1 files changed, 138 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/tests/coercion.rs b/crates/ra_hir_ty/src/tests/coercion.rs
index 42330b269..60ad6e9be 100644
--- a/crates/ra_hir_ty/src/tests/coercion.rs
+++ b/crates/ra_hir_ty/src/tests/coercion.rs
@@ -548,3 +548,141 @@ impl<TT> S<TT> {
     "###
     );
 }
+
+#[test]
+fn coerce_unsize_array() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+#[lang = "unsize"]
+pub trait Unsize<T> {}
+#[lang = "coerce_unsized"]
+pub trait CoerceUnsized<T> {}
+
+impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+fn test() {
+    let f: &[usize] = &[1, 2, 3];
+}
+"#, true),
+        @r###"
+    [162; 199) '{     ... 3]; }': ()
+    [172; 173) 'f': &[usize]
+    [186; 196) '&[1, 2, 3]': &[usize; _]
+    [187; 196) '[1, 2, 3]': [usize; _]
+    [188; 189) '1': usize
+    [191; 192) '2': usize
+    [194; 195) '3': usize
+    "###
+    );
+}
+
+#[test]
+fn coerce_unsize_trait_object() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+#[lang = "unsize"]
+pub trait Unsize<T> {}
+#[lang = "coerce_unsized"]
+pub trait CoerceUnsized<T> {}
+
+impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+trait Foo<T, U> {}
+trait Bar<U, T, X>: Foo<T, U> {}
+trait Baz<T, X>: Bar<usize, T, X> {}
+
+struct S<T, X>;
+impl<T, X> Foo<T, usize> for S<T, X> {}
+impl<T, X> Bar<usize, T, X> for S<T, X> {}
+impl<T, X> Baz<T, X> for S<T, X> {}
+
+fn test() {
+    let obj: &dyn Baz<i8, i16> = &S;
+    let obj: &dyn Bar<_, _, _> = obj;
+    let obj: &dyn Foo<_, _> = obj;
+    let obj2: &dyn Baz<i8, i16> = &S;
+    let _: &dyn Foo<_, _> = obj2;
+}
+"#, true),
+        @r###"
+    [388; 573) '{     ...bj2; }': ()
+    [398; 401) 'obj': &dyn Baz<i8, i16>
+    [423; 425) '&S': &S<i8, i16>
+    [424; 425) 'S': S<i8, i16>
+    [435; 438) 'obj': &dyn Bar<usize, i8, i16>
+    [460; 463) 'obj': &dyn Baz<i8, i16>
+    [473; 476) 'obj': &dyn Foo<i8, usize>
+    [495; 498) 'obj': &dyn Bar<usize, i8, i16>
+    [508; 512) 'obj2': &dyn Baz<i8, i16>
+    [534; 536) '&S': &S<i8, i16>
+    [535; 536) 'S': S<i8, i16>
+    [546; 547) '_': &dyn Foo<i8, usize>
+    [566; 570) 'obj2': &dyn Baz<i8, i16>
+    "###
+    );
+}
+
+#[test]
+fn coerce_unsize_super_trait_cycle() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+#[lang = "unsize"]
+pub trait Unsize<T> {}
+#[lang = "coerce_unsized"]
+pub trait CoerceUnsized<T> {}
+
+impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+trait A {}
+trait B: C + A {}
+trait C: B {}
+trait D: C
+
+struct S;
+impl A for S {}
+impl B for S {}
+impl C for S {}
+impl D for S {}
+
+fn test() {
+    let obj: &dyn D = &S;
+    let obj: &dyn A = obj;
+}
+"#, true),
+        @r###"
+    [292; 348) '{     ...obj; }': ()
+    [302; 305) 'obj': &dyn D
+    [316; 318) '&S': &S
+    [317; 318) 'S': S
+    [328; 331) 'obj': &dyn A
+    [342; 345) 'obj': &dyn D
+    "###
+    );
+}
+
+#[ignore]
+#[test]
+fn coerce_unsize_generic() {
+    // FIXME: Implement this
+    // https://doc.rust-lang.org/reference/type-coercions.html#unsized-coercions
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+#[lang = "unsize"]
+pub trait Unsize<T> {}
+#[lang = "coerce_unsized"]
+pub trait CoerceUnsized<T> {}
+
+impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+struct Foo<T> { t: T };
+struct Bar<T>(Foo<T>);
+
+fn test() {
+    let _: &Foo<[usize]> = &Foo { t: [1, 2, 3] };
+    let _: &Bar<[usize]> = &Bar(Foo { t: [1, 2, 3] });
+}
+"#, true),
+        @r###"
+    "###
+    );
+}