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.

src/test/ui/label/label_break_value_illegal_uses.stderr

@@ -27,7 +27,9 @@ error: expected one of `.`, `?`, `{`, or an operator, found `'b`
   --> $DIR/label_break_value_illegal_uses.rs:28:17
    |
 LL |     match false 'b: {} //~ ERROR expected one of `.`, `?`, `{`, or an operator
-   |                 ^^ expected one of `.`, `?`, `{`, or an operator here
+   |     -----       ^^ expected one of `.`, `?`, `{`, or an operator here
+   |     |
+   |     while parsing this match expression
 
 error: aborting due to 4 previous errors
 

src/test/ui/parser/fn-arg-doc-comment.rs

@@ -0,0 +1,37 @@
+pub fn f(
+    /// Comment
+    //~^ ERROR documentation comments cannot be applied to method arguments
+    //~| NOTE doc comments are not allowed here
+    id: u8,
+    /// Other
+    //~^ ERROR documentation comments cannot be applied to method arguments
+    //~| NOTE doc comments are not allowed here
+    a: u8,
+) {}
+
+fn foo(#[allow(dead_code)] id: i32) {}
+//~^ ERROR attributes cannot be applied to method arguments
+//~| NOTE attributes are not allowed here
+
+fn bar(id: #[allow(dead_code)] i32) {}
+//~^ ERROR attributes cannot be applied to a method argument's type
+//~| NOTE attributes are not allowed here
+
+fn main() {
+    // verify that the parser recovered and properly typechecked the args
+    f("", "");
+    //~^ ERROR mismatched types
+    //~| NOTE expected u8, found reference
+    //~| NOTE expected
+    //~| ERROR mismatched types
+    //~| NOTE expected u8, found reference
+    //~| NOTE expected
+    foo("");
+    //~^ ERROR mismatched types
+    //~| NOTE expected i32, found reference
+    //~| NOTE expected
+    bar("");
+    //~^ ERROR mismatched types
+    //~| NOTE expected i32, found reference
+    //~| NOTE expected
+}

src/test/ui/parser/fn-arg-doc-comment.stderr

@@ -0,0 +1,63 @@
+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
+
+error: documentation comments cannot be applied to method arguments
+  --> $DIR/fn-arg-doc-comment.rs:6:5
+   |
+LL |     /// Other
+   |     ^^^^^^^^^ doc comments are not allowed here
+
+error: attributes cannot be applied to method arguments
+  --> $DIR/fn-arg-doc-comment.rs:12:8
+   |
+LL | fn foo(#[allow(dead_code)] id: i32) {}
+   |        ^^^^^^^^^^^^^^^^^^^ attributes are not allowed here
+
+error: attributes cannot be applied to a method argument's type
+  --> $DIR/fn-arg-doc-comment.rs:16:12
+   |
+LL | fn bar(id: #[allow(dead_code)] i32) {}
+   |            ^^^^^^^^^^^^^^^^^^^ attributes are not allowed here
+
+error[E0308]: mismatched types
+  --> $DIR/fn-arg-doc-comment.rs:22:7
+   |
+LL |     f("", "");
+   |       ^^ expected u8, found reference
+   |
+   = note: expected type `u8`
+              found type `&'static str`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-arg-doc-comment.rs:22:11
+   |
+LL |     f("", "");
+   |           ^^ expected u8, found reference
+   |
+   = note: expected type `u8`
+              found type `&'static str`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-arg-doc-comment.rs:29:9
+   |
+LL |     foo("");
+   |         ^^ expected i32, found reference
+   |
+   = note: expected type `i32`
+              found type `&'static str`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-arg-doc-comment.rs:33:9
+   |
+LL |     bar("");
+   |         ^^ expected i32, found reference
+   |
+   = note: expected type `i32`
+              found type `&'static str`
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/parser/issue-33413.rs

@@ -11,5 +11,6 @@
 // compile-flags: -Z parse-only
 
 impl S {
-    fn f(*, a: u8) -> u8 {} //~ ERROR expected pattern, found `*`
+    fn f(*, a: u8) -> u8 {}
+    //~^ ERROR expected argument name, found `*`
 }

src/test/ui/parser/issue-33413.stderr

@@ -1,8 +1,8 @@
-error: expected pattern, found `*`
+error: expected argument name, found `*`
   --> $DIR/issue-33413.rs:14:10
    |
-LL |     fn f(*, a: u8) -> u8 {} //~ ERROR expected pattern, found `*`
-   |          ^ expected pattern
+LL |     fn f(*, a: u8) -> u8 {}
+   |          ^ expected argument name
 
 error: aborting due to previous error
 

src/test/ui/parser/match-refactor-to-expr.rs

@@ -12,7 +12,7 @@
 
 fn main() {
     let foo =
-        match
+        match //~ NOTE while parsing this match expression
         Some(4).unwrap_or_else(5)
         //~^ NOTE expected one of `.`, `?`, `{`, or an operator here
         ; //~ NOTE unexpected token

src/test/ui/parser/match-refactor-to-expr.stderr

@@ -1,8 +1,11 @@
 error: expected one of `.`, `?`, `{`, or an operator, found `;`
   --> $DIR/match-refactor-to-expr.rs:18:9
    |
-LL |         match
-   |         ----- help: try removing this `match`
+LL |         match //~ NOTE while parsing this match expression
+   |         -----
+   |         |
+   |         while parsing this match expression
+   |         help: try removing this `match`
 LL |         Some(4).unwrap_or_else(5)
    |                                  - expected one of `.`, `?`, `{`, or an operator here
 LL |         //~^ NOTE expected one of `.`, `?`, `{`, or an operator here

src/test/ui/parser/removed-syntax-mode.rs

@@ -10,4 +10,5 @@
 
 // compile-flags: -Z parse-only
 
-fn f(+x: isize) {} //~ ERROR expected pattern, found `+`
+fn f(+x: isize) {}
+//~^ ERROR expected argument name, found `+`

src/test/ui/parser/removed-syntax-mode.stderr

@@ -1,8 +1,8 @@
-error: expected pattern, found `+`
+error: expected argument name, found `+`
   --> $DIR/removed-syntax-mode.rs:13:6
    |
-LL | fn f(+x: isize) {} //~ ERROR expected pattern, found `+`
-   |      ^ expected pattern
+LL | fn f(+x: isize) {}
+   |      ^ expected argument name
 
 error: aborting due to previous error
 

src/test/ui/try-block/try-block-in-match.stderr

@@ -2,7 +2,9 @@ error: expected expression, found reserved keyword `try`
   --> $DIR/try-block-in-match.rs:16:11
    |
 LL |     match try { false } { _ => {} } //~ ERROR expected expression, found reserved keyword `try`
-   |           ^^^ expected expression
+   |     ----- ^^^ expected expression
+   |     |
+   |     while parsing this match expression
 
 error: aborting due to previous error