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Source file src/go/token/position.go

Documentation: go/token

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package token
  
  import (
  	"fmt"
  	"sort"
  	"sync"
  )
  
  // -----------------------------------------------------------------------------
  // Positions
  
  // Position describes an arbitrary source position
  // including the file, line, and column location.
  // A Position is valid if the line number is > 0.
  //
  type Position struct {
  	Filename string // filename, if any
  	Offset   int    // offset, starting at 0
  	Line     int    // line number, starting at 1
  	Column   int    // column number, starting at 1 (byte count)
  }
  
  // IsValid reports whether the position is valid.
  func (pos *Position) IsValid() bool { return pos.Line > 0 }
  
  // String returns a string in one of several forms:
  //
  //	file:line:column    valid position with file name
  //	line:column         valid position without file name
  //	file                invalid position with file name
  //	-                   invalid position without file name
  //
  func (pos Position) String() string {
  	s := pos.Filename
  	if pos.IsValid() {
  		if s != "" {
  			s += ":"
  		}
  		s += fmt.Sprintf("%d:%d", pos.Line, pos.Column)
  	}
  	if s == "" {
  		s = "-"
  	}
  	return s
  }
  
  // Pos is a compact encoding of a source position within a file set.
  // It can be converted into a Position for a more convenient, but much
  // larger, representation.
  //
  // The Pos value for a given file is a number in the range [base, base+size],
  // where base and size are specified when adding the file to the file set via
  // AddFile.
  //
  // To create the Pos value for a specific source offset (measured in bytes),
  // first add the respective file to the current file set using FileSet.AddFile
  // and then call File.Pos(offset) for that file. Given a Pos value p
  // for a specific file set fset, the corresponding Position value is
  // obtained by calling fset.Position(p).
  //
  // Pos values can be compared directly with the usual comparison operators:
  // If two Pos values p and q are in the same file, comparing p and q is
  // equivalent to comparing the respective source file offsets. If p and q
  // are in different files, p < q is true if the file implied by p was added
  // to the respective file set before the file implied by q.
  //
  type Pos int
  
  // The zero value for Pos is NoPos; there is no file and line information
  // associated with it, and NoPos.IsValid() is false. NoPos is always
  // smaller than any other Pos value. The corresponding Position value
  // for NoPos is the zero value for Position.
  //
  const NoPos Pos = 0
  
  // IsValid reports whether the position is valid.
  func (p Pos) IsValid() bool {
  	return p != NoPos
  }
  
  // -----------------------------------------------------------------------------
  // File
  
  // A File is a handle for a file belonging to a FileSet.
  // A File has a name, size, and line offset table.
  //
  type File struct {
  	set  *FileSet
  	name string // file name as provided to AddFile
  	base int    // Pos value range for this file is [base...base+size]
  	size int    // file size as provided to AddFile
  
  	// lines and infos are protected by mutex
  	mutex sync.Mutex
  	lines []int // lines contains the offset of the first character for each line (the first entry is always 0)
  	infos []lineInfo
  }
  
  // Name returns the file name of file f as registered with AddFile.
  func (f *File) Name() string {
  	return f.name
  }
  
  // Base returns the base offset of file f as registered with AddFile.
  func (f *File) Base() int {
  	return f.base
  }
  
  // Size returns the size of file f as registered with AddFile.
  func (f *File) Size() int {
  	return f.size
  }
  
  // LineCount returns the number of lines in file f.
  func (f *File) LineCount() int {
  	f.mutex.Lock()
  	n := len(f.lines)
  	f.mutex.Unlock()
  	return n
  }
  
  // AddLine adds the line offset for a new line.
  // The line offset must be larger than the offset for the previous line
  // and smaller than the file size; otherwise the line offset is ignored.
  //
  func (f *File) AddLine(offset int) {
  	f.mutex.Lock()
  	if i := len(f.lines); (i == 0 || f.lines[i-1] < offset) && offset < f.size {
  		f.lines = append(f.lines, offset)
  	}
  	f.mutex.Unlock()
  }
  
  // MergeLine merges a line with the following line. It is akin to replacing
  // the newline character at the end of the line with a space (to not change the
  // remaining offsets). To obtain the line number, consult e.g. Position.Line.
  // MergeLine will panic if given an invalid line number.
  //
  func (f *File) MergeLine(line int) {
  	if line <= 0 {
  		panic("illegal line number (line numbering starts at 1)")
  	}
  	f.mutex.Lock()
  	defer f.mutex.Unlock()
  	if line >= len(f.lines) {
  		panic("illegal line number")
  	}
  	// To merge the line numbered <line> with the line numbered <line+1>,
  	// we need to remove the entry in lines corresponding to the line
  	// numbered <line+1>. The entry in lines corresponding to the line
  	// numbered <line+1> is located at index <line>, since indices in lines
  	// are 0-based and line numbers are 1-based.
  	copy(f.lines[line:], f.lines[line+1:])
  	f.lines = f.lines[:len(f.lines)-1]
  }
  
  // SetLines sets the line offsets for a file and reports whether it succeeded.
  // The line offsets are the offsets of the first character of each line;
  // for instance for the content "ab\nc\n" the line offsets are {0, 3}.
  // An empty file has an empty line offset table.
  // Each line offset must be larger than the offset for the previous line
  // and smaller than the file size; otherwise SetLines fails and returns
  // false.
  // Callers must not mutate the provided slice after SetLines returns.
  //
  func (f *File) SetLines(lines []int) bool {
  	// verify validity of lines table
  	size := f.size
  	for i, offset := range lines {
  		if i > 0 && offset <= lines[i-1] || size <= offset {
  			return false
  		}
  	}
  
  	// set lines table
  	f.mutex.Lock()
  	f.lines = lines
  	f.mutex.Unlock()
  	return true
  }
  
  // SetLinesForContent sets the line offsets for the given file content.
  // It ignores position-altering //line comments.
  func (f *File) SetLinesForContent(content []byte) {
  	var lines []int
  	line := 0
  	for offset, b := range content {
  		if line >= 0 {
  			lines = append(lines, line)
  		}
  		line = -1
  		if b == '\n' {
  			line = offset + 1
  		}
  	}
  
  	// set lines table
  	f.mutex.Lock()
  	f.lines = lines
  	f.mutex.Unlock()
  }
  
  // A lineInfo object describes alternative file and line number
  // information (such as provided via a //line comment in a .go
  // file) for a given file offset.
  type lineInfo struct {
  	// fields are exported to make them accessible to gob
  	Offset   int
  	Filename string
  	Line     int
  }
  
  // AddLineInfo adds alternative file and line number information for
  // a given file offset. The offset must be larger than the offset for
  // the previously added alternative line info and smaller than the
  // file size; otherwise the information is ignored.
  //
  // AddLineInfo is typically used to register alternative position
  // information for //line filename:line comments in source files.
  //
  func (f *File) AddLineInfo(offset int, filename string, line int) {
  	f.mutex.Lock()
  	if i := len(f.infos); i == 0 || f.infos[i-1].Offset < offset && offset < f.size {
  		f.infos = append(f.infos, lineInfo{offset, filename, line})
  	}
  	f.mutex.Unlock()
  }
  
  // Pos returns the Pos value for the given file offset;
  // the offset must be <= f.Size().
  // f.Pos(f.Offset(p)) == p.
  //
  func (f *File) Pos(offset int) Pos {
  	if offset > f.size {
  		panic("illegal file offset")
  	}
  	return Pos(f.base + offset)
  }
  
  // Offset returns the offset for the given file position p;
  // p must be a valid Pos value in that file.
  // f.Offset(f.Pos(offset)) == offset.
  //
  func (f *File) Offset(p Pos) int {
  	if int(p) < f.base || int(p) > f.base+f.size {
  		panic("illegal Pos value")
  	}
  	return int(p) - f.base
  }
  
  // Line returns the line number for the given file position p;
  // p must be a Pos value in that file or NoPos.
  //
  func (f *File) Line(p Pos) int {
  	return f.Position(p).Line
  }
  
  func searchLineInfos(a []lineInfo, x int) int {
  	return sort.Search(len(a), func(i int) bool { return a[i].Offset > x }) - 1
  }
  
  // unpack returns the filename and line and column number for a file offset.
  // If adjusted is set, unpack will return the filename and line information
  // possibly adjusted by //line comments; otherwise those comments are ignored.
  //
  func (f *File) unpack(offset int, adjusted bool) (filename string, line, column int) {
  	f.mutex.Lock()
  	defer f.mutex.Unlock()
  	filename = f.name
  	if i := searchInts(f.lines, offset); i >= 0 {
  		line, column = i+1, offset-f.lines[i]+1
  	}
  	if adjusted && len(f.infos) > 0 {
  		// almost no files have extra line infos
  		if i := searchLineInfos(f.infos, offset); i >= 0 {
  			alt := &f.infos[i]
  			filename = alt.Filename
  			if i := searchInts(f.lines, alt.Offset); i >= 0 {
  				line += alt.Line - i - 1
  			}
  		}
  	}
  	return
  }
  
  func (f *File) position(p Pos, adjusted bool) (pos Position) {
  	offset := int(p) - f.base
  	pos.Offset = offset
  	pos.Filename, pos.Line, pos.Column = f.unpack(offset, adjusted)
  	return
  }
  
  // PositionFor returns the Position value for the given file position p.
  // If adjusted is set, the position may be adjusted by position-altering
  // //line comments; otherwise those comments are ignored.
  // p must be a Pos value in f or NoPos.
  //
  func (f *File) PositionFor(p Pos, adjusted bool) (pos Position) {
  	if p != NoPos {
  		if int(p) < f.base || int(p) > f.base+f.size {
  			panic("illegal Pos value")
  		}
  		pos = f.position(p, adjusted)
  	}
  	return
  }
  
  // Position returns the Position value for the given file position p.
  // Calling f.Position(p) is equivalent to calling f.PositionFor(p, true).
  //
  func (f *File) Position(p Pos) (pos Position) {
  	return f.PositionFor(p, true)
  }
  
  // -----------------------------------------------------------------------------
  // FileSet
  
  // A FileSet represents a set of source files.
  // Methods of file sets are synchronized; multiple goroutines
  // may invoke them concurrently.
  //
  type FileSet struct {
  	mutex sync.RWMutex // protects the file set
  	base  int          // base offset for the next file
  	files []*File      // list of files in the order added to the set
  	last  *File        // cache of last file looked up
  }
  
  // NewFileSet creates a new file set.
  func NewFileSet() *FileSet {
  	return &FileSet{
  		base: 1, // 0 == NoPos
  	}
  }
  
  // Base returns the minimum base offset that must be provided to
  // AddFile when adding the next file.
  //
  func (s *FileSet) Base() int {
  	s.mutex.RLock()
  	b := s.base
  	s.mutex.RUnlock()
  	return b
  
  }
  
  // AddFile adds a new file with a given filename, base offset, and file size
  // to the file set s and returns the file. Multiple files may have the same
  // name. The base offset must not be smaller than the FileSet's Base(), and
  // size must not be negative. As a special case, if a negative base is provided,
  // the current value of the FileSet's Base() is used instead.
  //
  // Adding the file will set the file set's Base() value to base + size + 1
  // as the minimum base value for the next file. The following relationship
  // exists between a Pos value p for a given file offset offs:
  //
  //	int(p) = base + offs
  //
  // with offs in the range [0, size] and thus p in the range [base, base+size].
  // For convenience, File.Pos may be used to create file-specific position
  // values from a file offset.
  //
  func (s *FileSet) AddFile(filename string, base, size int) *File {
  	s.mutex.Lock()
  	defer s.mutex.Unlock()
  	if base < 0 {
  		base = s.base
  	}
  	if base < s.base || size < 0 {
  		panic("illegal base or size")
  	}
  	// base >= s.base && size >= 0
  	f := &File{set: s, name: filename, base: base, size: size, lines: []int{0}}
  	base += size + 1 // +1 because EOF also has a position
  	if base < 0 {
  		panic("token.Pos offset overflow (> 2G of source code in file set)")
  	}
  	// add the file to the file set
  	s.base = base
  	s.files = append(s.files, f)
  	s.last = f
  	return f
  }
  
  // Iterate calls f for the files in the file set in the order they were added
  // until f returns false.
  //
  func (s *FileSet) Iterate(f func(*File) bool) {
  	for i := 0; ; i++ {
  		var file *File
  		s.mutex.RLock()
  		if i < len(s.files) {
  			file = s.files[i]
  		}
  		s.mutex.RUnlock()
  		if file == nil || !f(file) {
  			break
  		}
  	}
  }
  
  func searchFiles(a []*File, x int) int {
  	return sort.Search(len(a), func(i int) bool { return a[i].base > x }) - 1
  }
  
  func (s *FileSet) file(p Pos) *File {
  	s.mutex.RLock()
  	// common case: p is in last file
  	if f := s.last; f != nil && f.base <= int(p) && int(p) <= f.base+f.size {
  		s.mutex.RUnlock()
  		return f
  	}
  	// p is not in last file - search all files
  	if i := searchFiles(s.files, int(p)); i >= 0 {
  		f := s.files[i]
  		// f.base <= int(p) by definition of searchFiles
  		if int(p) <= f.base+f.size {
  			s.mutex.RUnlock()
  			s.mutex.Lock()
  			s.last = f // race is ok - s.last is only a cache
  			s.mutex.Unlock()
  			return f
  		}
  	}
  	s.mutex.RUnlock()
  	return nil
  }
  
  // File returns the file that contains the position p.
  // If no such file is found (for instance for p == NoPos),
  // the result is nil.
  //
  func (s *FileSet) File(p Pos) (f *File) {
  	if p != NoPos {
  		f = s.file(p)
  	}
  	return
  }
  
  // PositionFor converts a Pos p in the fileset into a Position value.
  // If adjusted is set, the position may be adjusted by position-altering
  // //line comments; otherwise those comments are ignored.
  // p must be a Pos value in s or NoPos.
  //
  func (s *FileSet) PositionFor(p Pos, adjusted bool) (pos Position) {
  	if p != NoPos {
  		if f := s.file(p); f != nil {
  			return f.position(p, adjusted)
  		}
  	}
  	return
  }
  
  // Position converts a Pos p in the fileset into a Position value.
  // Calling s.Position(p) is equivalent to calling s.PositionFor(p, true).
  //
  func (s *FileSet) Position(p Pos) (pos Position) {
  	return s.PositionFor(p, true)
  }
  
  // -----------------------------------------------------------------------------
  // Helper functions
  
  func searchInts(a []int, x int) int {
  	// This function body is a manually inlined version of:
  	//
  	//   return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1
  	//
  	// With better compiler optimizations, this may not be needed in the
  	// future, but at the moment this change improves the go/printer
  	// benchmark performance by ~30%. This has a direct impact on the
  	// speed of gofmt and thus seems worthwhile (2011-04-29).
  	// TODO(gri): Remove this when compilers have caught up.
  	i, j := 0, len(a)
  	for i < j {
  		h := i + (j-i)/2 // avoid overflow when computing h
  		// i ≤ h < j
  		if a[h] <= x {
  			i = h + 1
  		} else {
  			j = h
  		}
  	}
  	return i - 1
  }
  

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