example_test.go

     1  // Copyright 2015 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  // Only run where builders (build.golang.org) have
     6  // access to compiled packages for import.
     7  //
     8  //go:build !android && !ios && !js && !wasip1
     9  
    10  package types2_test
    11  
    12  // This file shows examples of basic usage of the go/types API.
    13  //
    14  // To locate a Go package, use (*go/build.Context).Import.
    15  // To load, parse, and type-check a complete Go program
    16  // from source, use golang.org/x/tools/go/loader.
    17  
    18  import (
    19  	"cmd/compile/internal/syntax"
    20  	"cmd/compile/internal/types2"
    21  	"fmt"
    22  	"log"
    23  	"regexp"
    24  	"slices"
    25  	"strings"
    26  )
    27  
    28  // ExampleScope prints the tree of Scopes of a package created from a
    29  // set of parsed files.
    30  func ExampleScope() {
    31  	// Parse the source files for a package.
    32  	var files []*syntax.File
    33  	for _, src := range []string{
    34  		`package main
    35  import "fmt"
    36  func main() {
    37  	freezing := FToC(-18)
    38  	fmt.Println(freezing, Boiling) }
    39  `,
    40  		`package main
    41  import "fmt"
    42  type Celsius float64
    43  func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
    44  func FToC(f float64) Celsius { return Celsius(f - 32 / 9 * 5) }
    45  const Boiling Celsius = 100
    46  func Unused() { {}; {{ var x int; _ = x }} } // make sure empty block scopes get printed
    47  `,
    48  	} {
    49  		files = append(files, mustParse(src))
    50  	}
    51  
    52  	// Type-check a package consisting of these files.
    53  	// Type information for the imported "fmt" package
    54  	// comes from $GOROOT/pkg/$GOOS_$GOOARCH/fmt.a.
    55  	conf := types2.Config{Importer: defaultImporter()}
    56  	pkg, err := conf.Check("temperature", files, nil)
    57  	if err != nil {
    58  		log.Fatal(err)
    59  	}
    60  
    61  	// Print the tree of scopes.
    62  	// For determinism, we redact addresses.
    63  	var buf strings.Builder
    64  	pkg.Scope().WriteTo(&buf, 0, true)
    65  	rx := regexp.MustCompile(` 0x[a-fA-F\d]*`)
    66  	fmt.Println(rx.ReplaceAllString(buf.String(), ""))
    67  
    68  	// Output:
    69  	// package "temperature" scope {
    70  	// .  const temperature.Boiling temperature.Celsius
    71  	// .  type temperature.Celsius float64
    72  	// .  func temperature.FToC(f float64) temperature.Celsius
    73  	// .  func temperature.Unused()
    74  	// .  func temperature.main()
    75  	// .  main scope {
    76  	// .  .  package fmt
    77  	// .  .  function scope {
    78  	// .  .  .  var freezing temperature.Celsius
    79  	// .  .  }
    80  	// .  }
    81  	// .  main scope {
    82  	// .  .  package fmt
    83  	// .  .  function scope {
    84  	// .  .  .  var c temperature.Celsius
    85  	// .  .  }
    86  	// .  .  function scope {
    87  	// .  .  .  var f float64
    88  	// .  .  }
    89  	// .  .  function scope {
    90  	// .  .  .  block scope {
    91  	// .  .  .  }
    92  	// .  .  .  block scope {
    93  	// .  .  .  .  block scope {
    94  	// .  .  .  .  .  var x int
    95  	// .  .  .  .  }
    96  	// .  .  .  }
    97  	// .  .  }
    98  	// .  }
    99  	// }
   100  }
   101  
   102  // ExampleInfo prints various facts recorded by the type checker in a
   103  // types2.Info struct: definitions of and references to each named object,
   104  // and the type, value, and mode of every expression in the package.
   105  func ExampleInfo() {
   106  	// Parse a single source file.
   107  	const input = `
   108  package fib
   109  
   110  type S string
   111  
   112  var a, b, c = len(b), S(c), "hello"
   113  
   114  func fib(x int) int {
   115  	if x < 2 {
   116  		return x
   117  	}
   118  	return fib(x-1) - fib(x-2)
   119  }`
   120  	// Type-check the package.
   121  	// We create an empty map for each kind of input
   122  	// we're interested in, and Check populates them.
   123  	info := types2.Info{
   124  		Types: make(map[syntax.Expr]types2.TypeAndValue),
   125  		Defs:  make(map[*syntax.Name]types2.Object),
   126  		Uses:  make(map[*syntax.Name]types2.Object),
   127  	}
   128  	pkg := mustTypecheck(input, nil, &info)
   129  
   130  	// Print package-level variables in initialization order.
   131  	fmt.Printf("InitOrder: %v\n\n", info.InitOrder)
   132  
   133  	// For each named object, print the line and
   134  	// column of its definition and each of its uses.
   135  	fmt.Println("Defs and Uses of each named object:")
   136  	usesByObj := make(map[types2.Object][]string)
   137  	for id, obj := range info.Uses {
   138  		posn := id.Pos()
   139  		lineCol := fmt.Sprintf("%d:%d", posn.Line(), posn.Col())
   140  		usesByObj[obj] = append(usesByObj[obj], lineCol)
   141  	}
   142  	var items []string
   143  	for obj, uses := range usesByObj {
   144  		slices.Sort(uses)
   145  		item := fmt.Sprintf("%s:\n  defined at %s\n  used at %s",
   146  			types2.ObjectString(obj, types2.RelativeTo(pkg)),
   147  			obj.Pos(),
   148  			strings.Join(uses, ", "))
   149  		items = append(items, item)
   150  	}
   151  	slices.Sort(items) // sort by line:col, in effect
   152  	fmt.Println(strings.Join(items, "\n"))
   153  	fmt.Println()
   154  
   155  	fmt.Println("Types and Values of each expression:")
   156  	items = nil
   157  	for expr, tv := range info.Types {
   158  		var buf strings.Builder
   159  		posn := syntax.StartPos(expr)
   160  		tvstr := tv.Type.String()
   161  		if tv.Value != nil {
   162  			tvstr += " = " + tv.Value.String()
   163  		}
   164  		// line:col | expr | mode : type = value
   165  		fmt.Fprintf(&buf, "%2d:%2d | %-19s | %-7s : %s",
   166  			posn.Line(), posn.Col(), types2.ExprString(expr),
   167  			mode(tv), tvstr)
   168  		items = append(items, buf.String())
   169  	}
   170  	slices.Sort(items)
   171  	fmt.Println(strings.Join(items, "\n"))
   172  
   173  	// Output:
   174  	// InitOrder: [c = "hello" b = S(c) a = len(b)]
   175  	//
   176  	// Defs and Uses of each named object:
   177  	// builtin len:
   178  	//   defined at <unknown position>
   179  	//   used at 6:15
   180  	// func fib(x int) int:
   181  	//   defined at fib:8:6
   182  	//   used at 12:20, 12:9
   183  	// type S string:
   184  	//   defined at fib:4:6
   185  	//   used at 6:23
   186  	// type int:
   187  	//   defined at <unknown position>
   188  	//   used at 8:12, 8:17
   189  	// type string:
   190  	//   defined at <unknown position>
   191  	//   used at 4:8
   192  	// var b S:
   193  	//   defined at fib:6:8
   194  	//   used at 6:19
   195  	// var c string:
   196  	//   defined at fib:6:11
   197  	//   used at 6:25
   198  	// var x int:
   199  	//   defined at fib:8:10
   200  	//   used at 10:10, 12:13, 12:24, 9:5
   201  	//
   202  	// Types and Values of each expression:
   203  	//  4: 8 | string              | type    : string
   204  	//  6:15 | len                 | builtin : func(fib.S) int
   205  	//  6:15 | len(b)              | value   : int
   206  	//  6:19 | b                   | var     : fib.S
   207  	//  6:23 | S                   | type    : fib.S
   208  	//  6:23 | S(c)                | value   : fib.S
   209  	//  6:25 | c                   | var     : string
   210  	//  6:29 | "hello"             | value   : string = "hello"
   211  	//  8:12 | int                 | type    : int
   212  	//  8:17 | int                 | type    : int
   213  	//  9: 5 | x                   | var     : int
   214  	//  9: 5 | x < 2               | value   : untyped bool
   215  	//  9: 9 | 2                   | value   : int = 2
   216  	// 10:10 | x                   | var     : int
   217  	// 12: 9 | fib                 | value   : func(x int) int
   218  	// 12: 9 | fib(x - 1)          | value   : int
   219  	// 12: 9 | fib(x - 1) - fib(x - 2) | value   : int
   220  	// 12:13 | x                   | var     : int
   221  	// 12:13 | x - 1               | value   : int
   222  	// 12:15 | 1                   | value   : int = 1
   223  	// 12:20 | fib                 | value   : func(x int) int
   224  	// 12:20 | fib(x - 2)          | value   : int
   225  	// 12:24 | x                   | var     : int
   226  	// 12:24 | x - 2               | value   : int
   227  	// 12:26 | 2                   | value   : int = 2
   228  }
   229  
   230  func mode(tv types2.TypeAndValue) string {
   231  	switch {
   232  	case tv.IsVoid():
   233  		return "void"
   234  	case tv.IsType():
   235  		return "type"
   236  	case tv.IsBuiltin():
   237  		return "builtin"
   238  	case tv.IsNil():
   239  		return "nil"
   240  	case tv.Assignable():
   241  		if tv.Addressable() {
   242  			return "var"
   243  		}
   244  		return "mapindex"
   245  	case tv.IsValue():
   246  		return "value"
   247  	default:
   248  		return "unknown"
   249  	}
   250  }
   251
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