stop returning errors when format foreign has trailing dollar

Author: TaKO8Ki

compiler/rustc_builtin_macros/src/format_foreign.rs

@@ -416,7 +416,7 @@ pub(crate) mod printf {
                         // Yes, this *is* the parameter.
                         Some(('$', end2)) => {
                             state = Flags;
-                            parameter = Some(at.slice_between(end).unwrap().parse().unwrap());
+                            parameter = at.slice_between(end).unwrap().parse().ok();
                             move_to!(end2);
                         }
                         // Wait, no, actually, it's the width.

tests/ui/macros/format-foreign-dollar-without-spec.rs

@@ -0,0 +1,4 @@
+fn main() {
+    println!("%65536$", 1);
+    //~^ ERROR never used
+}

tests/ui/macros/format-foreign-dollar-without-spec.stderr

@@ -0,0 +1,16 @@
+error: argument never used
+  --> $DIR/format-foreign-dollar-without-spec.rs:2:25
+   |
+LL |     println!("%65536$", 1);
+   |                         ^ argument never used
+   |
+note: format specifiers use curly braces, and the conversion specifier `
+      ` is unknown or unsupported
+  --> $DIR/format-foreign-dollar-without-spec.rs:2:15
+   |
+LL |     println!("%65536$", 1);
+   |               ^^^^^^^^
+   = note: printf formatting is not supported; see the documentation for `std::fmt`
+
+error: aborting due to 1 previous error
+