topic: extract the code listing all topics The code will become more complexe with formatter support and additional data in the verbose output. We extract the code in its own function first.

stack: introduce and explicite command to display the stack If is worth testing having the feature lives outside 'hg topic --list'. The 'stack' name is sub optimal because the conflict with 'status'. using "hg st" would still work as 'st' is hard coded, but this mean 'hg stack' has no short version.

testedwith: update to 3.9 This is might still 3.7 compatible but I'm no longer running the test and I would says the user base is small enough to not care.

topic: make sure we have the 'wlock' when setting topic We where writing the '.hg/topic' file without a lot. That was bad.

cleanup: removed unused mercurial.util import

compat: tolerate missing rebase extension

compat: mercurial dropped alias for hashlib.sha1

destination: add an XXX about handling destspace in destmerge This that we hopefully do not forget about this.

update: calculate 'partial' as core does

discovery: flake8

destination: flake8

style: update __init__.py

compat: adapt to the new destspace argument of destmerge The argument is currently ignored in the topic case for simplicity, but we properly accept it and propagate it to the original function to prevent crash and behavior regression in the non-topic case.

stack: prevent crash when topic is rooted on nullid We exclude null from displayed base. This was causing a crash when trying to display its description (we'll still have to handle the empty description case, but it is now less urgent).