bash completions are slow

While there are some hacks to speed up the code path, buildstream bash completions are currently fairly slow - notably, it is affected by slow the setuptools import.

We should ensure that the completions codepath completes as quickly as possible.

added ~1935083 Optimization labels

mentioned in merge request !231 (merged)

mentioned in merge request !232 (closed)

mentioned in merge request !234 (closed)

@gokcennurlu noted that we import a lot of libraries before we actually run the completions functionality, so it can still take 200ms to execute even once the pkg_resources import is avoided. We could speed things up by making sure we only import click when running from the bash-completion script. It's tricky to do this neatly though.

mentioned in commit 8af65fda

mentioned in merge request !256 (merged)

The performance here has improved significantly enough by !256 (merged) and other startup time performance improvements, such that it makes no sense to keep this open anymore.

closed