Vendor dependencies

Let's see how I like this workflow.

vendor/thiserror/tests/test_error.rs

@@ -0,0 +1,56 @@
+#![allow(dead_code)]
+
+use std::fmt::{self, Display};
+use std::io;
+use thiserror::Error;
+
+macro_rules! unimplemented_display {
+    ($ty:ty) => {
+        impl Display for $ty {
+            fn fmt(&self, _formatter: &mut fmt::Formatter) -> fmt::Result {
+                unimplemented!()
+            }
+        }
+    };
+}
+
+#[derive(Error, Debug)]
+struct BracedError {
+    msg: String,
+    pos: usize,
+}
+
+#[derive(Error, Debug)]
+struct TupleError(String, usize);
+
+#[derive(Error, Debug)]
+struct UnitError;
+
+#[derive(Error, Debug)]
+struct WithSource {
+    #[source]
+    cause: io::Error,
+}
+
+#[derive(Error, Debug)]
+struct WithAnyhow {
+    #[source]
+    cause: anyhow::Error,
+}
+
+#[derive(Error, Debug)]
+enum EnumError {
+    Braced {
+        #[source]
+        cause: io::Error,
+    },
+    Tuple(#[source] io::Error),
+    Unit,
+}
+
+unimplemented_display!(BracedError);
+unimplemented_display!(TupleError);
+unimplemented_display!(UnitError);
+unimplemented_display!(WithSource);
+unimplemented_display!(WithAnyhow);
+unimplemented_display!(EnumError);