Android JNI gen: Don't emit code for empty RegisterNatives()

base/android/jni_generator/jni_generator.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Extracts native methods from a Java file and generates the JNI bindings.
 If you change this, please run and update the tests."""
 
 import collections
 import errno
@@ skipping 722 matching lines @@
 
 }  // namespace
 
 $OPEN_NAMESPACE
 
 $CONSTANT_FIELDS
 
 // Step 2: method stubs.
 $METHOD_STUBS
 
-// Step 3: RegisterNatives.
+$STEP3_COMMENT

[Torne, 2016/08/02 12:31:40]

I'd really just leave the comment there; it's an autogenerated file, it's okay
for there to be empty sections. I don't think this is worth the complexity.

[no sievers, 2016/08/02 23:12:17]

Done.

 $JNI_NATIVE_METHODS
 $REGISTER_NATIVES
 $CLOSE_NAMESPACE
 
 #endif  // ${HEADER_GUARD}
 """)
     values = {
         'SCRIPT_NAME': self.options.script_name,
         'FULLY_QUALIFIED_CLASS': self.fully_qualified_class,
         'CLASS_PATH_DEFINITIONS': self.GetClassPathDefinitionsString(),
         'CONSTANT_FIELDS': self.GetConstantFieldsString(),
         'METHOD_STUBS': self.GetMethodStubsString(),
         'OPEN_NAMESPACE': self.GetOpenNamespaceString(),
+        'STEP3_COMMENT': '',
         'JNI_NATIVE_METHODS': self.GetJNINativeMethodsString(),
         'REGISTER_NATIVES': self.GetRegisterNativesString(),
         'CLOSE_NAMESPACE': self.GetCloseNamespaceString(),
         'HEADER_GUARD': self.header_guard,
         'INCLUDES': self.GetIncludesString(),
     }
+    assert (values['JNI_NATIVE_METHODS'] == '') ==
+        (values['REGISTER_NATIVES'] == '')
+    if values['JNI_NATIVE_METHODS'] != '':
+      values['STEP3_COMMENT'] = '// Step 3: RegisterNatives.'
     return WrapOutput(template.substitute(values))
 
   def GetClassPathDefinitionsString(self):
     ret = []
     ret += [self.GetClassPathDefinitions()]
     return '\n'.join(ret)
 
   def GetConstantFieldsString(self):
     if not self.constant_fields:
       return ''
@@ skipping 49 matching lines @@
       return ''
     template = Template("""\
 static const JNINativeMethod kMethods${JAVA_CLASS}[] = {
 ${KMETHODS}
 };
 """)
     return self.SubstituteNativeMethods(template)
 
   def GetRegisterNativesString(self):
     """Returns the code for RegisterNatives."""
+    natives = self.GetRegisterNativesImplString()
+    if not natives:
+      return ''
+
     template = Template("""\
 ${REGISTER_NATIVES_SIGNATURE} {
 ${EARLY_EXIT}
 ${NATIVES}
   return true;
 }
 """)
     signature = 'static bool RegisterNativesImpl(JNIEnv* env)'
     early_exit = ''
     if self.options.native_exports_optional:
       early_exit = """\
   if (base::android::IsManualJniRegistrationDisabled()) return true;
 """
 
-    natives = self.GetRegisterNativesImplString()
     values = {'REGISTER_NATIVES_SIGNATURE': signature,
               'EARLY_EXIT': early_exit,
               'NATIVES': natives,
              }
 
-    func_declaration = ''
-    if not natives:
-      func_declaration = Template("""\
-${REGISTER_NATIVES_SIGNATURE} __attribute__((unused));
-""").substitute(values)
-
-    return func_declaration + template.substitute(values)
+    return template.substitute(values)
 
   def GetRegisterNativesImplString(self):
     """Returns the shared implementation for RegisterNatives."""
     if not self.options.native_exports_optional:
       return ''
 
     template = Template("""\
   const int kMethods${JAVA_CLASS}Size = arraysize(kMethods${JAVA_CLASS});
 
   if (env->RegisterNatives(${JAVA_CLASS}_clazz(env),
@@ skipping 494 matching lines @@
   GenerateJNIHeader(input_file, output_file, options)
 
   if options.depfile:
     build_utils.WriteDepfile(
         options.depfile,
         build_utils.GetPythonDependencies())
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))