Auto merge of #55451 - estebank:arg-doc, r=pnkfelix

Custom diagnostic when trying to doc comment argument

When writing

```
pub fn f(
    /// Comment
    id: u8,
) {}
```

Produce a targeted diagnostic

```
error: documentation comments cannot be applied to method arguments
  --> $DIR/fn-arg-doc-comment.rs:2:5
   |
LL |     /// Comment
   |     ^^^^^^^^^^^ doc comments are not allowed here
```

Fix #54801.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libsyntax/util/parser_testing.rs b/src/libsyntax/util/parser_testing.rs
index 374154e6333..98e9272e6d8 100644
--- a/src/libsyntax/util/parser_testing.rs
+++ b/src/libsyntax/util/parser_testing.rs
@@ -68,7 +68,7 @@ pub fn string_to_item (source_str : String) -> Option<P<ast::Item>> {
 pub fn string_to_pat(source_str: String) -> P<ast::Pat> {
     let ps = ParseSess::new(FilePathMapping::empty());
     with_error_checking_parse(source_str, &ps, |p| {
-        p.parse_pat()
+        p.parse_pat(None)
     })
 }