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position.go: more flexible AddFile method
This will make it easier to use Pos values together with suffix arrays by slightly de- coupling the mapping of Pos values to global offsets. R=rsc CC=golang-dev https://golang.org/cl/3231041
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@ -63,12 +63,15 @@ func (pos Position) String() string {
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// It can be converted into a Position for a more convenient, but much
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// larger, representation.
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//
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// To create the Pos value for a specific source location, first add
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// The Pos value for a given file is a number in the range [base, base+size],
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// where base and size are specified when adding the file to the file set via
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// AddFile.
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//
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// To create the Pos value for a specific source offset, first add
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// the respective file to the current file set (via FileSet.AddFile)
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// and then call File.Pos(offset) of that file with the offset of
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// the source location. Given a Pos value p for a specific file set
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// fset, the corresponding Position value is obtained by calling
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// fset.Position(p).
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// and then call File.Pos(offset) for that file. Given a Pos value p
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// for a specific file set fset, the corresponding Position value is
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// obtained by calling fset.Position(p).
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//
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// Pos values can be compared directly with the usual comparison operators:
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// If two Pos values p and q are in the same file, comparing p and q is
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@ -100,7 +103,11 @@ func searchFiles(a []*File, x int) int {
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func (s *FileSet) file(p Pos) *File {
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if i := searchFiles(s.files, int(p)); i >= 0 {
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return s.files[i]
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f := s.files[i]
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// f.base <= int(p) by definition of searchFiles
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if int(p) <= f.base+f.size {
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return f
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}
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}
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return nil
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}
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@ -166,6 +173,12 @@ func (f *File) Name() string {
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}
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// Base returns the base offset of file f as registered with AddFile.
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func (f *File) Base() int {
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return f.base
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}
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// Size returns the size of file f as registered with AddFile.
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func (f *File) Size() int {
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return f.size
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@ -224,7 +237,7 @@ func (f *File) Pos(offset int) Pos {
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if offset > f.size {
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panic("illegal file offset")
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}
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return Pos(offset + f.base)
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return Pos(f.base + offset)
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}
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@ -296,19 +309,43 @@ func NewFileSet() *FileSet {
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}
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// AddFile adds a new file with a given filename and file size to a the
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// file set s and returns the file. Multiple files may have the same name.
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// File.Pos may be used to create file-specific position values from a
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// file offset.
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// Base returns the minimum base offset that must be provided to
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// AddFile when adding the next file.
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//
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func (s *FileSet) AddFile(filename string, size int) *File {
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func (s *FileSet) Base() int {
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return s.base
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}
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// AddFile adds a new file with a given filename, base offset, and file size
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// to the file set s and returns the file. Multiple files may have the same
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// name. The base offset must not be smaller than the FileSet's Base(), and
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// size must not be negative.
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//
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// Adding the file will set the file set's Base() value to base + size + 1
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// as the minimum base value for the next file. The following relationship
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// exists between a Pos value p for a given file offset offs:
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//
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// int(p) = base + offs
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//
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// with offs in the range [0, size] and thus p in the range [base, base+size].
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// For convenience, File.Pos may be used to create file-specific position
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// values from a file offset.
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//
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func (s *FileSet) AddFile(filename string, base, size int) *File {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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f := &File{s, filename, s.base, size, []int{0}, nil}
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s.base += size + 1 // +1 because EOF also has a position
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if s.base < 0 {
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if base < s.base || size < 0 {
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panic("illegal base or size")
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}
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// base >= s.base && size >= 0
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f := &File{s, filename, base, size, []int{0}, nil}
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base += size + 1 // +1 because EOF also has a position
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if base < 0 {
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panic("token.Pos offset overflow (> 2G of source code in file set)")
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}
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// add the file to the file set
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s.base = base
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s.index[f] = len(s.files)
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s.files = append(s.files, f)
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return f
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@ -78,10 +78,11 @@ func verifyPositions(t *testing.T, fset *FileSet, f *File, lines []int) {
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func TestPositions(t *testing.T) {
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const delta = 7 // a non-zero base offset increment
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fset := NewFileSet()
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for _, test := range tests {
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// add file and verify name and size
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f := fset.AddFile(test.filename, test.size)
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f := fset.AddFile(test.filename, fset.Base()+delta, test.size)
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if f.Name() != test.filename {
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t.Errorf("expected filename %q; got %q", test.filename, f.Name())
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}
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@ -118,7 +119,7 @@ func TestPositions(t *testing.T) {
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func TestLineInfo(t *testing.T) {
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fset := NewFileSet()
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f := fset.AddFile("foo", 500)
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f := fset.AddFile("foo", fset.Base(), 500)
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lines := []int{0, 42, 77, 100, 210, 220, 277, 300, 333, 401}
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// add lines individually and provide alternative line information
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for _, offs := range lines {
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