cmd/dist: add new misc/cgo/testsovar test

This change reintroduces CL 8523. CL 8523 was reverted because
it broke darwin and netbsd builds. Now that this test is part
of "go tool dist test" command we could skip OSes that fail.

Updates #10360

Change-Id: Iaaeb5b800126492f36415a439c333a218fe4ab67
Reviewed-on: https://go-review.googlesource.com/11119Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/cgo/testsovar/cgoso.go

+// 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 cgosotest
+
+// This test verifies that Go can access C variables
+// in shared object file via cgo.
+
+/*
+// intentionally write the same LDFLAGS differently
+// to test correct handling of LDFLAGS.
+#cgo windows CFLAGS: -DIMPORT_DLL
+#cgo linux LDFLAGS: -L. -lcgosotest
+#cgo dragonfly LDFLAGS: -L. -l cgosotest
+#cgo freebsd LDFLAGS: -L. -l cgosotest
+#cgo openbsd LDFLAGS: -L. -l cgosotest
+#cgo solaris LDFLAGS: -L. -lcgosotest
+#cgo netbsd LDFLAGS: -L. libcgosotest.so
+#cgo darwin LDFLAGS: -L. libcgosotest.dylib
+#cgo windows LDFLAGS: -L. libcgosotest.dll
+
+#include "cgoso_c.h"
+
+const char* getVar() {
+	    return exported_var;
+}
+*/
+import "C"
+
+import "fmt"
+
+func Test() {
+	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))
+	}
+}

misc/cgo/testsovar/cgoso_c.c

+// 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.
+
+// +build ignore
+
+const char *exported_var = "Hello world";

misc/cgo/testsovar/cgoso_c.h

+// 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.
+
+// +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/testsovar/main.go

+// 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.
+
+// +build ignore
+
+package main
+
+import "."
+
+func main() {
+	cgosotest.Test()
+}

src/cmd/dist/test.go

@@ -414,8 +414,21 @@ func (t *tester) registerTests() {
 			t.tests = append(t.tests, distTest{
 				name:    "testso",
 				heading: "../misc/cgo/testso",
-				fn:      t.cgoTestSO,
+				fn: func() error {
+					return t.cgoTestSO("misc/cgo/testso")
+				},
 			})
+			if t.goos == "darwin" {
+				fmt.Println("Skipping misc/cgo/testsovar test. See issue 10360 for details.")
+			} else {
+				t.tests = append(t.tests, distTest{
+					name:    "testsovar",
+					heading: "../misc/cgo/testsovar",
+					fn: func() error {
+						return t.cgoTestSO("misc/cgo/testsovar")
+					},
+				})
+			}
 		}
 		if t.supportedBuildmode("c-archive") {
 			t.registerTest("testcarchive", "../misc/cgo/testcarchive", "./test.bash")
@@ -724,8 +737,8 @@ func (t *tester) cgoTestSOSupported() bool {
 	return true
 }
 
-func (t *tester) cgoTestSO() error {
-	dir := filepath.Join(t.goroot, "misc/cgo/testso")
+func (t *tester) cgoTestSO(testpath string) error {
+	dir := filepath.Join(t.goroot, testpath)
 
 	// build shared object
 	output, err := exec.Command("go", "env", "CC").Output()
@@ -750,6 +763,7 @@ func (t *tester) cgoTestSO() error {
 		args = append(args, "-undefined", "suppress", "-flat_namespace")
 	case "windows":
 		ext = "dll"
+		args = append(args, "-DEXPORT_DLL")
 	}
 	sofname := "libcgosotest." + ext
 	args = append(args, "-o", sofname, "cgoso_c.c")