Make the error generated by using tuple indexing on an array more specific.

[Tom1380]

Attempting to compile this:

let a = [100, 100];
a.0;

will give this error:

error[E0609]: no field `0` on type `[{integer}; 2]`

I was thinking that a clearer error could be something along the lines of:

error[E----]: attempting to use tuple indexing on an array.

and give this hint:

help: change this to `a[0]`

[varkor]

This should be straightforward to add a help message for. This error message is emitted here:
https://github.com/rust-lang/rust/blob/352b852f5b199dad36b5dc62a24e9bad4c18a671/src/librustc_typeck/check/mod.rs#L3318-L3320
The match immediately afterwards is responsible for giving suggestions relevant to the particular type. You'd need to add a new case for ty::Array (defined here) and emit an appropriate message (there are examples for other types in the match expression), if the field is numeric.

If anyone'd like to tackle this, just post a reply here — I can give more details as needed (but it's always useful to try working things out yourself first, to get a feel for where to find things).

[Tom1380]

I don't have any experience with Rustc's codebase, but I would be willing to give it a try.

[varkor]

@Tom1380: great! If you need any help, you can post a comment here, or ask on Discord or #rustc. Once you add the help message, you'll need to add a test for it (there are plenty of examples in src/test/ui — you can run ./x.py test [filename] --bless to test and produce the output).