From ba30c082c026b5ef029e5d855a90ea56ef9487ec Mon Sep 17 00:00:00 2001
From: Matthew Dempsky <mdempsky@google.com>
Date: Thu, 14 Aug 2014 09:21:58 -0700
Subject: [PATCH] cmd/cgo: check for compiler errors in the C preamble

E.g., here's the new "go build" output:

$ go build misc/cgo/errors/issue8442.go
# command-line-arguments
could not determine kind of name for C.issue8442foo

gcc errors for preamble:
misc/cgo/errors/issue8442.go:11:19: error: unknown type name 'UNDEF'

Fixes #8442.

LGTM=iant
R=iant, alex.brainman
CC=golang-codereviews
https://golang.org/cl/129160043
---
 misc/cgo/errors/issue8442.go | 17 +++++++++++++++++
 misc/cgo/errors/test.bash    |  1 +
 src/cmd/cgo/gcc.go           | 15 ++++++++++++---
 3 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 misc/cgo/errors/issue8442.go

diff --git a/misc/cgo/errors/issue8442.go b/misc/cgo/errors/issue8442.go
new file mode 100644
index 0000000000..45daf8e59e
--- /dev/null
+++ b/misc/cgo/errors/issue8442.go
@@ -0,0 +1,17 @@
+// Copyright 2014 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.
+
+package main
+
+// Issue 8442.  Cgo output unhelpful error messages for
+// invalid C preambles.
+
+/*
+void issue8442foo(UNDEF*); // ERROR HERE
+*/
+import "C"
+
+func main() {
+	C.issue8442foo(nil)
+}
diff --git a/misc/cgo/errors/test.bash b/misc/cgo/errors/test.bash
index e5bf47a0dd..c96264389c 100755
--- a/misc/cgo/errors/test.bash
+++ b/misc/cgo/errors/test.bash
@@ -28,6 +28,7 @@ check err1.go
 check err2.go
 check err3.go
 check issue7757.go
+check issue8442.go
 
 rm -rf errs _obj
 exit 0
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 482b35197c..d77d56c22a 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -332,6 +332,7 @@ func (p *Package) guessKinds(f *File) []*Name {
 	const (
 		notType = 1 << iota
 		notConst
+		notDeclared
 	)
 	for _, line := range strings.Split(stderr, "\n") {
 		if !strings.Contains(line, ": error:") {
@@ -366,7 +367,7 @@ func (p *Package) guessKinds(f *File) []*Name {
 			completed = true
 
 		case "not-declared":
-			error_(token.NoPos, "%s", strings.TrimSpace(line[c2+1:]))
+			sniff[i] |= notDeclared
 		case "not-type":
 			sniff[i] |= notType
 		case "not-const":
@@ -375,12 +376,12 @@ func (p *Package) guessKinds(f *File) []*Name {
 	}
 
 	if !completed {
-		fatalf("%s did not produce error at completed:1\non input:\n%s", p.gccBaseCmd()[0], b.Bytes())
+		fatalf("%s did not produce error at completed:1\non input:\n%s\nfull error output:\n%s", p.gccBaseCmd()[0], b.Bytes(), stderr)
 	}
 
 	for i, n := range names {
 		switch sniff[i] {
-		case 0:
+		default:
 			error_(token.NoPos, "could not determine kind of name for C.%s", fixGo(n.Go))
 		case notType:
 			n.Kind = "const"
@@ -391,6 +392,14 @@ func (p *Package) guessKinds(f *File) []*Name {
 		}
 	}
 	if nerrors > 0 {
+		// Check if compiling the preamble by itself causes any errors,
+		// because the messages we've printed out so far aren't helpful
+		// to users debugging preamble mistakes.  See issue 8442.
+		preambleErrors := p.gccErrors([]byte(f.Preamble))
+		if len(preambleErrors) > 0 {
+			error_(token.NoPos, "\n%s errors for preamble:\n%s", p.gccBaseCmd()[0], preambleErrors)
+		}
+
 		fatalf("unresolved names")
 	}
 
-- 
2.48.1