[Bug] cannot assign to non-const array index

[0rphon]

🐛 Bug Report

Code snippet to reproduce

function main (x: u8) {
    let y = [0u8; 4];
    // works fine
    y[x] = 1u8;
    // error
    y[x > 1u8? 1u8 : 2u8] = 1u8;
}

Stack trace & error message

D:\Work\leo-playground>D:\Work\leo_repos\leo\target\release\leo clean && D:\Work\leo_repos\leo\target\release\leo run
      Done Finished in 1 milliseconds 

     Build Starting...
     Build Compiling main program... ("D:\\Work\\leo-playground\\src/main.leo")
     Build Number of constraints - 46
     Build Complete
      Done Finished in 5 milliseconds

     Setup Starting...
     Setup     --> D:\Work\leo-playground\src/main.leo:6:5
     |
   6 |     y[x > 1u8? 1u8 : 2u8] = 1u8;
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = Cannot assign to non-const array index
      Done Finished in 2 milliseconds

Error: Unable to setup, see command output for more details

Your Environment

• leo commit 04e9bf2
• rustc version 1.53.0-nightly
• Windows 10.0.19042 (Windows 10 Pro) [64-bit]

[0rphon]

im looking over some old bugs and i realized that this is likely related to #889

[damons]

Bumping up the priority on this as it's affecting our community pretty dramatically. Marking it so we fix it this sprint.

[0rphon]

@damons bump #889 as well since its related

[howardwu]

@collinc97 can you take a look at this?

[howardwu]

Assigning to @Protryon

[0rphon]

it seems like this only causes an invalid proof instead of an error now