cext: make HgRevlogIndex_GetParents private again The rust's direct-ffi code need to access this function. Now that it `direct-ffi` is no more. We can make this function `static` again. This change was suggested by `Yuya Nishihara`.

setup-rust: remove the legacy 'direct-ffi' variant This variant have been abandoned for a while. Keeping it around just get people confused.

hghave: add a `rust` keyword to detect the use of compiled rust code The content of some on disk cache can varies when using rust (because it is faster to do so in the rust variant). So we need to be able to detect this case for some test. Differential Revision: https://phab.mercurial-scm.org/D8162

nodemap: check that a simple lookup works fine I realised the code was not exercised much. Differential Revision: https://phab.mercurial-scm.org/D8180

debuginstall: print if Rust extensions are installed This should make it easier to use the Rust extensions. Another patch on will be exposing a version and more useful information, but it can only be done on top of this very patch, since it is targeting the stable branch and the API has already changed on the default branch. Differential Revision: https://phab.mercurial-scm.org/D8248

nodemap: fix missing r-prefix on regular expression Looking at this regular expression, it's pretty obvious from reading it that it wanted to match literal ., but since the r was missing on the pattern it was matching any character. I guess we're just lucky nothing bad happened as a result. This was automatically fixed by pyupgrade, but I split it out into its own change because it seemed important. Differential Revision: https://phab.mercurial-scm.org/D8254

tests: use pyflakes module instead of pyflakes executable This results in that the pyflakes version specific to the configured Python version is used. This way, both the Python 2-specific and the Python 3-specific pyflakes are run by the test suite (depending on the configured Python version). For downstream projects which are using Mercurial’s test infrastructure and are not yet ported to Python 3 (e.g. hg-git) it ensures that the correct pyflakes version is run even when the system’s default pyflakes is the Python 3-specific one.

copies-tests: add a case where with merge with an overwritten files This is similar to the BF/FB case, but in this case, the other branch updated the file. So an actual merge happens and the two "independant" file history has to be merged. Differential Revision: https://phab.mercurial-scm.org/D8242

copies-tests: add a case where a file is deleted/added but with a merge This is a case similar to DB/BD, but in this case the other branch updated the file. So an actual merge happens and the two "independant" file history has to be merged. Differential Revision: https://phab.mercurial-scm.org/D8241

copies-tests: add a test with a rename overwriting another file This is a variation of the "BD" case, but this time, the file is not "new", it is overwritten by another file being renamed. Differential Revision: https://phab.mercurial-scm.org/D8240