evolve: check that relocating makes sense in _solvedivergent() (issue5958)

tests: demonstrate content divergence causing "relocate node on top of itself"

cmdstate: introduce a "saver" contextmanager and use it in place of save() Previously, the state was only saved in some paths out of these functions. This can be problematic, if the user ctrl-c's (or `kill -9`'s) the process, or we exit out of `relocate` for anything besides the "expected" reason, we won't record that we were in the middle of an evolve. One of our users has discovered that this leaves hg in a weird state; the user did something like this: ``` $ hg evolve <something goes wrong with the merge tool, hits ctrl-c> <deals with the merge conflicts> $ hg evolve --continue abort: no interrupted evolve to continue $ hg evolve abort: uncommitted changes # Note: commands.status.verbose=True is set. $ hg status M foo # The repository is in an unfinished *update* state. # No unresolved merge conflicts # To continue: hg update ``` The user did an `hg update`, but it didn't actually do anything besides take it out of the unfinished update state (the files were still dirty in the working directory).

cmdstate: avoid setting a default argument to a mutable object (`{}`) If there's ever more than one cmdstate for the lifetime of the process, this can cause surprising behavior where the later cmdstates pick up options from the earlier ones. I've not seen any evidence this is actually causing any issues, but it's subtle enough that it should probably be fixed to help save significant debugging time later.

cmdstate: switch to new-style classes This isn't a huge issue and isn't necessary on Python3, but we're still Python2 compatible and we should be consistent (and strongly prefer new-style classes); this is the only class that is not deriving from object that I could find.

branching: merge stable into default

docs: add example for the `prune` command Giving at least one example helps clear up the syntax, especially since most options will follow a very similar pattern.

tests: add some more actions to test-issue-6028, describe what's being done This patch does two things: it explains what's happening in the test file so it's easier to understand, and also it adds checks that make sure something like swapping merge parents is not accidentally breaking anything. The primary reason to touch this test file was that it was broken by a change in core's merge.graft() that erroneously swapped merge parents. Since only evolve uses merge.graft() for merge commits and there aren't any tests in core for it, let's test it here. Plus, this test case is pretty simple and these additional checks don't make it too complicated.

topic: fix some API to make it more robust The new code can deal with changes in upstream mercurial.

rewriteutil: move allowdivergence check to foldcheck() foldcheck() calls precheck() first and then performs more fold-specific checks.

test: change to output around transaction timing CORE-TEST-OUTPUT-UPDATE: d7304434390f

branching: merge with stable There have been multiple fix on stable.