[llvm] [GitHub] Skip undefcheck if no relevant files changed (PR #126749)

[Aaron Siddhartha Mondal via llvm-commits]

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@@ -379,10 +381,6 @@ def format_run(self, changed_files: List[str], args: FormatArgs) -> Optional[str
         # Each file is prefixed like:
         # diff --git a/file b/file
         for file in re.split("^diff --git ", stdout, 0, re.MULTILINE):
-            # We skip checking in MIR files as undef is a valid token and not
-            # going away.
-            if file.endswith(".mir"):
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aaronmondal wrote:

I believe the change that initially added this was making wrong assumptions. This specifies on which files the check should run:

https://github.com/llvm/llvm-project/blob/76392421553f3b25552970812868f70721971451/llvm/utils/git/code-format-helper.py#L325-L331

Previously what happened is that if this list was empty the command that ran would be an unfiltered `git diff ...`. The stdout of that then contained all files in the diff. While the explicit inclusion in the loop worked, it fixed the issue in the wrong place because the check should only run on the files in the filter above in the first place.

Now we exit immediately if no relevant files changed. So if you only have `.mir` files in the diff the check won't run.

In the case where e.g. you have a `.cpp` file and a `.mir` file in the command that runs is something like `git diff ... x.cpp`. The stdout then will only contain the `.cpp` file. In other words, it's no longer possible for any files that aren't in the above list to get into this loop.

https://github.com/llvm/llvm-project/pull/126749