Improve type-name-incorrect-variance message

[tjkuson]

Summary

Change the type-name-incorrect-variance diagnostic message to include the detected variance and a name change recommendation. For example,

`TypeVar` name "T_co" does not reflect its contravariance; consider renaming it to "T_contra"

Related to #5651.

Test Plan

cargo test

[tjkuson]

I think something went wrong with GitHub Actions.

[charliermarsh]

What happens in the event that a variable is marked as both covariant and contravariant?

[github-actions]

PR Check Results

Ecosystem

ℹ️ ecosystem check detected changes. (+2, -2, 0 error(s))

disnake (+2, -2)

- disnake/ext/commands/base_core.py:39:38: PLC0105 `TypeVar` name "ApplicationCommandInteractionT" does not match variance
+ disnake/ext/commands/base_core.py:39:38: PLC0105 `TypeVar` name "ApplicationCommandInteractionT" does not reflect its covariance; consider renaming it to "ApplicationCommandInteractionT_co"
- disnake/i18n.py:53:11: PLC0105 `TypeVar` name "StringT" does not match variance
+ disnake/i18n.py:53:11: PLC0105 `TypeVar` name "StringT" does not reflect its covariance; consider renaming it to "StringT_co"

Rules changed: 1

Rule	Changes	Additions	Removals
PLC0105	4	2	2

Benchmark

Linux

group                                      main                                   pr
-----                                      ----                                   --
formatter/large/dataset.py                 1.01      8.6±0.07ms     4.7 MB/sec    1.00      8.5±0.08ms     4.8 MB/sec
formatter/numpy/ctypeslib.py               1.01   1822.7±2.95µs     9.1 MB/sec    1.00  1804.7±13.68µs     9.2 MB/sec
formatter/numpy/globals.py                 1.00    200.1±3.10µs    14.7 MB/sec    1.00    199.3±0.25µs    14.8 MB/sec
formatter/pydantic/types.py                1.02      4.1±0.01ms     6.2 MB/sec    1.00      4.1±0.01ms     6.3 MB/sec
linter/all-rules/large/dataset.py          1.01     14.3±0.07ms     2.9 MB/sec    1.00     14.2±0.04ms     2.9 MB/sec
linter/all-rules/numpy/ctypeslib.py        1.00      3.5±0.01ms     4.7 MB/sec    1.00      3.5±0.01ms     4.7 MB/sec
linter/all-rules/numpy/globals.py          1.00    361.0±1.03µs     8.2 MB/sec    1.00    362.8±0.84µs     8.1 MB/sec
linter/all-rules/pydantic/types.py         1.00      6.3±0.02ms     4.1 MB/sec    1.00      6.3±0.09ms     4.1 MB/sec
linter/default-rules/large/dataset.py      1.00      7.1±0.02ms     5.7 MB/sec    1.00      7.2±0.02ms     5.7 MB/sec
linter/default-rules/numpy/ctypeslib.py    1.00   1459.6±1.88µs    11.4 MB/sec    1.01  1467.7±10.88µs    11.3 MB/sec
linter/default-rules/numpy/globals.py      1.00    155.8±0.38µs    18.9 MB/sec    1.00    156.5±0.31µs    18.9 MB/sec
linter/default-rules/pydantic/types.py     1.00      3.2±0.01ms     8.0 MB/sec    1.00      3.2±0.01ms     8.0 MB/sec

Windows

group                                      main                                   pr
-----                                      ----                                   --
formatter/large/dataset.py                 1.01     11.5±0.52ms     3.5 MB/sec    1.00     11.4±0.43ms     3.6 MB/sec
formatter/numpy/ctypeslib.py               1.04      2.5±0.10ms     6.6 MB/sec    1.00      2.4±0.09ms     6.8 MB/sec
formatter/numpy/globals.py                 1.00   292.3±18.26µs    10.1 MB/sec    1.01   293.8±27.65µs    10.0 MB/sec
formatter/pydantic/types.py                1.02      5.6±0.22ms     4.6 MB/sec    1.00      5.5±0.18ms     4.6 MB/sec
linter/all-rules/large/dataset.py          1.00     19.6±0.76ms     2.1 MB/sec    1.01     19.7±0.58ms     2.1 MB/sec
linter/all-rules/numpy/ctypeslib.py        1.00      5.0±0.18ms     3.3 MB/sec    1.02      5.1±0.21ms     3.3 MB/sec
linter/all-rules/numpy/globals.py          1.02   615.3±21.05µs     4.8 MB/sec    1.00   604.8±25.36µs     4.9 MB/sec
linter/all-rules/pydantic/types.py         1.00      8.7±0.32ms     2.9 MB/sec    1.01      8.8±0.37ms     2.9 MB/sec
linter/default-rules/large/dataset.py      1.01      9.7±0.24ms     4.2 MB/sec    1.00      9.6±0.26ms     4.2 MB/sec
linter/default-rules/numpy/ctypeslib.py    1.00      2.1±0.07ms     8.1 MB/sec    1.00      2.0±0.08ms     8.1 MB/sec
linter/default-rules/numpy/globals.py      1.01   248.4±18.05µs    11.9 MB/sec    1.00   244.8±23.42µs    12.1 MB/sec
linter/default-rules/pydantic/types.py     1.03      4.5±0.19ms     5.7 MB/sec    1.00      4.3±0.14ms     5.9 MB/sec

[tjkuson]

What happens in the event that a variable is marked as both covariant and contravariant?

Currently, it ignores anything that is both covariant and contravariant. However, looking at the Pylint implementation, it emits

Type variable name does not reflect variance

It should be simple to emit a similar generic message. Do you think it's better to ignore invalid bivariant types or to emit a generic message instead?

[charliermarsh]

Hmm, I think ignoring them is fine actually, since this diagnostic can't actually be satisfied by renaming the variable.