feat(status): add error context

src/status/status.rs

@@ -1,5 +1,12 @@
 pub type Result<T> = std::result::Result<T, Status>;
 
+pub trait ResultExt<T> {
+    fn with_context<C, F>(self, context: F) -> Result<T>
+    where
+        C: Into<String>,
+        F: FnOnce() -> C;
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Code {
     InvalidArgument,
@@ -48,6 +55,10 @@ impl Status {
         self
     }
 
+    pub fn with_context(self, context: impl Into<String>) -> Self {
+        Self::new(self.code, context).with_source(self)
+    }
+
     pub fn code(&self) -> Code {
         self.code
     }
@@ -82,3 +93,16 @@ impl From<std::io::Error> for Status {
         Self::new(code, error.to_string()).with_source(error)
     }
 }
+
+impl<T, E> ResultExt<T> for std::result::Result<T, E>
+where
+    E: Into<Status>,
+{
+    fn with_context<C, F>(self, context: F) -> Result<T>
+    where
+        C: Into<String>,
+        F: FnOnce() -> C,
+    {
+        self.map_err(|error| error.into().with_context(context()))
+    }
+}

src/status/status_test.rs

@@ -1,6 +1,6 @@
 use std::error::Error;
 
-use status::{Code, Status};
+use status::{Code, ResultExt, Status};
 
 #[test]
 fn constructors_set_code_and_message() {
@@ -34,6 +34,29 @@ fn with_source_preserves_source_error() {
     assert_eq!("denied", status.source().unwrap().to_string());
 }
 
+#[test]
+fn with_context_preserves_code_and_wraps_status() {
+    let status = Status::not_found("missing input").with_context("failed to load config");
+
+    assert_eq!(Code::NotFound, status.code());
+    assert_eq!("failed to load config", status.message());
+    assert_eq!("NotFound: missing input", status.source().unwrap().to_string());
+}
+
+#[test]
+fn result_ext_adds_lazy_context() {
+    let result: status::Result<()> = Err(std::io::Error::new(
+        std::io::ErrorKind::PermissionDenied,
+        "denied",
+    ))
+    .with_context(|| "failed to read input");
+
+    let status = result.unwrap_err();
+    assert_eq!(Code::PermissionDenied, status.code());
+    assert_eq!("failed to read input", status.message());
+    assert_eq!("PermissionDenied: denied", status.source().unwrap().to_string());
+}
+
 #[test]
 fn io_error_maps_not_found() {
     let status = Status::from(std::io::Error::new(