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Source file src/go/token/position.go

Documentation: go/token

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

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