Preserve comments when sorting imports

[charliermarsh]

It's tough to come up with a strategy that does the "right" thing in all cases (in part, because it's hard to even define the "right" output in every case), but this PR preserves all comments, is stable across re-runs, and tries to do sensible things when merging across imports.

Resolves #675.

[charliermarsh]

I'll add a few examples here tomorrow.

[andersk]

There’s a slight Black incompatibility—Black requires this newline:

import math
import os

# a comment
import pathlib
import sys

while Ruff deletes it:

import math
import os
# a comment
import pathlib
import sys

[andersk]

Comments seem to be unexpectedly counted toward the length of the following line in some cases, causing the following import to wrap early:

import a
# ccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
from b import c

→

import a
# ccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
from b import (
    c,
)

[charliermarsh]

Woo thanks for trying! I noticed the second issue when running on Zulip :)

It's late here so will fix these both tomorrow (then hopefully merge).

[andersk]

Multi-line comments are unexpectedly sorted and deduplicated:

import io
# Old MacDonald had a farm,
# EIEIO
# And on his farm he had a cow,
# EIEIO
# With a moo-moo here and a moo-moo there
# Here a moo, there a moo, everywhere moo-moo
# Old MacDonald had a farm,
# EIEIO
from errno import EIO

→

import io
# And on his farm he had a cow,
# EIEIO
# Here a moo, there a moo, everywhere moo-moo
# Old MacDonald had a farm,
# With a moo-moo here and a moo-moo there
from errno import (
    EIO,
)

[charliermarsh]

Ok, I believe all of those are addressed. Here's the diff on Zulip: