revset: make generatorset.__nonzero__ lazy
The 'for r in self:' call could trigger full consumption of the generator while
we only need a single value. We also fast path if a single value got already
computed. See inline comment for more details.
This provide massive speedup for lazy operation using boolean testing.
max(::tip)
e5b507efb36e) wall 0.055609 comb 0.060000 user 0.060000 sys 0.000000 (best of 100)
after change) wall 0.000109 comb 0.000000 user 0.000000 sys 0.000000 (best of 19146)
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..