From 4cf22dfa2139f072e0ee937de343a0b0b0a77a22 Mon Sep 17 00:00:00 2001
From: Steven Fackler <sfackler@gmail.com>
Date: Wed, 27 Feb 2019 13:18:02 -0800
Subject: [PATCH] feat(error): implement `Error::source` when available

Closes #1768
---
 Cargo.toml   |  3 +++
 build.rs     |  9 +++++++++
 src/error.rs | 10 ++++++++++
 3 files changed, 22 insertions(+)
 create mode 100644 build.rs

diff --git a/Cargo.toml b/Cargo.toml
index 7591cb53e4..71fa608ecb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -38,6 +38,9 @@ tokio-threadpool = { version = "0.1.3", optional = true }
 tokio-timer = { version = "0.2", optional = true }
 want = "0.0.6"
 
+[build-dependencies]
+rustc_version = "0.2"
+
 [dev-dependencies]
 futures-timer = "0.1"
 num_cpus = "1.0"
diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000000..c34535fe4d
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,9 @@
+extern crate rustc_version;
+
+use rustc_version::{version, Version};
+
+fn main() {
+    if version().unwrap() >= Version::parse("1.30.0").unwrap() {
+        println!("cargo:rustc-cfg=error_source");
+    }
+}
diff --git a/src/error.rs b/src/error.rs
index 226dee4a4d..5bb75a3446 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -323,6 +323,7 @@ impl StdError for Error {
         }
     }
 
+    #[cfg(not(error_source))]
     fn cause(&self) -> Option<&StdError> {
         self
             .inner
@@ -330,6 +331,15 @@ impl StdError for Error {
             .as_ref()
             .map(|cause| &**cause as &StdError)
     }
+
+    #[cfg(error_source)]
+    fn source(&self) -> Option<&(StdError + 'static)> {
+        self
+            .inner
+            .cause
+            .as_ref()
+            .map(|cause| &**cause as &(StdError + 'static))
+    }
 }
 
 #[doc(hidden)]