Rollup merge of #89029 - notriddle:notriddle/issue-89013, r=estebank

feat(rustc_parse): recover from pre-RFC-2000 const generics syntax

Fixes #89013

src/test/ui/const-generics/parser-error-recovery/issue-89013-no-assoc.rs

@@ -0,0 +1,16 @@
+trait Foo<const N: usize> {
+    fn do_x(&self) -> [u8; N];
+}
+
+struct Bar;
+
+const T: usize = 42;
+
+impl Foo<const 3> for Bar {
+//~^ERROR expected lifetime, type, or constant, found keyword `const`
+    fn do_x(&self) -> [u8; 3] {
+        [0u8; 3]
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/parser-error-recovery/issue-89013-no-assoc.stderr

@@ -0,0 +1,14 @@
+error: expected lifetime, type, or constant, found keyword `const`
+  --> $DIR/issue-89013-no-assoc.rs:9:10
+   |
+LL | impl Foo<const 3> for Bar {
+   |          ^^^^^
+   |
+help: the `const` keyword is only needed in the definition of the type
+   |
+LL - impl Foo<const 3> for Bar {
+LL + impl Foo<3> for Bar {
+   | 
+
+error: aborting due to previous error
+

src/test/ui/const-generics/parser-error-recovery/issue-89013-no-kw.rs

@@ -0,0 +1,17 @@
+trait Foo<const N: usize> {
+    fn do_x(&self) -> [u8; N];
+}
+
+struct Bar;
+
+const T: usize = 42;
+
+impl Foo<N = 3> for Bar {
+//~^ ERROR cannot constrain an associated constant to a value
+//~| ERROR associated type bindings are not allowed here
+    fn do_x(&self) -> [u8; 3] {
+        [0u8; 3]
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/parser-error-recovery/issue-89013-no-kw.stderr

@@ -0,0 +1,18 @@
+error: cannot constrain an associated constant to a value
+  --> $DIR/issue-89013-no-kw.rs:9:10
+   |
+LL | impl Foo<N = 3> for Bar {
+   |          -^^^-
+   |          |   |
+   |          |   ...cannot be constrained to this value
+   |          this associated constant...
+
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-89013-no-kw.rs:9:10
+   |
+LL | impl Foo<N = 3> for Bar {
+   |          ^^^^^ associated type not allowed here
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0229`.

src/test/ui/const-generics/parser-error-recovery/issue-89013-type.rs

@@ -0,0 +1,16 @@
+trait Foo<const N: usize> {
+    fn do_x(&self) -> [u8; N];
+}
+
+struct Bar;
+
+const T: usize = 42;
+
+impl Foo<N = type 3> for Bar {
+//~^ERROR missing type to the right of `=`
+    fn do_x(&self) -> [u8; 3] {
+        [0u8; 3]
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/parser-error-recovery/issue-89013-type.stderr

@@ -0,0 +1,8 @@
+error: missing type to the right of `=`
+  --> $DIR/issue-89013-type.rs:9:13
+   |
+LL | impl Foo<N = type 3> for Bar {
+   |             ^---- expected type, found keyword `type`
+
+error: aborting due to previous error
+

src/test/ui/const-generics/parser-error-recovery/issue-89013.rs

@@ -0,0 +1,18 @@
+trait Foo<const N: usize> {
+    fn do_x(&self) -> [u8; N];
+}
+
+struct Bar;
+
+const T: usize = 42;
+
+impl Foo<N = const 3> for Bar {
+//~^ ERROR expected lifetime, type, or constant, found keyword `const`
+//~| ERROR cannot constrain an associated constant to a value
+//~| ERROR associated type bindings are not allowed here
+    fn do_x(&self) -> [u8; 3] {
+        [0u8; 3]
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/parser-error-recovery/issue-89013.stderr

@@ -0,0 +1,30 @@
+error: expected lifetime, type, or constant, found keyword `const`
+  --> $DIR/issue-89013.rs:9:14
+   |
+LL | impl Foo<N = const 3> for Bar {
+   |              ^^^^^
+   |
+help: the `const` keyword is only needed in the definition of the type
+   |
+LL - impl Foo<N = const 3> for Bar {
+LL + impl Foo<N = 3> for Bar {
+   | 
+
+error: cannot constrain an associated constant to a value
+  --> $DIR/issue-89013.rs:9:10
+   |
+LL | impl Foo<N = const 3> for Bar {
+   |          -^^^^^^^^^-
+   |          |         |
+   |          |         ...cannot be constrained to this value
+   |          this associated constant...
+
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-89013.rs:9:10
+   |
+LL | impl Foo<N = const 3> for Bar {
+   |          ^^^^^^^^^^^ associated type not allowed here
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0229`.