Rollup merge of #90114 - BoxyUwU:cg_defaults_tests, r=lcnr

Add some tests for const_generics_defaults

I think this covers some of the stuff required for stabilisation report, some of these tests are probably covering stuff we already have but it can't hurt to have more :)

r? ````@lcnr````

src/test/ui/const-generics/defaults/default-annotation.rs

@@ -2,7 +2,7 @@
 #![feature(staged_api)]
 #![feature(const_generics_defaults)]
 #![allow(incomplete_features)]
-// FIXME(const_generics): It seems like we aren't testing the right thing here,
+// FIXME(const_generics_defaults): It seems like we aren't testing the right thing here,
 // I would assume that we want the attributes to apply to the const parameter defaults
 // themselves.
 #![stable(feature = "const_default_test", since="none")]

src/test/ui/const-generics/defaults/doesnt_infer.rs

@@ -0,0 +1,15 @@
+#![feature(const_generics_defaults)]
+
+// test that defaulted const params are not used to help type inference
+
+struct Foo<const N: u32 = 2>;
+
+impl<const N: u32> Foo<N> {
+    fn foo() -> Self { loop {} }
+}
+
+fn main() {
+    let foo = Foo::<1>::foo();
+    let foo = Foo::foo();
+    //~^ error: type annotations needed for `Foo<{_: u32}>`
+}

src/test/ui/const-generics/defaults/doesnt_infer.stderr

@@ -0,0 +1,11 @@
+error[E0282]: type annotations needed for `Foo<{_: u32}>`
+  --> $DIR/doesnt_infer.rs:13:15
+   |
+LL |     let foo = Foo::foo();
+   |         ---   ^^^^^^^^ cannot infer the value of const parameter `N`
+   |         |
+   |         consider giving `foo` the explicit type `Foo<{_: u32}>`, where the type parameter `N` is specified
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.

src/test/ui/const-generics/defaults/rp_impl_trait.rs

@@ -0,0 +1,31 @@
+// run-pass
+#![feature(const_generics_defaults)]
+
+struct Uwu<const N: u32 = 1, const M: u32 = N>;
+
+trait Trait {}
+impl<const N: u32> Trait for Uwu<N> {}
+
+fn rawr<const N: u32>() -> impl Trait {
+    Uwu::<N>
+}
+
+trait Traitor<const N: u8 = 1, const M: u8 = N> { }
+
+impl<const N: u8> Traitor<N> for u32 {}
+impl Traitor<1, 1> for u64 {}
+
+fn uwu<const N: u8>() -> impl Traitor<N> {
+    1_u32
+}
+
+fn owo() -> impl Traitor {
+    1_u64
+}
+
+fn main() {
+    rawr::<3>();
+    rawr::<7>();
+    uwu::<{ u8::MAX }>();
+    owo();
+}

src/test/ui/const-generics/defaults/rp_impl_trait_fail.rs

@@ -0,0 +1,33 @@
+#![feature(const_generics_defaults)]
+
+struct Uwu<const N: u32 = 1, const M: u32 = N>;
+
+trait Trait {}
+impl<const N: u32> Trait for Uwu<N> {}
+
+fn rawr() -> impl Trait {
+    //~^ error: the trait bound `Uwu<10_u32, 12_u32>: Trait` is not satisfied
+    Uwu::<10, 12>
+}
+
+trait Traitor<const N: u8 = 1, const M: u8 = N> { }
+
+impl<const N: u8> Traitor<N, 2> for u32 {}
+impl Traitor<1, 2> for u64 {}
+
+
+fn uwu<const N: u8>() -> impl Traitor<N> {
+    //~^ error: the trait bound `u32: Traitor<N, N>` is not satisfied
+    1_u32
+}
+
+fn owo() -> impl Traitor {
+    //~^ error: the trait bound `u64: Traitor<1_u8, 1_u8>` is not satisfied
+    1_u64
+}
+
+fn main() {
+    rawr();
+    uwu();
+    owo();
+}

src/test/ui/const-generics/defaults/rp_impl_trait_fail.stderr

@@ -0,0 +1,30 @@
+error[E0277]: the trait bound `Uwu<10_u32, 12_u32>: Trait` is not satisfied
+  --> $DIR/rp_impl_trait_fail.rs:8:14
+   |
+LL | fn rawr() -> impl Trait {
+   |              ^^^^^^^^^^ the trait `Trait` is not implemented for `Uwu<10_u32, 12_u32>`
+   |
+   = help: the following implementations were found:
+             <Uwu<N> as Trait>
+
+error[E0277]: the trait bound `u32: Traitor<N, N>` is not satisfied
+  --> $DIR/rp_impl_trait_fail.rs:19:26
+   |
+LL | fn uwu<const N: u8>() -> impl Traitor<N> {
+   |                          ^^^^^^^^^^^^^^^ the trait `Traitor<N, N>` is not implemented for `u32`
+   |
+   = help: the following implementations were found:
+             <u32 as Traitor<N, 2_u8>>
+
+error[E0277]: the trait bound `u64: Traitor<1_u8, 1_u8>` is not satisfied
+  --> $DIR/rp_impl_trait_fail.rs:24:13
+   |
+LL | fn owo() -> impl Traitor {
+   |             ^^^^^^^^^^^^ the trait `Traitor<1_u8, 1_u8>` is not implemented for `u64`
+   |
+   = help: the following implementations were found:
+             <u64 as Traitor<1_u8, 2_u8>>
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/const-generics/defaults/trait_objects.rs

@@ -0,0 +1,45 @@
+// run-pass
+#![feature(const_generics_defaults)]
+
+trait Trait<const N: u8 = 12> {
+    fn uwu(&self) -> u8 {
+        N
+    }
+}
+
+impl Trait for u32 {}
+
+impl Trait<12> for u64 {
+    fn uwu(&self) -> u8 {
+        *self as u8
+    }
+}
+
+fn foo(arg: &dyn Trait) -> u8 {
+    arg.uwu()
+}
+
+trait Traitor<const N: u8 = 1, const M: u8 = N> {
+    fn owo(&self) -> u8 {
+        M
+    }
+}
+
+impl Traitor<2> for bool { }
+impl Traitor for u8 {
+    fn owo(&self) -> u8 {
+        *self
+    }
+}
+
+fn bar<const N: u8>(arg: &dyn Traitor<N>) -> u8 {
+    arg.owo()
+}
+
+fn main() {
+    assert_eq!(foo(&10_u32), 12);
+    assert_eq!(foo(&3_u64), 3);
+
+    assert_eq!(bar(&true), 2);
+    assert_eq!(bar(&1_u8), 1);
+}

src/test/ui/const-generics/defaults/trait_objects_fail.rs

@@ -0,0 +1,32 @@
+#![feature(const_generics_defaults)]
+
+trait Trait<const N: u8 = 12> {
+    fn uwu(&self) -> u8 {
+        N
+    }
+}
+
+impl Trait<2> for u32 {}
+
+fn foo(arg: &dyn Trait) -> u8 {
+    arg.uwu()
+}
+
+trait Traitor<const N: u8 = 1, const M: u8 = N> {
+    fn owo(&self) -> u8 {
+        M
+    }
+}
+
+impl Traitor<2, 3> for bool { }
+
+fn bar<const N: u8>(arg: &dyn Traitor<N>) -> u8 {
+    arg.owo()
+}
+
+fn main() {
+    foo(&10_u32);
+    //~^ error: the trait bound `u32: Trait` is not satisfied
+    bar(&true);
+    //~^ error: the trait bound `bool: Traitor<{_: u8}, {_: u8}>` is not satisfied
+}

src/test/ui/const-generics/defaults/trait_objects_fail.stderr

@@ -0,0 +1,27 @@
+error[E0277]: the trait bound `u32: Trait` is not satisfied
+  --> $DIR/trait_objects_fail.rs:28:9
+   |
+LL |     foo(&10_u32);
+   |     --- ^^^^^^^ the trait `Trait` is not implemented for `u32`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following implementations were found:
+             <u32 as Trait<2_u8>>
+   = note: required for the cast to the object type `dyn Trait`
+
+error[E0277]: the trait bound `bool: Traitor<{_: u8}, {_: u8}>` is not satisfied
+  --> $DIR/trait_objects_fail.rs:30:9
+   |
+LL |     bar(&true);
+   |     --- ^^^^^ the trait `Traitor<{_: u8}, {_: u8}>` is not implemented for `bool`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following implementations were found:
+             <bool as Traitor<2_u8, 3_u8>>
+   = note: required for the cast to the object type `dyn Traitor<{_: u8}, {_: u8}>`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/const-generics/defaults/wfness.rs

@@ -0,0 +1,21 @@
+#![feature(const_generics_defaults)]
+
+struct Ooopsies<const N: u8 = { u8::MAX + 1 }>;
+//~^ error: evaluation of constant value failed
+
+trait Trait<const N: u8> {}
+impl Trait<3> for () {}
+struct WhereClause<const N: u8 = 2> where (): Trait<N>;
+//~^ error: the trait bound `(): Trait<2_u8>` is not satisfied
+
+trait Traitor<T, const N: u8> {}
+struct WhereClauseTooGeneric<T = u32, const N: u8 = 2>(T) where (): Traitor<T, N>;
+
+// no error on struct def
+struct DependentDefaultWfness<const N: u8 = 1, T = WhereClause<N>>(T);
+fn foo() -> DependentDefaultWfness {
+    //~^ error: the trait bound `(): Trait<1_u8>` is not satisfied
+    loop {}
+}
+
+fn main() {}

src/test/ui/const-generics/defaults/wfness.stderr

@@ -0,0 +1,38 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/wfness.rs:3:33
+   |
+LL | struct Ooopsies<const N: u8 = { u8::MAX + 1 }>;
+   |                                 ^^^^^^^^^^^ attempt to compute `u8::MAX + 1_u8`, which would overflow
+
+error[E0277]: the trait bound `(): Trait<2_u8>` is not satisfied
+  --> $DIR/wfness.rs:8:47
+   |
+LL | struct WhereClause<const N: u8 = 2> where (): Trait<N>;
+   |                                               ^^^^^^^^ the trait `Trait<2_u8>` is not implemented for `()`
+   |
+   = help: the following implementations were found:
+             <() as Trait<3_u8>>
+note: required by `WhereClause`
+  --> $DIR/wfness.rs:8:1
+   |
+LL | struct WhereClause<const N: u8 = 2> where (): Trait<N>;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `(): Trait<1_u8>` is not satisfied
+  --> $DIR/wfness.rs:16:13
+   |
+LL | fn foo() -> DependentDefaultWfness {
+   |             ^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait<1_u8>` is not implemented for `()`
+   |
+   = help: the following implementations were found:
+             <() as Trait<3_u8>>
+note: required by a bound in `WhereClause`
+  --> $DIR/wfness.rs:8:47
+   |
+LL | struct WhereClause<const N: u8 = 2> where (): Trait<N>;
+   |                                               ^^^^^^^^ required by this bound in `WhereClause`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0080, E0277.
+For more information about an error, try `rustc --explain E0080`.

src/test/ui/const-generics/defaults/wrong-order.rs

@@ -5,4 +5,7 @@ struct A<T = u32, const N: usize> {
     arg: T,
 }
 
+struct Foo<const N: u8 = 3, T>(T);
+//~^ error: generic parameters with a default must be trailing
+
 fn main() {}

src/test/ui/const-generics/defaults/wrong-order.stderr

@@ -4,5 +4,11 @@ error: generic parameters with a default must be trailing
 LL | struct A<T = u32, const N: usize> {
    |          ^
 
-error: aborting due to previous error
+error: generic parameters with a default must be trailing
+  --> $DIR/wrong-order.rs:8:18
+   |
+LL | struct Foo<const N: u8 = 3, T>(T);
+   |                  ^
+
+error: aborting due to 2 previous errors