exit out of compare_number_of_generics early

Author: BoxyUwU

compiler/rustc_typeck/src/check/compare_method.rs

@@ -579,6 +579,27 @@ fn compare_self_type<'tcx>(
     Ok(())
 }
 
+/// Checks that the number of generics on a given assoc item in a trait impl is the same
+/// as the number of generics on the respective assoc item in the trait definition.
+///
+/// For example this code emits the errors in the following code:
+/// ```
+/// trait Trait {
+///     fn foo();
+///     type Assoc<T>;
+/// }
+///
+/// impl Trait for () {
+///     fn foo<T>() {}
+///     //~^ error
+///     type Assoc = u32;
+///     //~^ error
+/// }
+/// ```
+///
+/// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
+/// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
+/// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
 fn compare_number_of_generics<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_: &ty::AssocItem,
@@ -589,6 +610,15 @@ fn compare_number_of_generics<'tcx>(
     let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
     let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
 
+    // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
+    // in `compare_generic_param_kinds` which will give a nicer error message than something like:
+    // "expected 1 type parameter, found 0 type parameters"
+    if (trait_own_counts.types + trait_own_counts.consts)
+        == (impl_own_counts.types + impl_own_counts.consts)
+    {
+        return Ok(());
+    }
+
     let matchings = [
         ("type", trait_own_counts.types, impl_own_counts.types),
         ("const", trait_own_counts.consts, impl_own_counts.consts),

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

@@ -3,7 +3,7 @@ trait Trait {
 }
 impl Trait for () {
     fn foo<const M: u64>() {}
-    //~^ error: method `foo` has an incompatble generic parameter for trait
+    //~^ error: method `foo` has an incompatible generic parameter for trait
 }
 
 trait Other {
@@ -19,7 +19,7 @@ trait Uwu {
 }
 impl Uwu for () {
     fn baz<const N: i32>() {}
-    //~^ error: method `baz` has an incompatible generic parameter for trait
+    //~^ error: method `baz` has an incompatible const parameter type for trait
 }
 
 fn main() {}

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

@@ -1,38 +1,26 @@
-error[E0049]: method `foo` has 0 type parameters but its trait declaration has 1 type parameter
+error[E0053]: method `foo` has an incompatible generic parameter for trait
   --> $DIR/mismatched_ty_const_in_trait_impl.rs:5:12
    |
-LL |     fn foo<U>() {}
-   |            - expected 1 type parameter
-...
 LL |     fn foo<const M: u64>() {}
-   |            ^^^^^^^^^^^^ found 0 type parameters
-
-error[E0049]: method `foo` has 1 const parameter but its trait declaration has 0 const parameters
-  --> $DIR/mismatched_ty_const_in_trait_impl.rs:5:12
+   |            ^^^^^^^^^^^^
+   |
+note: the trait impl specifies `M` is a const parameter of type `u64`, but the declaration in trait `Trait::foo` requires it is a type parameter
+  --> $DIR/mismatched_ty_const_in_trait_impl.rs:2:12
    |
 LL |     fn foo<U>() {}
-   |            - expected 0 const parameters
-...
-LL |     fn foo<const M: u64>() {}
-   |            ^^^^^^^^^^^^ found 1 const parameter
+   |            ^
 
-error[E0049]: method `bar` has 1 type parameter but its trait declaration has 0 type parameters
+error[E0053]: method `bar` has an incompatible generic parameter for trait
   --> $DIR/mismatched_ty_const_in_trait_impl.rs:13:12
    |
-LL |     fn bar<const M: u8>() {}
-   |            ----------- expected 0 type parameters
-...
 LL |     fn bar<T>() {}
-   |            ^ found 1 type parameter
-
-error[E0049]: method `bar` has 0 const parameters but its trait declaration has 1 const parameter
-  --> $DIR/mismatched_ty_const_in_trait_impl.rs:13:12
+   |            ^
+   |
+note: the trait impl specifies `T` is a type parameter, but the declaration in trait `Other::bar` requires it is a const parameter of type `u8`
+  --> $DIR/mismatched_ty_const_in_trait_impl.rs:10:12
    |
 LL |     fn bar<const M: u8>() {}
-   |            ----------- expected 1 const parameter
-...
-LL |     fn bar<T>() {}
-   |            ^ found 0 const parameters
+   |            ^^^^^^^^^^^
 
 error[E0053]: method `baz` has an incompatible const parameter type for trait
   --> $DIR/mismatched_ty_const_in_trait_impl.rs:21:12
@@ -46,7 +34,6 @@ note: the const parameter `N` has type `i32`, but the declaration in trait `Uwu:
 LL |     fn baz<const N: u32>() {}
    |            ^^^^^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0049, E0053.
-For more information about an error, try `rustc --explain E0049`.
+For more information about this error, try `rustc --explain E0053`.

src/test/ui/generic-associated-types/const_params_have_right_type.rs

@@ -6,7 +6,7 @@ trait Trait {
 
 impl Trait for () {
     type Foo<const N: u64> = u32;
-    //~^ error: associated type `Foo` has an incompatible const parameter type
+    //~^ error: type `Foo` has an incompatible const parameter type
 }
 
 fn main() {}

src/test/ui/generic-associated-types/const_params_have_right_type.stderr

@@ -1,4 +1,4 @@
-error[E0053]: associated type `Foo` has an incompatible const parameter type for trait
+error[E0053]: type `Foo` has an incompatible const parameter type for trait
   --> $DIR/const_params_have_right_type.rs:8:14
    |
 LL |     type Foo<const N: u64> = u32;