windows: ensure pure posixfile fd doesn't escape by entering context manager There are tests in test-revlog-mmapindex.t and test-rebase-mq-skip.t that are fixed by this, but we usually don't use --pure on Windows. For whatever reason, the remaining --pure failures are various errors like $ENOTDIR$ and "Access is denied" have a trailing '.'.

vfs: ensure closewrapbase fh doesn't escape by entering context manager I'm not sure if there's a problem in practice here, as there's no test failure either way. The __exit__() and close() methods raise an exception, so maybe __exit__() and close() are being called directly on the underlying handle when delayclosedfile is used on a context manager? I doubt that was intended.

windows: ensure mixedfilemodewrapper fd doesn't escape by entering context mgr Otherwise it seems that the special read and write handling would be bypassed.

py3: ensure the proxied Windows fd doesn't escape by entering context manager The purpose of the proxy class is to provide the `name` attribute which contains the file path. But in tests that used a context manager, it still blew up complaining that 'int' doesn't have a 'startswith' function.

merge with stable

templatefuncs: specialize "no match" value of search() to allow % operation If Python had Maybe or Option, the type of the search() result would be Option<Mapping>, which can be considered as a 0/1 container of a Mapping. So it makes sense that {search(r'no match pattern', x) % "whatever"} is mapped to an empty string.

templatefuncs: add regexp search() function that extracts substring This can be used to extract an issue number from a commit message, for example: {search(r'\(issue([0-9]*)\)', desc) % '{1}'}

rust: changed Graph.parents to return [Revision; 2] This will allow for simple iteration on parent revisions, such as: for parent in graph.parents(rev)?.iter().cloned() This seems to be a zero overhead abstraction once built in release mode. Differential Revision: https://phab.mercurial-scm.org/D5415

rust: improved docstring In the previous wording, rustfmt wanted to cut at the == which is not very readable in my taste. Differential Revision: https://phab.mercurial-scm.org/D5414

revset: move subscript relation functions to its own dict This will help adding more relation functions in extensions. We skip short names (that consist of one letter) while raising UnknownIdentifier because such names cannot be suggested anyway: the similarity cutoff in dispatch._getsimilar() is currently 0.6.