cmd/compile/internal/syntax: permit /*line file:line:col*/ directives

R=go1.11

This implements parsing of /*line file:line*/ and /*line file:line:col*/
directives and also extends the optional column format to regular //line
directives, per #22662.

For a line directive to be recognized, its comment text must start with
the prefix "line " which is followed by one of the following:

:line
:line:col
filename:line
filename:line:col

with at least one : present. The line and col values must be unsigned
decimal integers; everything before is considered part of the filename.

Valid line directives are:

//line :123
//line :123:8
//line foo.go:123
//line C:foo.go:123	(filename is "C:foo.go")
//line C:foo.go:123:8	(filename is "C:foo.go")
/*line ::123*/		(filename is ":")

No matter the comment format, at the moment all directives act as if
they were in //line comments, and column information is ignored.
To be addressed in subsequent CLs.

For #22662.

Change-Id: I1a2dc54bacc94bc6cdedc5229ee13278971f314e
Reviewed-on: https://go-review.googlesource.com/86037
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 33 insertions, 5 deletions

diff --git a/src/cmd/compile/internal/syntax/scanner.go b/src/cmd/compile/internal/syntax/scanner.go
index 05391e5efb..be406d9753 100644
--- a/src/cmd/compile/internal/syntax/scanner.go
+++ b/src/cmd/compile/internal/syntax/scanner.go
@@ -577,6 +577,7 @@ func (s *scanner) skipLine(r rune) {
 
 func (s *scanner) lineComment() {
 	r := s.getr()
+
 	// directives must start at the beginning of the line (s.col == colbase)
 	if s.col != colbase || s.pragh == nil || (r != 'g' && r != 'l') {
 		s.skipLine(r)
@@ -608,20 +609,47 @@ func (s *scanner) lineComment() {
 	s.pragh(s.line, s.col+2, prefix+string(text)) // +2 since directive text starts after //
 }
 
-func (s *scanner) fullComment() {
-	for {
-		r := s.getr()
+func (s *scanner) skipComment(r rune) {
+	for r >= 0 {
 		for r == '*' {
 			r = s.getr()
 			if r == '/' {
 				return
 			}
 		}
-		if r < 0 {
-			s.errh(s.line, s.col, "comment not terminated")
+		r = s.getr()
+	}
+	s.errh(s.line, s.col, "comment not terminated")
+}
+
+func (s *scanner) fullComment() {
+	r := s.getr()
+
+	if s.pragh == nil || r != 'l' {
+		s.skipComment(r)
+		return
+	}
+	// s.pragh != nil && r == 'l'
+
+	// recognize line directive
+	const prefix = "line "
+	for _, m := range prefix {
+		if r != m {
+			s.skipComment(r)
 			return
 		}
+		r = s.getr()
 	}
+
+	// directive text without comment ending
+	s.startLit()
+	s.skipComment(r)
+	text := s.stopLit()
+	if i := len(text) - 2; i >= 0 && text[i] == '*' && text[i+1] == '/' {
+		text = text[:i]
+	}
+
+	s.pragh(s.line, s.col+2, prefix+string(text)) // +2 since directive text starts after /*
 }
 
 func (s *scanner) escape(quote rune) bool {