1 files changed, 51 insertions, 0 deletions
diff --git a/compiler/rustc_index/src/vec/tests.rs b/compiler/rustc_index/src/vec/tests.rs
new file mode 100644
index 00000000000..15c43c72c7b
--- /dev/null
+++ b/compiler/rustc_index/src/vec/tests.rs
@@ -0,0 +1,51 @@
+#![allow(dead_code)]
+newtype_index!(struct MyIdx { MAX = 0xFFFF_FFFA });
+
+#[test]
+fn index_size_is_optimized() {
+    use std::mem::size_of;
+
+    assert_eq!(size_of::<MyIdx>(), 4);
+    // Uses 0xFFFF_FFFB
+    assert_eq!(size_of::<Option<MyIdx>>(), 4);
+    // Uses 0xFFFF_FFFC
+    assert_eq!(size_of::<Option<Option<MyIdx>>>(), 4);
+    // Uses 0xFFFF_FFFD
+    assert_eq!(size_of::<Option<Option<Option<MyIdx>>>>(), 4);
+    // Uses 0xFFFF_FFFE
+    assert_eq!(size_of::<Option<Option<Option<Option<MyIdx>>>>>(), 4);
+    // Uses 0xFFFF_FFFF
+    assert_eq!(size_of::<Option<Option<Option<Option<Option<MyIdx>>>>>>(), 4);
+    // Uses a tag
+    assert_eq!(size_of::<Option<Option<Option<Option<Option<Option<MyIdx>>>>>>>(), 8);
+}
+
+#[test]
+fn range_iterator_iterates_forwards() {
+    let range = MyIdx::from_u32(1)..MyIdx::from_u32(4);
+    assert_eq!(
+        range.collect::<Vec<_>>(),
+        [MyIdx::from_u32(1), MyIdx::from_u32(2), MyIdx::from_u32(3)]
+    );
+}
+
+#[test]
+fn range_iterator_iterates_backwards() {
+    let range = MyIdx::from_u32(1)..MyIdx::from_u32(4);
+    assert_eq!(
+        range.rev().collect::<Vec<_>>(),
+        [MyIdx::from_u32(3), MyIdx::from_u32(2), MyIdx::from_u32(1)]
+    );
+}
+
+#[test]
+fn range_count_is_correct() {
+    let range = MyIdx::from_u32(1)..MyIdx::from_u32(4);
+    assert_eq!(range.count(), 3);
+}
+
+#[test]
+fn range_size_hint_is_correct() {
+    let range = MyIdx::from_u32(1)..MyIdx::from_u32(4);
+    assert_eq!(range.size_hint(), (3, Some(3)));
+}