tests/test-pull-pull-corruption.t

revset: remove existence check from min() and max()

min() and max() would first do an existence check. Unfortunately existence
checks can be slow in certain situations (like if the smartset is a list, and
quickly iterable in both ascending and descending directions, then doing an
existence check will start from the bottom, even if you want to check the
max()).

The fix is to not do the check, and just handle the error if it happens. In a
large repo, this speeds up:

hg log -r 'max(parents(. + .^) - (. + .^)  & ::master)'

from 3.5s to 0.85s. That revset is contrived and just for testing. In our
real case we used 'bundle()' in place of '. + .^'

Interesting perf numbers for the revset benchmarks:

max(draft() and ::tip) =>  0.027s to 0.0005s
max(author(lmoscovicz)) => 2.48s to 0.57s

min doesn't show any perf changes, but changing it as well will prevent a perf
regression in my next patch.

Result from revset benchmark

revset #0: draft() and ::tip
   min           max
0) 0.001971      0.001991
1) 0.001965      0.000428  21%

revset #1: ::tip and draft()
   min           max
0) 0.002017      0.001912
1) 0.001896  94% 0.000421  22%

revset #2: author(lmoscovicz)
   min           max
0) 1.049033      1.358913
1) 1.042508      0.319824  23%

revset #3: author(lmoscovicz) or author(mpm)
   min           max
0) 1.042512      1.367432
1) 1.019750      0.327750  23%

revset #4: author(mpm) or author(lmoscovicz)
   min           max
0) 1.050135      0.324924
1) 1.070698      0.319913

revset #5: roots((tip~100::) - (tip~100::tip))
   min           max
0) 0.000671      0.001018
1) 0.000605  90% 0.000946  92%

revset #6: roots((0::) - (0::tip))
   min           max
0) 0.149714      0.152369
1) 0.098677  65% 0.100374  65%

revset #7: (20000::) - (20000)
   min           max
0) 0.051019      0.042747
1) 0.035586  69% 0.016267  38%

Corrupt an hg repo with two pulls.
create one repo with a long history

  $ hg init source1
  $ cd source1
  $ touch foo
  $ hg add foo
  $ for i in 1 2 3 4 5 6 7 8 9 10; do
  >     echo $i >> foo
  >     hg ci -m $i
  > done
  $ cd ..

create one repo with a shorter history

  $ hg clone -r 0 source1 source2
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd source2
  $ echo a >> foo
  $ hg ci -m a
  $ cd ..

create a third repo to pull both other repos into it

  $ hg init corrupted
  $ cd corrupted

use a hook to make the second pull start while the first one is still running

  $ echo '[hooks]' >> .hg/hgrc
  $ echo 'prechangegroup = sleep 5' >> .hg/hgrc

start a pull...

  $ hg pull ../source1 > pull.out 2>&1 &

... and start another pull before the first one has finished

  $ sleep 1
  $ hg pull ../source2 2>/dev/null
  pulling from ../source2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ cat pull.out
  pulling from ../source1
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 10 changesets with 10 changes to 1 files
  (run 'hg update' to get a working copy)

see the result

  $ wait
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  1 files, 11 changesets, 11 total revisions

  $ cd ..