Imported Upstream version 1.2upstream/1.2

1 files changed, 29 insertions, 2 deletions

diff --git a/src/pkg/go/token/position.go b/src/pkg/go/token/position.go
index f5d999561..e6f0ae6a6 100644
--- a/src/pkg/go/token/position.go
+++ b/src/pkg/go/token/position.go
@@ -97,7 +97,7 @@ type File struct {
 	size int    // file size as provided to AddFile
 
 	// lines and infos are protected by set.mutex
-	lines []int
+	lines []int // lines contains the offset of the first character for each line (the first entry is always 0)
 	infos []lineInfo
 }
 
@@ -136,6 +136,29 @@ func (f *File) AddLine(offset int) {
 	f.set.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.set.mutex.Lock()
+	defer f.set.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 returns true if successful.
 // 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}.
@@ -314,7 +337,8 @@ func (s *FileSet) Base() int {
 // 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.
+// 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
@@ -329,6 +353,9 @@ func (s *FileSet) Base() int {
 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")
 	}