Numeric generic struct parameter panics when accessed uninitialized #5436
Comments
Yeah I think we should fail with that a type annotation is needed here. |
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@noir-lang/core Rust gives an error whenever a type's generic can't be deduced. For example: struct Foo<const N: u32> {}
impl<const N: u32> Foo<N> {
fn size(self) -> u32 {
N
}
}
fn main() {
let foo = Foo {}; // type annotations needed for `Foo<N>`
let x = foo.size();
}That said, the error happens regardless of fn main() {
let foo = Foo {}; // type annotations needed for `Foo<N>`
}However in Noir we don't error in that case. Here's a Noir program that compiles fine: struct Foo<N> { }
fn main() {
let foo = Foo {}; // No error here, `foo` is deduced to be `Foo<_>`
}But maybe the above program should give an error similar to Rust? What do you think? |
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I would prefer to error whenever a type's generic can't be deduced. Consider the following code: fn copy_from_slice<let N: u32>(xs: [u8]) -> [u8; N] {
let mut inp = xs;
let mut out = [0; N];
for i in 0..N {
let (x, rest) = inp.pop_front();
inp = rest;
out[i] = x;
}
out
}
let my_slice: [u8] = [0; 8].as_slice();
let output_array = copy_from_slice(my_slice);If we default |
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We should error in this case - I'm surprised we don't. Perhaps we treat these numeric generics as TypeVariableKind::Integers and thus default them instead? |
# Description ## Problem Resolves #5436 ## Summary The monomorphizer checks that no types exist that aren't unbound and can't have a default type. This is also the case for structs, but this check is done on field types after they are paired with generics. For example: ```rust struct Foo<T> { x: T } fn main() { let _ = Foo { x: 1 }; } ``` Here we pair `T` with the generic type of 1, then it's defaulted to `Field`, no error. However, it can happen that a generic parameter isn't mentioned at all in a struct field. For example: ```rust struct Foo<T> { } fn main() { let _ = Foo {}; } ``` Here `T` isn't paired with anything, so it's left unbound. However, because we only check that the resulting field types aren't unbound, no error happens. The solution in this PR is to check that generic parameters aren't unbound. This required a method like `convert_type`, called `check_type`, that only checks for this errors. The reason is that I wanted to avoid converting types twice. But let me know if that would be fine (or if there's another solution for this). ## Additional Context In Rust if a generic parameter isn't used in a field, an error about that is made. However, no error happens if the generic parameter is a `const` (similar to a `let N: u32` parameter in Noir) so here I chose to error un unbound generics, not check if a generic is unused. ## Documentation\* Check one: - [x] No documentation needed. - [ ] Documentation included in this PR. - [ ] **[For Experimental Features]** Documentation to be submitted in a separate PR. # PR Checklist\* - [x] I have tested the changes locally. - [x] I have formatted the changes with [Prettier](https://prettier.io/) and/or `cargo fmt` on default settings. --------- Co-authored-by: jfecher <jake@aztecprotocol.com>
Aim
Attempted to compile the following program:
Expected Behavior
Expected the program to either compile successfully (having defaulted
N = 0) or fail with a user error becauseNis uninitialized when declaringfoo.Bug
To Reproduce
Project Impact
None
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Workaround
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Workaround Description
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Additional Context
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Installation Method
None
Nargo Version
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NoirJS Version
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