Add `lint-v2` rule and implement it for Python with black. #8452

pierrechevalier83 · 2019-10-11T10:10:41Z

Problem

In the near future, we will want to add a pre-commit hook that helps us remember to automatically format our code with black.
Currently, the version of black that's integrated in pants will always modify the user's code, which may not be desirable in a pre_commit hook situation.

Solution

Add a lint-v2 rule which uses black with the --check flag to highlight unformatted files without actually modifying them.

Result

See integration tests for examples: User can call ./pants lint-v2 .... The command will fail if the files would be formatted, but won't rewrite the files.

illicitonion

Thanks!

illicitonion · 2019-10-11T13:52:47Z

src/python/pants/backend/python/subsystems/black.py

@@ -16,3 +16,5 @@ def register_options(cls, register):
    super().register_options(register)
    register('--config', advanced=True, type=file_option, fingerprint=True,
              help="Path to formatting tool's config file")
+    register('--check', advanced=True, type=bool, fingerprint=True,


Long-term, there's an interesting question of direction here.

Historically, we had the lint goal, which is basically fmt-without-formatting - in the future, would we like:

A lint goal alongside the fmt goal?

A fmt-wide flag called something like --check

A per-formatter flag called --check

I suspect long-term we want 1 or 2, and we should work that out before we name the v2 console_rule fmt, but while this is experimental until then, this works :)

stuhood

The pattern so far has been to have ./pants lint check for things like this, rather than to have ./pants fmt with whitelisted options.

The reasoning for this is that ./pants lint "never has sideeffects", while ./pants fmt obviously might. And as more side-effecting tasks are added to fmt, the chances of forgetting to add one of these "disable sideffects" options increases.

So as with lint/fmt in v1, would recommend using the existing "reformat this code" logic under a new lint-v2 rule (or under

pants/src/python/pants/backend/project_info/rules/source_file_validator.py

Lines 210 to 215 in 138746a

    
           # TODO: Switch this to `lint` once we figure out a good way for v1 tasks and v2 rules 
        
           # to share goal names. 
        
           @console_rule 
        
           def validate( 
        
             console: Console, hydrated_targets: HydratedTargets, validate_options: Validate.Options 
        
           ) -> Validate:

), but then adding an intermediate @rule comparing the resulting digest to the target's input digest to see whether the lint failed.

illicitonion · 2019-10-16T14:15:44Z

The code here looks good to me, but I'm still unsure of the long-term direction; I think that ignoring history, I probably would design these goals as fmt an fmt --check rather than fmt and lint - maybe this isn't where we want to make that change, but I think it's worth a discussion.

stuhood · 2019-10-16T15:52:08Z

The code here looks good to me, but I'm still unsure of the long-term direction; I think that ignoring history, I probably would design these goals as fmt an fmt --check rather than fmt and lint - maybe this isn't where we want to make that change, but I think it's worth a discussion.

The issue with ./pants fmt --check is that you probably also want to check other lints that are not formatting related. So then you need to run ./pants fmt --check lint. Maybe that's fine, and the distinction we draw is that only autoformatters go in fmt, and that the style checking that they represent is sufficiently distinct from other lints to be worth having split out?

My feeling though is that all realistic cases will want to run "all of the lints" (assuming that they are fast enough).

stuhood

Thanks.

But please wait for Benjy to chime in on the fmt --check vs lint distinction.

benjyw · 2019-10-17T02:38:21Z

Thanks - code looks good. After some thought, I come down on the side of putting this in a lint goal. For the reason Stu stated - we may have other linters that are not tied to formatters. And it makes more sense to run ./pants lint than ./pants lint fmt --check in order to get all the lint checks.

Another way to think of it is that "formatter in check mode" is an implementation detail of a lint rule.

Eric-Arellano · 2019-10-17T02:42:31Z

+1 to this being a lint goal.

(Haven’t checked the code at all.)

illicitonion

Thanks! Two minor things :)

illicitonion · 2019-10-17T09:50:32Z

src/python/pants/rules/core/lint.py

+  results = yield [
+          Get(LintResult, FmtTarget, target.adaptor)
+          for target in targets
+          # @union assumes that all targets passed implement the union, so we manually


See #8368 - you can now inject a UnionMembership to the rule, and call union_membership.is_member(FmtTarget, target.adaptor)

(At some point we'll probably want to also create a LintTarget Union, but piggybacking off of FmtTarget is probably sufficient until we either add a non-fmt lint, or rename this goal to be lint instead of lint-v2)

Will address in a separate PR to hopefully get this one merged today (I'm also dragging #8454 which is based on top of this, so would be keen on iterating fast if possible)

Done here: #8490

illicitonion · 2019-10-17T09:52:21Z

src/python/pants/rules/core/lint.py

+    if result.stderr:
+      console.print_stderr(result.stderr)
+    if result.exit_code != 0:
+      yield Lint(result.exit_code)


A console rule should only yield an output exactly one time.

Can you make your test_black_lint_should_fail_but_not_format_python_code test lint two incorrectly-formatted things? You should then see an error (the fix for which is probably to accumulate 0 or last-non-0 exit code, and yield that at the end)

I added a couple of tests: lint multiple files and lint multiple targets. With the latter, I could reproduce the issue you're describing (we don't report all failing targets). I fixed it as you described.

pierrechevalier83 · 2019-10-17T14:55:30Z

Just a comment to be explicit: the reasoning for lint vs fmt --check makes sense to me. I prepped the lint version of the PR for merging (rebased + addressed review comments)

src/python/pants/backend/python/rules/python_fmt.py

This is a prerequisite for ultimately adding a pre-commit hook that behaves similarly to our isort pre-commit hook (warns the user and lets them actually modify their code once they are ready for it) * Create a top level `lint-v2` rule; * Implement `lint_with_black` which implements that rule for python; * Deduplicate `lint_with_black` with `fmt_with_black`; * Make use of `FallibleExecuteProcessRequest` to make lint output less spammy.

Now we introduced a lint goal which takes the same kind of targets as an input, it makes sense to use a more general name.

pierrechevalier83 · 2019-10-30T14:26:51Z

The fight against flakey CI has been too intense. I'm reducing from 3 PRs to one to increase my likelihood of ever getting my code merged.
Closing in favour of #8553 which contains #8452, #8454 and #8490

This was referenced Oct 11, 2019

Run Black as part of pre_commit hook #8403

Closed

Add script to run black on files touched by local work #8454

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pierrechevalier83 force-pushed the pchevalier/black_check branch 2 times, most recently from f4f2091 to 82788a9 Compare October 16, 2019 11:22

pierrechevalier83 changed the title ~~Add --check argument to the black subsystem.~~ Add lint-v2 rule and implement it for Python with black. Oct 16, 2019

stuhood requested a review from benjyw October 16, 2019 15:52

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pierrechevalier83 force-pushed the pchevalier/black_check branch from 82788a9 to e7877b1 Compare October 17, 2019 14:12

illicitonion mentioned this pull request Oct 17, 2019

Unclear that multiple yields in a @console_rule will lead to early-return behaviour #8488

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pierrechevalier83 mentioned this pull request Oct 17, 2019

Use UnionMembership to reduce coupling in fmt and lint v2 rules #8490

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src/python/pants/backend/python/rules/python_fmt.py Outdated Show resolved Hide resolved

pierrechevalier83 force-pushed the pchevalier/black_check branch 3 times, most recently from f6e277e to f4519b9 Compare October 25, 2019 19:15

pierrechevalier83 mentioned this pull request Oct 25, 2019

tests/python/pants_test/base:exception_sink_integration is flaky #8127

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pierrechevalier83 force-pushed the pchevalier/black_check branch from f4519b9 to 0053383 Compare October 29, 2019 13:08

pierrechevalier83 added 2 commits October 30, 2019 10:35

Rename FmtTarget to TargetWithSources

7744b21

Now we introduced a lint goal which takes the same kind of targets as an input, it makes sense to use a more general name.

pierrechevalier83 force-pushed the pchevalier/black_check branch from 0053383 to 7744b21 Compare October 30, 2019 10:35

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pierrechevalier83 mentioned this pull request Oct 30, 2019

Add lint-v2 implementation for python with black, and script to be used in pre-commit hook #8553

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Add `lint-v2` rule and implement it for Python with black. #8452

Add `lint-v2` rule and implement it for Python with black. #8452

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pierrechevalier83 commented Oct 17, 2019

pierrechevalier83 commented Oct 30, 2019

	# TODO: Switch this to `lint` once we figure out a good way for v1 tasks and v2 rules
	# to share goal names.
	@console_rule
	def validate(
	console: Console, hydrated_targets: HydratedTargets, validate_options: Validate.Options
	) -> Validate:

Add lint-v2 rule and implement it for Python with black. #8452

Add lint-v2 rule and implement it for Python with black. #8452

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pierrechevalier83 commented Oct 11, 2019 • edited Loading

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pierrechevalier83 commented Oct 30, 2019

Add `lint-v2` rule and implement it for Python with black. #8452

Add `lint-v2` rule and implement it for Python with black. #8452

pierrechevalier83 commented Oct 11, 2019 •

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