profile: colorize output on Windows Previously, the ANSI codes were printed to the screen, throwing off the alignment. We could probably do this unconditionally, but it's kind of a hack, so I figured I'd limit the scope.

dispatch: don't clamp the range of the exit code twice We already limit the range to (0, 255) in the call to sys.exit(). The duplicated operation can't possibly be hurting us, but let's clean it up to avoid confusion.

bdiff: avoid pointer arithmetic on void* MSVC 2008 complains: mercurial/cext/bdiff.c(106) : error C2036: 'void *' : unknown size mercurial/cext/bdiff.c(107) : error C2036: 'void *' : unknown size Maybe it's a gcc extension? https://stackoverflow.com/questions/37460579/error-c2036-void-unknown-size

fuzz: add a quick README to try and document how to test new fuzzers Differential Revision: https://phab.mercurial-scm.org/D2633

fuzz: add a fuzzer for xdiff Based entirely on the fuzzer for bdiff. Differential Revision: https://phab.mercurial-scm.org/D2632

tests: add tests about diff quality These show the differences between bdiff and xdiff. Differential Revision: https://phab.mercurial-scm.org/D2604

run-tests: allow #require inside #if Used by the next patch. Differential Revision: https://phab.mercurial-scm.org/D2605

mdiff: add a config option to use xdiff algorithm The `experimental.xdiff` will affect the default diffopts and make mdiff use the xdiff algorithm for better diff quality. Differential Revision: https://phab.mercurial-scm.org/D2603

bdiff: add a xdiffblocks method This is similar to `bdiff.blocks`, but uses xdiff as the backend. The indent heuristic is turned on by default since it has little overhead and improves diff quality significantly. Differential Revision: https://phab.mercurial-scm.org/D2602

xdiff: reduce indent heuristic overhead Adds some threshold to avoid expensive cases, like: ``` #!python open('a', 'w').write(" \n" * 1000000) open('b', 'w').write(" \n" * 1000001) ``` The indent heuristic is O(N * 20) (N = 1000000) for the above case, and makes diff much slower. Before this patch (system git 2.14.2): ``` git diff --no-indent-heuristic a b 0.21s user 0.03s system 100% cpu 0.239 total git diff --indent-heuristic a b 0.77s user 0.02s system 99% cpu 0.785 total ``` After this patch (git 2fc74f41, with xdiffi.c patched): ``` # with the changed xdiffi.c git diff --indent-heuristic a b 0.16s user 0.01s system 90% cpu 0.188 total git diff --no-indent-heuristic a b 0.18s user 0.01s system 99% cpu 0.192 total ``` Now turning on indent-heuristic has no visible impact on performance. Differential Revision: https://phab.mercurial-scm.org/D2601