add a ui test specifically for linked issue 69232

Author: HTGAzureX1212

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -663,7 +663,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     p!(print_def_path(def_id, args));
                 } else {
                     let sig = self.tcx().fn_sig(def_id).instantiate(self.tcx(), args);
-                    p!("{{fn item ", print_value_path(def_id, args), " :", print(sig), "}}");
+                    p!("{{fn item ", print_value_path(def_id, args), ": ", print(sig), "}}");
                 }
             }
             ty::FnPtr(ref bare_fn) => p!(print(bare_fn)),

tests/ui/c-variadic/issue-69232.rs

@@ -0,0 +1,11 @@
+extern "C" {
+    fn foo(x: usize, ...);
+}
+
+fn test() -> u8 {
+    127
+}
+
+fn main() {
+    foo(1, test);
+}

tests/ui/c-variadic/issue-69232.stderr

@@ -0,0 +1,20 @@
+error[E0617]: can't pass `{fn item test: fn() -> u8}` to variadic function
+  --> $DIR/issue-69232.rs:10:12
+   |
+LL |     foo(1, test);
+   |            ^^^^
+   |
+   = help: a function item is zero-sized and needs to be casted into a function pointer to be used in FFI
+   = note: for more information on function items, visit https://doc.rust-lang.org/reference/types/function-item.html
+help: cast the value to `fn() -> u8`
+   |
+LL |     foo(1, test as fn() -> u8);
+   |            ~~~~~~~~~~~~~~~~~~
+help: cast the value into a function pointer
+   |
+LL |     foo(1, test as fn() -> u8);
+   |            ~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0617`.