Rollup merge of rust-lang#105966 - compiler-errors:issue-105936, r=eholk

Re-enable `Fn` trait call notation error for non-tuple argument

I have no idea why I delayed this bug... but also there doesn't seem to be a UI test that actually shows a change, so maybe that's why.

Fixes rust-lang#105936

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -214,7 +214,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  "cannot use call notation; the first type parameter \
  for the function trait is neither a tuple nor unit"
  )
- .delay_as_bug();
+ .emit();
  (self.err_args(provided_args.len()), None)
  }
  }

src/test/ui/unboxed-closures/non-tupled-call.rs

@@ -0,0 +1,17 @@
+#![feature(fn_traits, unboxed_closures, tuple_trait)]
+
+use std::default::Default;
+use std::marker::Tuple;
+
+fn wrap<P: Tuple + Default, T>(func: impl Fn<P, Output = T>) {
+ let x: P = Default::default();
+ // Should be: `func.call(x);`
+ func(x);
+ //~^ ERROR cannot use call notation; the first type parameter for the function trait is neither a tuple nor unit
+}
+
+fn foo() {}
+
+fn main() {
+ wrap(foo);
+}

src/test/ui/unboxed-closures/non-tupled-call.stderr

@@ -0,0 +1,9 @@
+error[E0059]: cannot use call notation; the first type parameter for the function trait is neither a tuple nor unit
+ --> $DIR/non-tupled-call.rs:9:5
+ |
+LL | func(x);
+ | ^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0059`.