From cfffe189f9e5d80408d65dfec4bb9a6e73786bdd Mon Sep 17 00:00:00 2001
From: David Greenberg <dsg123456789@gmail.com>
Date: Tue, 5 Sep 2017 21:07:31 -0600
Subject: [PATCH] Added support for quickmain to use `log` crate.

* Added crate feature `quickmain_log`

When `quickmain_log` is enabled, the `quick_main!` entry point writes
the terminating error chain to `log::error!` instead of stdout.
---
 CHANGELOG.md      |  1 +
 Cargo.toml        |  2 ++
 src/lib.rs        |  5 +++++
 src/quick_main.rs | 22 ++++++++++++++++++----
 4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ed0f12e3a..a2b9d035d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - [Mask the `quick_error` macro from the doc](https://github.com/rust-lang-nursery/error-chain/pull/210)
 - [Make generated `ErrorKind` enums non-exhaustive](https://github.com/rust-lang-nursery/error-chain/pull/193)
 - All 0.11.0-rc.2 changes
+- [Allow users of `quick_main!` to use the `log` crate](https://github.com/rust-lang-nursery/error-chain/pull/216)
 
 # 0.11.0-rc.2
 
diff --git a/Cargo.toml b/Cargo.toml
index 25b8cad0b..7299deb5a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,7 +20,9 @@ travis-ci = { repository = "rust-lang-nursery/error-chain" }
 
 [features]
 default = ["backtrace", "example_generated"]
+quickmain_log = ["log"]
 example_generated = []
 
 [dependencies]
 backtrace = { version = "0.3", optional = true }
+log = {version = "0.3", optional = true }
diff --git a/src/lib.rs b/src/lib.rs
index d0881fcef..e426e6480 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -540,6 +540,10 @@
 #[cfg(feature = "backtrace")]
 extern crate backtrace;
 
+#[cfg(feature = "quickmain_log")]
+#[macro_use]
+extern crate log;
+
 use std::error;
 use std::iter::Iterator;
 #[cfg(feature = "backtrace")]
@@ -559,6 +563,7 @@ mod error_chain;
 #[macro_use]
 mod quick_main;
 pub use quick_main::ExitCode;
+pub use quick_main::print_quickmain_error;
 #[cfg(feature = "example_generated")]
 pub mod example_generated;
 
diff --git a/src/quick_main.rs b/src/quick_main.rs
index f81e7d704..0e00aafd0 100644
--- a/src/quick_main.rs
+++ b/src/quick_main.rs
@@ -42,13 +42,10 @@
 macro_rules! quick_main {
     ($main:expr) => {
         fn main() {
-            use ::std::io::Write;
-
             ::std::process::exit(match $main() {
                 Ok(ret) => $crate::ExitCode::code(ret),
                 Err(ref e) => {
-                    write!(&mut ::std::io::stderr(), "{}", $crate::ChainedError::display_chain(e))
-                        .expect("Error writing to stderr");
+                    { $crate::print_quickmain_error(e); }
 
                     1
                 }
@@ -75,3 +72,20 @@ impl ExitCode for () {
         0
     }
 }
+
+/// When using `quick_main!`, prints the error if the program doesn't terminate successfully.
+pub fn print_quickmain_error<K,E: ::ChainedError<ErrorKind=K>>(e: &E) {
+    print_error_helper(e);
+}
+
+#[cfg(not(feature = "quickmain_log"))]
+fn print_error_helper<K,E: ::ChainedError<ErrorKind=K>>(e: &E) {
+    use ::std::io::Write;
+    write!(&mut ::std::io::stderr(), "{}", ::ChainedError::display_chain(e))
+        .expect("Error writing to stderr");
+}
+
+#[cfg(feature = "quickmain_log")]
+fn print_error_helper<K,E: ::ChainedError<ErrorKind=K>>(e: &E) {
+    { error!("{}", ::ChainedError::display_chain(e)) }
+}