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

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