1 files changed, 67 insertions, 0 deletions
diff --git a/third_party/rust/error-chain/examples/chain_err.rs b/third_party/rust/error-chain/examples/chain_err.rs
new file mode 100644
index 0000000000..c70a25dd60
--- /dev/null
+++ b/third_party/rust/error-chain/examples/chain_err.rs
@@ -0,0 +1,67 @@
+//! Demonstrates usage of `Error::caused` method. This method enables chaining errors
+//! like `ResultExt::chain_err` but doesn't require the presence of a `Result` wrapper.
+
+#[macro_use]
+extern crate error_chain;
+
+use std::fs::File;
+
+mod errors {
+    use super::LaunchStage;
+    use std::io;
+
+    error_chain! {
+        foreign_links {
+            Io(io::Error) #[doc = "Error during IO"];
+        }
+
+        errors {
+            Launch(phase: LaunchStage) {
+                description("An error occurred during startup")
+                display("Startup aborted: {:?} did not complete successfully", phase)
+            }
+
+            ConfigLoad(path: String) {
+                description("Config file not found")
+                display("Unable to read file `{}`", path)
+            }
+        }
+    }
+
+    impl From<LaunchStage> for ErrorKind {
+        fn from(v: LaunchStage) -> Self {
+            ErrorKind::Launch(v)
+        }
+    }
+}
+
+pub use errors::*;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum LaunchStage {
+    ConfigLoad,
+    ConfigParse,
+    ConfigResolve,
+}
+
+/// Read the service config from the file specified.
+fn load_config(rel_path: &str) -> Result<()> {
+    File::open(rel_path)
+        .map(|_| ())
+        .chain_err(|| ErrorKind::ConfigLoad(rel_path.to_string()))
+}
+
+/// Launch the service.
+fn launch(rel_path: &str) -> Result<()> {
+    load_config(rel_path).map_err(|e| match e {
+        e @ Error(ErrorKind::ConfigLoad(_), _) => e.chain_err(|| LaunchStage::ConfigLoad),
+        e => e.chain_err(|| "Unknown failure"),
+    })
+}
+
+fn main() {
+    let chain = launch("does_not_exist.json").unwrap_err();
+    for err in chain.iter() {
+        println!("{}", err);
+    }
+}