[llvm] [llvm][Docs] Explain how to handle excessive formatting changes (PR #126239)

[Andrzej Warzyński via llvm-commits]

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@@ -73,15 +73,33 @@ recent commit:
 
   % git clang-format HEAD~1
 
-Note that this modifies the files, but doesn't commit them -- you'll likely want
-to run
+.. note::
+  For some patches, formatting them may add changes that obscure the intent of
+  the patch. For example, adding to an enum that was not previously formatted
+  may result in the entire enum being reformatted. This happens because not all
+  of the LLVM Project conforms to clang-format at this time.
+
+  If you think that this might be the case for your changes, or are unsure, we
+  recommend that you add the formatting changes as a **separate commit** within
+  the Pull Request.
+
+  Reviewers may request that this formatting commit be made into a separate Pull
+  Request that will be merged before your actual changes.
+
+  This means that if the formatting changes are the first commit, you will have
+  an easier time doing this. If they are not, that is ok too, but you will have
+  to do a bit more work to separate it out.
+
+Note that ``git clang-format`` modifies the files, but doesn't commit them -- you'll likely want
+to run one of the following to add the changes to a commit:
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banach-space wrote:

[nit] Shouldn't this be trimmed to 80 cols?

https://github.com/llvm/llvm-project/pull/126239