sparse: move config parsing into core This patch marks the beginning of moving code from the sparse extension into core. The goal is to move as much of the functionality as possible into core, where it will be an experimental feature. The extension will likely continue to exist to enable the feature and provide UI elements. As part of the move, the repo method was converted to a module function. It doesn't need to exist on repos. An error message was also updated to reflect that an error isn't necessarily from the .hg/sparse file. The API should be updated later to pass in a filename so the error can be more descriptive. Copyright of the added file was copied from the sparse extension.

sparse: use vfs.tryread() vfs.exists() followed by a file read is an anti-pattern because it incurs an extra stat() to test for file presence. vfs.tryread() returns empty string on missing file and avoids the stat().

sparse: refactor sparsechecksum() This was relying on garbage collection to close the opened file, which is a bug. Both callers simply called into self.vfs to resolve the path. So refactor to use the vfs layer. While we're here, rename the method to reflect it is internal and to break anyone relying on the old behavior.

sparse: document config file format This was previously undocumented. Seems useful to have.

sparse: rename command to debugsparse Sparse checkout is still highly experimental and not protected by BC guarantees yet. We also haven't had a discussion on the UX. To discourage use, we rename the sparse command to debugsparse.

sparse: remove reference to simplecache This is a 3rd party extension authored by Facebook. References in core are not appropriate. It will be possible to restore this code/optimization via monkeypatching. So Facebook won't lose any functionality. The removed code is important for performance. So add a comment tracking it.

sparse: remove reference to hgwatchman This is a legacy extension. Now that the extension is in core, we only need to support what's in core, which is fsmonitor.

sparse: expand module docstring Clarify lack of BC guarantees. And say a bit more about the extension.

sparse: vendor Facebook-developed extension Facebook has developed an extension to enable "sparse" checkouts - a working directory with a subset of files. This feature is a critical component in enabling repositories to scale to infinite number of files while retaining reasonable performance. It's worth noting that sparse checkout is only one possible solution to this problem: another is virtual filesystems that realize files on first access. But given that virtual filesystems may not be accessible to all users, sparse checkout is necessary as a fallback. Per mailing list discussion at https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-March/095868.html we want to add sparse checkout to the Mercurial distribution via roughly the following mechanism: 1. Vendor extension as-is with minimal modifications (this patch) 2. Refactor extension so it is more clearly experimental and inline with Mercurial practices 3. Move code from extension into core where possible 4. Drop experimental labeling and/or move feature into core after sign-off from narrow clone feature owners This commit essentially copies the sparse extension and tests from revision 71e0a2aeca92a4078fe1b8c76e32c88ff1929737 of the https://bitbucket.org/facebook/hg-experimental repository. A list of modifications made as part of vendoring is as follows: * "EXPERIMENTAL" added to module docstring * Imports were changed to match Mercurial style conventions * "testedwith" value was updated to core Mercurial special value and comment boilerplate was inserted * A "clone_sparse" function was renamed to "clonesparse" to appease the style checker * Paths to the sparse extension in tests reflect built-in location * test-sparse-extensions.t was renamed to test-sparse-fsmonitor.t and references to "simplecache" were removed. The test always skips because it isn't trivial to run it given the way we currently run fsmonitor tests * A double empty line was removed from test-sparse-profiles.t There are aspects of the added code that are obviously not ideal. The goal is to make a minimal number of modifications as part of the vendoring to make it easier to track changes from the original implementation. Refactoring will occur in subsequent patches.

contrib: widen "direct use of `python`" net again I think I've now caught all of them. Differential Revision: https://phab.mercurial-scm.org/D15

tests: clean up a newly-introduced instance of `python` Differential Revision: https://phab.mercurial-scm.org/D16

tests: clean up even more direct `python` calls with $PYTHON This time ones that are prefixed with =, ", ', or `. This appears to be the last of them. Differential Revision: https://phab.mercurial-scm.org/D14

contrib: widen the "don't use `python`" net a little I'm still cleaning this up, but it's easier to do in bite-size chunks like this than all at once. The negative lookahead avoids one false positive category from some output related to finding Subversion bindings. Differential Revision: https://phab.mercurial-scm.org/D13

followlines: join merge parents line ranges in blockdescendants() (issue5595) In blockdescendants(), we had an assertion when line range of a merge changeset was not consistent depending on which parent was considered for computation. For instance, this might occur when file content (in lookup range) is significantly different between parent branches of the merge as demonstrated in added tests (where we almost completely rewrite the "baz" file while also introducing similarities with its content in the other branch we later merge to). Now, in such case, we combine line ranges from all parents by storing the envelope of both line ranges. This is conservative (the line range is extended, possibly unnecessarily) but at least this should avoid missing descendants with changes in a range that would fall in that of one parent but not in another one (the case of "baz: narrow change (2->2+)" changeset in tests).

workingfilectx: add exists, lexists Switch the lone call in merge.py to use it. As with past refactors, the goal is to make wctx hot-swappable with an in-memory context in the future. This change should be a no-op today.

vfs: add explanation about cost of checkambig=True in corner case

vfs: replace avoiding ambiguity in abstractvfs.rename with _avoidambig This centralizes common logic to forcibly avoid file stat ambiguity into _avoidambig(), which was introduced by previous patch.

vfs: copy if EPERM to avoid file stat ambiguity forcibly at closing Now, files (to be truncated) are opened with checkambig=True, only if localrepository caches it. Therefore, straightforward "copy if EPERM" is always reasonable to avoid file stat ambiguity at closing. This patch makes checkambigatclosing close wrapper copy the target file, and advance mtime on it after renaming, if EPERM. This can avoid file stat ambiguity, even if the target file is owned by another (see issue5418 and issue5584 for detail). This patch factors main logic out instead of changing checkambigatclosing._checkambig() directly, in order to reuse it.

transaction: apply checkambig=True only on limited files for similarity Now, transaction can determine whether avoidance of file stat ambiguity is needed for each files, by blacklist "checkambigfiles". For similarity to truncation in _playback(), this patch apply checkambig=True only on limited files in code paths below. - restoring files by util.copyfile(), in _playback() (checkambigfiles itself is examined at first, because it as a keyword argument might be None) - writing files at finalization of transaction, in _generatefiles() This patch reduces cost of checking stat at writing out and restoring files, which aren't filecache-ed.

transaction: avoid file stat ambiguity only for files in blacklist Advancing mtime by os.utime() fails for EPERM, if the target file is owned by another. bff5ccbe5ead and related changes made some code paths give advancing mtime up in such case, to fix issue5418. This causes file stat ambiguity (again), if it is owned by another. https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan To avoid file stat ambiguity in such case, especially for .hg/dirstate, ed66ec39933f made vfs.rename() copy the target file, and advance mtime of renamed one again, if EPERM (see issue5584 for detail). But straightforward "copy if EPERM" isn't reasonable for truncation of append-only files at rollbacking, because rollbacking might cost much for truncation of many filelogs, even though filelogs aren't filecache-ed. Therefore, this patch introduces blacklist "checkambigfiles", and avoids file stat ambiguity only for files specified in this blacklist. This patch consists of two parts below, which should be applied at once in order to avoid regression. - specify 'checkambig=True' at vfs.open(mode='a') in _playback() according to checkambigfiles - invoke _playback() with checkambigfiles - add transaction.__init__() checkambigfiles argument, for _abort() - make localrepo instantiate transaction with _cachedfiles - add rollback() checkambigfiles argument, for "hg rollback/recover" - make localrepo invoke rollback() with _cachedfiles After this patch, straightforward "copy if EPERM" will be reasonable at closing the file opened with checkambig=True, because this policy is applied only on files, which are listed in blacklist "checkambigfiles".

localrepo: store path and vfs location of cached properties This information is used to make transaction handle these files specially, in order to avoid file stat ambiguity of them. Gathering information about cached files via annotation classes can avoid overlooking properties newly introduced in the future.

template: add successors template Add a 'successorssets' template that returns the list of all closest known sucessorssets for a changectx. The elements of the list are changesets. The "closest successors" are the first locally known revisions encountered while, walking successors markers. It uses successorsets previously modified to support the closest argument. This logic respect repository filtering. So hidden revision will be skipped by this logic unless --hidden is specified. Since we only display the visible predecessors, this template will not display anything in most case. It makes a good candidate for inclusion in the default log output. I updated the test-obsmarker-template.t test file introduced with the predecessors template to test successorssets template.

template: add tests for more complex cases We add new tests for improving the coverage of existing obs-markers related template (predecessors) and the new one we are introducing (successorssets).

obsolete: closest divergent support Add a closest argument to successorssets changing the definition of latest successors. With "closest=false" (current behavior), latest successors are "leafs" on the obsmarker graph. They don't have any successor and are known locally. With "closest=true", latest successors are the closest locally-known changesets that are visible in the repository or repoview. Closest successors can be then obsolete, orphan. This will be used in a later patch to show the closest successor of changesets with the successorssets template.

obsolete: pass cache argument of successors set explicitly We plan to add a new argument to successorsets. But first we need to update all callers to pass cache argument explicitly to avoid arguments confusion.

obsolete: small doc update for 'successorssets' Clarify successorssets documentation before we start updating the main function. This patch serie will introduce the successorssets template, the opposite of predecessor templates. Successors will use successorssets function and requires some improvement so before doing that, we clean up successorssets a bit.

phabricator: do not read a same revision twice It's possible to set up non-linear dependencies in Phabricator like: o D4 |\ | o D3 | | o | D2 |/ o D1 The old `phabread` code will print D1 twice. This patch adds de-duplication to prevent that. Test Plan: Construct the above dependencies in a Phabricator test instance and make sure the old code prints D1 twice while the new code won't.

patch: make parsepatch optionally trim context lines Previously there is a suspicious `if False and delta > 0` which dates back to the beginning of hgext/record.py (b2607267236d). The "trimming context lines" feature could be useful (and is used by the next patch). So let's enable it. This patch adds a new `maxcontext` parameter to `recordhunk` and `parsepatch`, changing the `if False` condition to respect it. The old `trimcontext` implementation is also wrong - it does not update `toline` correctly and it does not do the right thing for `before` context. A doctest was added to guard us from making a similar mistake again. Since `maxcontext` is set to `None` (unlimited), there is no behavior change.

phabricator: try to fetch differential revisions in batch Previously, we read Differential Revisions one by one by calling `differential.query`. Fetching them one by one is suboptimal. Unfortunately, there is no Conduit API that allows us to get a stack of diffids using a single API call. This patch tries to be smarter using a simple heuristic: when fetching D59 as a stack, previous IDs like D51, D52, D53, ..., D58 are likely belonging to a same stack so just fetch them as well. Since `differential.query` only returns cheap metadata without expensive diff content, it shouldn't be a big problem for the server. Using a test Phabricator instance, this patch reduces `phabread` reading a 10 patch stack from about 13 to 30 seconds to 8 seconds.

phabricator: avoid calling differential.getcommitmessage Previously, we call differential.getcommitmessage API to get commit messages. Now we read that from "Differential Revision" object fetched via "differential.query" API. This removes one API call per patch.