dirstate-v2: add devel config option to control write behavior This will help us to write predictable tests checking behavior in each case.

dirstate: use more than a bool to control append behavior When writing dirstate-v2, we might either append to the existing file, or create a new file. We are about to introduce some configuration to control this behavior. As a prelude, we change the current way the behavior was automatically controlled to make the change smaller/clearer.

dirstate: cover each dirstate version when testing for status race Previously we were only testing it with the default (dirstate-v1 currently). Now we explicitly test each variant.

dirstate: test a `hg status` raced by another `hg status` This shows that `rhg` is misbehaving here.

dirstate: test a `hg status` raced by a `hg update` This shows that `rhg` is misbehaving here.

dirstate: test a `hg status` raced by a `hg commit` This shows that `rhg` is misbehaving here.

dirstate: test a `hg status` raced by a `hg add` This shows that `rhg` is misbehaving here.

dirstate: add a way to test races happening during status We add the `devel.sync.status.pre-dirstate-write-file` config option to easily test what happens when other operations happen during the window where `hg status` is done working but has not updated the cache on disk yet. We introduce the framework for testing such races too, actual tests will be added in the next changesets. For now the test is only checking dirstate-v1. We will extend the test coverage later too. Check test documentation for details. Code change from Raphaël Gomès <rgomes@octobus.net> Test change from Pierre-Yves David <pierre-yves.david@octobus.net>

testing: introduce util function to synchronize concurrent commands on files This is an extension of mechanisms that the tests have been using for a while. To be able to also control the execution in Rust, we introduce utility to perform such `wait_on_file` logic based on some configuration value. This will be used in the tests introduced in the next changesets.

hghave: drop py27 and py35 support These versions of python are no longer supported by Mercurial.

hghave: byteify a path passed to a core API It looks like this predicate isn't used at all(?)

dirstate: add some debug output when writing the dirstate This helps debugging Mercurial behavior in the dirstate-v2 case.

run-tests: make it possible to nest conditionals This is not that hard to implement and makes our life easier on a regular basis.

rust: box ConfigValueParseError to avoid large result types clippy emits a warning that all the Result types are way too large because of HgError includes ConfigValueParseError as one of the variants, so its size is 136 bytes. By boxing ConfigValueParseError we're hopefully making everything faster "for free".

dirstate: drop `identity` from the public API We no longer needs it.

delta-find: rename `delta-reuse-policy` to `pulled-delta-reuse-policy` This make it clearer which type of delta we are talking about.

config-item: declare undeclared path suboption This should prevent issue like the previous commit.

delta-find: declare the "paths..*:delta-reuse-policy option While looking into renaming the option I realized it was not declared.

delta-find: adjust the default candidate group chunk size We move from 10 to 20 as the default as some usage in the wild saw a small degradation in storage quality when using `10`.

record: extract a closure to the module level This clean up is almost as gratuituous as this closure was.

record: drop a now useless overlay that grab the lock Since 28dfb2df4ab9, commit grab the wlock and the extra layer grabing the lock in record is no longer needed. We clean up the code to make this simpler (and add a small assert for extra security against future change).

bundlerepo: fix string interpolation Matt Harbison is saying we cannot `%s` a type into a byte string and that seems reasonable.

bundlerepo: apply phase data stored in the bundle instead of assuming `draft` The phase information contained in the changegroup part and the explicit `phase-heads` part are now taken in account. Initial changes and test by Matt Harbison, code rework by Pierre-Yves David.

bundlerepo: handle changegroup induced phase movement in the associated method These movement comes from handling the changegroup part, so we keeps the code grouped. This will be important when handling more part (and more changegroup part in the future) This induce a small code duplication, but it does not looks terrible.