discovery: include timing in the debug output Having such date easily available is useful. It also prepare the inclusion of some discovery related data in blackbox.

tests: remove sys.executable from "required tools" In practice this doesn't appear to have been true for some time - we reference Python using the $PYTHON variable in all the tests now (which we have to for PyPy and Python 3), and I've been using ~/.../python.exe to test with tip of the cpython 3.6 release branch while working on manifest tests in Python 3 and everything seems to be just fine. The only real observable difference from this change is that I stop getting a warning about python.exe not being a thing on $PATH, which seems like an improvement.

perfbranchmap: add an option to purge the revbranch cache The perf extension needs to be able to reflect this reality too. (eg: 4s vs 60s on a Million-ish revisions repository).

push: add a way to allow concurrent pushes on unrelated heads Client has a mechanism for the server to check that nothing changed server side since the client prepared a push. That check is wide and any head changed on the server will lead to an aborted push. We introduce a way for the client to send a less strict checking. That logic will check that no heads impacted by the push have been affected. If other unrelated heads (including named branches heads) have been affected, the push will proceed. This is very helpful for repositories with high developers traffic on different heads, a common setup. That behavior is currently controlled by an experimental option. The config should live in the "server" section but bike-shedding of the name will happen in the next changesets. Servers advertise this capability through a new bundle2 capability 'checkeads', using the value 'related'. The 'test-push-race.t' is updated to check that new capabilities on the documented cases.

headsummary: expose the 'discardedheads' set in the headssummary That information will be useful to detect push race on related part of the history. See next changeset for details.

checkheads: perform obsolescence post processing directly in _headssummary The goal is to have the function directly return something meaningful and useful for the whole pull. Note: we skip adding post-processing in '_oldheadssummary' because if a client is too old for branchmap it will be too old for obsolescence too.

headssummary: directly feed the function with the 'pushop' object Our goal is to be able to perform the post processing directly into the '_headssummary' function. However before this patch the '_headsummary' function only had access to repo, remote, outgoing while the '_postprocessobsolete' function takes a 'pushop' object. Experience shows that having the 'pushop' object helps extensions so we update '_headssummary' to take a pushop object as argument.

checkheads: gather the postprocessing with other obsolescence specific code We extract this function from the loop and gather it with the rest of the obsolescence specific code. That will help to clarify the move of the whole logic inside the "heads summary" computation.

run-tests: add a way to list tests, with JSON and XUnit support Some test runners are interested in listing tests, so they can do their own filtering on top (usually based on attributes like historically observed runtime). Add support for that.

run-tests: install hg after computing tests to run We're going to add a way to list tests, and we don't need to install hg for that.

run-tests: make time field optional for xunit report We're going to use XUnit to list tests, and we don't have a time field in that case.

run-tests: factor out json write code into another method We're going to use this code to output a JSON-formatted listing of tests.