rust-cpython: replace dyn Iterator<..> of mapping with concrete type See the previous commit for why. The docstring is moved accordingly.

rust-cpython: replace dyn Iterator<..> of sequence with concrete type We wouldn't care the cost of the dynamic dispatch, but I feel a concrete type helps understanding error messages.

rust-dirstate: provide CopyMapIter and StateMapIter types They will be used in the declaration of Python iterator types.

rust-dirstate: specify concrete return type of DirsMultiset::iter() This allows us to put a returned iterator in a struct. We could implement DirsMultisetIter(hash_map::Keys<..>) struct to hide the implementation detail, but I think type alias is good enough for us.

discovery: replace "heads" by "changesets" in a output note (BC) When using `hg push --rev X`, the subset considered by discovery is only `::X`. In addition, `X` can be any local revisions not just local heads. As a result the message "all local heads known locally" can be misleading. We replace it with the more accurate "all local changesets known remotely". The message appears when in verbose not, so this is stricly speaking a BC breakage. I am not sure this would be a real issue in practice...

py3: drop incorrect fsencode(findexe(...)) in procutil I recently added the bad call, thinking that findexe() was a standard library function returning a string result, but it's actually our own function returning bytes. Thanks to Yuya for noticing. Differential Revision: https://phab.mercurial-scm.org/D6826

flagprocessors: small code update to clarify parameters 'raw' is really a third mode, not a small variant. Differential Revision: https://phab.mercurial-scm.org/D6807

flagprocessors: deprecate _processflags People should use the specialized version instead now. Differential Revision: https://phab.mercurial-scm.org/D6806

simplestorerepo: stop using `_processflags` directly We now use the specialized versions. Differential Revision: https://phab.mercurial-scm.org/D6805

revlog: stop using `_processflags` directly We now use the specialized versions. Differential Revision: https://phab.mercurial-scm.org/D6804

flagprocessors: use _processflagsraw in easy cases When there are no ambiguity regarding the `raw` value, we can simply use the new method. Differential Revision: https://phab.mercurial-scm.org/D6803

flagprocessors: use _processflagsread in simple cases When there are no ambiguity regarding the `raw` value, we can simply use the new method. Differential Revision: https://phab.mercurial-scm.org/D6802

flagprocessors: use _processflagswrite for write operation There are no ambiguity for 'write' operation so it is simple to replace. Differential Revision: https://phab.mercurial-scm.org/D6801

flagprocessors: introduce specialized functions This make the call site clearer and the open the way to more diverse return types. For now, the same old code is still in use under the hood. Differential Revision: https://phab.mercurial-scm.org/D6800

flagutil: use it in simplestorerepo This remove the other code duplication of the `_processflags` code. To be honest, this code looks very dead since it is not run by either developer nor buildbot. However, we update the code to make the task of reviving this less daunting. Differential Revision: https://phab.mercurial-scm.org/D6799

flagutil: make the error class used by the mixin configurable One of the code duplication use a different error class. So let's make it possible to do so. Differential Revision: https://phab.mercurial-scm.org/D6798

flagutil: use the new mixin use in remotefilelog This remove one of the code duplication. Hooray \o/. Differential Revision: https://phab.mercurial-scm.org/D6797

flagutil: introduce a flagprocessorsmixin class To avoid code duplication, we will provide a simple "ready to use" mixin that carry the appropriate logic. First we use it in standard revlog, we'll remove code duplication in later changesets. Differential Revision: https://phab.mercurial-scm.org/D6796

check-code: allow command substitution with $(command) Both `command` and $(command) are specified by POSIX. The latter nests better. I don't see why we shouldn't allow both (or only the latter). Differential Revision: https://phab.mercurial-scm.org/D6789

run-tests: rename `lcmd` variable to `line_cmd` This is clearer and more in line with some other variable names. (This is a gratuitous cleanup that I made while investigating a bug).

run-tests: rename `lout` variable to `out_line` This is clearer and more in line with some other variable names. (This is a gratuitous cleanup that I made while investigating a bug).

run-tests: clarify "l" variable as "out_rawline" More explicit variable name never hurt. (This is a gratuitous cleanup that I made while investigating a bug).

run-tests: use symbolic constant instead of arbitrary number line matching (This is a gratuitous cleanup that I made while investigating a bug).

rustfilepatterns: shorter code for concatenating slices Differential Revision: https://phab.mercurial-scm.org/D6765