no_std support (via an enabled-by-default "std" feature)

.travis.yml

@@ -36,10 +36,15 @@ env:
   - secure: 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
   - TRAVIS_CARGO_NIGHTLY_FEATURE=""
   matrix:
-  - FEATURES=--features=backtrace
-  - FEATURES=--no-default-features
+  - FEATURES="--features=backtrace"
+  - FEATURES="--no-default-features --features=std"
 
 matrix:
+  include:
+  # Only test build for no_std. The smoke tests won't compile.
+  - script: travis-cargo build -- $FEATURES
+    env: FEATURES="--no-default-features"
+    rust: nightly
   exclude:
-  - env: FEATURES=--features=backtrace
+  - env: FEATURES="--features=backtrace"
     rust: 1.10.0

Cargo.toml

@@ -19,8 +19,9 @@ license = "MIT/Apache-2.0"
 travis-ci = { repository = "brson/error-chain" }
 
 [features]
-default = ["backtrace", "example_generated"]
+default = ["backtrace", "example_generated", "std"]
 example_generated = []
+std = []
 
 [dependencies]
 backtrace = { version = "0.3", optional = true }