perf: factor selection of revisions involved in the merge out We will introduce more performance command around merge. As a first step we factor out pieces of `perfmergecalculate` that can be reused.

perf: allow to specify the base of the merge in perfmergecalculate We can now test the rebase case.

perf: add a --from flag to perfmergecalculate Before this change, `perfmergecalculate` was always benchmarking the merge of the working copy with another revision. We can now benchmark the `mergecalculate` call for any arbitrary pair of revision.

merge with stable

py3: fix test-narrow* which started failing because of recent changes #skip-blame because just r'' prefix Differential Revision: https://phab.mercurial-scm.org/D6447

manifest: add some documentation to _lazymanifest python code It was not particularly easy figuring out the design of this class and keeping track of how the pieces work. So might as well write some of it down for the next person.

manifest: avoid corruption by dropping removed files with pure (issue5801) Previously, removed files would simply be marked by overwriting the first byte with NUL and dropping their entry in `self.position`. But no effort was made to ignore them when compacting the dictionary into text form. This allowed them to slip into the manifest revision, since the code seems to be trying to minimize the string operations by copying as large a chunk as possible. As part of this, compact() walks the existing text based on entries in the `positions` list, and consumed everything up to the next position entry. This typically resulted in a ValueError complaining about unsorted manifest entries. Sometimes it seems that files do get dropped in large repos- it seems to correspond to there being a new entry that would take the same slot. A much more trivial problem is that if the only changes were removals, `_compact()` didn't even run because `__delitem__` doesn't add anything to `self.extradata`. Now there's an explicit variable to flag this, both to allow `_compact()` to run, and to avoid searching the manifest in cases where there are no removals. In practice, this behavior was mostly obscured by the check in fastdelta() which takes a different path that explicitly drops removed files if there are fewer than 1000 changes. However, timeless has a repo where after rebasing tens of commits, a totally different path[1] is taken that bypasses the change count check and hits this problem. [1] https://www.mercurial-scm.org/repo/hg/file/2338bdea4474/mercurial/manifest.py#l1511

tests: demonstrate broken manifest generation with the pure module This will be fixed next. But I don't fully understand how 'b.txt' is actually removed properly in the second test, given what's broken. Also, I'm not sure why 'bb.txt' is flagged as not being in the manifest, when it clearly appears to be.

tests: add test for {file_mods}, {file_adds}, {file_dels} on merge commit Differential Revision: https://phab.mercurial-scm.org/D6368

context: add ctx.files{modified,added,removed}() methods Changeset-centric copy tracing is currently very slow because it often reads manifests. One place it needs the manifest is in _chain(), where it removes a copy X->Y if Y has subsequently gotten removed. I want to speed that up by keeping track directly in the changeset of which files are removed in the changeset. These methods will be similar to ctx.p[12]copies() in that way: they will either read from the changeset or calculate the information from the manifests otherwise. Note that these are different from ctx.{modified,added,removed}() on merge commits. Those functions always compare to p1, but the new ones compare to both parents. filesadded() means "file does not exist in either parent but exists now", filesremoved() means "file existed in either parent but does not exist now", and filesmodified() means "file existed in either parent and still exists". The set of files in ctx.files() is the union of the files from the three new functions (and the three new ones are all disjoint sets). Also note that uncommitted merges are weird as usual. The invariant mentioned above still holds, but the functions compare to p1 (and are thus identical to the existing methods). Differential Revision: https://phab.mercurial-scm.org/D6367