commands: add debugdeltachain command We have debug commands for displaying overall revlog statistics (debugrevlog) and for dumping a revlog index (debugindex). As part of investigating various aspects of revlog behavior and performance, I found it important to have an understanding of how revlog delta chains behave in practice. This patch implements a "debugdeltachain" command. For each revision in a revlog, it dumps information about the delta chain. Which delta chain it is part of, length of the delta chain, distance since base revision, info about base revision, size of the delta chain, etc. The generic formatting facility is used, which means we can templatize output and get machine readable output like JSON. This command has already uncovered some weird history in mozilla-central I didn't know about. So I think it's valuable.

histedit: pick an appropriate base changeset by default (BC) Previously, `hg histedit` required a revision argument specifying which revision to use as the base for the current histedit operation. There was an undocumented and experimental "histedit.defaultrev" option that supported defining a single revision to be used if no argument is passed. Mercurial knows what changesets can be edited. And in most scenarios, people want to edit this history of everything on the current head that is rewritable. Making histedit do this by default and not require an explicit argument or additional configuration is a major usability win and will enable more people to use histedit. This patch changes the behavior of the experimental and undocumented "histedit.defaultrev" config option to select an appropriate base revision by default. Comprehensive tests exercising the edge cases in the new, somewhat complicated default revset have been added. Surprisingly, no tests broke. I guess we were never testing the behavior with no ANCESTOR argument (it used to fail with "abort: histedit requires exactly one ancestor revision"). The new behavior is much more user friendly. The functionality for choosing the default base revision has been moved to destutil.py, where it can easily be modified by extensions.

rebase: remove extra "if" from check of collapsing named branches

rebase: drop redundant functions to keep branch and graft source explicitly All entries in extra dict are propagated by default since 88fde8db5307.

color: drop useless override of ui.popbuffer() Because labels are applied at write() time since 717b75ae5bb0, colorui.popbuffer() is useless and it doesn't update _bufferapplylabels correctly. Removing it should fix the problem.

repoview: bypass changelog method to computed cache key Getting the data necessary for the cache key using the changelog/revlog method adds a significant overhead. Given how simple the underlying implementation is and often this code is ran, it makes sense to violate layering and directly compute the data. Testing `hg log` on Mozilla-central, this reduce the time spent on changelog cache validation by an extra half: before: 12.2s of 69s after: 6.1s of 62s Total speed up from this patch and it's parent is 3x (With stupid python profiler overhead) The global speedup without profiler overhead is still there, Before: 51s After: 39s (-23%)

repoview: stop recomputing cached key in all case As explained in the comment, we were computing the key of the cache value every time because of some obscure MQ test failure. I've dropped that code and ran the test again that failure is gone. I assume some transaction cleanup got rid of it. So we are dropping that code. This provide a significant speedup. Testing `hg log` on Mozilla-central this reduce the time spent on changelog cache validation by a third: before: 19.5s of 80s after: 12.2s of 69s (With stupid python profiler overhead)

commands.debugindexdot: use cmdutil.openrevlog() This pattern is used for all the other debug* commands that operate on revlogs. debugindexdot is an outlier. Make it conform.

commands: unify argument handling for revlog debug commands The same 3 options are used in a few locations and I'm about to add another. Might as well consolidate the pattern.

commit: fix rest syntax of examples This fixes the formatting of help/commit page and silence test-gendoc.t.

ui: optionally ignore sub-options from configitems() For convenience.

ui: add method to return option and all sub-options Apparently ":" has been blessed as a generic separator for options and sub-options. We formalize this by introducing an API for obtaining an option and all its sub-options. This will be used in a subsequent patch for declaring sub-options for [paths].