filemerge: move check for identical sides out of filemerge() `filemerge.filemerge()` returns `None` if no merge was necessary because the two sides were identical. I don't think it should be that function's responsibility to handle that case; we should ideally not even call `filemerge.filemerge()` if the two inputs identical. This patch therefore moves the check out to the caller (`mergestate.py`). The largefiles test changed because we now notice that the two sides made the same change, so we don't consider it a merge. Also note that the new message better matches the line above it in the test output. Differential Revision: https://phab.mercurial-scm.org/D12154

--- a/mercurial/filemerge.py	Mon Feb 07 20:12:09 2022 -0800
+++ b/mercurial/filemerge.py	Mon Feb 07 22:54:38 2022 -0800
@@ -989,10 +989,6 @@
 
     Returns whether the merge is complete, the return value of the merge, and
     a boolean indicating whether the file was deleted from disk."""
-
-    if not fco.cmp(fcd):  # files identical?
-        return None, False
-
     ui = repo.ui
     fd = fcd.path()
     uipathfn = scmutil.getuipathfn(repo)