llvm_tools: fix `cros lint` & mypy issues in patch_utils

`mypy` doesn't infer the right types for some of these lists, and
_really_ dislikes multiple calls to the same Callable with different
signatures.

`cros lint` was unhappy with `==` to compare fns, and unmentioned things
in docstrings.

BUG=b:332589934
TEST=repo upload

Change-Id: Ic6929e8524797b2fdc96db65a94c0f98ea9dd8bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/5420774
Commit-Queue: George Burgess <gbiv@chromium.org>
Reviewed-by: Jordan Abrahams-Whitehead <ajordanr@google.com>
Tested-by: George Burgess <gbiv@chromium.org>

2 files changed, 12 insertions, 15 deletions

diff --git a/llvm_tools/patch_utils.py b/llvm_tools/patch_utils.py
index b21cf314..b5383ac9 100644
--- a/llvm_tools/patch_utils.py
+++ b/llvm_tools/patch_utils.py
@@ -256,11 +256,8 @@ class PatchEntry:
                 f"Cannot apply: patch {abs_patch_path} is not a file"
             )
 
-        if not patch_cmd:
-            patch_cmd = gnu_patch
-
-        if patch_cmd == gnu_patch:
-            cmd = patch_cmd(root_dir, abs_patch_path) + (extra_args or [])
+        if not patch_cmd or patch_cmd is gnu_patch:
+            cmd = gnu_patch(root_dir, abs_patch_path) + (extra_args or [])
         else:
             cmd = patch_cmd(abs_patch_path) + (extra_args or [])
 
@@ -272,7 +269,7 @@ class PatchEntry:
             parsed_hunks = self.parsed_hunks()
             failed_hunks_id_dict = parse_failed_patch_output(e.stdout)
             failed_hunks = {}
-            if patch_cmd == gnu_patch:
+            if patch_cmd is gnu_patch:
                 for path, failed_hunk_ids in failed_hunks_id_dict.items():
                     hunks_for_file = parsed_hunks[path]
                     failed_hunks[path] = [
@@ -291,7 +288,7 @@ class PatchEntry:
         self, root_dir: Path, patch_cmd: Optional[Callable] = None
     ) -> PatchResult:
         """Dry run applying a patch to a given directory."""
-        extra_args = [] if patch_cmd == git_am else ["--dry-run"]
+        extra_args = [] if patch_cmd is git_am else ["--dry-run"]
         return self.apply(root_dir, patch_cmd, extra_args)
 
     def title(self) -> str:
@@ -376,6 +373,7 @@ def apply_all_from_json(
         svn_version: LLVM Subversion revision to patch.
         llvm_src_dir: llvm-project root-level source directory to patch.
         patches_json_fp: Filepath to the PATCHES.json file.
+        patch_cmd: The function to use when actually applying the patch.
         continue_on_failure: Skip any patches which failed to apply,
           rather than throw an Exception.
     """
@@ -565,6 +563,7 @@ def update_version_ranges_with_entries(
         svn_version: LLVM revision number.
         llvm_src_dir: llvm-project directory path.
         patch_entries: PatchEntry objects to modify.
+        patch_cmd: The function to use when actually applying the patch.
 
     Returns:
         Tuple of (modified entries, applied patches)
@@ -641,20 +640,18 @@ def remove_old_patches(
 
 
 def git_am(patch_path: Path) -> List[Union[str, Path]]:
-    cmd = ["git", "am", "--3way", str(patch_path)]
-    return cmd
+    return ["git", "am", "--3way", patch_path]
 
 
 def gnu_patch(root_dir: Path, patch_path: Path) -> List[Union[str, Path]]:
-    cmd = [
+    return [
         "patch",
         "-d",
-        str(root_dir.absolute()),
+        root_dir.absolute(),
         "-f",
         "-E",
         "-p1",
         "--no-backup-if-mismatch",
         "-i",
-        str(patch_path),
+        patch_path,
     ]
-    return cmd
diff --git a/llvm_tools/patch_utils_unittest.py b/llvm_tools/patch_utils_unittest.py
index 26a211ee..362a8dfd 100755
--- a/llvm_tools/patch_utils_unittest.py
+++ b/llvm_tools/patch_utils_unittest.py
@@ -170,7 +170,7 @@ a
             patch_dir, TestPatchUtils._default_json_dict()
         )
 
-        """Make a deepcopy of the case for testing commit patch option."""
+        # Make a deepcopy of the case for testing commit patch option.
         e1 = copy.deepcopy(e)
 
         with mock.patch("pathlib.Path.is_file", return_value=True):
@@ -178,7 +178,7 @@ a
                 result = e.apply(src_dir)
         self.assertTrue(result.succeeded)
 
-        """Test that commit patch option works."""
+        # Test that commit patch option works.
         with mock.patch("pathlib.Path.is_file", return_value=True):
             with mock.patch("subprocess.run", mock.MagicMock()):
                 result1 = e1.apply(src_dir, pu.git_am)