Revert "Adding an exclusion list to the coverage wrapper script."

This reverts commit 6b7213a4.

Reason for revert: This CL will break per-CL coverage gathering without CL 1496002, and that other CL is not ready yet.

Original change's description:
> Adding an exclusion list to the coverage wrapper script.
> 
> The script now assumes GN adds coverage flags to the cflags for each
> source file. The script removes the flag if the file is in an exclusion
> list, or if `--files-to-instrument` is set it will also remove flags if
> the file is not listed in that argument.
> 
> The script supports multiple exclusion lists that can be selected with
> the `--target-os` flag.
> 
> It's expected that GN will set these flags correctly and invoke the
> script in all coverage builds. http://crrev.com/c/1496002 does that.
> 
> 
> Bug: 918215
> Change-Id: I4454f67067a083581f31a22cfef85368825789f9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1495994
> Commit-Queue: Sajjad Mirza <sajjadm@google.com>
> Reviewed-by: Max Moroz <mmoroz@chromium.org>
> Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
> Reviewed-by: Roberto Carrillo <robertocn@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#637892}

TBR=stgao@chromium.org,robertocn@chromium.org,mmoroz@chromium.org,liaoyuke@chromium.org,sajjadm@google.com

Change-Id: I0cadb9c3d3ed0600648e273ffe58e7dc3f6ef7f8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 918215
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504960Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638167}

build/toolchain/clang_code_coverage_wrapper.py

@@ -2,19 +2,11 @@
 # Copyright 2018 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.
-"""Removes code coverage flags from invocations of the Clang C/C++ compiler.
+"""Adds code coverage flags to the invocations of the Clang C/C++ compiler.
 
-If the GN arg `use_clang_coverage=true`, this script will be invoked by default.
-GN will add coverage instrumentation flags to almost all source files.
-
-This script is used to remove instrumentation flags from a subset of the source
-files. By default, it will not remove flags from any files. If the option
---files-to-instrument is passed, this script will remove flags from all files
-except the ones listed in --files-to-instrument.
-
-This script also contains hard-coded exclusion lists of files to never
-instrument, indexed by target operating system. Files in these lists have their
-flags removed in both modes. The OS can be selected with --target-os.
+This script is used to instrument a subset of the source files, and the list of
+files to instrument is specified by an input file that is passed to this script
+as a command-line argument.
 
 The path to the coverage instrumentation input file should be relative to the
 root build directory, and the file consists of multiple lines where each line
@@ -45,8 +37,6 @@ import subprocess
 import sys
 
 # Flags used to enable coverage instrumentation.
-# Flags should be listed in the same order that they are added in
-# build/config/coverage/BUILD.gn
 _COVERAGE_FLAGS = [
     '-fprofile-instr-generate', '-fcoverage-mapping',
     # Following experimental flags remove unused header functions from the
@@ -56,41 +46,6 @@ _COVERAGE_FLAGS = [
     '-mllvm', '-limited-coverage-experimental=true'
 ]
 
-# Map of exclusion lists indexed by target OS.
-# If no target OS is defined, or one is defined that doesn't have a specific
-# entry, use the 'default' exclusion_list. Anything added to 'default' will
-# apply to all platforms that don't have their own specific list.
-_COVERAGE_EXCLUSION_LIST_MAP = {
-    'default': [],
-    'chromeos': [
-        # These files caused clang to crash while compiling them. They are
-        # excluded pending an investigation into the underlying compiler bug.
-        '../../third_party/webrtc/p2p/base/p2p_transport_channel.cc',
-        '../../third_party/icu/source/common/uts46.cpp',
-        '../../third_party/icu/source/common/ucnvmbcs.cpp',
-        '../../base/android/android_image_reader_compat.cc',
-    ]
-}
-
-
-def _remove_flags_from_command(command):
-  # We need to remove the coverage flags for this file, but we only want to
-  # remove them if we see the exact sequence defined in _COVERAGE_FLAGS.
-  # That ensures that we only remove the flags added by GN when
-  # "use_clang_coverage" is true. Otherwise, we would remove flags set by
-  # other parts of the build system.
-  start_flag = _COVERAGE_FLAGS[0]
-  num_flags = len(_COVERAGE_FLAGS)
-  start_idx = 0
-  try:
-    while True:
-      idx = command.index(start_flag, start_idx)
-      start_idx = idx + 1
-      if command[idx:idx+num_flags] == _COVERAGE_FLAGS:
-        del command[idx:idx+num_flags]
-        break
-  except ValueError:
-    pass
 
 def main():
   # TODO(crbug.com/898695): Make this wrapper work on Windows platform.
@@ -99,23 +54,16 @@ def main():
   arg_parser.add_argument(
       '--files-to-instrument',
       type=str,
+      required=True,
       help='Path to a file that contains a list of file names to instrument.')
-  arg_parser.add_argument(
-      '--target-os',
-      required=False,
-      help='The OS to compile for.')
   arg_parser.add_argument('args', nargs=argparse.REMAINDER)
   parsed_args = arg_parser.parse_args()
 
-  if (parsed_args.files_to_instrument and
-      not os.path.isfile(parsed_args.files_to_instrument)):
+  if not os.path.isfile(parsed_args.files_to_instrument):
     raise Exception('Path to the coverage instrumentation file: "%s" doesn\'t '
                     'exist.' % parsed_args.files_to_instrument)
 
   compile_command = parsed_args.args
-  if not any('clang' in s for s in compile_command):
-    return subprocess.call(compile_command)
-
   try:
     # The command is assumed to use Clang as the compiler, and the path to the
     # source file is behind the -c argument, and the path to the source path is
@@ -131,19 +79,12 @@ def main():
     raise Exception('Source file to be compiled is missing from the command.')
 
   compile_source_file = compile_command[index_dash_c + 1]
-  target_os = parsed_args.target_os
-  if target_os not in _COVERAGE_EXCLUSION_LIST_MAP:
-    target_os = 'default'
-  exclusion_list = _COVERAGE_EXCLUSION_LIST_MAP[target_os]
-
-  if compile_source_file in exclusion_list:
-    _remove_flags_from_command(compile_command)
-  elif parsed_args.files_to_instrument:
-    with open(parsed_args.files_to_instrument) as f:
-      if compile_source_file not in f.read():
-        _remove_flags_from_command(compile_command)
+  with open(parsed_args.files_to_instrument) as f:
+    if compile_source_file + '\n' in f.read():
+      compile_command.extend(_COVERAGE_FLAGS)
 
   return subprocess.call(compile_command)
 
+
 if __name__ == '__main__':
   sys.exit(main())