cmd/cgo: error, not panic, if not enough arguments to function

Fixes #13423.

Change-Id: I41bb45790cca36c57a107796f0eca61287acb2a9
Reviewed-on: https://go-review.googlesource.com/17332
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/errors/issue13423.go

@@ -0,0 +1,12 @@
+// Copyright 2015 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
+
+// #include <stdio.h>
+import "C"
+
+func main() {
+	_ = C.fopen() // ERROR HERE
+}

misc/cgo/errors/test.bash

@@ -40,6 +40,7 @@ check issue8442.go
 check issue11097a.go
 check issue11097b.go
 expect issue13129.go C.ushort
+check issue13423.go
 
 if ! go run ptr.go; then
 	exit 1

src/cmd/cgo/gcc.go

@@ -598,6 +598,12 @@ func (p *Package) rewriteCalls(f *File) {
 // each pointer argument x with _cgoCheckPointer(x).(T).
 func (p *Package) rewriteCall(f *File, call *ast.CallExpr, name *Name) {
 	for i, param := range name.FuncType.Params {
+		if len(call.Args) <= i {
+			// Avoid a crash; this will be caught when the
+			// generated file is compiled.
+			return
+		}
+
 		// An untyped nil does not need a pointer check, and
 		// when _cgoCheckPointer returns the untyped nil the
 		// type assertion we are going to insert will fail.
@@ -611,12 +617,6 @@ func (p *Package) rewriteCall(f *File, call *ast.CallExpr, name *Name) {
 			continue
 		}
 
-		if len(call.Args) <= i {
-			// Avoid a crash; this will be caught when the
-			// generated file is compiled.
-			return
-		}
-
 		c := &ast.CallExpr{
 			Fun: ast.NewIdent("_cgoCheckPointer"),
 			Args: []ast.Expr{