Test diagnostic output of type mismatches for types that have const

generics arguments.

src/test/ui/const-generics/types-mismatch-const-args.rs

@@ -0,0 +1,19 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+// tests the diagnostic output of type mismatches for types that have const generics arguments.
+
+use std::marker::PhantomData;
+
+struct A<'a, T, const X: u32, const Y: u32> {
+    data: PhantomData<&'a T>
+}
+
+fn a<'a, 'b>() {
+    let _: A<'a, u32, {2u32}, {3u32}> = A::<'a, u32, {4u32}, {3u32}> { data: PhantomData };
+    //~^ ERROR mismatched types
+    let _: A<'a, u16, {2u32}, {3u32}> = A::<'b, u32, {2u32}, {3u32}> { data: PhantomData };
+    //~^ ERROR mismatched types
+}
+
+pub fn main() {}

src/test/ui/const-generics/types-mismatch-const-args.stderr

@@ -0,0 +1,29 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/types-mismatch-const-args.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0308]: mismatched types
+  --> $DIR/types-mismatch-const-args.rs:13:41
+   |
+LL |     let _: A<'a, u32, {2u32}, {3u32}> = A::<'a, u32, {4u32}, {3u32}> { data: PhantomData };
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `2u32`, found `4u32`
+   |
+   = note: expected type `A<'_, _, 2u32, _>`
+              found type `A<'_, _, 4u32, _>`
+
+error[E0308]: mismatched types
+  --> $DIR/types-mismatch-const-args.rs:15:41
+   |
+LL |     let _: A<'a, u16, {2u32}, {3u32}> = A::<'b, u32, {2u32}, {3u32}> { data: PhantomData };
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u16, found u32
+   |
+   = note: expected type `A<'a, u16, _, _>`
+              found type `A<'b, u32, _, _>`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.