Vendor dependencies

Let's see how I like this workflow.

vendor/pin-project-lite/tests/ui/pin_project/conflict-unpin.rs

@@ -0,0 +1,40 @@
+use pin_project_lite::pin_project;
+
+// The same implementation.
+
+pin_project! { //~ ERROR E0119
+    struct Foo<T, U> {
+        #[pin]
+        future: T,
+        field: U,
+    }
+}
+
+// conflicting implementations
+impl<T, U> Unpin for Foo<T, U> where T: Unpin {} // Conditional Unpin impl
+
+// The implementation that under different conditions.
+
+pin_project! { //~ ERROR E0119
+    struct Bar<T, U> {
+        #[pin]
+        future: T,
+        field: U,
+    }
+}
+
+// conflicting implementations
+impl<T, U> Unpin for Bar<T, U> {} // Non-conditional Unpin impl
+
+pin_project! { //~ ERROR E0119
+    struct Baz<T, U> {
+        #[pin]
+        future: T,
+        field: U,
+    }
+}
+
+// conflicting implementations
+impl<T: Unpin, U: Unpin> Unpin for Baz<T, U> {} // Conditional Unpin impl
+
+fn main() {}