cmd/cgo: update JNI's jobject to uintptr check for newer Android NDKs

In Android's NDK16, jobject is now declared as:
    #ifdef __cplusplus
    class _jobject {};
    typedef _jobject*       jobject;
    #else /* not __cplusplus */
    typedef void*           jobject;
    #endif

This makes the jobject to uintptr check fail because it expects the
following definition:
    struct _jobject;
    typedef struct _jobject *jobject;

Update the type check to handle that new type definition in both C and
C++ modes.

Fixes #26213

Signed-off-by: Steeve Morin <steeve.morin@gmail.com>

misc/cgo/test/cgo_test.go

@@ -91,6 +91,7 @@ func Test24206(t *testing.T)                 { test24206(t) }
 func Test25143(t *testing.T)                 { test25143(t) }
 func Test23356(t *testing.T)                 { test23356(t) }
 func Test26066(t *testing.T)                 { test26066(t) }
+func Test26213(t *testing.T)                 { test26213(t) }
 
 func BenchmarkCgoCall(b *testing.B)  { benchCgoCall(b) }
 func BenchmarkGoString(b *testing.B) { benchGoString(b) }

misc/cgo/test/issue26213/jni.h

@@ -0,0 +1,29 @@
+// Copyright 2018 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.
+
+// It's going to be hard to include a whole real JVM to test this.
+// So we'll simulate a really easy JVM using just the parts we need.
+
+// This is the relevant part of jni.h.
+
+// On Android NDK16, jobject is defined like this in C and C++
+typedef void* jobject;
+
+typedef jobject jclass;
+typedef jobject jthrowable;
+typedef jobject jstring;
+typedef jobject jarray;
+typedef jarray jbooleanArray;
+typedef jarray jbyteArray;
+typedef jarray jcharArray;
+typedef jarray jshortArray;
+typedef jarray jintArray;
+typedef jarray jlongArray;
+typedef jarray jfloatArray;
+typedef jarray jdoubleArray;
+typedef jarray jobjectArray;
+
+typedef jobject jweak;
+
+// Note: jvalue is already a non-pointer type due to it being a C union.

misc/cgo/test/issue26213/test26213.go

@@ -0,0 +1,46 @@
+// Copyright 2018 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 issue26213
+
+/*
+#include "jni.h"
+*/
+import "C"
+import (
+	"testing"
+)
+
+func Test26213(t *testing.T) {
+	var x1 C.jobject = 0 // Note: 0, not nil. That makes sure we use uintptr for these types.
+	_ = x1
+	var x2 C.jclass = 0
+	_ = x2
+	var x3 C.jthrowable = 0
+	_ = x3
+	var x4 C.jstring = 0
+	_ = x4
+	var x5 C.jarray = 0
+	_ = x5
+	var x6 C.jbooleanArray = 0
+	_ = x6
+	var x7 C.jbyteArray = 0
+	_ = x7
+	var x8 C.jcharArray = 0
+	_ = x8
+	var x9 C.jshortArray = 0
+	_ = x9
+	var x10 C.jintArray = 0
+	_ = x10
+	var x11 C.jlongArray = 0
+	_ = x11
+	var x12 C.jfloatArray = 0
+	_ = x12
+	var x13 C.jdoubleArray = 0
+	_ = x13
+	var x14 C.jobjectArray = 0
+	_ = x14
+	var x15 C.jweak = 0
+	_ = x15
+}

misc/cgo/test/test26213.go

@@ -0,0 +1,15 @@
+// Copyright 2018 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 cgotest
+
+import (
+	"testing"
+
+	"./issue26213"
+)
+
+func test26213(t *testing.T) {
+	issue26213.Test26213(t)
+}

src/cmd/cgo/gcc.go

@@ -2704,13 +2704,31 @@ func (c *typeConv) badJNI(dt *dwarf.TypedefType) bool {
 			}
 		}
 
-		// Check that the typedef is:
+		// Check that the typedef is either:
-		//     struct _jobject;
+		// 1:
-		//     typedef struct _jobject *jobject;
+		//     	struct _jobject;
+		//     	typedef struct _jobject *jobject;
+		// 2: (in NDK16 in C++)
+		//     	class _jobject {};
+		//     	typedef _jobject* jobject;
+		// 3: (in NDK16 in C)
+		//     	typedef void* jobject;
 		if ptr, ok := w.Type.(*dwarf.PtrType); ok {
-			if str, ok := ptr.Type.(*dwarf.StructType); ok {
+			switch v := ptr.Type.(type) {
-				if str.StructName == "_jobject" && str.Kind == "struct" && len(str.Field) == 0 && str.Incomplete {
+			case *dwarf.VoidType:
-					return true
+				return true
+			case *dwarf.StructType:
+				if v.StructName == "_jobject" && len(v.Field) == 0 {
+					switch v.Kind {
+					case "struct":
+						if v.Incomplete {
+							return true
+						}
+					case "class":
+						if !v.Incomplete {
+							return true
+						}
+					}
 				}
 			}
 		}

src/cmd/dist/test.go

@@ -645,7 +645,7 @@ func (t *tester) registerTests() {
 					return nil
 				},
 			})
-			if cxx, _ := exec.LookPath(compilerEnvLookup(defaultcxx, goos, goarch)); cxx != "" {
+			if t.hasCxx() {
 				t.tests = append(t.tests, distTest{
 					name:    "swig_callback",
 					heading: "../misc/swig/callback",
@@ -1249,6 +1249,11 @@ func (t *tester) hasBash() bool {
 	return true
 }
 
+func (t *tester) hasCxx() bool {
+	cxx, _ := exec.LookPath(compilerEnvLookup(defaultcxx, goos, goarch))
+	return cxx != ""
+}
+
 func (t *tester) hasSwig() bool {
 	swig, err := exec.LookPath("swig")
 	if err != nil {