range pld.pkgs {
  2003  		if module.CheckImportPath(pkg.path) != nil {
  2004  			// Don't add packages with invalid paths. This means that
  2005  			// we don't try to load invalid imports of the main modules'
  2006  			// packages. We will still report an errors invalid imports
  2007  			// when we load the importing package.
  2008  			continue
  2009  		}
  2010  		if pkg.flags.has(pkgInAll) && !pkg.isTest() {
  2011  			all = append(all, pkg.path)
  2012  		}
  2013  	}
  2014  	sort.Strings(all)
  2015  	return all
  2016  }
  2017  
  2018  // checkMultiplePaths verifies that a given module path is used as itself
  2019  // or as a replacement for another module, but not both at the same time.
  2020  //
  2021  // (See https://golang.org/issue/26607 and https://golang.org/issue/34650.)
  2022  func (pld *packageLoader) checkMultiplePaths(ld *Loader) {
  2023  	if cached := pld.requirements.graph.Load(); cached != nil {
  2024  		if mg := cached.mg; mg != nil {
  2025  			// The check depends only on the build list and workspace replace
  2026  			// directives, both fixed for the lifetime of mg, so skip it on
  2027  			// subsequent calls sharing the same graph.
  2028  			mg.checkPathsOnce.Do(func() {
  2029  				checkMultiplePathsUncached(ld, pld, mg.BuildList())
  2030  			})
  2031  			return
  2032  		}
  2033  	}
  2034  	checkMultiplePathsUncached(ld, pld, pld.requirements.rootModules)
  2035  }
  2036  
  2037  func checkMultiplePathsUncached(ld *Loader, pld *packageLoader, mods []module.Version) {
  2038  	firstPath := map[module.Version]string{}
  2039  	for _, mod := range mods {
  2040  		src := resolveReplacement(ld, mod)
  2041  		if prev, ok := firstPath[src]; !ok {
  2042  			firstPath[src] = mod.Path
  2043  		} else if prev != mod.Path {
  2044  			pld.error(fmt.Errorf("%s@%s used for two different module paths (%s and %s)", src.Path, src.Version, prev, mod.Path))
  2045  		}
  2046  	}
  2047  }
  2048  
  2049  // checkTidyCompatibility emits an error if any package would be loaded from a
  2050  // different module under rs than under ld.requirements.
  2051  func (pld *packageLoader) checkTidyCompatibility(ld *Loader, ctx context.Context, rs *Requirements, compatVersion string) {
  2052  	goVersion := rs.GoVersion(ld)
  2053  	suggestUpgrade := false
  2054  	suggestEFlag := false
  2055  	suggestFixes := func() {
  2056  		if pld.AllowErrors {
  2057  			// The user is explicitly ignoring these errors, so don't bother them with
  2058  			// other options.
  2059  			return
  2060  		}
  2061  
  2062  		// We print directly to os.Stderr because this information is advice about
  2063  		// how to fix errors, not actually an error itself.
  2064  		// (The actual errors should have been logged already.)
  2065  
  2066  		fmt.Fprintln(os.Stderr)
  2067  
  2068  		goFlag := ""
  2069  		if goVersion != ld.MainModules.GoVersion(ld) {
  2070  			goFlag = " -go=" + goVersion
  2071  		}
  2072  
  2073  		compatFlag := ""
  2074  		if compatVersion != gover.Prev(goVersion) {
  2075  			compatFlag = " -compat=" + compatVersion
  2076  		}
  2077  		if suggestUpgrade {
  2078  			eDesc := ""
  2079  			eFlag := ""
  2080  			if suggestEFlag {
  2081  				eDesc = ", leaving some packages unresolved"
  2082  				eFlag = " -e"
  2083  			}
  2084  			fmt.Fprintf(os.Stderr, "To upgrade to the versions selected by go %s%s:\n\tgo mod tidy%s -go=%s && go mod tidy%s -go=%s%s\n", compatVersion, eDesc, eFlag, compatVersion, eFlag, goVersion, compatFlag)
  2085  		} else if suggestEFlag {
  2086  			// If some packages are missing but no package is upgraded, then we
  2087  			// shouldn't suggest upgrading to the Go 1.16 versions explicitly — that
  2088  			// wouldn't actually fix anything for Go 1.16 users, and *would* break
  2089  			// something for Go 1.17 users.
  2090  			fmt.Fprintf(os.Stderr, "To proceed despite packages unresolved in go %s:\n\tgo mod tidy -e%s%s\n", compatVersion, goFlag, compatFlag)
  2091  		}
  2092  
  2093  		fmt.Fprintf(os.Stderr, "If reproducibility with go %s is not needed:\n\tgo mod tidy%s -compat=%s\n", compatVersion, goFlag, goVersion)
  2094  
  2095  		fmt.Fprintf(os.Stderr, "For information about 'go mod tidy' compatibility, see:\n\thttps://go.dev/ref/mod#graph-pruning\n")
  2096  	}
  2097  
  2098  	mg, err := rs.Graph(ld, ctx)
  2099  	if err != nil {
  2100  		pld.error(fmt.Errorf("error loading go %s module graph: %w", compatVersion, err))
  2101  		pld.switchIfErrors(ctx)
  2102  		suggestFixes()
  2103  		pld.exitIfErrors(ctx)
  2104  		return
  2105  	}
  2106  
  2107  	// Re-resolve packages in parallel.
  2108  	//
  2109  	// We re-resolve each package — rather than just checking versions — to ensure
  2110  	// that we have fetched module source code (and, importantly, checksums for
  2111  	// that source code) for all modules that are necessary to ensure that imports
  2112  	// are unambiguous. That also produces clearer diagnostics, since we can say
  2113  	// exactly what happened to the package if it became ambiguous or disappeared
  2114  	// entirely.
  2115  	//
  2116  	// We re-resolve the packages in parallel because this process involves disk
  2117  	// I/O to check for package sources, and because the process of checking for
  2118  	// ambiguous imports may require us to download additional modules that are
  2119  	// otherwise pruned out in Go 1.17 — we don't want to block progress on other
  2120  	// packages while we wait for a single new download.
  2121  	type mismatch struct {
  2122  		mod module.Version
  2123  		err error
  2124  	}
  2125  	mismatchMu := make(chan map[*loadPkg]mismatch, 1)
  2126  	mismatchMu <- map[*loadPkg]mismatch{}
  2127  	for _, pkg := range pld.pkgs {
  2128  		if pkg.mod.Path == "" && pkg.err == nil {
  2129  			// This package is from the standard library (which does not vary based on
  2130  			// the module graph).
  2131  			continue
  2132  		}
  2133  
  2134  		pkg := pkg
  2135  		pld.work.Add(func() {
  2136  			mod, _, _, _, err := importFromModules(ld, ctx, pkg.path, rs, mg, pld.skipImportModFiles)
  2137  			if mod != pkg.mod {
  2138  				mismatches := <-mismatchMu
  2139  				mismatches[pkg] = mismatch{mod: mod, err: err}
  2140  				mismatchMu <- mismatches
  2141  			}
  2142  		})
  2143  	}
  2144  	<-pld.work.Idle()
  2145  
  2146  	mismatches := <-mismatchMu
  2147  	if len(mismatches) == 0 {
  2148  		// Since we're running as part of 'go mod tidy', the roots of the module
  2149  		// graph should contain only modules that are relevant to some package in
  2150  		// the package graph. We checked every package in the package graph and
  2151  		// didn't find any mismatches, so that must mean that all of the roots of
  2152  		// the module graph are also consistent.
  2153  		//
  2154  		// If we're wrong, Go 1.16 in -mod=readonly mode will error out with
  2155  		// "updates to go.mod needed", which would be very confusing. So instead,
  2156  		// we'll double-check that our reasoning above actually holds — if it
  2157  		// doesn't, we'll emit an internal error and hopefully the user will report
  2158  		// it as a bug.
  2159  		for _, m := range pld.requirements.rootModules {
  2160  			if v := mg.Selected(m.Path); v != m.Version {
  2161  				fmt.Fprintln(os.Stderr)
  2162  				base.Fatalf("go: internal error: failed to diagnose selected-version mismatch for module %s: go %s selects %s, but go %s selects %s\n\tPlease report this at https://go.dev/issue.", m.Path, goVersion, m.Version, compatVersion, v)
  2163  			}
  2164  		}
  2165  		return
  2166  	}
  2167  
  2168  	// Iterate over the packages (instead of the mismatches map) to emit errors in
  2169  	// deterministic order.
  2170  	for _, pkg := range pld.pkgs {
  2171  		mismatch, ok := mismatches[pkg]
  2172  		if !ok {
  2173  			continue
  2174  		}
  2175  
  2176  		if pkg.isTest() {
  2177  			// We already did (or will) report an error for the package itself,
  2178  			// so don't report a duplicate (and more verbose) error for its test.
  2179  			if _, ok := mismatches[pkg.testOf]; !ok {
  2180  				base.Fatalf("go: internal error: mismatch recorded for test %s, but not its non-test package", pkg.path)
  2181  			}
  2182  			continue
  2183  		}
  2184  
  2185  		switch {
  2186  		case mismatch.err != nil:
  2187  			// pkg resolved successfully, but errors out using the requirements in rs.
  2188  			//
  2189  			// This could occur because the import is provided by a single root (and
  2190  			// is thus unambiguous in a main module with a pruned module graph) and
  2191  			// also one or more transitive dependencies (and is ambiguous with an
  2192  			// unpruned graph).
  2193  			//
  2194  			// It could also occur because some transitive dependency upgrades the
  2195  			// module that previously provided the package to a version that no
  2196  			// longer does, or to a version for which the module source code (but
  2197  			// not the go.mod file in isolation) has a checksum error.
  2198  			if _, ok := errors.AsType[*ImportMissingError](mismatch.err); ok {
  2199  				selected := module.Version{
  2200  					Path:    pkg.mod.Path,
  2201  					Version: mg.Selected(pkg.mod.Path),
  2202  				}
  2203  				pld.error(fmt.Errorf("%s loaded from %v,\n\tbut go %s would fail to locate it in %s", pkg.stackText(), pkg.mod, compatVersion, selected))
  2204  			} else {
  2205  				if _, ok := errors.AsType[*AmbiguousImportError](mismatch.err); ok {
  2206  					// TODO: Is this check needed?
  2207  				}
  2208  				pld.error(fmt.Errorf("%s loaded from %v,\n\tbut go %s would fail to locate it:\n\t%v", pkg.stackText(), pkg.mod, compatVersion, mismatch.err))
  2209  			}
  2210  
  2211  			suggestEFlag = true
  2212  
  2213  			// Even if we press ahead with the '-e' flag, the older version will
  2214  			// error out in readonly mode if it thinks the go.mod file contains
  2215  			// any *explicit* dependency that is not at its selected version,
  2216  			// even if that dependency is not relevant to any package being loaded.
  2217  			//
  2218  			// We check for that condition here. If all of the roots are consistent
  2219  			// the '-e' flag suffices, but otherwise we need to suggest an upgrade.
  2220  			if !suggestUpgrade {
  2221  				for _, m := range pld.requirements.rootModules {
  2222  					if v := mg.Selected(m.Path); v != m.Version {
  2223  						suggestUpgrade = true
  2224  						break
  2225  					}
  2226  				}
  2227  			}
  2228  
  2229  		case pkg.err != nil:
  2230  			// pkg had an error in with a pruned module graph (presumably suppressed
  2231  			// with the -e flag), but the error went away using an unpruned graph.
  2232  			//
  2233  			// This is possible, if, say, the import is unresolved in the pruned graph
  2234  			// (because the "latest" version of each candidate module either is
  2235  			// unavailable or does not contain the package), but is resolved in the
  2236  			// unpruned graph due to a newer-than-latest dependency that is normally
  2237  			// pruned out.
  2238  			//
  2239  			// This could also occur if the source code for the module providing the
  2240  			// package in the pruned graph has a checksum error, but the unpruned
  2241  			// graph upgrades that module to a version with a correct checksum.
  2242  			//
  2243  			// pkg.err should have already been logged elsewhere — along with a
  2244  			// stack trace — so log only the import path and non-error info here.
  2245  			suggestUpgrade = true
  2246  			pld.error(fmt.Errorf("%s failed to load from any module,\n\tbut go %s would load it from %v", pkg.path, compatVersion, mismatch.mod))
  2247  
  2248  		case pkg.mod != mismatch.mod:
  2249  			// The package is loaded successfully by both Go versions, but from a
  2250  			// different module in each. This could lead to subtle (and perhaps even
  2251  			// unnoticed!) variations in behavior between builds with different
  2252  			// toolchains.
  2253  			suggestUpgrade = true
  2254  			pld.error(fmt.Errorf("%s loaded from %v,\n\tbut go %s would select %v\n", pkg.stackText(), pkg.mod, compatVersion, mismatch.mod.Version))
  2255  
  2256  		default:
  2257  			base.Fatalf("go: internal error: mismatch recorded for package %s, but no differences found", pkg.path)
  2258  		}
  2259  	}
  2260  
  2261  	pld.switchIfErrors(ctx)
  2262  	suggestFixes()
  2263  	pld.exitIfErrors(ctx)
  2264  }
  2265  
  2266  // scanDir is like imports.ScanDir but elides known magic imports from the list,
  2267  // so that we do not go looking for packages that don't really exist.
  2268  //
  2269  // The standard magic import is "C", for cgo.
  2270  //
  2271  // The only other known magic imports are appengine and appengine/*.
  2272  // These are so old that they predate "go get" and did not use URL-like paths.
  2273  // Most code today now uses google.golang.org/appengine instead,
  2274  // but not all code has been so updated. When we mostly ignore build tags
  2275  // during "go vendor", we look into "// +build appengine" files and
  2276  // may see these legacy imports. We drop them so that the module
  2277  // search does not look for modules to try to satisfy them.
  2278  func scanDir(modroot string, dir string, tags map[string]bool) (imports_, testImports []string, err error) {
  2279  	if ip, mierr := modindex.GetPackage(modroot, dir); mierr == nil {
  2280  		imports_, testImports, err = ip.ScanDir(tags)
  2281  		goto Happy
  2282  	} else if !errors.Is(mierr, modindex.ErrNotIndexed) {
  2283  		return nil, nil, mierr
  2284  	}
  2285  
  2286  	imports_, testImports, err = imports.ScanDir(dir, tags)
  2287  Happy:
  2288  
  2289  	filter := func(x []string) []string {
  2290  		w := 0
  2291  		for _, pkg := range x {
  2292  			if pkg != "C" && pkg != "appengine" && !strings.HasPrefix(pkg, "appengine/") &&
  2293  				pkg != "appengine_internal" && !strings.HasPrefix(pkg, "appengine_internal/") {
  2294  				x[w] = pkg
  2295  				w++
  2296  			}
  2297  		}
  2298  		return x[:w]
  2299  	}
  2300  
  2301  	return filter(imports_), filter(testImports), err
  2302  }
  2303  
  2304  // buildStacks computes minimal import stacks for each package,
  2305  // for use in error messages. When it completes, packages that
  2306  // are part of the original root set have pkg.stack == nil,
  2307  // and other packages have pkg.stack pointing at the next
  2308  // package up the import stack in their minimal chain.
  2309  // As a side effect, buildStacks also constructs ld.pkgs,
  2310  // the list of all packages loaded.
  2311  func (pld *packageLoader) buildStacks() {
  2312  	if len(pld.pkgs) > 0 {
  2313  		panic("buildStacks")
  2314  	}
  2315  	for _, pkg := range pld.roots {
  2316  		pkg.stack = pkg // sentinel to avoid processing in next loop
  2317  		pld.pkgs = append(pld.pkgs, pkg)
  2318  	}
  2319  	for i := 0; i < len(pld.pkgs); i++ { // not range: appending to ld.pkgs in loop
  2320  		pkg := pld.pkgs[i]
  2321  		for _, next := range pkg.imports {
  2322  			if next.stack == nil {
  2323  				next.stack = pkg
  2324  				pld.pkgs = append(pld.pkgs, next)
  2325  			}
  2326  		}
  2327  		if next := pkg.test; next != nil && next.stack == nil {
  2328  			next.stack = pkg
  2329  			pld.pkgs = append(pld.pkgs, next)
  2330  		}
  2331  	}
  2332  	for _, pkg := range pld.roots {
  2333  		pkg.stack = nil
  2334  	}
  2335  }
  2336  
  2337  // stackText builds the import stack text to use when
  2338  // reporting an error in pkg. It has the general form
  2339  //
  2340  //	root imports
  2341  //		other imports
  2342  //		other2 tested by
  2343  //		other2.test imports
  2344  //		pkg
  2345  func (pkg *loadPkg) stackText() string {
  2346  	var stack []*loadPkg
  2347  	for p := pkg; p != nil; p = p.stack {
  2348  		stack = append(stack, p)
  2349  	}
  2350  
  2351  	var buf strings.Builder
  2352  	for i := len(stack) - 1; i >= 0; i-- {
  2353  		p := stack[i]
  2354  		fmt.Fprint(&buf, p.path)
  2355  		if p.testOf != nil {
  2356  			fmt.Fprint(&buf, ".test")
  2357  		}
  2358  		if i > 0 {
  2359  			if stack[i-1].testOf == p {
  2360  				fmt.Fprint(&buf, " tested by\n\t")
  2361  			} else {
  2362  				fmt.Fprint(&buf, " imports\n\t")
  2363  			}
  2364  		}
  2365  	}
  2366  	return buf.String()
  2367  }
  2368  
  2369  // why returns the text to use in "go mod why" output about the given package.
  2370  // It is less ornate than the stackText but contains the same information.
  2371  func (pkg *loadPkg) why() string {
  2372  	var buf strings.Builder
  2373  	var stack []*loadPkg
  2374  	for p := pkg; p != nil; p = p.stack {
  2375  		stack = append(stack, p)
  2376  	}
  2377  
  2378  	for i := len(stack) - 1; i >= 0; i-- {
  2379  		p := stack[i]
  2380  		if p.testOf != nil {
  2381  			fmt.Fprintf(&buf, "%s.test\n", p.testOf.path)
  2382  		} else {
  2383  			fmt.Fprintf(&buf, "%s\n", p.path)
  2384  		}
  2385  	}
  2386  	return buf.String()
  2387  }
  2388  
  2389  // Why returns the "go mod why" output stanza for the given package,
  2390  // without the leading # comment.
  2391  // The package graph must have been loaded already, usually by LoadPackages.
  2392  // If there is no reason for the package to be in the current build,
  2393  // Why returns an empty string.
  2394  func (ld *Loader) Why(path string) string {
  2395  	pkg, ok := ld.pkgLoader.pkgCache.Get(path)
  2396  	if !ok {
  2397  		return ""
  2398  	}
  2399  	return pkg.why()
  2400  }
  2401  
  2402  // WhyDepth returns the number of steps in the Why listing.
  2403  // If there is no reason for the package to be in the current build,
  2404  // WhyDepth returns 0.
  2405  func (ld *Loader) WhyDepth(path string) int {
  2406  	n := 0
  2407  	pkg, _ := ld.pkgLoader.pkgCache.Get(path)
  2408  	for p := pkg; p != nil; p = p.stack {
  2409  		n++
  2410  	}
  2411  	return n
  2412  }
  2413  

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