Rollup merge of rust-lang#91385 - ecstatic-morse:pat-param-spec-suggest, r=estebank

Suggest the `pat_param` specifier before `|` on 2021 edition

Ran into this today after writing some Rust for the first time in a while.

r? `@estebank`

Author: matthiaskrgr

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -1027,6 +1027,24 @@ fn check_matcher_core(
                                 ),
                             );
                             err.span_label(sp, format!("not allowed after `{}` fragments", kind));
+
+                            if kind == NonterminalKind::PatWithOr
+                                && sess.edition == Edition::Edition2021
+                                && next_token.is_token(&BinOp(token::BinOpToken::Or))
+                            {
+                                let suggestion = quoted_tt_to_string(&TokenTree::MetaVarDecl(
+                                    span,
+                                    name,
+                                    Some(NonterminalKind::PatParam { inferred: false }),
+                                ));
+                                err.span_suggestion(
+                                    span,
+                                    &format!("try a `pat_param` fragment specifier instead"),
+                                    suggestion,
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+
                             let msg = "allowed there are: ";
                             match possible {
                                 &[] => {}

src/test/ui/macros/macro-pat-pattern-followed-by-or-in-2021.stderr

@@ -2,23 +2,29 @@ error: `$x:pat` is followed by `|`, which is not allowed for `pat` fragments
   --> $DIR/macro-pat-pattern-followed-by-or-in-2021.rs:3:28
    |
 LL | macro_rules! foo { ($x:pat | $y:pat) => {} }
-   |                            ^ not allowed after `pat` fragments
+   |                     ------ ^ not allowed after `pat` fragments
+   |                     |
+   |                     help: try a `pat_param` fragment specifier instead: `$x:pat_param`
    |
    = note: allowed there are: `=>`, `,`, `=`, `if` or `in`
 
 error: `$x:pat` is followed by `|`, which is not allowed for `pat` fragments
   --> $DIR/macro-pat-pattern-followed-by-or-in-2021.rs:4:32
    |
 LL | macro_rules! bar { ($($x:pat)+ | $($y:pat)+) => {} }
-   |                                ^ not allowed after `pat` fragments
+   |                       ------   ^ not allowed after `pat` fragments
+   |                       |
+   |                       help: try a `pat_param` fragment specifier instead: `$x:pat_param`
    |
    = note: allowed there are: `=>`, `,`, `=`, `if` or `in`
 
 error: `$pat:pat` may be followed by `|`, which is not allowed for `pat` fragments
   --> $DIR/macro-pat-pattern-followed-by-or-in-2021.rs:7:36
    |
 LL |     ( $expr:expr , $( $( $pat:pat )|+ => $expr_arm:expr ),+ ) => {
-   |                                    ^ not allowed after `pat` fragments
+   |                          --------  ^ not allowed after `pat` fragments
+   |                          |
+   |                          help: try a `pat_param` fragment specifier instead: `$pat:pat_param`
    |
    = note: allowed there are: `=>`, `,`, `=`, `if` or `in`
 

src/test/ui/macros/macro-pat2021-pattern-followed-by-or.stderr

@@ -2,23 +2,29 @@ error: `$x:pat` is followed by `|`, which is not allowed for `pat` fragments
   --> $DIR/macro-pat2021-pattern-followed-by-or.rs:4:28
    |
 LL | macro_rules! foo { ($x:pat | $y:pat) => {} }
-   |                            ^ not allowed after `pat` fragments
+   |                     ------ ^ not allowed after `pat` fragments
+   |                     |
+   |                     help: try a `pat_param` fragment specifier instead: `$x:pat_param`
    |
    = note: allowed there are: `=>`, `,`, `=`, `if` or `in`
 
 error: `$x:pat` is followed by `|`, which is not allowed for `pat` fragments
   --> $DIR/macro-pat2021-pattern-followed-by-or.rs:7:28
    |
 LL | macro_rules! ogg { ($x:pat | $y:pat_param) => {} }
-   |                            ^ not allowed after `pat` fragments
+   |                     ------ ^ not allowed after `pat` fragments
+   |                     |
+   |                     help: try a `pat_param` fragment specifier instead: `$x:pat_param`
    |
    = note: allowed there are: `=>`, `,`, `=`, `if` or `in`
 
 error: `$pat:pat` may be followed by `|`, which is not allowed for `pat` fragments
   --> $DIR/macro-pat2021-pattern-followed-by-or.rs:9:35
    |
 LL |     ( $expr:expr , $( $( $pat:pat)|+ => $expr_arm:pat),+ ) => {
-   |                                   ^ not allowed after `pat` fragments
+   |                          -------- ^ not allowed after `pat` fragments
+   |                          |
+   |                          help: try a `pat_param` fragment specifier instead: `$pat:pat_param`
    |
    = note: allowed there are: `=>`, `,`, `=`, `if` or `in`