fix: revert from macro_metavar_expr usage to custom hash_map_internals macro for constant count in with_capacity invocation

Author: stifskere

library/std/src/lib.rs

@@ -294,6 +294,7 @@
 #![feature(f128)]
 #![feature(ffi_const)]
 #![feature(formatting_options)]
+#![feature(hash_map_internals)]
 #![feature(hash_map_macro)]
 #![feature(if_let_guard)]
 #![feature(intra_doc_pointers)]
@@ -302,7 +303,6 @@
 #![feature(lang_items)]
 #![feature(link_cfg)]
 #![feature(linkage)]
-#![feature(macro_metavar_expr)]
 #![feature(macro_metavar_expr_concat)]
 #![feature(maybe_uninit_fill)]
 #![feature(min_specialization)]

library/std/src/macros.rs

@@ -380,6 +380,17 @@ macro_rules! dbg {
     };
 }
 
+#[doc(hidden)]
+#[macro_export]
+#[unstable(feature = "hash_map_internals", issue = "none")]
+macro_rules! repetition_utils {
+    (@count $($tokens:tt),*) => {{
+        [$($crate::repetition_count!(@replace $tokens => ())),*].len()
+    }};
+
+    (@replace $x:tt => $y:tt) => { $y }
+}
+
 /// Creates a [`HashMap`] containing the arguments.
 ///
 /// This macro creates or either an empty [`HashMap`] using
@@ -423,15 +434,17 @@ macro_rules! dbg {
 /// [`HashMap::new`]: crate::collections::HashMap::new
 /// [`HashMap::insert`]: crate::collections::HashMap::insert
 #[macro_export]
-#[allow_internal_unstable(macro_metavar_expr)]
+#[allow_internal_unstable(hash_map_internals)]
 #[unstable(feature = "hash_map_macro", issue = "144032")]
 macro_rules! hash_map {
     () => {{
         $crate::collections::HashMap::new()
     }};
 
     ( $( $key:expr => $value:expr ),* $(,)? ) => {{
-        let mut map = $crate::collections::HashMap::with_capacity( ${count($key)} );
+        let mut map = $crate::collections::HashMap::with_capacity(
+            const { $crate::repetition_utils(@count $($key),*) }
+        );
         $( map.insert($key, $value); )*
         map
     }}