Fix sparse intersect bug, add more sparse / dense tests

Author: willcrichton

compiler/rustc_index/src/bit_set.rs

@@ -272,7 +272,7 @@ fn dense_sparse_intersect<T: Idx>(
     sparse: &SparseBitSet<T>,
 ) -> (SparseBitSet<T>, bool) {
     let mut sparse_copy = sparse.clone();
-    sparse_intersect(&mut sparse_copy, |el| !dense.contains(*el));
+    sparse_intersect(&mut sparse_copy, |el| dense.contains(*el));
     let n = sparse_copy.len();
     (sparse_copy, n != dense.count())
 }

compiler/rustc_index/src/bit_set/tests.rs

@@ -108,14 +108,25 @@ fn hybrid_bitset() {
     assert!(!sparse01358.union(&hybrid)); // no change
     assert!(hybrid.union(&sparse01358));
     assert!(hybrid.superset(&sparse01358) && sparse01358.superset(&hybrid));
-    assert!(!dense10.union(&sparse01358));
     assert!(!dense256.union(&dense10));
 
+    // dense / sparse where dense superset sparse
+    assert!(!dense10.clone().union(&sparse01358));
+    assert!(sparse01358.clone().union(&dense10));
     assert!(dense10.clone().intersect(&sparse01358));
     assert!(!sparse01358.clone().intersect(&dense10));
     assert!(dense10.clone().subtract(&sparse01358));
     assert!(sparse01358.clone().subtract(&dense10));
 
+    // dense / sparse where sparse superset dense
+    let dense038 = sparse038.to_dense();
+    assert!(!sparse0381.clone().union(&dense038));
+    assert!(dense038.clone().union(&sparse0381));
+    assert!(sparse0381.clone().intersect(&dense038));
+    assert!(!dense038.clone().intersect(&sparse0381));
+    assert!(sparse0381.clone().subtract(&dense038));
+    assert!(dense038.clone().subtract(&sparse0381));
+
     let mut dense = dense10.clone();
     assert!(dense.union(&dense256));
     assert!(dense.superset(&dense256) && dense256.superset(&dense));