changelog: load pending file directly When changelogs are written, a copy of the index (or inline revlog) may be written to an 00changelog.i.a file to facilitate hooks and other processes having access to the pending data before it is finalized. The way it works today, the localrepo class loads the changelog like normal. Then, if it detects a pending transaction, it asks the changelog class to load a pending changelog. The changelog class looks for a 00changelog.i.a file. If it exists, it is loaded and internal data structures on the new revlog class are copied to the original instance. The existing mechanism is inefficient because it loads 2 revlog files. The index, node map, and chunk cache for 00changelog.i are thrown away and replaced by those for 00changelog.i.a. The existing mechanism is also brittle because it is a layering violation to access the data structures being accessed. For example, the code copies the "chunk cache" because for inline revlogs this cache contains the raw revision chunks and allows the original changelog/revlog instance to access revision data for these pending revisions. This whole behavior of course relies on the revlog constructor reading the entirety of an inline revlog into memory and caching it. That's why it is brittle. (I discovered all this as part of modifying behavior of the chunk cache.) This patch streamlines the loading of a pending 00changelog.i.a revlog by doing it directly in the changelog constructor if told to do so. When this code path is active, we no longer load the 00changelog.i file at all. The only negative outcome I see from this change is if loading 00changelog.i was somehow facilitating a role. But I can't imagine what that would be because we throw away its data (the index data structures are replaced and inline revision data is replaced via the chunk cache) and since 00changelog.i.a is a copy of 00changelog.i, file content should be identical, so there should be no meaninful file integrity checking at play. I think this was all just sub-optimal code.

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# policy.py - module policy logic for Mercurial.

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#

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# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>

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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 __future__ import absolute_import

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import os

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import sys

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# Rules for how modules can be loaded. Values are:

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#

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#    c - require C extensions

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#    allow - allow pure Python implementation when C loading fails

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#    cffi - required cffi versions (implemented within pure module)

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#    cffi-allow - allow pure Python implementation if cffi version is missing

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#    py - only load pure Python modules

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#

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# By default, fall back to the pure modules so the in-place build can

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# run without recompiling the C extensions. This will be overridden by

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# __modulepolicy__ generated by setup.py.

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policy = b'allow'

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policynoc = (b'cffi', b'cffi-allow', b'py')

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policynocffi = (b'c', b'py')

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try:

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    from . import __modulepolicy__

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    policy = __modulepolicy__.modulepolicy

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except ImportError:

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    pass

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# PyPy doesn't load C extensions.

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#

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# The canonical way to do this is to test platform.python_implementation().

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# But we don't import platform and don't bloat for it here.

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if r'__pypy__' in sys.builtin_module_names:

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    policy = b'cffi'

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# Our C extensions aren't yet compatible with Python 3. So use pure Python

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# on Python 3 for now.

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if sys.version_info[0] >= 3:

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    policy = b'py'

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# Environment variable can always force settings.

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if sys.version_info[0] >= 3:

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    if r'HGMODULEPOLICY' in os.environ:

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        policy = os.environ[r'HGMODULEPOLICY'].encode(r'utf-8')

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else:

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    policy = os.environ.get(r'HGMODULEPOLICY', policy)