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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 < 1 {
   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  // LineStart returns the Pos value of the start of the specified line.
   213  // It ignores any alternative positions set using AddLineColumnInfo.
   214  // LineStart panics if the 1-based line number is invalid.
   215  func (f *File) LineStart(line int) Pos {
   216  	if line < 1 {
   217  		panic("illegal line number (line numbering starts at 1)")
   218  	}
   219  	f.mutex.Lock()
   220  	defer f.mutex.Unlock()
   221  	if line > len(f.lines) {
   222  		panic("illegal line number")
   223  	}
   224  	return Pos(f.base + f.lines[line-1])
   225  }
   226  
   227  // A lineInfo object describes alternative file, line, and column
   228  // number information (such as provided via a //line directive)
   229  // for a given file offset.
   230  type lineInfo struct {
   231  	// fields are exported to make them accessible to gob
   232  	Offset       int
   233  	Filename     string
   234  	Line, Column int
   235  }
   236  
   237  // AddLineInfo is like AddLineColumnInfo with a column = 1 argument.
   238  // It is here for backward-compatibility for code prior to Go 1.11.
   239  //
   240  func (f *File) AddLineInfo(offset int, filename string, line int) {
   241  	f.AddLineColumnInfo(offset, filename, line, 1)
   242  }
   243  
   244  // AddLineColumnInfo adds alternative file, line, and column number
   245  // information for a given file offset. The offset must be larger
   246  // than the offset for the previously added alternative line info
   247  // and smaller than the file size; otherwise the information is
   248  // ignored.
   249  //
   250  // AddLineColumnInfo is typically used to register alternative position
   251  // information for line directives such as //line filename:line:column.
   252  //
   253  func (f *File) AddLineColumnInfo(offset int, filename string, line, column int) {
   254  	f.mutex.Lock()
   255  	if i := len(f.infos); i == 0 || f.infos[i-1].Offset < offset && offset < f.size {
   256  		f.infos = append(f.infos, lineInfo{offset, filename, line, column})
   257  	}
   258  	f.mutex.Unlock()
   259  }
   260  
   261  // Pos returns the Pos value for the given file offset;
   262  // the offset must be <= f.Size().
   263  // f.Pos(f.Offset(p)) == p.
   264  //
   265  func (f *File) Pos(offset int) Pos {
   266  	if offset > f.size {
   267  		panic("illegal file offset")
   268  	}
   269  	return Pos(f.base + offset)
   270  }
   271  
   272  // Offset returns the offset for the given file position p;
   273  // p must be a valid Pos value in that file.
   274  // f.Offset(f.Pos(offset)) == offset.
   275  //
   276  func (f *File) Offset(p Pos) int {
   277  	if int(p) < f.base || int(p) > f.base+f.size {
   278  		panic("illegal Pos value")
   279  	}
   280  	return int(p) - f.base
   281  }
   282  
   283  // Line returns the line number for the given file position p;
   284  // p must be a Pos value in that file or NoPos.
   285  //
   286  func (f *File) Line(p Pos) int {
   287  	return f.Position(p).Line
   288  }
   289  
   290  func searchLineInfos(a []lineInfo, x int) int {
   291  	return sort.Search(len(a), func(i int) bool { return a[i].Offset > x }) - 1
   292  }
   293  
   294  // unpack returns the filename and line and column number for a file offset.
   295  // If adjusted is set, unpack will return the filename and line information
   296  // possibly adjusted by //line comments; otherwise those comments are ignored.
   297  //
   298  func (f *File) unpack(offset int, adjusted bool) (filename string, line, column int) {
   299  	f.mutex.Lock()
   300  	defer f.mutex.Unlock()
   301  	filename = f.name
   302  	if i := searchInts(f.lines, offset); i >= 0 {
   303  		line, column = i+1, offset-f.lines[i]+1
   304  	}
   305  	if adjusted && len(f.infos) > 0 {
   306  		// few files have extra line infos
   307  		if i := searchLineInfos(f.infos, offset); i >= 0 {
   308  			alt := &f.infos[i]
   309  			filename = alt.Filename
   310  			if i := searchInts(f.lines, alt.Offset); i >= 0 {
   311  				// i+1 is the line at which the alternative position was recorded
   312  				d := line - (i + 1) // line distance from alternative position base
   313  				line = alt.Line + d
   314  				if alt.Column == 0 {
   315  					// alternative column is unknown => relative column is unknown
   316  					// (the current specification for line directives requires
   317  					// this to apply until the next PosBase/line directive,
   318  					// not just until the new newline)
   319  					column = 0
   320  				} else if d == 0 {
   321  					// the alternative position base is on the current line
   322  					// => column is relative to alternative column
   323  					column = alt.Column + (offset - alt.Offset)
   324  				}
   325  			}
   326  		}
   327  	}
   328  	return
   329  }
   330  
   331  func (f *File) position(p Pos, adjusted bool) (pos Position) {
   332  	offset := int(p) - f.base
   333  	pos.Offset = offset
   334  	pos.Filename, pos.Line, pos.Column = f.unpack(offset, adjusted)
   335  	return
   336  }
   337  
   338  // PositionFor returns the Position value for the given file position p.
   339  // If adjusted is set, the position may be adjusted by position-altering
   340  // //line comments; otherwise those comments are ignored.
   341  // p must be a Pos value in f or NoPos.
   342  //
   343  func (f *File) PositionFor(p Pos, adjusted bool) (pos Position) {
   344  	if p != NoPos {
   345  		if int(p) < f.base || int(p) > f.base+f.size {
   346  			panic("illegal Pos value")
   347  		}
   348  		pos = f.position(p, adjusted)
   349  	}
   350  	return
   351  }
   352  
   353  // Position returns the Position value for the given file position p.
   354  // Calling f.Position(p) is equivalent to calling f.PositionFor(p, true).
   355  //
   356  func (f *File) Position(p Pos) (pos Position) {
   357  	return f.PositionFor(p, true)
   358  }
   359  
   360  // -----------------------------------------------------------------------------
   361  // FileSet
   362  
   363  // A FileSet represents a set of source files.
   364  // Methods of file sets are synchronized; multiple goroutines
   365  // may invoke them concurrently.
   366  //
   367  type FileSet struct {
   368  	mutex sync.RWMutex // protects the file set
   369  	base  int          // base offset for the next file
   370  	files []*File      // list of files in the order added to the set
   371  	last  *File        // cache of last file looked up
   372  }
   373  
   374  // NewFileSet creates a new file set.
   375  func NewFileSet() *FileSet {
   376  	return &FileSet{
   377  		base: 1, // 0 == NoPos
   378  	}
   379  }
   380  
   381  // Base returns the minimum base offset that must be provided to
   382  // AddFile when adding the next file.
   383  //
   384  func (s *FileSet) Base() int {
   385  	s.mutex.RLock()
   386  	b := s.base
   387  	s.mutex.RUnlock()
   388  	return b
   389  
   390  }
   391  
   392  // AddFile adds a new file with a given filename, base offset, and file size
   393  // to the file set s and returns the file. Multiple files may have the same
   394  // name. The base offset must not be smaller than the FileSet's Base(), and
   395  // size must not be negative. As a special case, if a negative base is provided,
   396  // the current value of the FileSet's Base() is used instead.
   397  //
   398  // Adding the file will set the file set's Base() value to base + size + 1
   399  // as the minimum base value for the next file. The following relationship
   400  // exists between a Pos value p for a given file offset offs:
   401  //
   402  //	int(p) = base + offs
   403  //
   404  // with offs in the range [0, size] and thus p in the range [base, base+size].
   405  // For convenience, File.Pos may be used to create file-specific position
   406  // values from a file offset.
   407  //
   408  func (s *FileSet) AddFile(filename string, base, size int) *File {
   409  	s.mutex.Lock()
   410  	defer s.mutex.Unlock()
   411  	if base < 0 {
   412  		base = s.base
   413  	}
   414  	if base < s.base || size < 0 {
   415  		panic("illegal base or size")
   416  	}
   417  	// base >= s.base && size >= 0
   418  	f := &File{set: s, name: filename, base: base, size: size, lines: []int{0}}
   419  	base += size + 1 // +1 because EOF also has a position
   420  	if base < 0 {
   421  		panic("token.Pos offset overflow (> 2G of source code in file set)")
   422  	}
   423  	// add the file to the file set
   424  	s.base = base
   425  	s.files = append(s.files, f)
   426  	s.last = f
   427  	return f
   428  }
   429  
   430  // Iterate calls f for the files in the file set in the order they were added
   431  // until f returns false.
   432  //
   433  func (s *FileSet) Iterate(f func(*File) bool) {
   434  	for i := 0; ; i++ {
   435  		var file *File
   436  		s.mutex.RLock()
   437  		if i < len(s.files) {
   438  			file = s.files[i]
   439  		}
   440  		s.mutex.RUnlock()
   441  		if file == nil || !f(file) {
   442  			break
   443  		}
   444  	}
   445  }
   446  
   447  func searchFiles(a []*File, x int) int {
   448  	return sort.Search(len(a), func(i int) bool { return a[i].base > x }) - 1
   449  }
   450  
   451  func (s *FileSet) file(p Pos) *File {
   452  	s.mutex.RLock()
   453  	// common case: p is in last file
   454  	if f := s.last; f != nil && f.base <= int(p) && int(p) <= f.base+f.size {
   455  		s.mutex.RUnlock()
   456  		return f
   457  	}
   458  	// p is not in last file - search all files
   459  	if i := searchFiles(s.files, int(p)); i >= 0 {
   460  		f := s.files[i]
   461  		// f.base <= int(p) by definition of searchFiles
   462  		if int(p) <= f.base+f.size {
   463  			s.mutex.RUnlock()
   464  			s.mutex.Lock()
   465  			s.last = f // race is ok - s.last is only a cache
   466  			s.mutex.Unlock()
   467  			return f
   468  		}
   469  	}
   470  	s.mutex.RUnlock()
   471  	return nil
   472  }
   473  
   474  // File returns the file that contains the position p.
   475  // If no such file is found (for instance for p == NoPos),
   476  // the result is nil.
   477  //
   478  func (s *FileSet) File(p Pos) (f *File) {
   479  	if p != NoPos {
   480  		f = s.file(p)
   481  	}
   482  	return
   483  }
   484  
   485  // PositionFor converts a Pos p in the fileset into a Position value.
   486  // If adjusted is set, the position may be adjusted by position-altering
   487  // //line comments; otherwise those comments are ignored.
   488  // p must be a Pos value in s or NoPos.
   489  //
   490  func (s *FileSet) PositionFor(p Pos, adjusted bool) (pos Position) {
   491  	if p != NoPos {
   492  		if f := s.file(p); f != nil {
   493  			return f.position(p, adjusted)
   494  		}
   495  	}
   496  	return
   497  }
   498  
   499  // Position converts a Pos p in the fileset into a Position value.
   500  // Calling s.Position(p) is equivalent to calling s.PositionFor(p, true).
   501  //
   502  func (s *FileSet) Position(p Pos) (pos Position) {
   503  	return s.PositionFor(p, true)
   504  }
   505  
   506  // -----------------------------------------------------------------------------
   507  // Helper functions
   508  
   509  func searchInts(a []int, x int) int {
   510  	// This function body is a manually inlined version of:
   511  	//
   512  	//   return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1
   513  	//
   514  	// With better compiler optimizations, this may not be needed in the
   515  	// future, but at the moment this change improves the go/printer
   516  	// benchmark performance by ~30%. This has a direct impact on the
   517  	// speed of gofmt and thus seems worthwhile (2011-04-29).
   518  	// TODO(gri): Remove this when compilers have caught up.
   519  	i, j := 0, len(a)
   520  	for i < j {
   521  		h := i + (j-i)/2 // avoid overflow when computing h
   522  		// i ≤ h < j
   523  		if a[h] <= x {
   524  			i = h + 1
   525  		} else {
   526  			j = h
   527  		}
   528  	}
   529  	return i - 1
   530  }
   531  

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