On unused binding or binding not present in all patterns, suggest potential typo of unit struct/variant or const

[estebank]

When encountering an or-pattern with a binding not available in all patterns, look for consts and unit struct/variants that have similar names as the binding to detect typos.

error[E0408]: variable `Ban` is not bound in all patterns
  --> $DIR/binding-typo.rs:22:9
   |
LL |         (Foo, _) | (Ban, Foo) => {}
   |         ^^^^^^^^    --- variable not in all patterns
   |         |
   |         pattern doesn't bind `Ban`
   |
help: you might have meant to use the similarly named unit variant `Bar`
   |
LL -         (Foo, _) | (Ban, Foo) => {}
LL +         (Foo, _) | (Bar, Foo) => {}
   |

For items that are not in the immedate scope, suggest the full path for them:

error[E0408]: variable `Non` is not bound in all patterns
  --> $DIR/binding-typo-2.rs:51:16
   |
LL |         (Non | Some(_))=> {}
   |          ---   ^^^^^^^ pattern doesn't bind `Non`
   |          |
   |          variable not in all patterns
   |
help: you might have meant to use the similarly named unit variant `None`
   |
LL -         (Non | Some(_))=> {}
LL +         (core::option::Option::None | Some(_))=> {}
   |

When encountering a typo in a pattern that gets interpreted as an unused binding, look for unit struct/variant of the same type as the binding:

error: unused variable: `Non`
  --> $DIR/binding-typo-2.rs:36:9
   |
LL |         Non => {}
   |         ^^^
   |
help: if this is intentional, prefix it with an underscore
   |
LL |         _Non => {}
   |         +
help: you might have meant to pattern match on the similarly named variant `None`
   |
LL -         Non => {}
LL +         std::prelude::v1::None => {}
   |

Suggest constant on unused binding in a pattern

error: unused variable: `Batery`
  --> $DIR/binding-typo-2.rs:110:9
   |
LL |         Batery => {}
   |         ^^^^^^
   |
help: if this is intentional, prefix it with an underscore
   |
LL |         _Batery => {}
   |         +
help: you might have meant to pattern match on the similarly named constant `Battery`
   |
LL |         Battery => {}
   |            +

Fix #51976.

[rustbot]

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[fee1-dead]

Hmmm. I'm not entirely sure whether this actually fixes the original issue as the original issue is about a variant in scope. I would like to see the original issue in a test.

[estebank]

Changed because that lint now emits:

error: variable `object` is assigned to, but never used
  --> $DIR/mut-arg-of-borrowed-type-meant-to-be-arg-of-mut-borrow.rs:11:23
   |
LL | fn change_object2(mut object: &Object) {
   |                       ^^^^^^
   |
   = note: consider using `_object` instead
note: the lint level is defined here
  --> $DIR/mut-arg-of-borrowed-type-meant-to-be-arg-of-mut-borrow.rs:2:29
   |
LL | #![deny(unused_assignments, unused_variables)]
   |                             ^^^^^^^^^^^^^^^^
help: you might have meant to pattern match on the similarly named struct `Object` (notice the capitalization)
   |
LL - fn change_object2(mut object: &Object) {
LL + fn change_object2(mut Object: &Object) {
   |

which would make this test no longer run-rustfixable.

[estebank]

This is the original case in the ticket, where it was a simple typo and the binding was available in the other or-pattern.

[estebank]

This is the case where the typo'd variant is not even present in the other or-pattern.

[estebank]

Test when an or-pattern isn't involved.

[fee1-dead]

Sorry, I lack capacity at the moment and have to reroll.

r? compiler

[jackh726]

@bors r+

[bors]

📌 Commit 86085b4 has been approved by jackh726

It is now in the queue for this repository.

[Zalathar]

Perf results from rollup (regressions and improvements):

• Rollup of 24 pull requests #146185 (comment)
• comparison URL