Add new tests, fix up old tests

src/test/ui/autoref-autoderef/deref-into-array.rs

@@ -0,0 +1,17 @@
+// check-pass
+
+struct Test<T>([T; 1]);
+
+impl<T> std::ops::Deref for Test<T> {
+    type Target = [T; 1];
+
+    fn deref(&self) -> &[T; 1] {
+        &self.0
+    }
+}
+
+fn main() {
+    let out = Test([(); 1]);
+    let blah = out.len();
+    println!("{}", blah);
+}

src/test/ui/coercion/issue-73886.rs

@@ -1,6 +1,4 @@
 fn main() {
-    let _ = &&[0] as &[_];
-    //~^ ERROR non-primitive cast: `&&[i32; 1]` as `&[_]`
     let _ = 7u32 as Option<_>;
     //~^ ERROR non-primitive cast: `u32` as `Option<_>`
 }

src/test/ui/coercion/issue-73886.stderr

@@ -1,17 +1,11 @@
-error[E0605]: non-primitive cast: `&&[i32; 1]` as `&[_]`
-  --> $DIR/issue-73886.rs:2:13
-   |
-LL |     let _ = &&[0] as &[_];
-   |             ^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
-
 error[E0605]: non-primitive cast: `u32` as `Option<_>`
-  --> $DIR/issue-73886.rs:4:13
+  --> $DIR/issue-73886.rs:2:13
    |
 LL |     let _ = 7u32 as Option<_>;
    |             ^^^^^^^^^^^^^^^^^ help: consider using the `From` trait instead: `Option<_>::from(7u32)`
    |
    = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0605`.

src/test/ui/const-generics/deref-into-array-generic.rs

@@ -0,0 +1,27 @@
+// check-pass
+
+struct Test<T, const N: usize>([T; N]);
+
+impl<T: Copy + Default, const N: usize> Default for Test<T, N> {
+    fn default() -> Self {
+        Self([T::default(); N])
+    }
+}
+
+impl<T, const N: usize> std::ops::Deref for Test<T, N> {
+    type Target = [T; N];
+
+    fn deref(&self) -> &[T; N] {
+        &self.0
+    }
+}
+
+fn test() -> Test<u64, 16> {
+    let test = Test::default();
+    println!("{}", test.len());
+    test
+}
+
+fn main() {
+    test();
+}