Add suggest Vec::push when the wrong method is used

[chenyukang]

Fixes #87212

append is commonly used in Python, suggest push if possible.

[rustbot]

r? @oli-obk

rustbot has assigned @oli-obk.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[chenyukang]

maybe it's better to check coerce between recv_ty and expected ty?

[oli-obk]

While this suggestion is really precise and targeted, would it be sufficient to use #[rustc_confusables(...)] on push?

cc #59450

[jieyouxu]

While this suggestion is really precise and targeted, would it be sufficient to use #[rustc_confusables(...)] on push?

cc #59450

I think estebank is also adding/improving some infrastructure for this, cf. #120730?

[estebank]

Indeed it will be better to leverage rustc_confusables for this, and #120730 expands its capabilities a bit to handle these cases:

error[E0308]: mismatched types
    --> f100.rs:5:18
     |
5    |     stuff.append(Thing); //~ ERROR mismatched types
     |           ------ ^^^^^ expected `&mut Vec<Thing>`, found `Thing`
     |           |
     |           arguments to this method are incorrect
     |
     = note: expected mutable reference `&mut Vec<Thing>`
                           found struct `Thing`
note: method defined here
    --> /home/gh-estebank/rust/library/alloc/src/vec/mod.rs:2025:12
     |
2025 |     pub fn append(&mut self, other: &mut Self) {
     |            ^^^^^^
help: you might have meant to use `push`
     |
5    |     stuff.push(Thing); //~ ERROR mismatched types
     |           ~~~~

error[E0308]: mismatched types
    --> f100.rs:11:18
     |
11   |     stuff.append(Thing); //~ ERROR mismatched types
     |           ------ ^^^^^ expected `&mut Vec<_>`, found `Thing`
     |           |
     |           arguments to this method are incorrect
     |
     = note: expected mutable reference `&mut Vec<_>`
                           found struct `Thing`
note: method defined here
    --> /home/gh-estebank/rust/library/alloc/src/vec/mod.rs:2025:12
     |
2025 |     pub fn append(&mut self, other: &mut Self) {
     |            ^^^^^^
help: you might have meant to use `push`
     |
11   |     stuff.push(Thing); //~ ERROR mismatched types
     |           ~~~~

error[E0308]: mismatched types
    --> f100.rs:17:18
     |
17   |     stuff.append(Thing); //~ ERROR mismatched types
     |           ------ ^^^^^ expected `&mut Vec<i32>`, found `Thing`
     |           |
     |           arguments to this method are incorrect
     |
     = note: expected mutable reference `&mut Vec<i32>`
                           found struct `Thing`
note: method defined here
    --> /home/gh-estebank/rust/library/alloc/src/vec/mod.rs:2025:12
     |
2025 |     pub fn append(&mut self, other: &mut Self) {
     |            ^^^^^^
note: you might have meant to use method `push`
    --> /home/gh-estebank/rust/library/alloc/src/vec/mod.rs:1920:5
     |
1920 |     pub fn push(&mut self, value: T) {
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[chenyukang]

emm, the issue was not linked with a PR 😂
closing it.

[estebank]

@chenyukang yeah, it's a shame we have some overlapping tickets that are not linked to each other leading to situations like this one :-/