Typevariables can be bound while searching for methods

[jfecher]

Aim

struct Foo<A, B> {
    field: B,
}

impl Foo<u8, u8> {
    fn foo(_self: Self) -> Field { 1 }
}

impl Foo<u16, Field> {
    fn foo(_self: Self) -> Field { 2 }
}

fn main() {
    let field: Field = 0;
    let f = Foo { field };
    assert(f.foo() == 2);
}

Expected Behavior

The program to execute successfully

Bug

The program non-deterministically fails with:

error: No method named 'foo' found for type 'Foo<u8, Field>'
   ┌─ /.../short/src/main.nr:18:12
   │
18 │     assert(f.foo() == 2);
   │            -------
   │

Aborting due to 1 previous error

From this we can see:

• In, the original type of f, Foo<_, Field>, the type variable is being bound to u8 when seeing if the first method matches. When it does not match, the binding is not undone which causes the second method to fail to type check as well. If the binding was correctly undone, Foo<_, Field> would otherwise be compatible with the second method's object type Foo<u16, Field>.
• The program only fails sometimes. This means the ordering of the methods in the method search is non-deterministic.

To Reproduce

Installation Method

None

Nargo Version

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

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