Enable calling context on Option<T> by adding an OptionExt trait.

Author: marmistrz

src/lib.rs

@@ -43,6 +43,7 @@ mod box_std;
 mod compat;
 mod context;
 mod result_ext;
+mod option_ext;
 
 use core::any::TypeId;
 use core::fmt::{Debug, Display};
@@ -52,6 +53,7 @@ pub use backtrace::Backtrace;
 pub use compat::Compat;
 pub use context::Context;
 pub use result_ext::ResultExt;
+pub use option_ext::OptionExt;
 
 #[cfg(feature = "failure_derive")]
 #[allow(unused_imports)]

src/option_ext.rs

@@ -0,0 +1,52 @@
+use Context;
+use core::fmt::Display;
+
+/// Extension methods for `Option`.
+pub trait OptionExt<T> {
+
+    /// Wraps the error type in a context type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[cfg(all(feature = "std", feature = "derive"))]
+    /// # #[macro_use] extern crate failure;
+    /// #
+    /// # #[cfg(all(feature = "std", feature = "derive"))]
+    /// # #[macro_use] extern crate failure_derive;
+    /// #
+    /// # fn main() {
+    /// #    tests::run_test();
+    /// # }
+    /// #
+    /// # #[cfg(not(all(feature = "std", feature = "derive")))] mod tests { pub fn run_test() { } }
+    /// #
+    /// # #[cfg(all(feature = "std", feature = "derive"))] mod tests {
+    /// #
+    /// # use failure::{self, OptionExt};
+    /// #
+    /// #
+    /// # pub fn run_test() {
+    /// let opt: Option<String> = None;
+    /// let x = opt.ok_or_context(format!("An error occured")).unwrap_err();
+    ///
+    /// let x = format!("{}", x);
+    ///
+    /// assert_eq!(x, "An error occured");
+    /// # }
+    ///
+    /// # }
+    /// ```
+    fn ok_or_context<D>(self, context: D) -> Result<T, Context<D>>
+    where
+        D: Display + Send + Sync + 'static;
+}
+
+impl<T> OptionExt<T> for Option<T> {
+    fn ok_or_context<D>(self, context: D) -> Result<T, Context<D>>
+    where
+        D: Display + Send + Sync + 'static,
+    {
+        self.ok_or_else(|| Context::new(context))
+    }
+}