Suggest if let on let refutable binding

[estebank]

Fix #58385.

[rust-highfive]

r? @cramertj

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[cramertj]

Should this note perhaps be in the rustc --explain rather than inline here? it seems like it's a lot of extra text

[cramertj]

r=me (fine either way WRT my comment above)

It's sort of unfortunate how much extra space these hints take up, but it seems like they provide useful additional information.

[estebank]

@cramertj I can turn the following

error[E0005]: refutable pattern in local binding: `std::i32::MIN..=-1i32` and `1i32..=std::i32::MAX` not covered
  --> $DIR/const-match-check.rs:31:24
   |
LL |     let x: [i32; { let 0 = 0; 0 }] = [];
   |                        ^ patterns `std::i32::MIN..=-1i32` and `1i32..=std::i32::MAX` not covered
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
help: you might want to use `if let` to ignore the variant that isn't matched
   |
LL |     let x: [i32; { if let 0 = 0 { /* */ } 0 }] = [];
   |                    ^^^^^^^^^^^^^^^^^^^^^^

into

error[E0005]: refutable pattern in local binding: `std::i32::MIN..=-1i32` and `1i32..=std::i32::MAX` not covered
  --> $DIR/const-match-check.rs:31:24
   |
LL |     let x: [i32; { let 0 = 0; 0 }] = [];
   |                    ----^-----
   |                    |   |
   |                    |   patterns `std::i32::MIN..=-1i32` and `1i32..=std::i32::MAX` not covered
   |                    help: you might want to use `if let` instead: `if let 0 = 0 { /* */ }`
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html

but I fear that readability actually suffers.

[estebank]

it seems like it's a lot of extra text

I kind of agree, but I fail to see what I can remove without compromising on onboarding experience. I think it makes sense merge this as is and after we have real life experience with it we can cut it back if it proves to be too annoying in real codebases.

@bors r=cramertj

[bors]

📌 Commit 4bb1592 has been approved by cramertj

[Centril]

Suggested change

	format!("if {} {{ /* */ }}", &snippet[..snippet.len() - 1]),
	format!("if {} {{ /* ... */ }}", &snippet[..snippet.len() - 1]),

[Centril]

but I fear that readability actually suffers.

That could be fixed by having some vertical space between the two inline labels/notes.