Add `repeated_where_clause_or_trait_bound` lint #8703

aldhsu · 2022-04-15T12:07:12Z

I thought I would try and scratch my own itch for #8674.

Is comparing the Res the correct way for ensuring we have the same trait?
Is there a way to get the spans for the bounds and clauses for suggestions?
I tried to use GenericParam::bounds_span_for_suggestions but it only gave me an empty span at the end of the spans.
I tried WhereClause::span_for_predicates_or_empty_place and it included the comma.
Is there a simpler way to get the trait names? I have used the spans of the traits because I didn't see a way to get it off the Res or Def.

changelog: Add [`repeated_where_clause_or_trait_bound`] lint.

rust-highfive · 2022-04-15T12:07:15Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @flip1995 (or someone else) soon.

Please see the contribution instructions for more information.

giraffate

Can this lint avoid catching a case like this?

use std::ops::Add;

fn add<T: Add<u32> + Add<u64>>() {}

Other cases like this: https://github.com/rayon-rs/rayon/blob/v1.5.0/src/iter/product.rs#L10
https://github.com/rayon-rs/rayon/blob/v1.5.0/src/iter/product.rs#L10

aldhsu · 2022-04-28T06:58:05Z

Good catch @giraffate! This also uncovers a bug in the existing TRAIT_DUPLICATION_IN_BOUNDS lint.

I'll have a think about it because it is a recursive problem. ie. bounds contains other bounds.

Do you have any suggestions for doing an easy comparison? The only solution that has occurred to me at the moment is to collect the nested generic params into some sort of nested structure and collect something comparable so I can compare that rather than the Res. I was thinking it might be easier to get the whole text of a bounds span for a generic and compare that.

bors · 2022-05-05T13:32:45Z

☔ The latest upstream changes (presumably #8788) made this pull request unmergeable. Please resolve the merge conflicts.

flip1995 · 2022-05-06T12:31:28Z

You should rebase your branch on top of the current master. Some things changed with how generics are lowered in rustc just a few days ago. You might have to revisit some parts of the code.

This might help with the impl Trait case: rust-lang/rust#96770

aldhsu · 2022-05-07T11:54:28Z

Thanks for the heads up @flip1995. I have pushed a fixup that addresses the changes.

I left it unsquashed so how the generic lowering works now could be discussed.

I wasn't able to fix an issue with supporting the unstable associated_type_bounds feature.
Could you help me understand how the new lowering works with nested trait bounds? ie.

#![feature(associated_type_bounds)]

fn flatten_twice_good<T>(iter: T) -> Flatten<Flatten<T>>
where
    T: Iterator<Item: IntoIterator<Item: IntoIterator>>,
{
    iter.flatten().flatten()
}

c9c31f3 handled this because bounds could contain their nested bounds. I haven't been able to follow how WhereBoundPredicate can nest WhereBoundPredicates yet.

flip1995 · 2022-05-10T11:05:46Z

I wouldn't worry too much about supporting this feature with this lint. I'd suggest to just leave a FIXME comment that this should be addressed once this feature gets stabilized, which might take quite some time.

aldhsu · 2022-05-11T11:46:14Z

Squashed and added the fixme.

There is one other outstanding issue I haven't been able to figure out.

This case should be detected.

rust-clippy/tests/ui/repeated_where_clause_or_trait_bound.rs

Lines 40 to 42 in 6040fa6

    
           trait BadSelfTraitBound: Clone + Clone + Clone { 
        
               fn f(); 
        
           }

Doing some debugging on the Generic, no predicates exist. This only happens for the self trait bound and not the where clause. I haven't dug any further than that.

flip1995 · 2022-05-11T12:39:55Z

For your example you should find those bounds in the ItemKind::Trait. It's the tuple field with the GenericBounds type.

aldhsu · 2022-05-12T11:57:44Z

Thanks for the tip @flip1995. I got access to an ItemKind::Trait by implementing check_item of the LateLintPass for Traitbounds. Is this what you meant?

flip1995 · 2022-05-12T14:21:04Z

Thanks! I'd like to delegate the remaining review of this lint to @dswij. @dswij if you already have too many assigned PRs feel free to bounce it back to me though.

aldhsu · 2022-05-17T10:29:57Z

@rustbot ready

dswij

Thanks for addressing the comments! It looks good to me.

I'm not sure whether this lint should be in nursery group though, I don't see this having lots of false warnings either. Need some opinion on this, what do you guys think? @xFrednet @flip1995

xFrednet · 2022-05-18T17:11:23Z

Thank you for the review @flip1995 offered to do the final review (probably after their vacation :))

I'm not sure whether this lint should be in nursery group though, I don't see this having lots of false warnings either. Need some opinion on this, what do you guys think?

I think the final group should be pedantic. TRAIT_DUPLICATION_IN_BOUNDS which is similar, is currently in the nursery group due to some braking changes in rustc. I believe that they're fixed now, but I'm not totally sure. If they are fixed, we should change the lint group. Until then, I would keep this in the same group as TRAIT_DUPLICATION_IN_BOUNDS. @flip1995 is more up-to-date on this AFAIK 🙃

aldhsu · 2022-05-19T10:54:47Z

@dswij I put it in the nursery group because the other trait bound ones were put in there. I didn't have the confidence to say that the new lint was ready when the original lints it was based off were moved to nursery 😅. Original group was pedantic as @xFrednet said.

Offtopic: What is the process of growing out of nursery? I'm going to pick up #8757

xFrednet · 2022-05-19T14:17:39Z

Offtopic: What is the process of growing out of nursery? I'm going to pick up #8757

It depends on the reason why the lint was moved to the nursery group. The general rule is, that lints can be moved to their respective group once all issues have been resolved.

In this case I remember somebody working on fixing the issues. I'm just not sure if they've finished their work. It could be, that they've been fixed on the rust side and will be enabled again during the weekend. I'll try to keep an eye on it :)

bors · 2022-05-20T21:54:46Z

☔ The latest upstream changes (presumably #8856) made this pull request unmergeable. Please resolve the merge conflicts.

flip1995

Thanks for the review @dswij and thanks for addressing it @aldhsu!

I left some comments. Not sure if this requires a new lint.

clippy_lints/src/trait_bounds.rs

aldhsu · 2022-05-29T11:56:58Z

Thanks for the review @flip1995! I have addressed your comments.

bors · 2022-07-07T16:00:01Z

☔ The latest upstream changes (presumably #9132) made this pull request unmergeable. Please resolve the merge conflicts.

flip1995

So sorry, I completely forgot about this PR... I would do the renaming now, it shouldn't be too much work. If you lost the motivation to work on this after that long time, I'll address this myself in order not to lose this awesome work.

flip1995 · 2022-07-08T14:40:06Z

clippy_lints/src/trait_bounds.rs

+
+            span_lint_and_sugg(
+                cx,
+                REPEATED_WHERE_CLAUSES_OR_TRAIT_BOUNDS,


Merging the lints would just mean to change this line and adapt the documentation of the other lint a bit. I don't really want to merge a new lint, that will be renamed later, because if we mistime things, the temporary lint name will get into stable and we have to go through the renaming procedure or backport things.

@flip1995 ah got it. Of course the lint would be just under the same name! I was thinking it had to be done in the same pass.

Merging under the existing lint name raises some extra noise with UI test errors since the original lint "catches" some extra errors (#8757). Since this is actually a bug, I have left a comment that the errors generated in stderr should be removed once #8757 is fixed.

With regards to fixing, I've just turned off rustfix since I can't get the fixed file to compile without fixing the original lint.

Once this PR is merged I can work on reducing the noise in the errors so that it's not reporting the same errors twice slightly differently. This sounds ok to me since the lint is back in nursery.

aldhsu · 2022-07-09T04:53:34Z

@flip1995 I can address it. I had it in my head that "merging" the lint meant doing it in the same pass. I should be able to get it done this weekend.

Thanks for calling it awesome!

aldhsu · 2022-07-09T11:21:57Z

@rustbot ready

flip1995

Thanks for addressing this so quickly. I have a few small comments left. Overall this LGTM 👍

clippy_lints/src/trait_bounds.rs

flip1995 · 2022-07-11T07:03:25Z

tests/ui/trait_duplication_in_bounds.rs

+    // This should not warn but currently does see #8757
+    fn good_generic<T: GenericTrait<u64> + GenericTrait<u32>>(arg0: T) {
+        unimplemented!();
+    }


If this is the only test case that trips up rustfix, I'd suggest to move it into its own file named something like trait_duplication_in_bounds_8757.rs. That way, you can keep rustfix enabled and still have a regression test for the issue.

Or are there other cases that would break rustfix?

Yes, there are other cases that break rustfix.

The existing lint of trait_duplication_in_bounds raises a lint for pretty much all the new examples added. I believe the original intention of the lint is supposed to only be for traits appearing in both trait bounds and where clauses as that seems to be the only kinds of tests. I think it's a bug that it picks up duplicates within trait bounds and where clauses. This is evident because the errors produced for these cases are misleading.

Example:

fn bad_foo<T: Clone + Clone + Clone + Copy, U: Clone + Copy>(arg0: T, argo1: U) { unimplemented!(); }

error: this trait bound is already specified in the where clause --> $DIR/trait_duplication_in_bounds.rs:103:19 | LL | fn bad_foo<T: Clone + Clone + Clone + Copy, U: Clone + Copy>(arg0: T, argo1: U) { | ^^^^^ | = help: consider removing this trait bound

this trait bound is already specified in the where clause
It's error refers to a where clause but there aren't any.

I can fix this issue along with #8757 .
At that time I can split the fixables and unfixables like I see done with the other test files.

Ah ok, that's interesting. It seems that the old lint already triggers on the cases, the newly added lint code should check for, just with a worse error message + suggestion. I think this is even worse than #8757. Since this lint is in nursery I'd be ok merging this. But I would open an issue about it, even when you start working on resolving this right away.

Ok will do 👍🏼

Issue here #9151

flip1995 · 2022-07-11T15:09:25Z

Can you squash some of the commits please? After that this is good to go 👍

aldhsu · 2022-07-12T12:12:21Z

@flip1995 squashed. Thanks for the review!

flip1995 · 2022-07-12T15:18:03Z

Thanks! Sorry again for forgetting about this PR

@bors r+

bors · 2022-07-12T15:18:06Z

📌 Commit 8878d67 has been approved by flip1995

It is now in the queue for this repository.

bors · 2022-07-12T15:48:59Z

⌛ Testing commit 8878d67 with merge 9ebacd4...

bors · 2022-07-12T16:07:35Z

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 9ebacd4 to master...

rust-highfive assigned flip1995 Apr 15, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Apr 15, 2022

aldhsu changed the title ~~Add `[repeated_where_clause_or_trait_bound]`~~ Add [repeated_where_clause_or_trait_bound] Apr 15, 2022

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aldhsu changed the title ~~Add [repeated_where_clause_or_trait_bound]~~ Add [repeated_where_clause_or_trait_bound] Apr 18, 2022

aldhsu changed the title ~~Add [repeated_where_clause_or_trait_bound]~~ Add [repeated_where_clause_or_trait_bound] Apr 18, 2022

aldhsu changed the title ~~Add [repeated_where_clause_or_trait_bound]~~ Add `[repeated_where_clause_or_trait_bound]` Apr 18, 2022

aldhsu changed the title ~~Add `[repeated_where_clause_or_trait_bound]`~~ Add repeated_where_clause_or_trait_bound lint Apr 19, 2022

giraffate reviewed Apr 27, 2022

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aldhsu mentioned this pull request Apr 28, 2022

trait_duplication_in_bounds lint doesn't consider generics #8757

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Lint for repeated traits within trait bounds or where clauses.

8878d67

aldhsu force-pushed the add_repeated_where_clause_or_trait_bound branch from 188e4a8 to 8878d67 Compare July 12, 2022 12:04

bors merged commit 9ebacd4 into rust-lang:master Jul 12, 2022

aldhsu mentioned this pull request Jul 13, 2022

Remove duplicate trait bound or where clause #8674

Closed

Add repeated_where_clause_or_trait_bound lint #8703

Add repeated_where_clause_or_trait_bound lint #8703

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Add `repeated_where_clause_or_trait_bound` lint #8703

Add `repeated_where_clause_or_trait_bound` lint #8703

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