push: rework the computation of fallbackheads to be correct The previous computation tried to be smart but ended up being wrong. This was caught by phase movement test while reworking the phase discovery logic to be faster. The previous logic was failing to catch case where the pushed set was not based on a common heads (i.e. when the discovery seemed to have "over discovered" content, outside the pushed set) In the following graph, `e` is a common head and we `hg push -r f`. We need to detect `c` as a fallback heads and we previous failed to do so:: e | d f |/ c | b | a The performance impact of the change seems minimal. On the most impacted repository at hand (mozilla-try), the slowdown seems mostly mixed in the overall noise `hg push` but seems to be in the hundred of milliseconds order of magnitude. When using rust, we seems to be a bit faster, probably because we leverage more accelaratd internals. I added a couple of performance related common for further investigation later on.

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# txnutil.py - transaction related utilities

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#

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#  Copyright FUJIWARA Katsunori <foozy@lares.dti.ne.jp> and others

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#

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# This software may be used and distributed according to the terms of the

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# GNU General Public License version 2 or any later version.

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from . import encoding

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def mayhavepending(root):

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    """return whether 'root' may have pending changes, which are

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    visible to this process.

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    """

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    return root == encoding.environ.get(b'HG_PENDING')

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def trypending(root, vfs, filename, **kwargs):

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    """Open  file to be read according to HG_PENDING environment variable

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    This opens '.pending' of specified 'filename' only when HG_PENDING

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    is equal to 'root'.

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    This returns '(fp, is_pending_opened)' tuple.

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    """

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    if mayhavepending(root):

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        try:

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            return (vfs(b'%s.pending' % filename, **kwargs), True)

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        except FileNotFoundError:

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            pass

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    return (vfs(filename, **kwargs), False)