[clang-format] Add --fallback-style to git-clang-format

[apdofficial]

This MR implements a fallback style option for the cases when no .clang-format is available.

I need a pipeline workflow where some repositories don't have a .clang-format file. I want to allow specifying a fallback style so that formatting can still run consistently in those cases.

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[llvmbot]

@llvm/pr-subscribers-clang-format

Author: Andrej Pištek (apdofficial)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/137609.diff

1 Files Affected:

• (modified) clang/tools/clang-format/git-clang-format (+22-2)

diff --git a/clang/tools/clang-format/git-clang-format b/clang/tools/clang-format/git-clang-format
index e709803d9a3f1..99373630d59f5 100755
--- a/clang/tools/clang-format/git-clang-format
+++ b/clang/tools/clang-format/git-clang-format
@@ -189,6 +189,14 @@ def main():
         default=config.get("clangformat.style", None),
         help="passed to clang-format",
     ),
+    p.add_argument(
+        "--fallback-style",
+        default=None,
+        help="The name of the predefined style used as a"
+        "fallback in case clang-format is invoked with"
+        "-style=file, but can not find the .clang-format"
+        "file to use.",
+    ),
     p.add_argument(
         "-v",
         "--verbose",
@@ -279,7 +287,11 @@ def main():
         old_tree = create_tree_from_workdir(changed_lines)
         revision = None
     new_tree = run_clang_format_and_save_to_tree(
-        changed_lines, revision, binary=opts.binary, style=opts.style
+        changed_lines,
+        revision,
+        binary=opts.binary,
+        style=opts.style,
+        fallback_style=opts.fallback_style,
     )
     if opts.verbose >= 1:
         print("old tree: %s" % old_tree)
@@ -531,7 +543,11 @@ def create_tree_from_index(filenames):
 
 
 def run_clang_format_and_save_to_tree(
-    changed_lines, revision=None, binary="clang-format", style=None
+    changed_lines,
+    revision=None,
+    binary="clang-format",
+    style=None,
+    fallback_style=None,
 ):
     """Run clang-format on each file and save the result to a git tree.
 
@@ -583,6 +599,7 @@ def run_clang_format_and_save_to_tree(
                 revision=revision,
                 binary=binary,
                 style=style,
+                fallback_style=fallback_style,
                 env=env,
             )
             yield "%s %s\t%s" % (mode, blob_id, filename)
@@ -616,6 +633,7 @@ def clang_format_to_blob(
     revision=None,
     binary="clang-format",
     style=None,
+    fallback_style=None,
     env=None,
 ):
     """Run clang-format on the given file and save the result to a git blob.
@@ -628,6 +646,8 @@ def clang_format_to_blob(
     clang_format_cmd = [binary]
     if style:
         clang_format_cmd.extend(["--style=" + style])
+    if fallback_style:
+        clang_format_cmd.extend(["--fallback-style=" + fallback_style])
     clang_format_cmd.extend(
         [
             "--lines=%s:%s" % (start_line, start_line + line_count - 1)

[owenca]

Please add a description so that we'll understand why you need this new option.

[apdofficial]

@llvm/pr-subscribers-clang-format

Author: Andrej Pištek (apdofficial)
Changes

Please let me know whether the updated description is sufficient. If not, I can update it. Thank you.

[mydeveloperday]

For those repos that don't have a .clang-format why not just add one with whatever your fallback style is?

BasedOnStyle: <whatever_you_need>

I know this seems like a reasonable feature but it just causes another set of functionality we have to think about, I don't see the values to people who actually use clang-format? isn't the purpose here to encourage those who don't use clang-format to use it...

[apdofficial]

@mydeveloperday, that is a valid question.

The reason is that we have many legacy repositories that do not have a .clang-format file. The legacy repositories are in a maintenance phase, and most importantly, they follow a custom code style. We want to implement a standard code style without refactoring the legacy code. This means adding a .clang-format file would not truthfully reflect the actual code style in the legacy repositories. This MR enables checking only the newly added code according to the new code style.