evolve: handle relocation during divergence resolution producing no changes
When resolving divergence and the two divergent commits have different
parents, we start by rebasing one of them to have the same parent as
the other. That step can result in no changes to commit. When it does,
we would crash with a TypeError before this patch.
This patch fixes it by instead creating an empty commit in that
scenario. The existing code then continues to attempt to merge it,
which produces no changes, and no commit is created on top. The other
side of the divergence is marked as successor as usual, so orphans
from the side that became empty will be evolved to the right place
(see test).
#!/bin/bash
set -euox pipefail
unset GREP_OPTIONS
compatbranches=$(hg branches --quiet | grep 'mercurial-' | grep -v ':' | sort -n --reverse)
prev='stable'
topic=${1:-'test-compat'}
for branch in $compatbranches; do
# Logic in the revsets below:
# 1. There is target topic on stable or compatibility branch: merge all
# those commits, they are related to our work and need to pass tests on all
# compatibility branches.
# 2. There is no target topic: avoid any commits that have topic set, they
# are definitely unrelated to what we're doing.
# In other words, if you want to test certain commits, assign them all to
# one topic and provide that topic as the first argument to this script.
uptarget="first(max(branch('$branch') and topic('$topic')) or max(branch('$branch') and not topic()))"
hg up -r "$uptarget"
hg topic "$topic"
mergetarget="first(max(branch('$prev') and topic('$topic')) or max(branch('$prev') and not topic()))"
hg merge -r "$mergetarget"
hg commit -m "test-compat: merge $prev into $branch"
prev=$branch
done