Emit clear error for index into zero-sized Arrays

[JulianKnodt]

Previously GEP on zero-sized arrays, would fail. This change fixes arrays to instead emit runtime arrays. I do not know if this will lead to any runtime cost, but it fixes all the compile errors.

I did try out [(); 0].map(|()| 1), and found that that does not compile.

Fixes #151

[LegNeato]

Awesome, thanks for the PR! 🍻 I'm not super familiar with this code but the change looks reasonable to me. I'll wait for some other maintainers to look at it before reviewing 🤙

Looks like you need to run cargo fmt to pass CI.

[JulianKnodt]

Somehow this passes locally but not on CI 🤣, I'll have to test a bit more

[JulianKnodt]

I've changed my expectation, previously it was erroring for accessing zero sized arrays, but it was hidden behind a deny that is on by default. Instead, I think we should always panic, but with a clear error message. I'm unsure what the behavior would be if that expression were allowed to be compiled.

[LegNeato]

Can we make the error messages match rustc? For example:

error[E0080]: evaluation of constant value failed
 --> src/main.rs:2:18
  |
2 | const VAL: u32 = ARR[0];
  |                  ^^^^^^ index out of bounds: the length is 0 but the index is 0

For more information about this error, try `rustc --explain E0080`.

[JulianKnodt]

I can, I do worry that since it's not the actual error it may be more confusing

[LegNeato]

Sorry, for the error messages I meant matching the same case in rustc to the case here where it makes sense. I'll leave it up to you to change them so they make sense!

A couple of small comments, thanks again for the PR and sorry for the slow response!

[LegNeato]

We should look into this case, no?

[JulianKnodt]

yea, I want to see if it compiles to include a panic, but I'm unsure of how to run the rest to see what happens

Is it run automatically by compiletest

[LegNeato]

No, sadly compiletest just checks it compiles. We don't have any automated runtime tests right now sadly. I usually just drop the code in one of the examples when I am doing a quick manual test.