tests/test-manifest-merging

findrenames: Optimise "addremove -s100" by matching files by their SHA1 hashes.

We speed up 'findrenames' for the usecase when a user specifies they
want a similarity of 100% by matching files by their exact SHA1 hash
value. This reduces the number of comparisons required to find exact
matches from O(n^2) to O(n).

While it would be nice if we could just use mercurial's pre-calculated
SHA1 hash for existing files, this hash includes the file's ancestor
information making it unsuitable for our purposes. Instead, we calculate
the hash of old content from scratch.

The following benchmarks were taken on the current head of crew:

addremove 100% similarity:
  rm -rf *; hg up -C; mv tests tests.new
  hg --time addremove -s100 --dry-run

  before:  real 176.350 secs (user 128.890+0.000 sys 47.430+0.000)
  after:   real   2.130 secs (user   1.890+0.000 sys  0.240+0.000)

addremove 75% similarity:
  rm -rf *; hg up -C; mv tests tests.new; \
      for i in tests.new/*; do echo x >> $i; done
  hg --time addremove -s75  --dry-run

  before: real 264.560 secs (user 215.130+0.000 sys 49.410+0.000)
  after:  real 218.710 secs (user 172.790+0.000 sys 45.870+0.000)

#!/bin/sh

echo % init foo-base
hg init foo-base

echo % create alpha in first repo
cd foo-base
echo 'alpha' > alpha
hg ci -A -m 'add alpha' -d '1 0'
cd ..

echo % clone foo-base to foo-work
hg clone foo-base foo-work

echo % create beta in second repo
cd foo-work
echo 'beta' > beta
hg ci -A -m 'add beta' -d '2 0'
cd ..

echo % create gamma in first repo
cd foo-base
echo 'gamma' > gamma
hg ci -A -m 'add gamma' -d '3 0'
cd ..

echo % pull into work and merge
cd foo-work
hg pull -q
hg merge

echo % revert to changeset 1 to simulate a failed merge
rm alpha beta gamma
hg up -C 1