fastannotate: record some TODO items from indygreg's review Some of these I'll address more or less right away, but some will take a while for us to resolve. Differential Revision: https://phab.mercurial-scm.org/D4200

fastannotate: write out files from server in a predictable order This is mostly for test output stabilization, but it *might* be slightly better with a ton of annotate caches because we'll write to one directory at a time rather than bouncing around randomly. Differential Revision: https://phab.mercurial-scm.org/D3995

fastannotate: initial import from Facebook's hg-experimental I made as few changes as I could to get the tests to pass, but this was a bit involved due to some churn in the blame code since someone last gave fastannotate any TLC. There's still follow-up work here to rip out support for old versions of hg and to integrate the protocol with modern standards. Some performance numbers (all on my 2016 MacBook Pro with a 2.6Ghz i7): Mercurial mercurial/manifest.py traditional blame time: real 1.050 secs (user 0.990+0.000 sys 0.060+0.000) build cache time: real 5.900 secs (user 5.720+0.000 sys 0.110+0.000) fastannotate time: real 0.120 secs (user 0.100+0.000 sys 0.020+0.000) Mercurial mercurial/localrepo.py traditional blame time: real 3.330 secs (user 3.220+0.000 sys 0.070+0.000) build cache time: real 30.610 secs (user 30.190+0.000 sys 0.230+0.000) fastannotate time: real 0.180 secs (user 0.160+0.000 sys 0.020+0.000) mozilla-central dom/ipc/ContentParent.cpp traditional blame time: real 7.640 secs (user 7.210+0.000 sys 0.380+0.000) build cache time: real 98.650 secs (user 97.000+0.000 sys 0.950+0.000) fastannotate time: real 1.580 secs (user 1.340+0.000 sys 0.240+0.000) mozilla-central dom/base/nsDocument.cpp traditional blame time: real 17.110 secs (user 16.490+0.000 sys 0.500+0.000) build cache time: real 399.750 secs (user 394.520+0.000 sys 2.610+0.000) fastannotate time: real 1.780 secs (user 1.530+0.000 sys 0.240+0.000) So building the cache is expensive (but might be faster with xdiff enabled), but the blame results are *way* faster. Differential Revision: https://phab.mercurial-scm.org/D3994