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

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