[Bug] ternary in loop causes conditional select unsatisfiable

[0rphon]

🐛 Bug Report

Code snippet to reproduce

function main () {
    for x in 0u8..10u8 {
        let y = (false? 1u8 : x) == 2u8? 3u8 : 4u8;
    }
}

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 5 milliseconds 

     Build Starting...
     Build Compiling main program... ("D:\\Work\\leo_playground\\src/main.leo")
      Done Finished in 7 milliseconds

Error:     -->  3:18
     |
     |                   ^^^^^^^^^^^^^^
     |
     = the gadget operation `conditional select` failed due to synthesis error `Unsatisfiable`

Your Environment

• leo commit 6d378c3
• rustc version 1.50.0
• Windows 10.0.19042 (Windows 10 Pro) [64-bit]

[0rphon]

most likely related to #758

[ljedrz]

I investigated this a bit, and it looks like the loop index is wrongly assigned the U32 type; this is how the 2 compared values (1u8 : x) look like internally in the Integer::conditionally_select operation that fails with SynthesisError::Unsatisfiable:

a: U8(
    UInt8 { 
        bits: [
            Constant(true), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false),
        ], 
        negated: false, 
        value: Some(1) 
    }
)

b: U32(
    UInt32 { 
        bits: [
            Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), 
            Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false),
            Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), 
            Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false), Constant(false),
        ], 
        negated: false, 
        value: Some(0) 
    }
)

[ljedrz]

Confirmed; this is essentially a duplicate of #758 that just throws a different error.