mobile/bind: let Java toString call String method if available

Bind generates a default toString for Go structs. If the struct has
a String() string method, use that instead.

Change-Id: If83a6f5c9ad03abbd0b939b9120ff8dd2135f713
Reviewed-on: https://go-review.googlesource.com/20656
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/genjava.go

@@ -48,8 +48,12 @@ func (g *javaGen) genStruct(obj *types.TypeName, T *types.Struct) {
 		g.Printf("public final native void set%s(%s v);\n\n", f.Name(), g.javaType(f.Type()))
 	}
 
+	var isStringer bool
 	for _, m := range methods {
 		g.genFuncSignature(m, false, false)
+		t := m.Type().(*types.Signature)
+		isStringer = isStringer || (m.Name() == "String" && t.Params().Len() == 0 && t.Results().Len() == 1 &&
+			types.Identical(t.Results().At(0).Type(), types.Typ[types.String]))
 	}
 
 	g.Printf("@Override public boolean equals(Object o) {\n")
@@ -85,19 +89,22 @@ func (g *javaGen) genStruct(obj *types.TypeName, T *types.Struct) {
 	g.Printf("});\n")
 	g.Printf("}\n\n")
 
-	// TODO(crawshaw): use String() string if it is defined.
 	g.Printf("@Override public String toString() {\n")
 	g.Indent()
-	g.Printf("StringBuilder b = new StringBuilder();\n")
-	g.Printf(`b.append("%s").append("{");`, obj.Name())
-	g.Printf("\n")
-	for _, f := range fields {
-		n := f.Name()
-		g.Printf(`b.append("%s:").append(get%s()).append(",");`, n, n)
+	if isStringer {
+		g.Printf("return String();\n")
+	} else {
+		g.Printf("StringBuilder b = new StringBuilder();\n")
+		g.Printf(`b.append("%s").append("{");`, obj.Name())
+		g.Printf("\n")
+		for _, f := range fields {
+			n := f.Name()
+			g.Printf(`b.append("%s:").append(get%s()).append(",");`, n, n)
+			g.Printf("\n")
+		}
+		g.Printf(`return b.append("}").toString();`)
 		g.Printf("\n")
 	}
-	g.Printf(`return b.append("}").toString();`)
-	g.Printf("\n")
 	g.Outdent()
 	g.Printf("}\n")
 

bind/testdata/structs.go

@@ -34,3 +34,7 @@ type (
 
 func (s *S2) M() {
 }
+
+func (_ *S2) String() string {
+	return ""
+}

bind/testdata/structs.go.golden

@@ -86,6 +86,15 @@ func proxystructs_S2_M(refnum C.int32_t) {
 	v.M()
 }
 
+//export proxystructs_S2_String
+func proxystructs_S2_String(refnum C.int32_t) C.nstring {
+	ref := _seq.FromRefNum(int32(refnum))
+	v := ref.Get().(*structs.S2)
+	res_0 := v.String()
+	_res_0 := encodeString(res_0)
+	return _res_0
+}
+
 //export proxystructs_I_M
 func proxystructs_I_M(refnum C.int32_t) {
 	ref := _seq.FromRefNum(int32(refnum))

bind/testdata/structs.java.c.golden

@@ -106,6 +106,14 @@ Java_go_structs_Structs_00024S2_M(JNIEnv* env, jobject this) {
     proxystructs_S2_M(o);
 }
 
+JNIEXPORT jstring JNICALL
+Java_go_structs_Structs_00024S2_String(JNIEnv* env, jobject this) {
+    int32_t o = go_seq_to_refnum(env, this);
+    nstring r0 = proxystructs_S2_String(o);
+    jstring _r0 = go_seq_to_java_string(env, r0);
+    return _r0;
+}
+
 JNIEXPORT void JNICALL
 Java_go_structs_Structs_00024I_00024Proxy_M(JNIEnv* env, jobject this) {
     int32_t o = go_seq_to_refnum(env, this);

bind/testdata/structs.java.golden

@@ -73,6 +73,7 @@ public abstract class Structs {
         public final go.Seq.Ref ref() { return ref; }
         
         public native void M();
+        public native String String();
         @Override public boolean equals(Object o) {
             if (o == null || !(o instanceof S2)) {
                 return false;
@@ -86,9 +87,7 @@ public abstract class Structs {
         }
         
         @Override public String toString() {
-            StringBuilder b = new StringBuilder();
-            b.append("S2").append("{");
-            return b.append("}").toString();
+            return String();
         }
     }
     

bind/testdata/structs.objc.h.golden

@@ -32,6 +32,7 @@
 
 - (id)initWithRef:(id)ref;
 - (void)m;
+- (NSString*)string;
 @end
 
 @protocol GoStructsI

bind/testdata/structs.objc.m.golden

@@ -95,6 +95,13 @@ static NSString* errDomain = @"go.structs";
 	proxystructs_S2_M(refnum);
 }
 
+- (NSString*)string {
+	int32_t refnum = go_seq_go_to_refnum(self._ref);
+	nstring r0 = proxystructs_S2_String(refnum);
+	NSString *_ret0_ = go_seq_to_objc_string(r0);
+	return _ret0_;
+}
+
 @end
 
 @implementation GoStructsI {