Rollup merge of rust-lang#99435 - CAD97:revert-dollar-dollar-crate, r…

…=Mark-Simulacrum

Revert "Stabilize $$ in Rust 1.63.0"

This mechanically reverts commit 9edaa76, the one commit from rust-lang#95860.

rust-lang#99035; the behavior of `$$crate` is potentially unexpected and not ready to be stabilized. rust-lang#99193 attempts to forbid `$$crate` without also destabilizing `$$` more generally.

`@rustbot` modify labels +T-compiler +T-lang +P-medium +beta-nominated +relnotes

(applying the labels I think are accurate from the issue and alternative partial revert)

cc `@Mark-Simulacrum`

compiler/rustc_expand/src/mbe/quoted.rs

@@ -234,6 +234,8 @@ fn parse_tree(
                             sess,
                             &Token { kind: token::Dollar, span },
                         );
+                    } else {
+                        maybe_emit_macro_metavar_expr_feature(features, sess, span);
                     }
                     TokenTree::token(token::Dollar, span)
                 }

src/test/ui/macros/rfc-3086-metavar-expr/required-features.rs → src/test/ui/macros/rfc-3086-metavar-expr/required-feature.rs

@@ -5,6 +5,18 @@ macro_rules! count {
     };
 }
 
+macro_rules! dollar_dollar {
+    () => {
+        macro_rules! bar {
+            ( $$( $$any:tt )* ) => { $$( $$any )* };
+            //~^ ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+        }
+    };
+}
+
 macro_rules! index {
     ( $( $e:stmt ),* ) => {
         $( ${ignore(e)} ${index()} )*

src/test/ui/macros/rfc-3086-metavar-expr/required-features.stderr → src/test/ui/macros/rfc-3086-metavar-expr/required-feature.stderr

@@ -1,5 +1,5 @@
 error[E0658]: meta-variable expressions are unstable
-  --> $DIR/required-features.rs:3:10
+  --> $DIR/required-feature.rs:3:10
    |
 LL |         ${ count(e) }
    |          ^^^^^^^^^^^^
@@ -8,7 +8,43 @@ LL |         ${ count(e) }
    = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
 
 error[E0658]: meta-variable expressions are unstable
-  --> $DIR/required-features.rs:10:13
+  --> $DIR/required-feature.rs:11:16
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:20
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                    ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:39
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                                       ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:43
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                                           ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:22:13
    |
 LL |         $( ${ignore(e)} ${index()} )*
    |             ^^^^^^^^^^^
@@ -17,7 +53,7 @@ LL |         $( ${ignore(e)} ${index()} )*
    = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
 
 error[E0658]: meta-variable expressions are unstable
-  --> $DIR/required-features.rs:10:26
+  --> $DIR/required-feature.rs:22:26
    |
 LL |         $( ${ignore(e)} ${index()} )*
    |                          ^^^^^^^^^
@@ -26,7 +62,7 @@ LL |         $( ${ignore(e)} ${index()} )*
    = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
 
 error[E0658]: meta-variable expressions are unstable
-  --> $DIR/required-features.rs:18:19
+  --> $DIR/required-feature.rs:30:19
    |
 LL |         0 $( + 1 ${ignore(i)} )*
    |                   ^^^^^^^^^^^
@@ -35,7 +71,7 @@ LL |         0 $( + 1 ${ignore(i)} )*
    = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
 
 error[E0658]: meta-variable expressions are unstable
-  --> $DIR/required-features.rs:25:13
+  --> $DIR/required-feature.rs:37:13
    |
 LL |         $( ${ignore(e)} ${length()} )*
    |             ^^^^^^^^^^^
@@ -44,14 +80,14 @@ LL |         $( ${ignore(e)} ${length()} )*
    = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
 
 error[E0658]: meta-variable expressions are unstable
-  --> $DIR/required-features.rs:25:26
+  --> $DIR/required-feature.rs:37:26
    |
 LL |         $( ${ignore(e)} ${length()} )*
    |                          ^^^^^^^^^^
    |
    = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
    = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
 
-error: aborting due to 6 previous errors
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0658`.