Add two const generics regression tests

src/test/ui/const-generics/issue-61522-array-len-succ.rs

@@ -0,0 +1,14 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+pub struct MyArray<const COUNT: usize>([u8; COUNT + 1]);
+//~^ ERROR constant expression depends on a generic parameter
+
+impl<const COUNT: usize> MyArray<COUNT> {
+    fn inner(&self) -> &[u8; COUNT + 1] {
+        //~^ ERROR constant expression depends on a generic parameter
+        &self.0
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/issue-61522-array-len-succ.stderr

@@ -0,0 +1,26 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61522-array-len-succ.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: constant expression depends on a generic parameter
+  --> $DIR/issue-61522-array-len-succ.rs:4:40
+   |
+LL | pub struct MyArray<const COUNT: usize>([u8; COUNT + 1]);
+   |                                        ^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error: constant expression depends on a generic parameter
+  --> $DIR/issue-61522-array-len-succ.rs:8:24
+   |
+LL |     fn inner(&self) -> &[u8; COUNT + 1] {
+   |                        ^^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error: aborting due to 2 previous errors
+

src/test/ui/const-generics/issue-66596-impl-trait-for-str-const-arg.rs

@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+trait Trait<const NAME: &'static str> {
+    type Assoc;
+}
+
+impl Trait<"0"> for () {
+    type Assoc = ();
+}
+
+fn main() {
+    let _: <() as Trait<"0">>::Assoc = ();
+}

src/test/ui/const-generics/issue-66596-impl-trait-for-str-const-arg.stderr

@@ -0,0 +1,8 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-66596-impl-trait-for-str-const-arg.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+