go/scanner: interpret filenames in //line filename:line comments

	    relative to the source file directory

R=r, rsc
CC=golang-dev
https://golang.org/cl/3752041

src/pkg/go/scanner/scanner.go

@@ -22,6 +22,7 @@ package scanner
 import (
 	"bytes"
 	"go/token"
+	"path"
 	"strconv"
 	"unicode"
 	"utf8"
@@ -35,6 +36,7 @@ import (
 type Scanner struct {
 	// immutable state
 	file *token.File  // source file handle
+	dir  string       // directory portion of file.Name()
 	src  []byte       // source
 	err  ErrorHandler // error reporting; or nil
 	mode uint         // scanning mode
@@ -111,6 +113,7 @@ const (
 func (S *Scanner) Init(fset *token.FileSet, filename string, src []byte, err ErrorHandler, mode uint) *token.File {
 	// Explicitly initialize all fields since a scanner may be reused.
 	S.file = fset.AddFile(filename, fset.Base(), len(src))
+	S.dir, _ = path.Split(filename)
 	S.src = src
 	S.err = err
 	S.mode = mode
@@ -174,8 +177,13 @@ func (S *Scanner) interpretLineComment(text []byte) {
 		if i := bytes.Index(text, []byte{':'}); i > 0 {
 			if line, err := strconv.Atoi(string(text[i+1:])); err == nil && line > 0 {
 				// valid //line filename:line comment;
+				filename := path.Clean(string(text[len(prefix):i]))
+				if filename[0] != '/' {
+					// make filename relative to current directory
+					filename = path.Join(S.dir, filename)
+				}
 				// update scanner position
-				S.file.AddLineInfo(S.lineOffset, string(text[len(prefix):i]), line-1) // -1 since comment applies to next line
+				S.file.AddLineInfo(S.lineOffset, filename, line-1) // -1 since comment applies to next line
 			}
 		}
 	}

src/pkg/go/scanner/scanner_test.go

@@ -449,20 +449,20 @@ var segments = []struct {
 	line     int    // line number for current token
 }{
 	// exactly one token per line since the test consumes one token per segment
-	{"  line1", "TestLineComments", 1},
-	{"\nline2", "TestLineComments", 2},
-	{"\nline3  //line File1.go:100", "TestLineComments", 3}, // bad line comment, ignored
-	{"\nline4", "TestLineComments", 4},
-	{"\n//line File1.go:100\n  line100", "File1.go", 100},
-	{"\n//line File2.go:200\n  line200", "File2.go", 200},
-	{"\n//line :1\n  line1", "", 1},
-	{"\n//line foo:42\n  line42", "foo", 42},
-	{"\n //line foo:42\n  line44", "foo", 44},           // bad line comment, ignored
-	{"\n//line foo 42\n  line46", "foo", 46},            // bad line comment, ignored
-	{"\n//line foo:42 extra text\n  line48", "foo", 48}, // bad line comment, ignored
-	{"\n//line foo:42\n  line42", "foo", 42},
-	{"\n//line foo:42\n  line42", "foo", 42},
-	{"\n//line File1.go:100\n  line100", "File1.go", 100},
+	{"  line1", "dir/TestLineComments", 1},
+	{"\nline2", "dir/TestLineComments", 2},
+	{"\nline3  //line File1.go:100", "dir/TestLineComments", 3}, // bad line comment, ignored
+	{"\nline4", "dir/TestLineComments", 4},
+	{"\n//line File1.go:100\n  line100", "dir/File1.go", 100},
+	{"\n//line File2.go:200\n  line200", "dir/File2.go", 200},
+	{"\n//line :1\n  line1", "dir", 1},
+	{"\n//line foo:42\n  line42", "dir/foo", 42},
+	{"\n //line foo:42\n  line44", "dir/foo", 44},           // bad line comment, ignored
+	{"\n//line foo 42\n  line46", "dir/foo", 46},            // bad line comment, ignored
+	{"\n//line foo:42 extra text\n  line48", "dir/foo", 48}, // bad line comment, ignored
+	{"\n//line /bar:42\n  line42", "/bar", 42},
+	{"\n//line ./foo:42\n  line42", "dir/foo", 42},
+	{"\n//line a/b/c/File1.go:100\n  line100", "dir/a/b/c/File1.go", 100},
 }
 
 
@@ -476,7 +476,7 @@ func TestLineComments(t *testing.T) {
 
 	// verify scan
 	var S Scanner
-	file := S.Init(fset, "TestLineComments", []byte(src), nil, 0)
+	file := S.Init(fset, "dir/TestLineComments", []byte(src), nil, 0)
 	for _, s := range segments {
 		p, _, lit := S.Scan()
 		pos := file.Position(p)