add pre-commit and black support

[guihao-liang]

downstream of #2943

(tc58) ➜  gui-1-36 git:(01-24-pre-commit) ✗ git commit -m "add pre-commit and black support"
Trim Trailing Whitespace.................................................Passed
Fix End of Files.........................................................Passed
Check Yaml...............................................................Passed
Check for added large files..............................................Passed
black................................................(no files to check)Skipped
[01-24-pre-commit c94fdd374] add pre-commit and black support
 3 files changed, 50 insertions(+)
 create mode 100644 .pre-commit-config.yaml
 create mode 100644 pyproject.toml

When I do this commit, it performs a bunch of correctness checks for me. The setup is one-time thing.

[guihao-liang]

Trim Trailing Whitespace.................................................Passed
Fix End of Files.........................................................Passed
Check Yaml...........................................(no files to check)Skipped
Check for added large files..............................................Passed
black................................................(no files to check)Skipped
[01-24-pre-commit da42b5367] install pre-commit hooks when ./configure
 2 files changed, 4 insertions(+), 7 deletions(-)

You will love this tool.

[znation]

Does it block committing if a check fails? Is it easy to opt out of this behavior (either in general, or for a specific commit)?

[guihao-liang]

Does it block committing if a check fails? Is it easy to opt out of this behavior (either in general, or for a specific commit)?

If the check fails, it won't let you commit. You can skip the check by using

# SKIP=<check_id> git commit -m "blah"
SKIP=check_yaml git commit -m "blah" # will force to skip yaml check

Yes! It's easy to opt-out. I can add script to opt-out. But for us, I think it's better everybody opts in.

[guihao-liang]

@znation @TobyRoseman, I provide an option for the user to opt-out. Just let me know if you have more questions.

[guihao-liang]

Adding per-commit introduces a failure in pytest, #2972, which is resolved by #2973. Ready to merge.

[guihao-liang]

Passed all relevant tests. Ready to merge hand in hand with #2943.

[TobyRoseman]

We don't support Python 3.8. So you probably don't want that here.

[guihao-liang]

That's right! I will delete it.

[TobyRoseman]

Is there a reason you removed the >=8.1?

[guihao-liang]

I think pip 8.1 is really old now. We don't have to hardcode it. The current pip is already 20.0.2. >=8.1 is redundant.

[TobyRoseman]

ok, you have the --upgrade so that should work.

[TobyRoseman]

ok, you have the --upgrade so that should work.