Unhelpful `type annotations needed` when calling method on result of index op

[oli-obk]

Code

struct Foo;

impl Foo {
    fn foo(&self) {}
}

fn main() {
    let thing: Vec<Foo> = vec![];
    
    let foo = |i| {
        thing[i].foo();
    };
}

Current output

error[E0282]: type annotations needed
  --> src/main.rs:11:9
   |
11 |         thing[i].foo();
   |         ^^^^^^^^ cannot infer type

Desired output

error[E0282]: type annotations needed
  --> src/main.rs:11:9
   |
11 |         thing[i].foo();
   |               ^ cannot infer type

Rationale and extra context

Should also probably explain that the index op's output type depends on the input type, so it needs to know what input type it is at this point.

Other cases

No response

Rust Version

rustc 1.78.0 (9b00956e5 2024-04-29)
binary: rustc
commit-hash: 9b00956e56009bab2aa15d7bff10916599e3d6d6
commit-date: 2024-04-29
host: x86_64-unknown-linux-gnu
release: 1.78.0
LLVM version: 18.1.2
Compiler returned: 0

Anything else?

No response

[mu001999]

@rustbot claim

[frogtd]

This issue in the wild (Rust discord server):

let n: usize = 10;
let bools: Vec<bool> = vec![false; n];
let is_false = |x| !bools[x];

The fact the error doesn't call out the error type either and selects the whole expression is quite unfortunate.