Auto merge of #108312 - michaelwoerister:hash-set-not-hash-stable, r=eholk

Do not implement HashStable for HashSet (MCP 533)

This PR removes all occurrences of `HashSet` in query results, replacing it either with `FxIndexSet` or with `UnordSet`, and then removes the `HashStable` implementation of `HashSet`. This is part of implementing [MCP 533](https://github.com/rust-lang/compiler-team/issues/533), that is, removing the `HashStable` implementations of all collection types with unstable iteration order.

The changes are mostly mechanical. The only place where additional sorting is happening is in Miri's override implementation of the `exported_symbols` query.

2 files changed, 36 insertions, 13 deletions

diff --git a/compiler/rustc_data_structures/src/stable_hasher.rs b/compiler/rustc_data_structures/src/stable_hasher.rs
index e0d77cdaebb..de9842156d6 100644
--- a/compiler/rustc_data_structures/src/stable_hasher.rs
+++ b/compiler/rustc_data_structures/src/stable_hasher.rs
@@ -617,18 +617,10 @@ where
     }
 }
 
-impl<K, R, HCX> HashStable<HCX> for ::std::collections::HashSet<K, R>
-where
-    K: ToStableHashKey<HCX> + Eq,
-    R: BuildHasher,
-{
-    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
-        stable_hash_reduce(hcx, hasher, self.iter(), self.len(), |hasher, hcx, key| {
-            let key = key.to_stable_hash_key(hcx);
-            key.hash_stable(hcx, hasher);
-        });
-    }
-}
+// It is not safe to implement HashStable for HashSet or any other collection type
+// with unstable but observable iteration order.
+// See https://github.com/rust-lang/compiler-team/issues/533 for further information.
+impl<V, HCX> !HashStable<HCX> for std::collections::HashSet<V> {}
 
 impl<K, V, HCX> HashStable<HCX> for ::std::collections::BTreeMap<K, V>
 where
diff --git a/compiler/rustc_data_structures/src/unord.rs b/compiler/rustc_data_structures/src/unord.rs
index f35f18e51cb..5c2435a0122 100644
--- a/compiler/rustc_data_structures/src/unord.rs
+++ b/compiler/rustc_data_structures/src/unord.rs
@@ -109,6 +109,12 @@ impl<T, I: Iterator<Item = T>> UnordItems<T, I> {
     }
 }
 
+impl<T> UnordItems<T, std::iter::Empty<T>> {
+    pub fn empty() -> Self {
+        UnordItems(std::iter::empty())
+    }
+}
+
 impl<'a, T: Clone + 'a, I: Iterator<Item = &'a T>> UnordItems<&'a T, I> {
     #[inline]
     pub fn cloned(self) -> UnordItems<T, impl Iterator<Item = T>> {
@@ -133,6 +139,20 @@ impl<T: Ord, I: Iterator<Item = T>> UnordItems<T, I> {
         items
     }
 
+    #[inline]
+    pub fn into_sorted_stable_ord(self, use_stable_sort: bool) -> Vec<T>
+    where
+        T: Ord + StableOrd,
+    {
+        let mut items: Vec<T> = self.0.collect();
+        if use_stable_sort {
+            items.sort();
+        } else {
+            items.sort_unstable()
+        }
+        items
+    }
+
     pub fn into_sorted_small_vec<HCX, const LEN: usize>(self, hcx: &HCX) -> SmallVec<[T; LEN]>
     where
         T: ToStableHashKey<HCX>,
@@ -176,6 +196,11 @@ impl<V: Eq + Hash> UnordSet<V> {
     }
 
     #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+
+    #[inline]
     pub fn insert(&mut self, v: V) -> bool {
         self.inner.insert(v)
     }
@@ -253,7 +278,7 @@ impl<V: Eq + Hash> UnordSet<V> {
     // We can safely extend this UnordSet from a set of unordered values because that
     // won't expose the internal ordering anywhere.
     #[inline]
-    pub fn extend<I: Iterator<Item = V>>(&mut self, items: UnordItems<V, I>) {
+    pub fn extend_unord<I: Iterator<Item = V>>(&mut self, items: UnordItems<V, I>) {
         self.inner.extend(items.0)
     }
 
@@ -277,6 +302,12 @@ impl<V: Hash + Eq> FromIterator<V> for UnordSet<V> {
     }
 }
 
+impl<V: Hash + Eq> From<FxHashSet<V>> for UnordSet<V> {
+    fn from(value: FxHashSet<V>) -> Self {
+        UnordSet { inner: value }
+    }
+}
+
 impl<HCX, V: Hash + Eq + HashStable<HCX>> HashStable<HCX> for UnordSet<V> {
     #[inline]
     fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {