cmd/compile/internal/syntax: compiler directives must start at beginning of line

- ignore them, if they don't.
- added tests

Fixes #18393.

Change-Id: I13f87b81ac6b9138ab5031bb3dd6bebc4c548156
Reviewed-on: https://go-review.googlesource.com/37020
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Author: griesemer

src/cmd/compile/internal/syntax/parser_test.go

@@ -195,7 +195,7 @@ func TestLineDirectives(t *testing.T) {
 		{`//line :x`, "invalid line number: x", "", 1, 8},
 		{`//line foo :`, "invalid line number: ", "", 1, 12},
 		{`//line foo:123abc`, "invalid line number: 123abc", "", 1, 11},
-		{`/**///line foo:x`, "invalid line number: x", "", 1, 15},
+		{`/**///line foo:x`, "syntax error: package statement must be first", "", 1, 16}, //line directive not at start of line - ignored
 		{`//line foo:0`, "invalid line number: 0", "", 1, 11},
 		{fmt.Sprintf(`//line foo:%d`, lineMax+1), fmt.Sprintf("invalid line number: %d", lineMax+1), "", 1, 11},
 

src/cmd/compile/internal/syntax/scanner.go

@@ -45,10 +45,11 @@ func (s *scanner) init(src io.Reader, errh, pragh func(line, col uint, msg strin
 // calls the error handler installed with init. The handler
 // must exist.
 //
-// If a //line or //go: directive is encountered, next
-// calls the pragma handler installed with init, if not nil.
+// If a //line or //go: directive is encountered at the start
+// of a line, next calls the directive handler pragh installed
+// with init, if not nil.
 //
-// The (line, col) position passed to the error and pragma
+// The (line, col) position passed to the error and directive
 // handler is always at or after the current source reading
 // position.
 func (s *scanner) next() {
@@ -561,13 +562,14 @@ func (s *scanner) skipLine(r rune) {
 
 func (s *scanner) lineComment() {
 	r := s.getr()
-	if s.pragh == nil || (r != 'g' && r != 'l') {
+	// directives must start at the beginning of the line (s.col == 0)
+	if s.col != 0 || s.pragh == nil || (r != 'g' && r != 'l') {
 		s.skipLine(r)
 		return
 	}
-	// s.pragh != nil && (r == 'g' || r == 'l')
+	// s.col == 0 && s.pragh != nil && (r == 'g' || r == 'l')
 
-	// recognize pragmas
+	// recognize directives
 	prefix := "go:"
 	if r == 'l' {
 		prefix = "line "
@@ -580,15 +582,15 @@ func (s *scanner) lineComment() {
 		r = s.getr()
 	}
 
-	// pragma text without line ending (which may be "\r\n" if Windows),
+	// directive text without line ending (which may be "\r\n" if Windows),
 	s.startLit()
 	s.skipLine(r)
 	text := s.stopLit()
 	if i := len(text) - 1; i >= 0 && text[i] == '\r' {
 		text = text[:i]
 	}
 
-	s.pragh(s.line, s.col+2, prefix+string(text)) // +2 since pragma text starts after //
+	s.pragh(s.line, s.col+2, prefix+string(text)) // +2 since directive text starts after //
 }
 
 func (s *scanner) fullComment() {

test/fixedbugs/issue18393.go

@@ -0,0 +1,24 @@
+// errorcheck
+
+// Copyright 2017 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.
+
+// Test that compiler directives are ignored if they
+// don't start at the beginning of the line.
+
+package p
+
+//line issue18393.go:20
+import 42 // error on line 20
+
+
+/* //line not at start of line: ignored */ //line issue18393.go:30
+var x     // error on line 24, not 30
+
+
+// ERROR "missing import path"
+
+
+
+// ERROR "syntax error: unexpected newline, expecting type"