revset: extract private constant of {nullrev, wdirrev} set I'll add a few more users of this constant to get around wdir identifiers.

help: suggest merge() revset instead of -m/--only-merges Suggested by Dr Rainer Woitok.

tests: update annotate tests to work around simplemerge bug test-annotate.t and test-fastannotate.hg were failing with --pure since 57203e0210f8 (copies: calculate mergecopies() based on pathcopies(), 2019-04-11). It turned out to be because the pure file merge code behaved differently. I'm guessing it's the mdiff.get_matching_blocks() that behaves differently, but I haven't confirmed that. With this content in the base: a a a And this on the local side: a z a And this on the other side: a a a b4 c b6 It produced this conflict: a z a <<<<<<< working copy: b80e3e32f75a - test: c ||||||| base a ======= a b4 c b5 >>>>>>> merge rev: 64afcdf8e29e - test: mergeb I don't care enough about the pure Python code to fix it, so this patch just updates the tests to manually resolve the conflict. Differential Revision: https://phab.mercurial-scm.org/D6351