Don't drop PResult without handling the error

Author: LeSeulArtichaut

compiler/rustc_parse/src/parser/item.rs

@@ -1474,7 +1474,10 @@ impl<'a> Parser<'a> {
                 self.sess.gated_spans.gate(sym::unnamed_fields, lo);
             } else {
                 let err = if self.check_fn_front_matter(false) {
-                    let _ = self.parse_fn(&mut Vec::new(), |_| true, lo);
+                    // We use `parse_fn` to get a span for the function
+                    if let Err(mut db) = self.parse_fn(&mut Vec::new(), |_| true, lo) {
+                        db.delay_as_bug();
+                    }
                     let mut err = self.struct_span_err(
                         lo.to(self.prev_token.span),
                         &format!("functions are not allowed in {} definitions", adt_ty),

src/test/ui/parser/fn-field-parse-error-ice.rs

@@ -0,0 +1,10 @@
+// Regression test for #85794
+
+struct Baz {
+    inner : dyn fn ()
+    //~^ ERROR expected `,`, or `}`, found keyword `fn`
+    //~| ERROR functions are not allowed in struct definitions
+    //~| ERROR cannot find type `dyn` in this scope
+}
+
+fn main() {}

src/test/ui/parser/fn-field-parse-error-ice.stderr

@@ -0,0 +1,24 @@
+error: expected `,`, or `}`, found keyword `fn`
+  --> $DIR/fn-field-parse-error-ice.rs:4:16
+   |
+LL |     inner : dyn fn ()
+   |                ^ help: try adding a comma: `,`
+
+error: functions are not allowed in struct definitions
+  --> $DIR/fn-field-parse-error-ice.rs:4:17
+   |
+LL |     inner : dyn fn ()
+   |                 ^^
+   |
+   = help: unlike in C++, Java, and C#, functions are declared in `impl` blocks
+   = help: see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information
+
+error[E0412]: cannot find type `dyn` in this scope
+  --> $DIR/fn-field-parse-error-ice.rs:4:13
+   |
+LL |     inner : dyn fn ()
+   |             ^^^ not found in this scope
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0412`.