[WIP] const-stabilize Hash{Map/Set}::new

compiler/rustc_const_eval/messages.ftl

@@ -385,7 +385,9 @@ const_eval_unreachable_unwind =
 const_eval_unsigned_offset_from_overflow =
     `ptr_offset_from_unsigned` called when first pointer has smaller offset than second: {$a_offset} < {$b_offset}
 const_eval_unsized_local = unsized locals are not supported
+
 const_eval_unstable_const_fn = `{$def_path}` is not yet stable as a const fn
+const_eval_unstable_declared_here = `{$def_path}` declared unstable here
 
 const_eval_unstable_in_stable =
     const-stable function cannot use `#[feature({$gate})]`

compiler/rustc_const_eval/src/errors.rs

@@ -129,6 +129,9 @@ pub(crate) struct UnstableConstFn {
     #[primary_span]
     pub span: Span,
     pub def_path: String,
+
+    #[label(const_eval_unstable_declared_here)]
+    pub declared: Span,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -992,8 +992,10 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     // `extern` functions, and these have no way to get marked `const`. So instead we
                     // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
                     if self.ccx.is_const_stable_const_fn() || tcx.is_intrinsic(callee) {
-                        self.check_op(ops::FnCallUnstable(callee, None));
-                        return;
+                        if !super::rustc_allow_const_fn_unstable(tcx, caller, sym::any) {
+                            self.check_op(ops::FnCallUnstable(callee, None));
+                            return;
+                        }
                     }
                 }
                 trace!("permitting call");

compiler/rustc_const_eval/src/transform/check_consts/ops.rs

@@ -339,10 +339,11 @@ impl<'tcx> NonConstOp<'tcx> for FnCallUnstable {
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         let FnCallUnstable(def_id, feature) = *self;
 
-        let mut err = ccx
-            .tcx
-            .sess
-            .create_err(errors::UnstableConstFn { span, def_path: ccx.tcx.def_path_str(def_id) });
+        let mut err = ccx.tcx.sess.create_err(errors::UnstableConstFn {
+            span,
+            def_path: ccx.tcx.def_path_str(def_id),
+            declared: ccx.tcx.def_span(def_id),
+        });
 
         if ccx.is_const_stable_const_fn() {
             err.help("const-stable functions can only call other const-stable functions");

library/std/src/collections/hash/map.rs

@@ -282,7 +282,18 @@ impl<K, V, S> HashMap<K, V, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    #[rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")]
+    #[cfg_attr(
+        bootstrap,
+        rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")
+    )]
+    #[cfg_attr(
+        not(bootstrap),
+        rustc_const_stable(
+            feature = "const_collections_with_hasher",
+            since = "CURRENT_RUSTC_VERSION"
+        )
+    )]
+    #[rustc_allow_const_fn_unstable(any)]
     pub const fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
         HashMap { base: base::HashMap::with_hasher(hash_builder) }
     }

library/std/src/collections/hash/set.rs

@@ -369,7 +369,18 @@ impl<T, S> HashSet<T, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    #[rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")]
+    #[cfg_attr(
+        bootstrap,
+        rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")
+    )]
+    #[cfg_attr(
+        not(bootstrap),
+        rustc_const_stable(
+            feature = "const_collections_with_hasher",
+            since = "CURRENT_RUSTC_VERSION"
+        )
+    )]
+    #[rustc_allow_const_fn_unstable(any)]
     pub const fn with_hasher(hasher: S) -> HashSet<T, S> {
         HashSet { base: base::HashSet::with_hasher(hasher) }
     }

library/std/src/lib.rs

@@ -297,6 +297,7 @@
 #![feature(no_sanitize)]
 #![feature(platform_intrinsics)]
 #![feature(prelude_import)]
+#![feature(rustc_allow_const_fn_unstable)]
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]
 #![feature(staged_api)]
@@ -308,6 +309,7 @@
 //
 // Library features (core):
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(const_collections_with_hasher))]
 #![feature(char_internals)]
 #![feature(core_intrinsics)]
 #![feature(duration_constants)]
@@ -387,7 +389,6 @@
 //
 // Only for const-ness:
 // tidy-alphabetical-start
-#![feature(const_collections_with_hasher)]
 #![feature(const_hash)]
 #![feature(const_io_structs)]
 #![feature(const_ip)]