feat: impl StackError for anyhow:::Error (#14)

## Description

Adds `impl StackError for anyhow::Error` under the `anyhow` feature
flag.

## Breaking Changes

<!-- Optional, if there are any breaking changes document them,
including how to migrate older code. -->

## Notes & open questions

<!-- Any notes, remarks or open questions you have to make about the PR.
-->

## Change checklist

- [ ] Self-review.
- [ ] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [ ] Tests if relevant.
- [ ] All breaking changes documented.

Author: Frando

Cargo.toml

@@ -23,5 +23,5 @@ inherits = 'dev'
 opt-level = 1
 
 [features]
-default = []
+default = ["anyhow"]
 anyhow = ["dep:anyhow"]

README.md

@@ -100,7 +100,7 @@ Caused by:
 
 ### Feature flags
 
-* `anyhow` (off by default): Enables `From<anyhow::Error> for AnyError`
+* `anyhow` (off by default): Enables `From<anyhow::Error> for AnyError` and `impl StackError for anyhow::Error`
 
 ## License
 

src/error.rs

@@ -357,6 +357,37 @@ impl_stack_error_for_std_error!(std::string::FromUtf8Error);
 impl_stack_error_for_std_error!(std::net::AddrParseError);
 impl_stack_error_for_std_error!(std::array::TryFromSliceError);
 
+#[cfg(feature = "anyhow")]
+impl StackError for anyhow::Error {
+    fn as_std(&self) -> &(dyn std::error::Error + Send + Sync + 'static) {
+        std::convert::AsRef::as_ref(self)
+    }
+
+    fn into_std(self: Box<Self>) -> Box<dyn std::error::Error + Send + Sync> {
+        self.into_boxed_dyn_error()
+    }
+
+    fn as_dyn(&self) -> &dyn StackError {
+        self
+    }
+
+    fn meta(&self) -> Option<&Meta> {
+        None
+    }
+
+    fn source(&self) -> Option<ErrorRef<'_>> {
+        anyhow::Error::chain(self).next().map(ErrorRef::std)
+    }
+
+    fn fmt_message(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+
+    fn is_transparent(&self) -> bool {
+        false
+    }
+}
+
 impl<T: StackError + std::error::Error + Sized + 'static> StackError for Arc<T> {
     fn as_std(&self) -> &(dyn std::error::Error + Send + Sync + 'static) {
         (**self).as_std()

src/lib.rs

@@ -65,7 +65,7 @@
 //!
 //! ### Feature flags
 //!
-//! * `anyhow` (off by default): Enables `From<anyhow::Error> for AnyError`
+//! * `anyhow` (off by default): Enables `From<anyhow::Error> for AnyError` and `impl StackError for anyhow::Error`
 //!
 //! ## Example
 //!

src/tests.rs

@@ -531,3 +531,16 @@ fn downcast() {
     let err_ref: &MyError = err.source().unwrap().downcast_ref().unwrap();
     assert!(matches!(err_ref, MyError::A { .. }));
 }
+
+#[test]
+#[cfg(feature = "anyhow")]
+fn test_anyhow_compat2() -> Result {
+    fn ok() -> anyhow::Result<()> {
+        Ok(())
+    }
+    ok().map_err(AnyError::from_anyhow)?;
+    let _err = AnyError::from(anyhow::anyhow!("fail"));
+    ok().context("ctx")?;
+    ok()?;
+    Ok(())
+}