Vendor dependencies

Let's see how I like this workflow.

vendor/thiserror/tests/ui/no-display.rs

@@ -0,0 +1,12 @@
+use thiserror::Error;
+
+#[derive(Debug)]
+struct NoDisplay;
+
+#[derive(Error, Debug)]
+#[error("thread: {thread}")]
+pub struct Error {
+    thread: NoDisplay,
+}
+
+fn main() {}