Add test for issue-72352

Author: JohnTitor

src/test/ui/const-generics/issues/issue-72352.rs

@@ -0,0 +1,21 @@
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+use std::ffi::{CStr, CString};
+
+unsafe fn unsafely_do_the_thing<const F: fn(&CStr) -> usize>(ptr: *const i8) -> usize {
+    //~^ ERROR: using function pointers as const generic parameters is forbidden
+    F(CStr::from_ptr(ptr))
+}
+
+fn safely_do_the_thing(s: &CStr) -> usize {
+    s.to_bytes().len()
+}
+
+fn main() {
+    let baguette = CString::new("baguette").unwrap();
+    let ptr = baguette.as_ptr();
+    println!("{}", unsafe {
+        unsafely_do_the_thing::<safely_do_the_thing>(ptr)
+    });
+}

src/test/ui/const-generics/issues/issue-72352.stderr

@@ -0,0 +1,8 @@
+error: using function pointers as const generic parameters is forbidden
+  --> $DIR/issue-72352.rs:6:42
+   |
+LL | unsafe fn unsafely_do_the_thing<const F: fn(&CStr) -> usize>(ptr: *const i8) -> usize {
+   |                                          ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+