Identical arguments on assert macro family

[ThibsG]

Lint when identical args are used on assert_eq!, debug_assert_eq!, assert_ne! and debug_assert_ne! macros.

Added to the lint eq_op.

Common functions added to utils/higher.rs

Fixes: #3574
Fixes: #4694

changelog: Lint on identical args when calling assert_eq!, debug_assert_eq!, assert_ne! and debug_assert_ne! macros

[rust-highfive]

r? @Manishearth

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[ThibsG]

I've been looking at mutable_debug_assertion lint that links to #4694. I will probably give it a try in a future PR, it could be nice to have less duplicated code for these two lints.

[Manishearth]

r? @ebroto since you've already started, feel free to bounce back the review if you're busy!

[flip1995]

2 things:

1. (you already noticed that) This would greatly profit from Add {debug_,}assert{,-eq,-ne} to utils/higher.rs #4694 being implemented first
2. counter example: assert_ne!(my_special_iter.next(), my_special_iter.next()) could be a valid test for some iterator implementation on a type.

[ThibsG]

1. (you already noticed that) This would greatly profit from Add {debug_,}assert{,-eq,-ne} to utils/higher.rs #4694 being implemented first

Ok I will implement #4694 in this PR 😉

2. counter example: assert_ne!(my_special_iter.next(), my_special_iter.next()) could be a valid test for some iterator implementation on a type.

It doesn't lint, because eq_expr_value is disabling side effects. But I will add this as it is a good test case though.

[ebroto]

It looks like we have to split the eq_op tests in order to avoid the stderr file limit.

[ThibsG]

👀 oops will do.

By the way, in #4694 (comment), @flip1995 was wishing the following:

A great extension of this would be to also return the format_arg expressions. So for assert!(expr, "some {} things", fmt_expr) it would return [expr, fmt_expr], but we can do this in a second iteration.

Is it still wanted?

[ebroto]

Is it still wanted?

I would say so, but I think it can be left for a follow-up PR. This is already an improvement on Clippy's toolset, and a cool enhancement of the lint. Thank you!

[ebroto]

@bors r+

[bors]

📋 Looks like this PR is still in progress, ignoring approval.

Hint: Remove WIP from this PR's title when it is ready for review.

[ebroto]

@bors r+

[bors]

📌 Commit 16b5f37 has been approved by ebroto

[bors]

⌛ Testing commit 16b5f37 with merge eaffd0e...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: ebroto
Pushing eaffd0e to master...

[flip1995]

Awesome! Thanks for implementing this :)