Fix diagnostics for @ .. binding pattern in tuples and tuple structs

[chrissimpkins]

Fixes #72574
Associated #72534 #72373

Includes a new suggestion with Applicability::MaybeIncorrect confidence level.

Before

tuple

error: `..` patterns are not allowed here
 --> src/main.rs:4:19
  |
4 |         (_a, _x @ ..) => {}
  |                   ^^
  |
  = note: only allowed in tuple, tuple struct, and slice patterns

error[E0308]: mismatched types
 --> src/main.rs:4:9
  |
3 |     match x {
  |           - this expression has type `({integer}, {integer}, {integer})`
4 |         (_a, _x @ ..) => {}
  |         ^^^^^^^^^^^^^ expected a tuple with 3 elements, found one with 2 elements
  |
  = note: expected tuple `({integer}, {integer}, {integer})`
             found tuple `(_, _)`

error: aborting due to 2 previous errors

tuple struct

error: `..` patterns are not allowed here
 --> src/main.rs:6:25
  |
6 |         Binder(_a, _x @ ..) => {}
  |                         ^^
  |
  = note: only allowed in tuple, tuple struct, and slice patterns

error[E0023]: this pattern has 2 fields, but the corresponding tuple struct has 3 fields
 --> src/main.rs:6:9
  |
1 | struct Binder(i32, i32, i32);
  | ----------------------------- tuple struct defined here
...
6 |         Binder(_a, _x @ ..) => {}
  |         ^^^^^^^^^^^^^^^^^^^ expected 3 fields, found 2

error: aborting due to 2 previous errors

After

Note: final output edited during source review discussion, see thread for details

tuple

error: `_x @` is not allowed in a tuple
 --> src/main.rs:4:14
  |
4 |         (_a, _x @ ..) => {}
  |              ^^^^^^^ is only allowed in a slice
  |
help: replace with `..` or use a different valid pattern
  |
4 |         (_a, ..) => {}
  |              ^^

error[E0308]: mismatched types
 --> src/main.rs:4:9
  |
3 |     match x {
  |           - this expression has type `({integer}, {integer}, {integer})`
4 |         (_a, _x @ ..) => {}
  |         ^^^^^^^^^^^^^ expected a tuple with 3 elements, found one with 1 element
  |
  = note: expected tuple `({integer}, {integer}, {integer})`
             found tuple `(_,)`

error: aborting due to 2 previous errors

tuple struct

error: `_x @` is not allowed in a tuple struct
 --> src/main.rs:6:20
  |
6 |         Binder(_a, _x @ ..) => {}
  |                    ^^^^^^^ is only allowed in a slice
  |
help: replace with `..` or use a different valid pattern
  |
6 |         Binder(_a, ..) => {}
  |                    ^^

error[E0023]: this pattern has 1 field, but the corresponding tuple struct has 3 fields
 --> src/main.rs:6:9
  |
1 | struct Binder(i32, i32, i32);
  | ----------------------------- tuple struct defined here
...
6 |         Binder(_a, _x @ ..) => {}
  |         ^^^^^^^^^^^^^^^^^^^ expected 3 fields, found 1

error: aborting due to 2 previous errors

r? @estebank

[chrissimpkins]

Modified the suggestion slightly to better address attempts to define a BindingMode in the binding.

e.g.,

error: `_x @` is not allowed in a tuple
 --> src/main.rs:4:14
  |
4 |         (_a, ref mut _x @ ..) => {}
  |              ^^^^^^^^^^^^^^^ is only allowed in a slice
  |
help: replace with `..` or use a different valid pattern
  |
4 |         (_a, ..) => {}
  |              ^^

error[E0308]: mismatched types
 --> src/main.rs:4:9
  |
3 |     match x {
  |           - this expression has type `({integer}, {integer}, {integer})`
4 |         (_a, ref mut _x @ ..) => {}
  |         ^^^^^^^^^^^^^^^^^^^^^ expected a tuple with 3 elements, found one with 1 element
  |
  = note: expected tuple `({integer}, {integer}, {integer})`
             found tuple `(_,)`

error: aborting due to 2 previous errors

[estebank]

A few nitpicks, let me know what you think.

[chrissimpkins]

Thanks Esteban! I committed the two new suggestions and will push updated test files.

[chrissimpkins]

Tests updated with the latest round of changes in dbb2d6b

[chrissimpkins]

@estebank I'll wait for this to pass the CI tests and then will squash. Let me know if you feel that any other changes are needed. This looks good 👍

error: `_x @` is not allowed in a tuple
 --> src/main.rs:4:14
  |
4 |         (_a, ref mut _x @ ..) => {}
  |              ^^^^^^^^^^^^^^^ this is only allowed in slice patterns
  |
  = help: remove this and bind each tuple field independently
help: if you don't need to use the contents of _x, discard the tuple's remaining fields
  |
4 |         (_a, ..) => {}
  |              ^^

error: aborting due to previous error

[chrissimpkins]

Squashed to 27ed143

All set on my end. Please let me know if there is anything else that I need to address. Thanks again Esteban.

[estebank]

@bors r+ rollup

[bors]

📌 Commit 27ed143 has been approved by estebank