Adopt black code style

[pwildenhain]

Related to Closes #481

While there are a ton of diffs, I'm noticing some patterns:

1. Many changes related to preferring double quotes over single quotes
2. Many changes related to indenting long lines
3. Many diffs in the dialects package alone

There are also a few linting CI failures, the flake8-black plugin mentions that there are a few flake8 rules you would want to disable when using alongside black

What do you think @alanmcruickshank? Do you think black is an improvement?
If so, do you think we should go for it now, or wait?
If not, do you have other suggestions for code formatters? I feel like a code linting/formatting library should have something like this 😁 😉

[alanmcruickshank]

HA! Yeah.... I take your point on lots of diffs!

I've skimmed through the suggested changes, and on the whole it looks pretty reasonable.

I feel like a code linting/formatting library should have something like this 😁 😉

...well exactly.

Given the scale of this we should plan when to merge, but it's going to be painful whenever we do it, so we're just going to have to lean into that.

There are also a few linting CI failures, the flake8-black plugin mentions that there are a few flake8 rules you would want to disable when using alongside black

What are the conflicts? I think they're the things we should hash out now and then the rest is just a case of timing.

... oh and we should totally make sure we've got a markdown badge for this if we're going to the effort of doing it... 🤷

[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)

[pwildenhain]

What are the conflicts?

This is the recommended configuration settings for using flake8-black

[flake8]
# Recommend matching the black line length (default 88),
# rather than using the flake8 default of 79:
max-line-length = 88
extend-ignore =
    # See https://github.com/PyCQA/pycodestyle/issues/373
    E203,

E203 is the reason the linting CI is failing now (spaces before semi-colons)

And you know I want the fancy badge 📛 ✨ 😎

we should plan when to merge, but it's going to be painful whenever we do it

If you want, I can quickly add the plugin, with configuration, and the new badge. Or we can close this for now, and come back to this later.

For what it's worth, black only took 2 seconds to run, which was awesome ⚡

[alanmcruickshank]

Let's do it. You only live once 🤘

[pwildenhain]

We're good to go! Pinging 🔔 the other maintainers so they're aware of this change

[codecov]

Codecov Report

Merging #485 into master will not change coverage.
The diff coverage is 92.21%.

@@           Coverage Diff           @@
##           master     #485   +/-   ##
=======================================
  Coverage   92.91%   92.91%           
=======================================
  Files          29       29           
  Lines        4786     4786           
=======================================
  Hits         4447     4447           
  Misses        339      339           

Flag	Coverage Δ
#py36	92.80% <92.21%> (ø)
#py37	92.80% <92.21%> (ø)
#py38	92.74% <92.21%> (ø)
#py39	92.74% <92.21%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/sqlfluff/parser/segment_generator.py	100.00% <ø> (ø)
src/sqlfluff/rules/config_info.py	100.00% <ø> (ø)
src/sqlfluff/rules/std.py	94.25% <ø> (ø)
src/sqlfluff/dialects/base.py	87.09% <42.85%> (ø)
src/sqlfluff/parser/segments_base.py	91.92% <80.00%> (ø)
src/sqlfluff/parser/segments_common.py	91.55% <80.00%> (ø)
src/sqlfluff/cli/formatters.py	95.83% <86.20%> (ø)
src/sqlfluff/parser/grammar.py	89.60% <87.83%> (ø)
src/sqlfluff/parser/match.py	87.69% <88.88%> (ø)
src/sqlfluff/cli/commands.py	90.83% <91.01%> (ø)
... and 18 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5188824...9ffae69. Read the comment docs.

[nolanbconaway]

yes! great call @pwildenhain !

[NiallRees]

🎉

[alanmcruickshank]

One nit on the badge. Otherwise I've skimmed though all of the changes and I think they're going to be quite useful. If nothing else it's reminded me how far this project has come!

[alanmcruickshank]

It's a nit, but can we add ?style=flat-square to the url here? That should give the badge the same square edges as all the others.

[pwildenhain]

🤷‍♂️ No idea why code coverage suffered, but I believe this is good to go 🚢

[alanmcruickshank]

Good to go - Merging now 👍