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|
//! Comprehensive test for type parameter constraints in trait implementations
//!
//! This tests various scenarios of type parameter usage in trait implementations:
//! - Properly constrained parameters through trait bounds
//! - Unconstrained parameters that should cause compilation errors
//! - Complex constraint scenarios with `where` clauses and associated types
//! - Conflicting implementations detection
trait Foo<A> {
fn get(&self, A: &A) {}
}
trait Bar {
type Out;
}
impl<T> Foo<T> for [isize; 0] {
// OK: T is used in the trait bound `Foo<T>`
}
impl<T, U> Foo<T> for [isize; 1] {
//~^ ERROR the type parameter `U` is not constrained
// T is constrained by `Foo<T>`, but U is completely unused
}
impl<T, U> Foo<T> for [isize; 2]
where
T: Bar<Out = U>,
{
// OK: T is constrained by `Foo<T>`, U is constrained by the where clause
}
impl<T: Bar<Out = U>, U> Foo<T> for [isize; 3] {
// OK: Same as above but using bound syntax instead of where clause
}
impl<T, U> Foo<T> for U {
//~^ ERROR conflicting implementations of trait `Foo<_>` for type `[isize; 0]`
// This conflicts with the first impl when U = [isize; 0]
}
impl<T, U> Bar for T {
//~^ ERROR the type parameter `U` is not constrained
type Out = U;
// Using U only in associated type definition is insufficient for constraint
}
impl<T, U> Bar for T
where
T: Bar<Out = U>,
{
//~^^^^ ERROR the type parameter `U` is not constrained by the impl trait, self type, or predicates
//~| ERROR conflicting implementations of trait `Bar`
// Self-referential constraint doesn't properly constrain U
}
impl<T, U, V> Foo<T> for T
where
(T, U): Bar<Out = V>,
{
//~^^^^ ERROR the type parameter `U` is not constrained
//~| ERROR the type parameter `V` is not constrained
//~| ERROR conflicting implementations of trait `Foo<[isize; 0]>` for type `[isize; 0]`
// V is bound through output type, but U and V are not properly constrained as inputs
}
impl<T, U, V> Foo<(T, U)> for T
where
(T, U): Bar<Out = V>,
{
//~^^^^ ERROR conflicting implementations of trait `Foo<([isize; 0], _)>` for type `[isize; 0]`
// Both T and U are constrained through `Foo<(T, U)>`, but creates conflicting impl
}
fn main() {}
|
