From b94f341baccebd574fbf3dd23445d0dfc9bf73d9 Mon Sep 17 00:00:00 2001
From: "Devon H. O'Dell" <devon.odell@gmail.com>
Date: Fri, 21 May 2010 17:31:18 -0700
Subject: [PATCH] cgo: better error for no C symbols

R=rsc, iant
CC=golang-dev, graeme.perrow
https://golang.org/cl/1193046
---
 src/cmd/cgo/main.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go
index 070146c9acb..ac82ae91841 100644
--- a/src/cmd/cgo/main.go
+++ b/src/cmd/cgo/main.go
@@ -83,6 +83,11 @@ func main() {
 		// Reset p.Preamble so that we don't end up with conflicting headers / defines
 		p.Preamble = builtinProlog
 		openProg(input, p)
+
+		if len(p.Vardef) == 0 && len(p.Funcdef) == 0 && len(p.Enumdef) == 0 && len(p.Constdef) == 0 {
+			fatal("no C symbols were used in cgo file " + input)
+		}
+
 		for _, cref := range p.Crefs {
 			// Convert C.ulong to C.unsigned long, etc.
 			if expand, ok := expandName[cref.Name]; ok {