const_evaluatable_checked: fix occurs check

src/test/ui/const-generics/occurs-check/unused-substs-5.rs

@@ -0,0 +1,20 @@
+#![feature(const_generics, const_evaluatable_checked)]
+#![allow(incomplete_features)]
+
+// `N + 1` also depends on `T` here even if it doesn't use it.
+fn q<T, const N: usize>(_: T) -> [u8; N + 1] {
+    todo!()
+}
+
+fn supplier<T>() -> T {
+    todo!()
+}
+
+fn catch_me<const N: usize>() where [u8; N + 1]: Default {
+    let mut x = supplier();
+    x = q::<_, N>(x); //~ ERROR mismatched types
+}
+
+fn main() {
+    catch_me::<3>();
+}

src/test/ui/const-generics/occurs-check/unused-substs-5.stderr

@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> $DIR/unused-substs-5.rs:15:9
+   |
+LL |     x = q::<_, N>(x);
+   |         ^^^^^^^^^^^^
+   |         |
+   |         cyclic type of infinite size
+   |         help: try using a conversion method: `q::<_, N>(x).to_vec()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.