Source file src/go/token/position.go
1 // Copyright 2010 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 token 6 7 import ( 8 "cmp" 9 "fmt" 10 "slices" 11 "strconv" 12 "sync" 13 "sync/atomic" 14 ) 15 16 // If debug is set, invalid offset and position values cause a panic 17 // (go.dev/issue/57490). 18 const debug = false 19 20 // ----------------------------------------------------------------------------- 21 // Positions 22 23 // Position describes an arbitrary source position 24 // including the file, line, and column location. 25 // A Position is valid if the line number is > 0. 26 type Position struct { 27 Filename string // filename, if any 28 Offset int // offset, starting at 0 29 Line int // line number, starting at 1 30 Column int // column number, starting at 1 (byte count) 31 } 32 33 // IsValid reports whether the position is valid. 34 func (pos *Position) IsValid() bool { return pos.Line > 0 } 35 36 // String returns a string in one of several forms: 37 // 38 // file:line:column valid position with file name 39 // file:line valid position with file name but no column (column == 0) 40 // line:column valid position without file name 41 // line valid position without file name and no column (column == 0) 42 // file invalid position with file name 43 // - invalid position without file name 44 func (pos Position) String() string { 45 s := pos.Filename 46 if pos.IsValid() { 47 if s != "" { 48 s += ":" 49 } 50 s += strconv.Itoa(pos.Line) 51 if pos.Column != 0 { 52 s += fmt.Sprintf(":%d", pos.Column) 53 } 54 } 55 if s == "" { 56 s = "-" 57 } 58 return s 59 } 60 61 // Pos is a compact encoding of a source position within a file set. 62 // It can be converted into a [Position] for a more convenient, but much 63 // larger, representation. 64 // 65 // The Pos value for a given file is a number in the range [base, base+size], 66 // where base and size are specified when a file is added to the file set. 67 // The difference between a Pos value and the corresponding file base 68 // corresponds to the byte offset of that position (represented by the Pos value) 69 // from the beginning of the file. Thus, the file base offset is the Pos value 70 // representing the first byte in the file. 71 // 72 // To create the Pos value for a specific source offset (measured in bytes), 73 // first add the respective file to the current file set using [FileSet.AddFile] 74 // and then call [File.Pos](offset) for that file. Given a Pos value p 75 // for a specific file set fset, the corresponding [Position] value is 76 // obtained by calling fset.Position(p). 77 // 78 // Pos values can be compared directly with the usual comparison operators: 79 // If two Pos values p and q are in the same file, comparing p and q is 80 // equivalent to comparing the respective source file offsets. If p and q 81 // are in different files, p < q is true if the file implied by p was added 82 // to the respective file set before the file implied by q. 83 type Pos int 84 85 // The zero value for [Pos] is NoPos; there is no file and line information 86 // associated with it, and NoPos.IsValid() is false. NoPos is always 87 // smaller than any other [Pos] value. The corresponding [Position] value 88 // for NoPos is the zero value for [Position]. 89 const NoPos Pos = 0 90 91 // IsValid reports whether the position is valid. 92 func (p Pos) IsValid() bool { 93 return p != NoPos 94 } 95 96 // ----------------------------------------------------------------------------- 97 // File 98 99 // A File is a handle for a file belonging to a [FileSet]. 100 // A File has a name, size, and line offset table. 101 // 102 // Use [FileSet.AddFile] to create a File. 103 // A File may belong to more than one FileSet; see [FileSet.AddExistingFiles]. 104 type File struct { 105 name string // file name as provided to AddFile 106 base int // Pos value range for this file is [base...base+size] 107 size int // file size as provided to AddFile 108 109 // lines and infos are protected by mutex 110 mutex sync.Mutex 111 lines []int // lines contains the offset of the first character for each line (the first entry is always 0) 112 infos []lineInfo 113 } 114 115 // Name returns the file name of file f as registered with AddFile. 116 func (f *File) Name() string { 117 return f.name 118 } 119 120 // Base returns the base offset of file f as registered with AddFile. 121 func (f *File) Base() int { 122 return f.base 123 } 124 125 // Size returns the size of file f as registered with AddFile. 126 func (f *File) Size() int { 127 return f.size 128 } 129 130 // LineCount returns the number of lines in file f. 131 func (f *File) LineCount() int { 132 f.mutex.Lock() 133 n := len(f.lines) 134 f.mutex.Unlock() 135 return n 136 } 137 138 // AddLine adds the line offset for a new line. 139 // The line offset must be larger than the offset for the previous line 140 // and smaller than the file size; otherwise the line offset is ignored. 141 func (f *File) AddLine(offset int) { 142 f.mutex.Lock() 143 if i := len(f.lines); (i == 0 || f.lines[i-1] < offset) && offset < f.size { 144 f.lines = append(f.lines, offset) 145 } 146 f.mutex.Unlock() 147 } 148 149 // MergeLine merges a line with the following line. It is akin to replacing 150 // the newline character at the end of the line with a space (to not change the 151 // remaining offsets). To obtain the line number, consult e.g. [Position.Line]. 152 // MergeLine will panic if given an invalid line number. 153 func (f *File) MergeLine(line int) { 154 if line < 1 { 155 panic(fmt.Sprintf("invalid line number %d (should be >= 1)", line)) 156 } 157 f.mutex.Lock() 158 defer f.mutex.Unlock() 159 if line >= len(f.lines) { 160 panic(fmt.Sprintf("invalid line number %d (should be < %d)", line, len(f.lines))) 161 } 162 // To merge the line numbered <line> with the line numbered <line+1>, 163 // we need to remove the entry in lines corresponding to the line 164 // numbered <line+1>. The entry in lines corresponding to the line 165 // numbered <line+1> is located at index <line>, since indices in lines 166 // are 0-based and line numbers are 1-based. 167 copy(f.lines[line:], f.lines[line+1:]) 168 f.lines = f.lines[:len(f.lines)-1] 169 } 170 171 // Lines returns the effective line offset table of the form described by [File.SetLines]. 172 // Callers must not mutate the result. 173 func (f *File) Lines() []int { 174 f.mutex.Lock() 175 lines := f.lines 176 f.mutex.Unlock() 177 return lines 178 } 179 180 // SetLines sets the line offsets for a file and reports whether it succeeded. 181 // The line offsets are the offsets of the first character of each line; 182 // for instance for the content "ab\nc\n" the line offsets are {0, 3}. 183 // An empty file has an empty line offset table. 184 // Each line offset must be larger than the offset for the previous line 185 // and smaller than the file size; otherwise SetLines fails and returns 186 // false. 187 // Callers must not mutate the provided slice after SetLines returns. 188 func (f *File) SetLines(lines []int) bool { 189 // verify validity of lines table 190 size := f.size 191 for i, offset := range lines { 192 if i > 0 && offset <= lines[i-1] || size <= offset { 193 return false 194 } 195 } 196 197 // set lines table 198 f.mutex.Lock() 199 f.lines = lines 200 f.mutex.Unlock() 201 return true 202 } 203 204 // SetLinesForContent sets the line offsets for the given file content. 205 // It ignores position-altering //line comments. 206 func (f *File) SetLinesForContent(content []byte) { 207 var lines []int 208 line := 0 209 for offset, b := range content { 210 if line >= 0 { 211 lines = append(lines, line) 212 } 213 line = -1 214 if b == '\n' { 215 line = offset + 1 216 } 217 } 218 219 // set lines table 220 f.mutex.Lock() 221 f.lines = lines 222 f.mutex.Unlock() 223 } 224 225 // LineStart returns the [Pos] value of the start of the specified line. 226 // It ignores any alternative positions set using [File.AddLineColumnInfo]. 227 // LineStart panics if the 1-based line number is invalid. 228 func (f *File) LineStart(line int) Pos { 229 if line < 1 { 230 panic(fmt.Sprintf("invalid line number %d (should be >= 1)", line)) 231 } 232 f.mutex.Lock() 233 defer f.mutex.Unlock() 234 if line > len(f.lines) { 235 panic(fmt.Sprintf("invalid line number %d (should be < %d)", line, len(f.lines))) 236 } 237 return Pos(f.base + f.lines[line-1]) 238 } 239 240 // A lineInfo object describes alternative file, line, and column 241 // number information (such as provided via a //line directive) 242 // for a given file offset. 243 type lineInfo struct { 244 // fields are exported to make them accessible to gob 245 Offset int 246 Filename string 247 Line, Column int 248 } 249 250 // AddLineInfo is like [File.AddLineColumnInfo] with a column = 1 argument. 251 // It is here for backward-compatibility for code prior to Go 1.11. 252 func (f *File) AddLineInfo(offset int, filename string, line int) { 253 f.AddLineColumnInfo(offset, filename, line, 1) 254 } 255 256 // AddLineColumnInfo adds alternative file, line, and column number 257 // information for a given file offset. The offset must be larger 258 // than the offset for the previously added alternative line info 259 // and smaller than the file size; otherwise the information is 260 // ignored. 261 // 262 // AddLineColumnInfo is typically used to register alternative position 263 // information for line directives such as //line filename:line:column. 264 func (f *File) AddLineColumnInfo(offset int, filename string, line, column int) { 265 f.mutex.Lock() 266 if i := len(f.infos); (i == 0 || f.infos[i-1].Offset < offset) && offset < f.size { 267 f.infos = append(f.infos, lineInfo{offset, filename, line, column}) 268 } 269 f.mutex.Unlock() 270 } 271 272 // fixOffset fixes an out-of-bounds offset such that 0 <= offset <= f.size. 273 func (f *File) fixOffset(offset int) int { 274 switch { 275 case offset < 0: 276 if !debug { 277 return 0 278 } 279 case offset > f.size: 280 if !debug { 281 return f.size 282 } 283 default: 284 return offset 285 } 286 287 // only generate this code if needed 288 if debug { 289 panic(fmt.Sprintf("offset %d out of bounds [%d, %d] (position %d out of bounds [%d, %d])", 290 0 /* for symmetry */, offset, f.size, 291 f.base+offset, f.base, f.base+f.size)) 292 } 293 return 0 294 } 295 296 // Pos returns the Pos value for the given file offset. 297 // 298 // If offset is negative, the result is the file's start 299 // position; if the offset is too large, the result is 300 // the file's end position (see also go.dev/issue/57490). 301 // 302 // The following invariant, though not true for Pos values 303 // in general, holds for the result p: 304 // f.Pos(f.Offset(p)) == p. 305 func (f *File) Pos(offset int) Pos { 306 return Pos(f.base + f.fixOffset(offset)) 307 } 308 309 // Offset returns the offset for the given file position p. 310 // 311 // If p is before the file's start position (or if p is NoPos), 312 // the result is 0; if p is past the file's end position, 313 // the result is the file size (see also go.dev/issue/57490). 314 // 315 // The following invariant, though not true for offset values 316 // in general, holds for the result offset: 317 // f.Offset(f.Pos(offset)) == offset 318 func (f *File) Offset(p Pos) int { 319 return f.fixOffset(int(p) - f.base) 320 } 321 322 // Line returns the line number for the given file position p; 323 // p must be a [Pos] value in that file or [NoPos]. 324 func (f *File) Line(p Pos) int { 325 return f.Position(p).Line 326 } 327 328 func searchLineInfos(a []lineInfo, x int) int { 329 i, found := slices.BinarySearchFunc(a, x, func(a lineInfo, x int) int { 330 return cmp.Compare(a.Offset, x) 331 }) 332 if !found { 333 // We want the lineInfo containing x, but if we didn't 334 // find x then i is the next one. 335 i-- 336 } 337 return i 338 } 339 340 // unpack returns the filename and line and column number for a file offset. 341 // If adjusted is set, unpack will return the filename and line information 342 // possibly adjusted by //line comments; otherwise those comments are ignored. 343 func (f *File) unpack(offset int, adjusted bool) (filename string, line, column int) { 344 f.mutex.Lock() 345 filename = f.name 346 if i := searchInts(f.lines, offset); i >= 0 { 347 line, column = i+1, offset-f.lines[i]+1 348 } 349 if adjusted && len(f.infos) > 0 { 350 // few files have extra line infos 351 if i := searchLineInfos(f.infos, offset); i >= 0 { 352 alt := &f.infos[i] 353 filename = alt.Filename 354 if i := searchInts(f.lines, alt.Offset); i >= 0 { 355 // i+1 is the line at which the alternative position was recorded 356 d := line - (i + 1) // line distance from alternative position base 357 line = alt.Line + d 358 if alt.Column == 0 { 359 // alternative column is unknown => relative column is unknown 360 // (the current specification for line directives requires 361 // this to apply until the next PosBase/line directive, 362 // not just until the new newline) 363 column = 0 364 } else if d == 0 { 365 // the alternative position base is on the current line 366 // => column is relative to alternative column 367 column = alt.Column + (offset - alt.Offset) 368 } 369 } 370 } 371 } 372 // TODO(mvdan): move Unlock back under Lock with a defer statement once 373 // https://go.dev/issue/38471 is fixed to remove the performance penalty. 374 f.mutex.Unlock() 375 return 376 } 377 378 func (f *File) position(p Pos, adjusted bool) (pos Position) { 379 offset := f.fixOffset(int(p) - f.base) 380 pos.Offset = offset 381 pos.Filename, pos.Line, pos.Column = f.unpack(offset, adjusted) 382 return 383 } 384 385 // PositionFor returns the Position value for the given file position p. 386 // If p is out of bounds, it is adjusted to match the File.Offset behavior. 387 // If adjusted is set, the position may be adjusted by position-altering 388 // //line comments; otherwise those comments are ignored. 389 // p must be a Pos value in f or NoPos. 390 func (f *File) PositionFor(p Pos, adjusted bool) (pos Position) { 391 if p != NoPos { 392 pos = f.position(p, adjusted) 393 } 394 return 395 } 396 397 // Position returns the Position value for the given file position p. 398 // If p is out of bounds, it is adjusted to match the File.Offset behavior. 399 // Calling f.Position(p) is equivalent to calling f.PositionFor(p, true). 400 func (f *File) Position(p Pos) (pos Position) { 401 return f.PositionFor(p, true) 402 } 403 404 // ----------------------------------------------------------------------------- 405 // FileSet 406 407 // A FileSet represents a set of source files. 408 // Methods of file sets are synchronized; multiple goroutines 409 // may invoke them concurrently. 410 // 411 // The byte offsets for each file in a file set are mapped into 412 // distinct (integer) intervals, one interval [base, base+size] 413 // per file. [FileSet.Base] represents the first byte in the file, and size 414 // is the corresponding file size. A [Pos] value is a value in such 415 // an interval. By determining the interval a [Pos] value belongs 416 // to, the file, its file base, and thus the byte offset (position) 417 // the [Pos] value is representing can be computed. 418 // 419 // When adding a new file, a file base must be provided. That can 420 // be any integer value that is past the end of any interval of any 421 // file already in the file set. For convenience, [FileSet.Base] provides 422 // such a value, which is simply the end of the Pos interval of the most 423 // recently added file, plus one. Unless there is a need to extend an 424 // interval later, using the [FileSet.Base] should be used as argument 425 // for [FileSet.AddFile]. 426 // 427 // A [File] may be removed from a FileSet when it is no longer needed. 428 // This may reduce memory usage in a long-running application. 429 type FileSet struct { 430 mutex sync.RWMutex // protects the file set 431 base int // base offset for the next file 432 tree tree // tree of files in ascending base order 433 last atomic.Pointer[File] // cache of last file looked up 434 } 435 436 // NewFileSet creates a new file set. 437 func NewFileSet() *FileSet { 438 return &FileSet{ 439 base: 1, // 0 == NoPos 440 } 441 } 442 443 // Base returns the minimum base offset that must be provided to 444 // [FileSet.AddFile] when adding the next file. 445 func (s *FileSet) Base() int { 446 s.mutex.RLock() 447 b := s.base 448 s.mutex.RUnlock() 449 return b 450 } 451 452 // AddFile adds a new file with a given filename, base offset, and file size 453 // to the file set s and returns the file. Multiple files may have the same 454 // name. The base offset must not be smaller than the [FileSet.Base], and 455 // size must not be negative. As a special case, if a negative base is provided, 456 // the current value of the [FileSet.Base] is used instead. 457 // 458 // Adding the file will set the file set's [FileSet.Base] value to base + size + 1 459 // as the minimum base value for the next file. The following relationship 460 // exists between a [Pos] value p for a given file offset offs: 461 // 462 // int(p) = base + offs 463 // 464 // with offs in the range [0, size] and thus p in the range [base, base+size]. 465 // For convenience, [File.Pos] may be used to create file-specific position 466 // values from a file offset. 467 func (s *FileSet) AddFile(filename string, base, size int) *File { 468 // Allocate f outside the critical section. 469 f := &File{name: filename, size: size, lines: []int{0}} 470 471 s.mutex.Lock() 472 defer s.mutex.Unlock() 473 if base < 0 { 474 base = s.base 475 } 476 if base < s.base { 477 panic(fmt.Sprintf("invalid base %d (should be >= %d)", base, s.base)) 478 } 479 f.base = base 480 if size < 0 { 481 panic(fmt.Sprintf("invalid size %d (should be >= 0)", size)) 482 } 483 // base >= s.base && size >= 0 484 base += size + 1 // +1 because EOF also has a position 485 if base < 0 { 486 panic("token.Pos offset overflow (> 2G of source code in file set)") 487 } 488 // add the file to the file set 489 s.base = base 490 s.tree.add(f) 491 s.last.Store(f) 492 return f 493 } 494 495 // AddExistingFiles adds the specified files to the 496 // FileSet if they are not already present. 497 // The caller must ensure that no pair of Files that 498 // would appear in the resulting FileSet overlap. 499 func (s *FileSet) AddExistingFiles(files ...*File) { 500 // This function cannot be implemented as: 501 // 502 // for _, file := range files { 503 // if prev := fset.File(token.Pos(file.Base())); prev != nil { 504 // if prev != file { 505 // panic("FileSet contains a different file at the same base") 506 // } 507 // continue 508 // } 509 // file2 := fset.AddFile(file.Name(), file.Base(), file.Size()) 510 // file2.SetLines(file.Lines()) 511 // } 512 // 513 // because all calls to AddFile must be in increasing order. 514 // AddExistingFilesFiles lets us augment an existing FileSet 515 // sequentially, so long as all sets of files have disjoint ranges. 516 // This approach also does not preserve line directives. 517 518 s.mutex.Lock() 519 defer s.mutex.Unlock() 520 521 for _, f := range files { 522 s.tree.add(f) 523 s.base = max(s.base, f.Base()+f.Size()+1) 524 } 525 } 526 527 // RemoveFile removes a file from the [FileSet] so that subsequent 528 // queries for its [Pos] interval yield a negative result. 529 // This reduces the memory usage of a long-lived [FileSet] that 530 // encounters an unbounded stream of files. 531 // 532 // Removing a file that does not belong to the set has no effect. 533 func (s *FileSet) RemoveFile(file *File) { 534 s.last.CompareAndSwap(file, nil) // clear last file cache 535 536 s.mutex.Lock() 537 defer s.mutex.Unlock() 538 539 pn, _ := s.tree.locate(file.key()) 540 if *pn != nil && (*pn).file == file { 541 s.tree.delete(pn) 542 } 543 } 544 545 // Iterate calls yield for the files in the file set in ascending Base 546 // order until yield returns false. 547 func (s *FileSet) Iterate(yield func(*File) bool) { 548 s.mutex.RLock() 549 defer s.mutex.RUnlock() 550 551 // Unlock around user code. 552 // The iterator is robust to modification by yield. 553 // Avoid range here, so we can use defer. 554 s.tree.all()(func(f *File) bool { 555 s.mutex.RUnlock() 556 defer s.mutex.RLock() 557 return yield(f) 558 }) 559 } 560 561 func (s *FileSet) file(p Pos) *File { 562 // common case: p is in last file. 563 if f := s.last.Load(); f != nil && f.base <= int(p) && int(p) <= f.base+f.size { 564 return f 565 } 566 567 s.mutex.RLock() 568 defer s.mutex.RUnlock() 569 570 pn, _ := s.tree.locate(key{int(p), int(p)}) 571 if n := *pn; n != nil { 572 // Update cache of last file. A race is ok, 573 // but an exclusive lock causes heavy contention. 574 s.last.Store(n.file) 575 return n.file 576 } 577 return nil 578 } 579 580 // File returns the file that contains the position p. 581 // If no such file is found (for instance for p == [NoPos]), 582 // the result is nil. 583 func (s *FileSet) File(p Pos) (f *File) { 584 if p != NoPos { 585 f = s.file(p) 586 } 587 return 588 } 589 590 // PositionFor converts a [Pos] p in the fileset into a [Position] value. 591 // If adjusted is set, the position may be adjusted by position-altering 592 // //line comments; otherwise those comments are ignored. 593 // p must be a [Pos] value in s or [NoPos]. 594 func (s *FileSet) PositionFor(p Pos, adjusted bool) (pos Position) { 595 if p != NoPos { 596 if f := s.file(p); f != nil { 597 return f.position(p, adjusted) 598 } 599 } 600 return 601 } 602 603 // Position converts a [Pos] p in the fileset into a Position value. 604 // Calling s.Position(p) is equivalent to calling s.PositionFor(p, true). 605 func (s *FileSet) Position(p Pos) (pos Position) { 606 return s.PositionFor(p, true) 607 } 608 609 // ----------------------------------------------------------------------------- 610 // Helper functions 611 612 func searchInts(a []int, x int) int { 613 // This function body is a manually inlined version of: 614 // 615 // return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1 616 // 617 // With better compiler optimizations, this may not be needed in the 618 // future, but at the moment this change improves the go/printer 619 // benchmark performance by ~30%. This has a direct impact on the 620 // speed of gofmt and thus seems worthwhile (2011-04-29). 621 // TODO(gri): Remove this when compilers have caught up. 622 i, j := 0, len(a) 623 for i < j { 624 h := int(uint(i+j) >> 1) // avoid overflow when computing h 625 // i ≤ h < j 626 if a[h] <= x { 627 i = h + 1 628 } else { 629 j = h 630 } 631 } 632 return i - 1 633 } 634