misc/cgo/testso: add test for fixed issue 4339

Update #4339.

Change-Id: Ic1a7535562b8b824ba166777725f7ba5b9623d77
Reviewed-on: https://go-review.googlesource.com/8523
Run-TryBot: Minux Ma <minux@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/testso/cgoso.c

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+#include "cgoso_c.h"
 #include "_cgo_export.h"
 
 #ifdef WIN32
@@ -12,3 +13,7 @@ void init() {
 #else
 void init() {}
 #endif
+
+const char* getVar() {
+    return exported_var;
+}

misc/cgo/testso/cgoso.go

@@ -5,6 +5,7 @@
 package cgosotest
 
 /*
+#cgo windows CFLAGS: -DIMPORT_DLL
 // intentionally write the same LDFLAGS differently
 // to test correct handling of LDFLAGS.
 #cgo linux LDFLAGS: -L. -lcgosotest
@@ -15,14 +16,32 @@ package cgosotest
 #cgo darwin LDFLAGS: -L. libcgosotest.dylib
 #cgo windows LDFLAGS: -L. libcgosotest.dll
 
+#include "cgoso_c.h"
+
 void init(void);
 void sofunc(void);
+const char* getVar(void);
 */
 import "C"
 
+import "fmt"
+
 func Test() {
 	C.init()
 	C.sofunc()
+	testExportedVar()
+}
+
+func testExportedVar() {
+	const want = "Hello world"
+	got := C.GoString(C.getVar())
+	if got != want {
+		panic(fmt.Sprintf("testExportedVar: got %q, but want %q", got, want))
+	}
+	got = C.GoString(C.exported_var)
+	if got != want {
+		panic(fmt.Sprintf("testExportedVar: got %q, but want %q", got, want))
+	}
 }
 
 //export goCallback

misc/cgo/testso/cgoso_c.c

@@ -4,6 +4,8 @@
 
 // +build ignore
 
+#include "cgoso_c.h"
+
 #ifdef WIN32
 // A Windows DLL is unable to call an arbitrary function in
 // the main executable. Work around that by making the main
@@ -28,3 +30,5 @@ void sofunc(void)
 {
 	goCallback();
 }
+
+const char *exported_var = "Hello world";

misc/cgo/testso/cgoso_c.h

+// Copyright 2011 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.
+
+// +build ignore
+
+#ifdef WIN32
+#if defined(EXPORT_DLL)
+#    define VAR __declspec(dllexport)
+#elif defined(IMPORT_DLL)
+#    define VAR __declspec(dllimport)
+#endif
+#else
+#    define VAR
+#endif
+
+VAR const char *exported_var;

misc/cgo/testso/test.bat

@@ -4,7 +4,7 @@
 
 @echo off
 
-gcc -c cgoso_c.c
+gcc -c cgoso_c.c -DEXPORT_DLL
 gcc -shared -o libcgosotest.dll cgoso_c.o
 if not exist libcgosotest.dll goto fail
 go build main.go