Vendor dependencies

Let's see how I like this workflow.

vendor/anyhow/tests/test_source.rs

@@ -0,0 +1,62 @@
+use anyhow::anyhow;
+use std::error::Error as StdError;
+use std::fmt::{self, Display};
+use std::io;
+
+#[derive(Debug)]
+enum TestError {
+    Io(io::Error),
+}
+
+impl Display for TestError {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TestError::Io(e) => Display::fmt(e, formatter),
+        }
+    }
+}
+
+impl StdError for TestError {
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        match self {
+            TestError::Io(io) => Some(io),
+        }
+    }
+}
+
+#[test]
+fn test_literal_source() {
+    let error = anyhow!("oh no!");
+    assert!(error.source().is_none());
+}
+
+#[test]
+fn test_variable_source() {
+    let msg = "oh no!";
+    let error = anyhow!(msg);
+    assert!(error.source().is_none());
+
+    let msg = msg.to_owned();
+    let error = anyhow!(msg);
+    assert!(error.source().is_none());
+}
+
+#[test]
+fn test_fmt_source() {
+    let error = anyhow!("{} {}!", "oh", "no");
+    assert!(error.source().is_none());
+}
+
+#[test]
+fn test_io_source() {
+    let io = io::Error::new(io::ErrorKind::Other, "oh no!");
+    let error = anyhow!(TestError::Io(io));
+    assert_eq!("oh no!", error.source().unwrap().to_string());
+}
+
+#[test]
+fn test_anyhow_from_anyhow() {
+    let error = anyhow!("oh no!").context("context");
+    let error = anyhow!(error);
+    assert_eq!("oh no!", error.source().unwrap().to_string());
+}