.clang-format

merge: add tests for commit with no content change

It isn't easy to say when to reuse the p1 manifest. Basically, that's only
when wctx.files() is empty, but we need to know that wctx.files() is not
the same as repo['.'].files() after the commit.

This patch adds several examples of commits with empty ctx/wctx.files().
I don't think this is exhaustive, but it contains at least one failure
mode in which a converted repo result in a different hash.

I also note that the manifest revlog does NOT follow the DAG shape of the
changelog since p1 manifest is reused if wctx.files() is empty even at merge.
I don't know whether it is intentional or not, but it's the behavior since
2011, 301725c3df9a "localrepo: reuse parent manifest in commitctx if no files
have changed."

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