cmd/compile: reject unknown //go: comments in std library

Fixes #18331

Change-Id: Ie5c6685be3002533b84604ff1f13f2f0850f29e2
Reviewed-on: https://go-review.googlesource.com/45010
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -198,6 +198,9 @@ var typecheckok bool
 
 var compiling_runtime bool
 
+// Compiling the standard library
+var compiling_std bool
+
 var compiling_wrappers int
 
 var use_writebarrier bool

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

@@ -174,6 +174,7 @@ func Main(archInit func(*Arch)) {
 	Nacl = objabi.GOOS == "nacl"
 
 	flag.BoolVar(&compiling_runtime, "+", false, "compiling runtime")
+	flag.BoolVar(&compiling_std, "std", false, "compiling standard library")
 	objabi.Flagcount("%", "debug non-static initializers", &Debug['%'])
 	objabi.Flagcount("B", "disable bounds checking", &Debug['B'])
 	objabi.Flagcount("C", "disable printing of columns in error messages", &Debug['C']) // TODO(gri) remove eventually

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

@@ -1153,6 +1153,18 @@ func (p *noder) error(err error) {
 	p.err <- err.(syntax.Error)
 }
 
+// pragmas that are allowed in the std lib, but don't have
+// a syntax.Pragma value (see lex.go) associated with them.
+var allowedStdPragmas = map[string]bool{
+	"go:cgo_export_static":  true,
+	"go:cgo_export_dynamic": true,
+	"go:cgo_import_static":  true,
+	"go:cgo_import_dynamic": true,
+	"go:cgo_ldflag":         true,
+	"go:cgo_dynamic_linker": true,
+	"go:generate":           true,
+}
+
 // pragma is called concurrently if files are parsed concurrently.
 func (p *noder) pragma(pos src.Pos, text string) syntax.Pragma {
 	switch {
@@ -1181,6 +1193,9 @@ func (p *noder) pragma(pos src.Pos, text string) syntax.Pragma {
 		if !compiling_runtime && prag&runtimePragmas != 0 {
 			p.error(syntax.Error{Pos: pos, Msg: fmt.Sprintf("//%s only allowed in runtime", verb)})
 		}
+		if prag == 0 && !allowedStdPragmas[verb] && compiling_std {
+			p.error(syntax.Error{Pos: pos, Msg: fmt.Sprintf("//%s is not allowed in the standard library", verb)})
+		}
 		return prag
 	}
 

src/cmd/go/internal/work/build.go

@@ -2195,6 +2195,9 @@ func (gcToolchain) gc(b *Builder, p *load.Package, archive, obj string, asmhdr b
 	if p.Name == "main" {
 		gcargs[1] = "main"
 	}
+	if p.Standard {
+		gcargs = append(gcargs, "-std")
+	}
 	compilingRuntime := p.Standard && (p.ImportPath == "runtime" || strings.HasPrefix(p.ImportPath, "runtime/internal"))
 	if compilingRuntime {
 		// runtime compiles with a special gc flag to emit

src/go/types/stdlib_test.go

@@ -104,10 +104,10 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 			case "errorcheck":
 				expectErrors = true
 				for _, arg := range fields[1:] {
-					if arg == "-0" || arg == "-+" {
+					if arg == "-0" || arg == "-+" || arg == "-std" {
 						// Marked explicitly as not expected errors (-0),
-						// or marked as compiling_runtime, which is only done
-						// to trigger runtime-only error output.
+						// or marked as compiling runtime/stdlib, which is only done
+						// to trigger runtime/stdlib-only error output.
 						// In both cases, the code should typecheck.
 						expectErrors = false
 						break

test/fixedbugs/issue18331.go

+// errorcheck -std
+// 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.
+// Issue 18331: We should catch invalid pragma verbs
+// for code that resides in the standard library.
+package issue18331
+
+//go:unknown // ERROR "//go:unknown is not allowed in the standard library"
+func foo()
+
+//go:nowritebarrierc // ERROR "//go:nowritebarrierc is not allowed in the standard library"
+func bar()
+
+//go:noesape // ERROR "//go:noesape is not allowed in the standard library"
+func groot()
+
+//go:noescape
+func hey() { // ERROR "can only use //go:noescape with external func implementations"
+}