Test Box derive for sized and unsized types

tests/derive_box/fails/unsized_type_self_receiver.rs

@@ -0,0 +1,18 @@
+use blanket::blanket;
+use impls::impls;
+
+#[blanket(derive(Box))]
+pub trait StringLike {
+    fn into_utf8(self) -> Vec<u8>;
+}
+
+impl StringLike for str {
+    fn into_utf8(self) -> Vec<u8> {
+        self.as_bytes().into()
+    }
+}
+
+fn main() {
+    assert!(impls!(str:      StringLike));
+    assert!(impls!(Box<str>: StringLike));
+}

tests/derive_box/fails/unsized_type_self_receiver.stderr

@@ -0,0 +1,12 @@
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> tests/derive_box/fails/unsized_type_self_receiver.rs:10:18
+   |
+10 |     fn into_utf8(self) -> Vec<u8> {
+   |                  ^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = help: unsized fn params are gated as an unstable feature
+help: function arguments must have a statically known size, borrowed types always have a known size
+   |
+10 |     fn into_utf8(&self) -> Vec<u8> {
+   |                  +

tests/derive_box/successes/unsized_type.rs

@@ -0,0 +1,18 @@
+use blanket::blanket;
+use impls::impls;
+
+#[blanket(derive(Box))]
+pub trait StringLike {
+    fn is_utf8(&self) -> bool;
+}
+
+impl StringLike for str {
+    fn is_utf8(&self) -> bool {
+        true
+    }
+}
+
+fn main() {
+    assert!(impls!(str:      StringLike));
+    assert!(impls!(Box<str>: StringLike));
+}