llvm_tools: add a simple cherrypick script

Given a SHA, this script will cherrypick the CL from LLVM, add it to the
appropriate filesdir, and update PATCHES.json with an appropriate
comment.

No testing is included, since the code is pretty straightline, and it's
expected to be used interactively. In other words, if it breaks,
*shrug*.

BUG=chromium:1057428
TEST=Ran on a few test-cases.

Change-Id: I8cb361bb29ec239316847a781a1edfd7941c7551
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2095772
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>

2 files changed, 174 insertions, 0 deletions

diff --git a/llvm_tools/README.md b/llvm_tools/README.md
index 52bc263f..5d27a962 100644
--- a/llvm_tools/README.md
+++ b/llvm_tools/README.md
@@ -470,3 +470,20 @@ from get_llvm_hash import GetGoogle3LLVMVersion
 
 GetGoogle3LLVMVersion(stable=True)
 ```
+
+### `cherrypick_cl.py`
+
+#### Usage
+
+This script updates sys-devel/llvm with an LLVM cherrypick of your choosing, and
+copies the cherrypick into sys-devel/llvm/files/cherry.
+
+Usage:
+
+```
+./cherrypick_cl.py --sha 174c3eb69f19ff2d6a3eeae31d04afe77e62c021
+```
+
+It tries to autodetect a lot of things (e.g., sys-devel/llvm's path, the
+"start"/"end" revisions to set, etc.) For more information, please see the
+`--help`
diff --git a/llvm_tools/cherrypick_cl.py b/llvm_tools/cherrypick_cl.py
new file mode 100755
index 00000000..68a11a4c
--- /dev/null
+++ b/llvm_tools/cherrypick_cl.py
@@ -0,0 +1,157 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# pylint: disable=cros-logging-import
+
+"""Adds a cherrypick to LLVM's PATCHES.json."""
+
+from __future__ import print_function
+
+import argparse
+import json
+import logging
+import os
+import shlex
+import subprocess
+import sys
+
+import get_llvm_hash
+import git_llvm_rev
+
+
+def add_cherrypick(patches_json_path: str, patches_dir: str,
+                   relative_patches_dir: str, start_version: git_llvm_rev.Rev,
+                   llvm_dir: str, rev: git_llvm_rev.Rev, sha: str):
+  with open(patches_json_path, encoding='utf-8') as f:
+    patches_json = json.load(f)
+
+  file_name = sha + '.patch'
+  rel_patch_path = os.path.join(relative_patches_dir, file_name)
+
+  for p in patches_json:
+    rel_path = p['rel_patch_path']
+    if rel_path == rel_patch_path:
+      raise ValueError('Patch at %r already exists in PATCHES.json' % rel_path)
+    if sha in rel_path:
+      logging.warning(
+          'Similarly-named patch already exists in PATCHES.json: %r', rel_path)
+
+  with open(os.path.join(patches_dir, file_name), 'wb') as f:
+    subprocess.check_call(['git', 'show', sha], stdout=f, cwd=llvm_dir)
+
+  commit_subject = subprocess.check_output(
+      ['git', 'log', '-n1', '--format=%s', sha], cwd=llvm_dir, encoding='utf-8')
+
+  patches_json.append({
+      'comment': commit_subject.strip(),
+      'rel_patch_path': rel_patch_path,
+      'start_version': start_version.number,
+      'end_version': rev.number,
+  })
+
+  temp_file = patches_json_path + '.tmp'
+  with open(temp_file, 'w', encoding='utf-8') as f:
+    json.dump(patches_json, f, indent=4, separators=(',', ': '))
+  os.rename(temp_file, patches_json_path)
+
+
+def parse_ebuild_for_assignment(llvm_path: str, var_name: str) -> str:
+  # '_pre' filters the LLVM 9.0 ebuild, which we never want to target, from
+  # this list.
+  candidates = [
+      x for x in os.listdir(llvm_path)
+      if x.endswith('.ebuild') and x.startswith('llvm') and '_pre' in x
+  ]
+
+  if not candidates:
+    raise ValueError('No LLVM ebuilds found under %r' % llvm_path)
+
+  ebuild = os.path.join(llvm_path, max(candidates))
+  with open(ebuild, encoding='utf-8') as f:
+    var_name_eq = var_name + '='
+    for orig_line in f:
+      if not orig_line.startswith(var_name_eq):
+        continue
+
+      # We shouldn't see much variety here, so do the simplest thing possible.
+      line = orig_line[len(var_name_eq):]
+      # Remove comments
+      line = line.split('#')[0]
+      # Remove quotes
+      line = shlex.split(line)
+      if len(line) != 1:
+        raise ValueError('Expected exactly one quoted value in %r' % orig_line)
+      return line[0].strip()
+
+  raise ValueError('No %s= line found in %r' % (var_name, ebuild))
+
+
+# Resolves a git ref (or similar) to a LLVM SHA.
+def resolve_llvm_ref(llvm_dir: str, sha: str) -> str:
+  return subprocess.check_output(
+      ['git', 'rev-parse', sha],
+      encoding='utf-8',
+      cwd=llvm_dir,
+  ).strip()
+
+
+def main():
+  logging.basicConfig(
+      format='%(asctime)s: %(levelname)s: %(filename)s:%(lineno)d: %(message)s',
+      level=logging.INFO,
+  )
+
+  parser = argparse.ArgumentParser(description=__doc__)
+  parser.add_argument(
+      '--llvm', help='Path to sys-devel/llvm. Will autodetect if not provided.')
+  parser.add_argument(
+      '--start_sha',
+      default='llvm-next',
+      help='LLVM SHA that the patch should start applying at. You can specify '
+      '"llvm" or "llvm-next", as well. Defaults to %(default)s.')
+  parser.add_argument(
+      '--sha', help='LLVM git SHA. Either this or --sha must be specified.')
+  args = parser.parse_args()
+
+  if args.llvm:
+    llvm = args.llvm
+  else:
+    my_dir = os.path.dirname(os.path.realpath(__file__))
+    llvm = os.path.join(
+        my_dir, '../../../third_party/chromiumos-overlay/sys-devel/llvm')
+    if not os.path.isdir(llvm):
+      raise ValueError("Couldn't autodetect llvm")
+
+  llvm = os.path.realpath(llvm)
+
+  patches_json_path = os.path.join(llvm, 'files/PATCHES.json')
+  relative_patches_dir = 'cherry'
+  patches_dir = os.path.join(llvm, 'files', relative_patches_dir)
+
+  llvm_config = git_llvm_rev.LLVMConfig(
+      remote='origin', dir=get_llvm_hash.GetAndUpdateLLVMProjectInLLVMTools())
+
+  start_sha = args.start_sha
+  if start_sha == 'llvm':
+    start_sha = parse_ebuild_for_assignment(llvm, 'LLVM_HASH')
+    logging.info('Autodetected llvm hash == %s', start_sha)
+  elif start_sha == 'llvm-next':
+    start_sha = parse_ebuild_for_assignment(llvm, 'LLVM_NEXT_HASH')
+    logging.info('Autodetected llvm-next hash == %s', start_sha)
+
+  start_sha = resolve_llvm_ref(llvm_config.dir, start_sha)
+  start_rev = git_llvm_rev.translate_sha_to_rev(llvm_config, start_sha)
+  sha = resolve_llvm_ref(llvm_config.dir, args.sha)
+  rev = git_llvm_rev.translate_sha_to_rev(llvm_config, sha)
+
+  logging.info('Will cherrypick %s (%s), with start == %s', rev, sha, start_sha)
+  add_cherrypick(patches_json_path, patches_dir, relative_patches_dir,
+                 start_rev, llvm_config.dir, rev, sha)
+  logging.info('Complete.')
+
+
+if __name__ == '__main__':
+  sys.exit(main())