Mutable comptime globals treated as constants

[jfecher]

Aim

comptime mut global COUNTER = 0;

fn main() {
    comptime { increment() };
    comptime { increment() };
    
    assert_eq(get_counter(), 2);
}

fn get_counter() -> Field {
    COUNTER
}

comptime fn increment() {
    COUNTER += 1;

    let expected = get_counter();
    let actual = COUNTER;
    assert_eq(get_counter(), COUNTER, f"{expected} = {actual}");
}

Expected Behavior

The program to execute without error

Bug

Fails with:

error: 1 = 2
   ┌─ src/main.nr:5:16
   │
 5 │     comptime { increment() };
   │                -----------
   ·
19 │     assert_eq(get_counter(), COUNTER, f"{expected} = {actual}");
   │     ----------------------------------------------------------- Assertion failed
   │

Because get_counter is first elaborated within the comptime increment call, the value for COUNTER within it gets locked in as a constant - the current value of that constant which is 1 when it is first called. When it is later mutated and get_counter is called again, the value was inlined as a constant so the value is still 1 when it should be 2.

To Reproduce

Workaround

None

Workaround Description

No response

Additional Context

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Project Impact

None

Blocker Context

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Nargo Version

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NoirJS Version

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Proving Backend Tooling & Version

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