Backtrace generation is now a feature

Fixes #52.

Author: Yamakaky

Cargo.toml

@@ -13,5 +13,8 @@ repository = "https://github.com/brson/error-chain"
 
 license = "MIT OR Apache-2.0"
 
+[features]
+default = ["backtrace"]
+
 [dependencies]
-backtrace = "0.2.1"
+backtrace = {version = "0.2.1", optional = true}

src/lib.rs

@@ -304,16 +304,23 @@
 //! and `chain_err` invocations of compatible types. To read the
 //! backtrace just call the `backtrace()` method.
 //!
+//! Backtrace generation can be disabled by turning off the `backtrace` feature.
+//!
 //! ## Iteration
 //!
 //! The `iter` method returns an iterator over the chain of error boxes.
 //!
 //! [error-type]: https://github.com/DanielKeep/rust-error-type
 //! [quick-error]: https://github.com/tailhook/quick-error
 
+#[cfg(feature = "backtrace")]
 extern crate backtrace;
 
+#[cfg(feature = "backtrace")]
 pub use backtrace::Backtrace;
+#[cfg(not(feature = "backtrace"))]
+#[derive(Debug)]
+pub enum Backtrace {}
 
 mod quick_error;
 
@@ -689,9 +696,15 @@ impl<'a> Iterator for ErrorChainIter<'a> {
 /// Returns a backtrace of the current call stack if `RUST_BACKTRACE`
 /// is set to anything but ``0``, and `None` otherwise.  This is used
 /// in the generated error implementations.
+#[cfg(feature = "backtrace")]
 pub fn make_backtrace() -> Option<Arc<Backtrace>> {
     match std::env::var_os("RUST_BACKTRACE") {
         Some(ref val) if val != "0" => Some(Arc::new(Backtrace::new())),
         _ => None
     }
 }
+
+#[cfg(not(feature = "backtrace"))]
+pub fn make_backtrace() -> Option<Arc<Backtrace>> {
+    None
+}

tests/tests.rs

@@ -130,6 +130,7 @@ fn empty() {
 }
 
 #[test]
+#[cfg(feature = "backtrace")]
 fn has_backtrace_depending_on_env() {
     use std::env;