merge: fix race that could cause wrong size in dirstate The problem is that hg merge/update/etc work the following way: 1. figure out what files to update 2. apply the update to disk 3. apply the update to in-memory dirstate 4. write dirstate where step3 looks at the filesystem and assumes it sees the result of step2. If a file is changed between step2 and step3, step3 will record incorrect information in the dirstate. I avoid this by passing the size step3 needs directly from step2, for the common path (not implemented for change/delete conflicts for instance). I didn't fix the same race for the exec bit for now, because it's less likely to be problematic and I had trouble due to the fact that the dirstate stores the permissions differently from the manifest (st_mode vs '' 'l' 'x'), in combination with tests that pretend that symlinks are not supported. However, I moved the lstat from step3 to step2, which should tighten the race window markedly, both for the exec bit and for the mtime. Differential Revision: https://phab.mercurial-scm.org/D6475

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Checking the size/permissions/file-type of files stored in the

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dirstate after an update where the files are changed concurrently

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outside of hg's control.

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  $ hg init repo

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  $ cd repo

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  $ echo a > a

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  $ hg commit -qAm _

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  $ echo aa > a

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  $ hg commit -m _

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  $ hg debugdirstate --no-dates

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  n 644          3 (set  |unset)               a (re)

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  $ cat >> $TESTTMP/dirstaterace.py << EOF

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  > from mercurial import (

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  >     extensions,

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  >     merge,

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  > )

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  > def extsetup(ui):

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  >     extensions.wrapfunction(merge, 'applyupdates', wrap)

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  > def wrap(orig, *args, **kwargs):

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  >     res = orig(*args, **kwargs)

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  >     with open("a", "w"):

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  >         pass # just truncate the file

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  >     return res

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  > EOF

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Do an update where file 'a' is changed between hg writing it to disk

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and hg writing the dirstate. The dirstate is correct nonetheless, and

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so hg status correctly shows a as clean.

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  $ hg up -r 0 --config extensions.race=$TESTTMP/dirstaterace.py

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  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

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  $ hg debugdirstate --no-dates

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  n 644          2 (set  |unset)               a (re)

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  $ echo a > a; hg status; hg diff