Rollup merge of #68143 - skinny121:const-param-type-elided-lifetime, r=petrochenkov

Forbid elided lifetimes within const generic parameter types

Disallows `fn foo<const T: &u32>()`, the lifetime must be explicitly given, i.e. `fn foo<const T: &'static u32>()`.

Fixes #67883

src/test/ui/const-generics/const-param-elided-lifetime.rs

@@ -0,0 +1,24 @@
+// Elided lifetimes within the type of a const generic parameters is disallowed. This matches the
+// behaviour of trait bounds where `fn foo<T: Ord<&u8>>() {}` is illegal. Though we could change
+// elided lifetimes within the type of a const generic parameters to be 'static, like elided
+// lifetimes within const/static items.
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct A<const N: &u8>;
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+trait B {}
+
+impl<const N: &u8> A<N> { //~ ERROR `&` without an explicit lifetime name cannot be used here
+    fn foo<const M: &u8>(&self) {}
+    //~^ ERROR `&` without an explicit lifetime name cannot be used here
+}
+
+impl<const N: &u8> B for A<N> {}
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+
+fn bar<const N: &u8>() {}
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+
+fn main() {}

src/test/ui/const-generics/const-param-elided-lifetime.stderr

@@ -0,0 +1,40 @@
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/const-param-elided-lifetime.rs:9:19
+   |
+LL | struct A<const N: &u8>;
+   |                   ^ explicit lifetime name needed here
+
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/const-param-elided-lifetime.rs:13:15
+   |
+LL | impl<const N: &u8> A<N> {
+   |               ^ explicit lifetime name needed here
+
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/const-param-elided-lifetime.rs:14:21
+   |
+LL |     fn foo<const M: &u8>(&self) {}
+   |                     ^ explicit lifetime name needed here
+
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/const-param-elided-lifetime.rs:18:15
+   |
+LL | impl<const N: &u8> B for A<N> {}
+   |               ^ explicit lifetime name needed here
+
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/const-param-elided-lifetime.rs:21:17
+   |
+LL | fn bar<const N: &u8>() {}
+   |                 ^ explicit lifetime name needed here
+
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/const-param-elided-lifetime.rs:6:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: aborting due to 5 previous errors
+