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Unnecessary type repetition in trait bound #3764

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xd009642 opened this issue Feb 14, 2019 · 2 comments · Fixed by #5761
Closed

Unnecessary type repetition in trait bound #3764

xd009642 opened this issue Feb 14, 2019 · 2 comments · Fixed by #5761
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A-lint Area: New lints L-complexity Lint: Belongs in the complexity lint group

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@xd009642
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So I raised this on rust-lang/rust#58471 and it was suggested this is better as a clippy lint so pasting the issue text here for quick reference:

My where clauses in traits recently had some unnecessary noise that the compiler could warn against:

What I was doing:

impl<T> SomeTrait<T> where T: Clone, T: Debug

What I should have been doing:

impl<T> SomeTrait<T> where T: Clone + Debug

I'd be happy to implement this myself if there's a consensus on adding this as a warning, though I may > need some mentoring 👍

The offer to help with a PR myself still stands, I had a quick check of the lints and didn't spot it.
@xd009642 xd009642 mentioned this issue Feb 14, 2019
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@oli-obk oli-obk added A-lint Area: New lints L-complexity Lint: Belongs in the complexity lint group labels Feb 15, 2019
@oli-obk
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oli-obk commented Feb 15, 2019

There are theoretically infinte ways to write where bounds. So as a first step just doing unification of T: Foo, T: Bar to T: Foo + Bar seems like a good idea.

This lint should not trigger inside macros (as it doesn't matter there and some macros might get hard to write), so you should use the in_macro function to bail out if we're inside a macro.

You can implement the check_generics method and access the where_clauses field on the generics argument. If you want any help with the implementation, don't hesitate to ask here.

@xd009642 xd009642 mentioned this issue Feb 15, 2019
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@xd009642
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I've just done a draft pull request. It's roughly there and builds but doesn't yet work.

bors added a commit that referenced this issue Jul 29, 2019
@bors
Auto merge of #3766 - xd009642:issue-3764, r=flip1995
62536e0 
trait bounds lint - repeated types

This PR is to tackle #3764 it's still a WIP and doesn't work but this is an initial stab. It builds though I haven't added any tests as I'm not sure where lint tests should go?

Unfortunately, it seems id isn't tied to the type itself but I guess where it is in the AST? Looking at https://manishearth.github.io/rust-internals-docs/syntax/ast/struct.Ty.html I can't see any members that would let me tell if a type was repeated in multiple trait bounds.

There may be other issues with how I've implemented this so any assistance is appreciated!
bors added a commit that referenced this issue Jul 29, 2019
@bors
Auto merge of #3766 - xd009642:issue-3764, r=flip1995
23c6452 
trait bounds lint - repeated types

This PR is to tackle #3764 it's still a WIP and doesn't work but this is an initial stab. It builds though I haven't added any tests as I'm not sure where lint tests should go?

Unfortunately, it seems id isn't tied to the type itself but I guess where it is in the AST? Looking at https://manishearth.github.io/rust-internals-docs/syntax/ast/struct.Ty.html I can't see any members that would let me tell if a type was repeated in multiple trait bounds.

There may be other issues with how I've implemented this so any assistance is appreciated!

changelog: Add new lint: `type_repetition_in_bounds`
bors added a commit that referenced this issue Jul 30, 2019
@bors
Auto merge of #3766 - xd009642:issue-3764, r=flip1995
c3e9136 
trait bounds lint - repeated types

This PR is to tackle #3764 it's still a WIP and doesn't work but this is an initial stab. It builds though I haven't added any tests as I'm not sure where lint tests should go?

Unfortunately, it seems id isn't tied to the type itself but I guess where it is in the AST? Looking at https://manishearth.github.io/rust-internals-docs/syntax/ast/struct.Ty.html I can't see any members that would let me tell if a type was repeated in multiple trait bounds.

There may be other issues with how I've implemented this so any assistance is appreciated!

changelog: Add new lint: `type_repetition_in_bounds`
@ThibsG ThibsG mentioned this issue Jul 3, 2020
Merged
@bors bors closed this as completed in fff8e72 Jul 3, 2020
@bors bors closed this as completed in #5761 Jul 3, 2020
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Improvements for type_repetition_in_bounds lint ThibsG/rust-clippy
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@oli-obk @xd009642