Rewrite some proguard rules when building for cronet.

Bug: 1004516
Change-Id: I5c489ce94d9bea9d7b16fd8954008a28f7ddb8a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1808116Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697402}

components/cronet/android/BUILD.gn

@@ -498,6 +498,9 @@ action("cronet_combine_proguard_flags") {
   script = "//components/cronet/tools/generate_proguard_file.py"
   sources = [
     "//base/android/proguard/chromium_code.flags",
+
+    # Massage the proguard rules to work with AppReduce.
+    "//components/cronet/android/cronet_appreduce_workaround.patch",
     "//components/cronet/android/cronet_impl_native_proguard.cfg",
   ]
   outputs = [

components/cronet/android/cronet_appreduce_workaround.patch

+This patchfile is a stop-gap solution to accomodate differences in syntax for
+AppReduce, which is used internally in place of ProGuard. See crbug.com/1004516.
+
+This patches base/android/proguard/chromium_code.flags.
+
+It can be re-generated using these steps:
+
+cd src
+export ORIG_FLAGS="base/android/proguard/chromium_code.flags"
+cp $ORIG_FLAGS modified.flags
+$EDITOR modified.flags
+diff -u "$ORIG_FLAGS" modified.flags > "components/cronet/android/cronet_appreduce_workaround.patch"
+
+To test whether the patch applies cleanly use:
+
+autoninja -C out/Release cronet_combine_proguard_flags
+
+--- base/android/proguard/chromium_code.flags	2019-09-16 16:39:21.108477065 -0700
++++ modified.flags	2019-09-17 12:12:17.487606737 -0700
+@@ -50,9 +50,12 @@
+ -assumenosideeffects class ** {
+   # Remove @RemovableInRelease methods so long as return values are unused.
+   @org.chromium.base.annotations.RemovableInRelease <methods>;
++}
++
++-assumevalues class ** {
+   # Remove object @RemovableInRelease methods even when return value is used.
+-  # Note: * in return type does not match primitives.
+-  @org.chromium.base.annotations.RemovableInRelease * *(...) return null;
++  # Note: ** in return type does not match primitives.
++  @org.chromium.base.annotations.RemovableInRelease ** *(...) return null;
+   # Remove boolean @RemovableInRelease methods even when return value is used.
+   @org.chromium.base.annotations.RemovableInRelease boolean *(...) return false;
+ }

components/cronet/tools/generate_proguard_file.py

@@ -4,20 +4,42 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# Tool that combines a sequence of input proguard files and outputs a single
+# proguard file.
+#
+# The final output file is formed by concatenating all of the
+# input proguard files, and then sequentally applying any .patch files that
+# were given in the input.
+#
+# This tool requires the ability to shell execute the 'patch' tool, and is
+# expected to only be run on Linux.
+
 import optparse
 import sys
+import subprocess
+
+
+def ReadFile(path):
+  with open(path, 'rb') as f:
+    return f.read()
+
+
+def IsPatchFile(path):
+  return path.endswith('.patch')
 
-# Combines files in |input_files| as one proguard file and write that to
-# |output_file|
-def GenerateProguardFile(output_file, input_files):
+
+def ApplyPatch(output_file, patch_file):
   try:
-    with open(output_file, "wb") as target:
-      for input_file in input_files:
-        f = open(input_file, "rb")
-        for line in f:
-          target.write(line)
-  except IOError:
-    raise Exception("Proguard file generation failed")
+    subprocess.check_call(['patch', '--quiet', output_file, patch_file])
+  except:
+    message = '''
+Failed applying patch %s to %s
+
+For help on fixing read the documentation in the patch file.
+
+'''
+    sys.stderr.write(message % (patch_file, output_file))
+    raise
 
 
 def main():
@@ -26,7 +48,18 @@ def main():
           help='Output file for the generated proguard file')
 
   options, input_files = parser.parse_args()
-  GenerateProguardFile(options.output_file, input_files)
+
+  proguard_files = [path for path in input_files if not IsPatchFile(path)]
+  patch_files = [path for path in input_files if IsPatchFile(path)]
+
+  # Concatenate all the proguard files.
+  with open(options.output_file, 'wb') as target:
+    for input_file in proguard_files:
+      target.write(ReadFile(input_file))
+
+  # Apply any patch files.
+  for patch_file in patch_files:
+    ApplyPatch(options.output_file, patch_file)
 
 
 if __name__ == '__main__':