cmd/compile: file line number for //go:xxx directives

Minimally invasive; fixes a regression from 1.7.

Fixes #18459.

Change-Id: I93b3b5c05706eaff8ae97a237f770838c1f8778c
Reviewed-on: https://go-review.googlesource.com/34721Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/gc/noder.go

@@ -1055,6 +1055,7 @@ func (p *noder) pragma(pos, line int, text string) syntax.Pragma {
 		lookup(f[1]).Linkname = f[2]
 
 	case strings.HasPrefix(text, "go:cgo_"):
+		lineno = p.baseline + int32(line) - 1 // pragcgo may call yyerror
 		pragcgobuf += pragcgo(text)
 		fallthrough // because of //go:cgo_unsafe_args
 	default:
@@ -1062,6 +1063,7 @@ func (p *noder) pragma(pos, line int, text string) syntax.Pragma {
 		if i := strings.Index(text, " "); i >= 0 {
 			verb = verb[:i]
 		}
+		lineno = p.baseline + int32(line) - 1 // pragmaValue may call yyerror
 		return syntax.Pragma(pragmaValue(verb))
 	}
 

src/go/types/stdlib_test.go

@@ -157,6 +157,7 @@ func TestStdFixed(t *testing.T) {
 		"issue11362.go", // canonical import path check
 		"issue15002.go", // uses Mmap; testTestDir should consult build tags
 		"issue16369.go", // go/types handles this correctly - not an issue
+		"issue18459.go", // go/types doesn't check validity of //go:xxx directives
 	)
 }
 

test/fixedbugs/issue18459.go

+// errorcheck
+
+// Copyright 2016 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.
+
+// Verify that we have a line number for this error.
+
+package main
+
+//go:nowritebarrier // ERROR "go:nowritebarrier only allowed in runtime"
+func main() {
+}