1 files changed, 36 insertions, 0 deletions
diff --git a/compiler/rustc_hir/src/tests.rs b/compiler/rustc_hir/src/tests.rs
new file mode 100644
index 000000000..4636d5152
--- /dev/null
+++ b/compiler/rustc_hir/src/tests.rs
@@ -0,0 +1,36 @@
+use crate::definitions::{DefKey, DefPathData, DisambiguatedDefPathData};
+use rustc_span::def_id::{DefPathHash, StableCrateId};
+
+#[test]
+fn def_path_hash_depends_on_crate_id() {
+    // This test makes sure that *both* halves of a DefPathHash depend on
+    // the crate-id of the defining crate. This is a desirable property
+    // because the crate-id can be more easily changed than the DefPath
+    // of an item, so, in the case of a crate-local DefPathHash collision,
+    // the user can simply "role the dice again" for all DefPathHashes in
+    // the crate by changing the crate disambiguator (e.g. via bumping the
+    // crate's version number).
+
+    let id0 = StableCrateId::new("foo", false, vec!["1".to_string()]);
+    let id1 = StableCrateId::new("foo", false, vec!["2".to_string()]);
+
+    let h0 = mk_test_hash(id0);
+    let h1 = mk_test_hash(id1);
+
+    assert_ne!(h0.stable_crate_id(), h1.stable_crate_id());
+    assert_ne!(h0.local_hash(), h1.local_hash());
+
+    fn mk_test_hash(stable_crate_id: StableCrateId) -> DefPathHash {
+        let parent_hash = DefPathHash::new(stable_crate_id, 0);
+
+        let key = DefKey {
+            parent: None,
+            disambiguated_data: DisambiguatedDefPathData {
+                data: DefPathData::CrateRoot,
+                disambiguator: 0,
+            },
+        };
+
+        key.compute_stable_hash(parent_hash)
+    }
+}