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Source file src/pkg/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	// TODO(gri) consider making this a separate package outside the go directory.
     6	
     7	package token
     8	
     9	import (
    10		"fmt"
    11		"sort"
    12		"sync"
    13	)
    14	
    15	// -----------------------------------------------------------------------------
    16	// Positions
    17	
    18	// Position describes an arbitrary source position
    19	// including the file, line, and column location.
    20	// A Position is valid if the line number is > 0.
    21	//
    22	type Position struct {
    23		Filename string // filename, if any
    24		Offset   int    // offset, starting at 0
    25		Line     int    // line number, starting at 1
    26		Column   int    // column number, starting at 1 (character count)
    27	}
    28	
    29	// IsValid returns true if the position is valid.
    30	func (pos *Position) IsValid() bool { return pos.Line > 0 }
    31	
    32	// String returns a string in one of several forms:
    33	//
    34	//	file:line:column    valid position with file name
    35	//	line:column         valid position without file name
    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:%d", pos.Line, pos.Column)
    46		}
    47		if s == "" {
    48			s = "-"
    49		}
    50		return s
    51	}
    52	
    53	// Pos is a compact encoding of a source position within a file set.
    54	// It can be converted into a Position for a more convenient, but much
    55	// larger, representation.
    56	//
    57	// The Pos value for a given file is a number in the range [base, base+size],
    58	// where base and size are specified when adding the file to the file set via
    59	// AddFile.
    60	//
    61	// To create the Pos value for a specific source offset, first add
    62	// the respective file to the current file set (via FileSet.AddFile)
    63	// and then call File.Pos(offset) for that file. Given a Pos value p
    64	// for a specific file set fset, the corresponding Position value is
    65	// obtained by calling fset.Position(p).
    66	//
    67	// Pos values can be compared directly with the usual comparison operators:
    68	// If two Pos values p and q are in the same file, comparing p and q is
    69	// equivalent to comparing the respective source file offsets. If p and q
    70	// are in different files, p < q is true if the file implied by p was added
    71	// to the respective file set before the file implied by q.
    72	//
    73	type Pos int
    74	
    75	// The zero value for Pos is NoPos; there is no file and line information
    76	// associated with it, and NoPos().IsValid() is false. NoPos is always
    77	// smaller than any other Pos value. The corresponding Position value
    78	// for NoPos is the zero value for Position.
    79	//
    80	const NoPos Pos = 0
    81	
    82	// IsValid returns true if the position is valid.
    83	func (p Pos) IsValid() bool {
    84		return p != NoPos
    85	}
    86	
    87	// -----------------------------------------------------------------------------
    88	// File
    89	
    90	// A File is a handle for a file belonging to a FileSet.
    91	// A File has a name, size, and line offset table.
    92	//
    93	type File struct {
    94		set  *FileSet
    95		name string // file name as provided to AddFile
    96		base int    // Pos value range for this file is [base...base+size]
    97		size int    // file size as provided to AddFile
    98	
    99		// lines and infos are protected by set.mutex
   100		lines []int // lines contains the offset of the first character for each line (the first entry is always 0)
   101		infos []lineInfo
   102	}
   103	
   104	// Name returns the file name of file f as registered with AddFile.
   105	func (f *File) Name() string {
   106		return f.name
   107	}
   108	
   109	// Base returns the base offset of file f as registered with AddFile.
   110	func (f *File) Base() int {
   111		return f.base
   112	}
   113	
   114	// Size returns the size of file f as registered with AddFile.
   115	func (f *File) Size() int {
   116		return f.size
   117	}
   118	
   119	// LineCount returns the number of lines in file f.
   120	func (f *File) LineCount() int {
   121		f.set.mutex.RLock()
   122		n := len(f.lines)
   123		f.set.mutex.RUnlock()
   124		return n
   125	}
   126	
   127	// AddLine adds the line offset for a new line.
   128	// The line offset must be larger than the offset for the previous line
   129	// and smaller than the file size; otherwise the line offset is ignored.
   130	//
   131	func (f *File) AddLine(offset int) {
   132		f.set.mutex.Lock()
   133		if i := len(f.lines); (i == 0 || f.lines[i-1] < offset) && offset < f.size {
   134			f.lines = append(f.lines, offset)
   135		}
   136		f.set.mutex.Unlock()
   137	}
   138	
   139	// MergeLine merges a line with the following line. It is akin to replacing
   140	// the newline character at the end of the line with a space (to not change the
   141	// remaining offsets). To obtain the line number, consult e.g. Position.Line.
   142	// MergeLine will panic if given an invalid line number.
   143	//
   144	func (f *File) MergeLine(line int) {
   145		if line <= 0 {
   146			panic("illegal line number (line numbering starts at 1)")
   147		}
   148		f.set.mutex.Lock()
   149		defer f.set.mutex.Unlock()
   150		if line >= len(f.lines) {
   151			panic("illegal line number")
   152		}
   153		// To merge the line numbered <line> with the line numbered <line+1>,
   154		// we need to remove the entry in lines corresponding to the line
   155		// numbered <line+1>. The entry in lines corresponding to the line
   156		// numbered <line+1> is located at index <line>, since indices in lines
   157		// are 0-based and line numbers are 1-based.
   158		copy(f.lines[line:], f.lines[line+1:])
   159		f.lines = f.lines[:len(f.lines)-1]
   160	}
   161	
   162	// SetLines sets the line offsets for a file and returns true if successful.
   163	// The line offsets are the offsets of the first character of each line;
   164	// for instance for the content "ab\nc\n" the line offsets are {0, 3}.
   165	// An empty file has an empty line offset table.
   166	// Each line offset must be larger than the offset for the previous line
   167	// and smaller than the file size; otherwise SetLines fails and returns
   168	// false.
   169	//
   170	func (f *File) SetLines(lines []int) bool {
   171		// verify validity of lines table
   172		size := f.size
   173		for i, offset := range lines {
   174			if i > 0 && offset <= lines[i-1] || size <= offset {
   175				return false
   176			}
   177		}
   178	
   179		// set lines table
   180		f.set.mutex.Lock()
   181		f.lines = lines
   182		f.set.mutex.Unlock()
   183		return true
   184	}
   185	
   186	// SetLinesForContent sets the line offsets for the given file content.
   187	func (f *File) SetLinesForContent(content []byte) {
   188		var lines []int
   189		line := 0
   190		for offset, b := range content {
   191			if line >= 0 {
   192				lines = append(lines, line)
   193			}
   194			line = -1
   195			if b == '\n' {
   196				line = offset + 1
   197			}
   198		}
   199	
   200		// set lines table
   201		f.set.mutex.Lock()
   202		f.lines = lines
   203		f.set.mutex.Unlock()
   204	}
   205	
   206	// A lineInfo object describes alternative file and line number
   207	// information (such as provided via a //line comment in a .go
   208	// file) for a given file offset.
   209	type lineInfo struct {
   210		// fields are exported to make them accessible to gob
   211		Offset   int
   212		Filename string
   213		Line     int
   214	}
   215	
   216	// AddLineInfo adds alternative file and line number information for
   217	// a given file offset. The offset must be larger than the offset for
   218	// the previously added alternative line info and smaller than the
   219	// file size; otherwise the information is ignored.
   220	//
   221	// AddLineInfo is typically used to register alternative position
   222	// information for //line filename:line comments in source files.
   223	//
   224	func (f *File) AddLineInfo(offset int, filename string, line int) {
   225		f.set.mutex.Lock()
   226		if i := len(f.infos); i == 0 || f.infos[i-1].Offset < offset && offset < f.size {
   227			f.infos = append(f.infos, lineInfo{offset, filename, line})
   228		}
   229		f.set.mutex.Unlock()
   230	}
   231	
   232	// Pos returns the Pos value for the given file offset;
   233	// the offset must be <= f.Size().
   234	// f.Pos(f.Offset(p)) == p.
   235	//
   236	func (f *File) Pos(offset int) Pos {
   237		if offset > f.size {
   238			panic("illegal file offset")
   239		}
   240		return Pos(f.base + offset)
   241	}
   242	
   243	// Offset returns the offset for the given file position p;
   244	// p must be a valid Pos value in that file.
   245	// f.Offset(f.Pos(offset)) == offset.
   246	//
   247	func (f *File) Offset(p Pos) int {
   248		if int(p) < f.base || int(p) > f.base+f.size {
   249			panic("illegal Pos value")
   250		}
   251		return int(p) - f.base
   252	}
   253	
   254	// Line returns the line number for the given file position p;
   255	// p must be a Pos value in that file or NoPos.
   256	//
   257	func (f *File) Line(p Pos) int {
   258		// TODO(gri) this can be implemented much more efficiently
   259		return f.Position(p).Line
   260	}
   261	
   262	func searchLineInfos(a []lineInfo, x int) int {
   263		return sort.Search(len(a), func(i int) bool { return a[i].Offset > x }) - 1
   264	}
   265	
   266	// info returns the file name, line, and column number for a file offset.
   267	func (f *File) info(offset int) (filename string, line, column int) {
   268		filename = f.name
   269		if i := searchInts(f.lines, offset); i >= 0 {
   270			line, column = i+1, offset-f.lines[i]+1
   271		}
   272		if len(f.infos) > 0 {
   273			// almost no files have extra line infos
   274			if i := searchLineInfos(f.infos, offset); i >= 0 {
   275				alt := &f.infos[i]
   276				filename = alt.Filename
   277				if i := searchInts(f.lines, alt.Offset); i >= 0 {
   278					line += alt.Line - i - 1
   279				}
   280			}
   281		}
   282		return
   283	}
   284	
   285	func (f *File) position(p Pos) (pos Position) {
   286		offset := int(p) - f.base
   287		pos.Offset = offset
   288		pos.Filename, pos.Line, pos.Column = f.info(offset)
   289		return
   290	}
   291	
   292	// Position returns the Position value for the given file position p;
   293	// p must be a Pos value in that file or NoPos.
   294	//
   295	func (f *File) Position(p Pos) (pos Position) {
   296		if p != NoPos {
   297			if int(p) < f.base || int(p) > f.base+f.size {
   298				panic("illegal Pos value")
   299			}
   300			pos = f.position(p)
   301		}
   302		return
   303	}
   304	
   305	// -----------------------------------------------------------------------------
   306	// FileSet
   307	
   308	// A FileSet represents a set of source files.
   309	// Methods of file sets are synchronized; multiple goroutines
   310	// may invoke them concurrently.
   311	//
   312	type FileSet struct {
   313		mutex sync.RWMutex // protects the file set
   314		base  int          // base offset for the next file
   315		files []*File      // list of files in the order added to the set
   316		last  *File        // cache of last file looked up
   317	}
   318	
   319	// NewFileSet creates a new file set.
   320	func NewFileSet() *FileSet {
   321		return &FileSet{
   322			base: 1, // 0 == NoPos
   323		}
   324	}
   325	
   326	// Base returns the minimum base offset that must be provided to
   327	// AddFile when adding the next file.
   328	//
   329	func (s *FileSet) Base() int {
   330		s.mutex.RLock()
   331		b := s.base
   332		s.mutex.RUnlock()
   333		return b
   334	
   335	}
   336	
   337	// AddFile adds a new file with a given filename, base offset, and file size
   338	// to the file set s and returns the file. Multiple files may have the same
   339	// name. The base offset must not be smaller than the FileSet's Base(), and
   340	// size must not be negative. As a special case, if a negative base is provided,
   341	// the current value of the FileSet's Base() is used instead.
   342	//
   343	// Adding the file will set the file set's Base() value to base + size + 1
   344	// as the minimum base value for the next file. The following relationship
   345	// exists between a Pos value p for a given file offset offs:
   346	//
   347	//	int(p) = base + offs
   348	//
   349	// with offs in the range [0, size] and thus p in the range [base, base+size].
   350	// For convenience, File.Pos may be used to create file-specific position
   351	// values from a file offset.
   352	//
   353	func (s *FileSet) AddFile(filename string, base, size int) *File {
   354		s.mutex.Lock()
   355		defer s.mutex.Unlock()
   356		if base < 0 {
   357			base = s.base
   358		}
   359		if base < s.base || size < 0 {
   360			panic("illegal base or size")
   361		}
   362		// base >= s.base && size >= 0
   363		f := &File{s, filename, base, size, []int{0}, nil}
   364		base += size + 1 // +1 because EOF also has a position
   365		if base < 0 {
   366			panic("token.Pos offset overflow (> 2G of source code in file set)")
   367		}
   368		// add the file to the file set
   369		s.base = base
   370		s.files = append(s.files, f)
   371		s.last = f
   372		return f
   373	}
   374	
   375	// Iterate calls f for the files in the file set in the order they were added
   376	// until f returns false.
   377	//
   378	func (s *FileSet) Iterate(f func(*File) bool) {
   379		for i := 0; ; i++ {
   380			var file *File
   381			s.mutex.RLock()
   382			if i < len(s.files) {
   383				file = s.files[i]
   384			}
   385			s.mutex.RUnlock()
   386			if file == nil || !f(file) {
   387				break
   388			}
   389		}
   390	}
   391	
   392	func searchFiles(a []*File, x int) int {
   393		return sort.Search(len(a), func(i int) bool { return a[i].base > x }) - 1
   394	}
   395	
   396	func (s *FileSet) file(p Pos) *File {
   397		s.mutex.RLock()
   398		// common case: p is in last file
   399		if f := s.last; f != nil && f.base <= int(p) && int(p) <= f.base+f.size {
   400			s.mutex.RUnlock()
   401			return f
   402		}
   403		// p is not in last file - search all files
   404		if i := searchFiles(s.files, int(p)); i >= 0 {
   405			f := s.files[i]
   406			// f.base <= int(p) by definition of searchFiles
   407			if int(p) <= f.base+f.size {
   408				s.mutex.RUnlock()
   409				s.mutex.Lock()
   410				s.last = f // race is ok - s.last is only a cache
   411				s.mutex.Unlock()
   412				return f
   413			}
   414		}
   415		s.mutex.RUnlock()
   416		return nil
   417	}
   418	
   419	// File returns the file that contains the position p.
   420	// If no such file is found (for instance for p == NoPos),
   421	// the result is nil.
   422	//
   423	func (s *FileSet) File(p Pos) (f *File) {
   424		if p != NoPos {
   425			f = s.file(p)
   426		}
   427		return
   428	}
   429	
   430	// Position converts a Pos in the fileset into a general Position.
   431	func (s *FileSet) Position(p Pos) (pos Position) {
   432		if p != NoPos {
   433			if f := s.file(p); f != nil {
   434				pos = f.position(p)
   435			}
   436		}
   437		return
   438	}
   439	
   440	// -----------------------------------------------------------------------------
   441	// Helper functions
   442	
   443	func searchInts(a []int, x int) int {
   444		// This function body is a manually inlined version of:
   445		//
   446		//   return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1
   447		//
   448		// With better compiler optimizations, this may not be needed in the
   449		// future, but at the moment this change improves the go/printer
   450		// benchmark performance by ~30%. This has a direct impact on the
   451		// speed of gofmt and thus seems worthwhile (2011-04-29).
   452		// TODO(gri): Remove this when compilers have caught up.
   453		i, j := 0, len(a)
   454		for i < j {
   455			h := i + (j-i)/2 // avoid overflow when computing h
   456			// i ≤ h < j
   457			if a[h] <= x {
   458				i = h + 1
   459			} else {
   460				j = h
   461			}
   462		}
   463		return i - 1
   464	}
   465	

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