Add non --full support to python git cl format

Parses git diff for changed python files in a method similar to
clang-diff and feeds the resulting line ranges into yapf.

Also sets the default style to the yapf file included in depot tools
by searching parent directories of each changed file to find a yapf
style config (.style.yapf). If none is found the default style
file will be the chromium .style.yapf included in depot tools.

Note: Even if line ranges are specified, yapf will fix indentation
issues for the entire file.
This is intended see https://github.com/google/yapf/issues/499
This may cause some issues if git cl format is run on a file
with lots of indentation issues or on a file or when run on a
third_party file that is formatted with pep8 and does not include
a .style.yapf and may make many more changes then the user expects.

Still undecided on whether this should be turned on by default but
if not I think the non --full support is a positive change anyways.

Bug:846432
Change-Id: Ib85797f4a8e1021870901ff465ec10f7e70deb87
Reviewed-on: https://chromium-review.googlesource.com/1249642
Commit-Queue: Aiden Benner <abenner@google.com>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>

git_cl.py

@@ -81,6 +81,9 @@ REFS_THAT_ALIAS_TO_OTHER_REFS = {
 DEFAULT_LINT_REGEX = r"(.*\.cpp|.*\.cc|.*\.h)"
 DEFAULT_LINT_IGNORE_REGEX = r"$^"
 
+# File name for yapf style config files.
+YAPF_CONFIG_FILENAME = '.style.yapf'
+
 # Buildbucket master name prefix.
 MASTER_PREFIX = 'master.'
 
@@ -666,6 +669,88 @@ def print_try_jobs(options, builds):
   print('Total: %d try jobs' % total)
 
 
+def _ComputeDiffLineRanges(files, upstream_commit):
+  """Gets the changed line ranges for each file since upstream_commit.
+
+  Parses a git diff on provided files and returns a dict that maps a file name
+  to an ordered list of range tuples in the form (start_line, count).
+  Ranges are in the same format as a git diff.
+  """
+  # If files is empty then diff_output will be a full diff.
+  if len(files) == 0:
+    return {}
+
+  # Take diff and find the line ranges where there are changes.
+  diff_cmd = BuildGitDiffCmd('-U0', upstream_commit, files, allow_prefix=True)
+  diff_output = RunGit(diff_cmd)
+
+  pattern = r'(?:^diff --git a/(?:.*) b/(.*))|(?:^@@.*\+(.*) @@)'
+  # 2 capture groups
+  # 0 == fname of diff file
+  # 1 == 'diff_start,diff_count' or 'diff_start'
+  # will match each of
+  # diff --git a/foo.foo b/foo.py
+  # @@ -12,2 +14,3 @@
+  # @@ -12,2 +17 @@
+  # running re.findall on the above string with pattern will give
+  # [('foo.py', ''), ('', '14,3'), ('', '17')]
+
+  curr_file = None
+  line_diffs = {}
+  for match in re.findall(pattern, diff_output, flags=re.MULTILINE):
+    if match[0] != '':
+      # Will match the second filename in diff --git a/a.py b/b.py.
+      curr_file = match[0]
+      line_diffs[curr_file] = []
+    else:
+      # Matches +14,3
+      if ',' in match[1]:
+        diff_start, diff_count = match[1].split(',')
+      else:
+        # Single line changes are of the form +12 instead of +12,1.
+        diff_start = match[1]
+        diff_count = 1
+
+      diff_start = int(diff_start)
+      diff_count = int(diff_count)
+
+      # If diff_count == 0 this is a removal we can ignore.
+      line_diffs[curr_file].append((diff_start, diff_count))
+
+  return line_diffs
+
+
+def _FindYapfConfigFile(fpath,
+                        yapf_config_cache,
+                        top_dir=None,
+                        default_style=None):
+  """Checks if a yapf file is in any parent directory of fpath until top_dir.
+
+  Recursively checks parent directories to find yapf file
+  and if no yapf file is found returns default_style.
+  Uses yapf_config_cache as a cache for previously found files.
+  """
+  # Return result if we've already computed it.
+  if fpath in yapf_config_cache:
+    return yapf_config_cache[fpath]
+
+  # Check if there is a style file in the current directory.
+  yapf_file = os.path.join(fpath, YAPF_CONFIG_FILENAME)
+  dirname = os.path.dirname(fpath)
+  if os.path.isfile(yapf_file):
+    ret = yapf_file
+  elif fpath == top_dir or dirname == fpath:
+    # If we're at the top level directory, or if we're at root
+    # use the chromium default yapf style.
+    ret = default_style
+  else:
+    # Otherwise recurse on the current directory.
+    ret = _FindYapfConfigFile(dirname, yapf_config_cache, top_dir,
+                              default_style)
+  yapf_config_cache[fpath] = ret
+  return ret
+
+
 def write_try_results_json(output_file, builds):
   """Writes a subset of the data from fetch_try_jobs to a file as JSON.
 
@@ -5772,12 +5857,15 @@ def CMDowners(parser, args):
       override_files=change.OriginalOwnersFiles()).run()
 
 
-def BuildGitDiffCmd(diff_type, upstream_commit, args):
+def BuildGitDiffCmd(diff_type, upstream_commit, args, allow_prefix=False):
   """Generates a diff command."""
   # Generate diff for the current branch's changes.
-  diff_cmd = ['-c', 'core.quotePath=false', 'diff',
-              '--no-ext-diff', '--no-prefix', diff_type,
-              upstream_commit, '--']
+  diff_cmd = ['-c', 'core.quotePath=false', 'diff', '--no-ext-diff']
+
+  if not allow_prefix:
+    diff_cmd += ['--no-prefix']
+
+  diff_cmd += [diff_type, upstream_commit, '--']
 
   if args:
     for arg in args:
@@ -5898,26 +5986,59 @@ def CMDformat(parser, args):
 
   # Similar code to above, but using yapf on .py files rather than clang-format
   # on C/C++ files
-  if opts.python:
+  if opts.python and python_diff_files:
     yapf_tool = gclient_utils.FindExecutable('yapf')
     if yapf_tool is None:
       DieWithError('yapf not found in PATH')
 
-    if opts.full:
-      if python_diff_files:
-        if opts.dry_run or opts.diff:
-          cmd = [yapf_tool, '--diff'] + python_diff_files
+    # If we couldn't find a yapf file we'll default to the chromium style
+    # specified in depot_tools.
+    depot_tools_path = os.path.dirname(os.path.abspath(__file__))
+    chromium_default_yapf_style = os.path.join(depot_tools_path,
+                                               YAPF_CONFIG_FILENAME)
+
+    # Note: yapf still seems to fix indentation of the entire file
+    # even if line ranges are specified.
+    # See https://github.com/google/yapf/issues/499
+    if not opts.full:
+      py_line_diffs = _ComputeDiffLineRanges(python_diff_files, upstream_commit)
+
+    # Used for caching.
+    yapf_configs = {}
+    for f in python_diff_files:
+      # Find the yapf style config for the current file, defaults to depot
+      # tools default.
+      yapf_config = _FindYapfConfigFile(
+          os.path.abspath(f), yapf_configs, top_dir,
+          chromium_default_yapf_style)
+
+      cmd = [yapf_tool, '--style', yapf_config, f]
+
+      has_formattable_lines = False
+      if not opts.full:
+        # Only run yapf over changed line ranges.
+        for diff_start, diff_len in py_line_diffs[f]:
+          diff_end = diff_start + diff_len - 1
+          # Yapf errors out if diff_end < diff_start but this
+          # is a valid line range diff for a removal.
+          if diff_end >= diff_start:
+            has_formattable_lines = True
+            cmd += ['-l', '{}-{}'.format(diff_start, diff_end)]
+        # If all line diffs were removals we have nothing to format.
+        if not has_formattable_lines:
+          continue
+
+      if opts.diff or opts.dry_run:
+        cmd += ['--diff']
+        # Will return non-zero exit code if non-empty diff.
         stdout = RunCommand(cmd, error_ok=True, cwd=top_dir)
         if opts.diff:
           sys.stdout.write(stdout)
         elif len(stdout) > 0:
           return_value = 2
       else:
-          RunCommand([yapf_tool, '-i'] + python_diff_files, cwd=top_dir)
-    else:
-      # TODO(sbc): yapf --lines mode still has some issues.
-      # https://github.com/google/yapf/issues/154
-      DieWithError('--python currently only works with --full')
+        cmd += ['-i']
+        RunCommand(cmd, cwd=top_dir)
 
   # Dart's formatter does not have the nice property of only operating on
   # modified chunks, so hard code full.