Revert "Reduce the amount of untracked state in TyCtxt"

compiler/rustc_data_structures/src/stable_hasher.rs

@@ -550,3 +550,35 @@ pub fn hash_stable_hashmap<HCX, K, V, R, SK, F>(
     entries.sort_unstable_by(|&(ref sk1, _), &(ref sk2, _)| sk1.cmp(sk2));
     entries.hash_stable(hcx, hasher);
 }
+
+/// A vector container that makes sure that its items are hashed in a stable
+/// order.
+#[derive(Debug)]
+pub struct StableVec<T>(Vec<T>);
+
+impl<T> StableVec<T> {
+    pub fn new(v: Vec<T>) -> Self {
+        StableVec(v)
+    }
+}
+
+impl<T> ::std::ops::Deref for StableVec<T> {
+    type Target = Vec<T>;
+
+    fn deref(&self) -> &Vec<T> {
+        &self.0
+    }
+}
+
+impl<T, HCX> HashStable<HCX> for StableVec<T>
+where
+    T: HashStable<HCX> + ToStableHashKey<HCX>,
+{
+    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
+        let StableVec(ref v) = *self;
+
+        let mut sorted: Vec<_> = v.iter().map(|x| x.to_stable_hash_key(hcx)).collect();
+        sorted.sort_unstable();
+        sorted.hash_stable(hcx, hasher);
+    }
+}