Deal with -Wunused-parameter in libchrome build rule.

So, now we do not need modification in libchrome to workaround
the error.

Bug: 73270448
Test: Build locally. Treehugger.
Change-Id: I38fe79c1e01fd39a4bdd7121bb58b9b6d9a3da89

1 files changed, 93 insertions, 0 deletions

diff --git a/libchrome_tools/include_generator.py b/libchrome_tools/include_generator.py
new file mode 100755
index 0000000000..efffd3952c
--- /dev/null
+++ b/libchrome_tools/include_generator.py
@@ -0,0 +1,93 @@
+#!/usr/bin/python
+
+# Copyright (C) 2018 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Generates wrapped include files to workaround -Wunused-parameter errors.
+
+In Chrome repository, "-Wunused-parameter" is disabled, and several header
+files in Chrome repository have actually unused-parameter.
+One of the typical scenarios is; in Chrome, Observer class is often defined
+as follows:
+
+class Foo {
+ public:
+  class Observer {
+   public:
+    virtual void OnSomeEvent(EventArg arg) {}
+    virtual void OnAnotherEvent(EventArg arg) {}
+    ...
+  };
+  ...
+};
+
+Here, On...Event() methods do nothing by default, and subclasses will override
+only necessary ones.
+In this use case, argument names can also work as documentation, and overrides
+can use these good interface-defined default names as a starting point for
+their implementation.
+
+On the other hand, in Android, -Wunused-parameter is enabled by default.
+Thus, if such a project includes header files from libchrome, it could cause
+a compile error (by the warning and "-Werror").
+
+To avoid such a situation, libchrome exports include files wrapped by the
+pragmas as follows.
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+${actual_include_file_content}
+#pragma GCC diagnostic pop
+
+so, the unused-parameter warning generated by the libchrome include headers
+will be ignored.
+Note that these GCC pragmas are also supported by clang for compatibility. cf)
+https://clang.llvm.org/docs/UsersManual.html#controlling-diagnostics-via-pragmas
+
+Usage: include_generator.py $(in) $(out)
+"""
+
+import sys
+
+
+def _generate(input_path, output_path):
+    """Generates a include file wrapped by pragmas.
+
+    Reads the file at |input_path| and output the content with wrapping by
+    #pragma to ignore unused-parameter warning into the file at |output_path|.
+    If the parent directories of |output_path| do not exist, creates them.
+
+    Args:
+        input_path: Path to the source file. Expected this is a chrome's header
+            file.
+        output_path: Path to the output file.
+    """
+    with open(input_path, 'r') as f:
+        content = f.read()
+
+    with open(output_path, 'w') as f:
+        f.writelines([
+            '// Generated by %s\n' % sys.argv[0],
+            '#pragma GCC diagnostic push\n'
+            '#pragma GCC diagnostic ignored "-Wunused-parameter"\n',
+            content,
+            '#pragma GCC diagnostic pop\n'])
+
+
+def main():
+    _generate(*sys.argv[1:])
+
+
+if __name__ == '__main__':
+    main()