compiler: Mangle generated method names that conflict with java.lang.Object methods (#12332)

Generated gRPC method names in the BlockingV2Stub can conflict with
final methods on `java.lang.Object` (e.g., `toString()`, `hashCode()`)
for client-streaming and bidi-streaming RPCs. This occurs because
they are generated with no arguments, leading to a compilation error.
One such case in #12331.

This change introduces a dedicated list of no-argument method names
from java.lang.Object and applies name-mangling (appending an
underscore) only when generating these specific methods in the
v2 blocking stub.

This resolves the compilation failure while ensuring that the behavior
for all other stubs remains unchanged.

Fixes: #12331

Author: shivaspeaks

compiler/src/java_plugin/cpp/java_generator.cpp

@@ -143,11 +143,24 @@ static std::set<std::string> java_keywords = {
   "false",
 };
 
+// Methods on java.lang.Object that take no arguments.
+static std::set<std::string> java_object_methods = {
+    "clone",
+    "finalize",
+    "getClass",
+    "hashCode",
+    "notify",
+    "notifyAll",
+    "toString",
+    "wait",
+};
+
 // Adjust a method name prefix identifier to follow the JavaBean spec:
 //   - decapitalize the first letter
 //   - remove embedded underscores & capitalize the following letter
-//  Finally, if the result is a reserved java keyword, append an underscore.
-static std::string MixedLower(std::string word) {
+//  Finally, if the result is a reserved java keyword or an Object method,
+// append an underscore.
+static std::string MixedLower(std::string word, bool mangle_object_methods = false) {
   std::string w;
   w += tolower(word[0]);
   bool after_underscore = false;
@@ -159,7 +172,9 @@ static std::string MixedLower(std::string word) {
       after_underscore = false;
     }
   }
-  if (java_keywords.find(w) != java_keywords.end()) {
+  if (java_keywords.find(w) != java_keywords.end() ||
+      (mangle_object_methods &&
+       java_object_methods.find(w) != java_object_methods.end())) {
     return w + "_";
   }
   return w;
@@ -180,8 +195,9 @@ static std::string ToAllUpperCase(std::string word) {
   return w;
 }
 
-static inline std::string LowerMethodName(const MethodDescriptor* method) {
-  return MixedLower(std::string(method->name()));
+static inline std::string LowerMethodName(const MethodDescriptor* method,
+                                          bool mangle_object_methods = false) {
+  return MixedLower(std::string(method->name()), mangle_object_methods);
 }
 
 static inline std::string MethodPropertiesFieldName(const MethodDescriptor* method) {
@@ -676,10 +692,12 @@ static void PrintStub(
     const MethodDescriptor* method = service->method(i);
     (*vars)["input_type"] = MessageFullJavaName(method->input_type());
     (*vars)["output_type"] = MessageFullJavaName(method->output_type());
-    (*vars)["lower_method_name"] = LowerMethodName(method);
-    (*vars)["method_method_name"] = MethodPropertiesGetterName(method);
     bool client_streaming = method->client_streaming();
     bool server_streaming = method->server_streaming();
+    bool mangle_object_methods = (call_type == BLOCKING_V2_CALL && client_streaming)
+      || (call_type == BLOCKING_CALL && client_streaming && server_streaming);
+    (*vars)["lower_method_name"] = LowerMethodName(method, mangle_object_methods);
+    (*vars)["method_method_name"] = MethodPropertiesGetterName(method);
 
     if (call_type == BLOCKING_CALL && client_streaming) {
       // Blocking client interface with client streaming is not available