No overflow errors at compilation for add/sub constants operations.

[pventuzelo]

Aim

We (https://github.com/FuzzingLabs) find that the compiler fails to raise overflow errors at compilation while adding/subtracting two constants together.

Expected Behavior

The documentation explicitly states that this particular error occurs during the creation of a proof of correct execution. However, it's important to note that Noir language closely resembles Rust, and in this case, such errors are raised during the compilation process.

Bug

1. Create a Noir project with the following command: nargo new test_issue
2. Paste the code below into the file [main.nr](http://main.nr/)
3. Compile the project using the following command: nargo compile

fn main() {
    // No error is raised if all static values are less than u8 max
    let var1: u8 = 255 + 1;

    // Similarly, no error is raised when using a variable with a static value
    let var: u8 = 255;
    let var2: u8 = var + var;

    // This also applies in the negative direction and other integer types
    let var3: i64 = -18446744073709551616 - 1;
}

To Reproduce

No response

Installation Method

None

Nargo Version

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

No response

[TomAFrench]

Note that this behaviour is by design such that tests will still produce println output. We previously would halt compilation and return an error but that resulted in poor UX as shown in #3207.

We could restore this behaviour but would have to add an allow_unsatisfiable parameter to force creation of an invalid circuit for tests.

[asterite]

Also Rust doesn't error in this case:

fn main() {
    let x: u8 = 255 + 1;
}

[michaeljklein]

This is now tested in https://github.com/noir-lang/noir/blob/master/compiler/noirc_frontend/src/tests/bound_checks.rs and I just sanity-checked this specific case:

❯ ~/.nargo/bin/nargo compile
warning: unused variable var1
  ┌─ src/main.nr:3:9
  │
3 │     let var1: u8 = 255 + 1;
  │         ---- unused variable 
  │

warning: unused variable var2
  ┌─ src/main.nr:7:9
  │
7 │     let var2: u8 = var + var;
  │         ---- unused variable 
  │

warning: unused variable var3
   ┌─ src/main.nr:10:9
   │
10 │     let var3: i64 = -18446744073709551616 - 1;
   │         ---- unused variable 
   │

error: The value `-18446744073709551616` cannot fit into `i64` which has range `-9223372036854775808..=9223372036854775807`
   ┌─ src/main.nr:10:21
   │
10 │     let var3: i64 = -18446744073709551616 - 1;
   │                     ---------------------
   │

Aborting due to 1 previous error

@TomAFrench will reopen if you think it needs a more specific regression test.