Add anyhow integration to gix-error

gix-error/Cargo.toml

@@ -13,7 +13,11 @@ rust-version = "1.82"
 
 [dependencies]
 bstr = { version = "1.12.0", default-features = false, features = ["std"] }
+anyhow = { version = "1.0", optional = true }
 
 [dev-dependencies]
 insta = "1.46.0"
 
+[features]
+anyhow = ["dep:anyhow"]
+

gix-error/src/anyhow.rs

@@ -0,0 +1,189 @@
+//! Conversions to `anyhow::Error` for interoperability.
+//!
+//! This module provides conversions from `Exn<T>` and `Error` types to `anyhow::Error`,
+//! flattening the tree of error frames into a linear chain of sources.
+
+use crate::{Error, Exn, Frame};
+use std::fmt;
+
+/// A wrapper error that provides a linear chain through the error tree.
+///
+/// This error is used to convert from `Exn` or `Error` to `anyhow::Error`,
+/// presenting the first child as the source, which then presents its first child, and so on.
+struct ChainedFrameError {
+    message: String,
+    debug: String,
+    source: Option<Box<ChainedFrameError>>,
+}
+
+impl ChainedFrameError {
+    /// Create a chain from a frame by walking the first-child path.
+    fn from_frame(frame: &Frame) -> Self {
+        let message = frame.as_error().to_string();
+        let debug = format!("{:?}", frame.as_error());
+
+        // Create the source chain by following the first child
+        let source = frame.children().first().map(|child| {
+            Box::new(ChainedFrameError::from_frame(child))
+        });
+
+        ChainedFrameError {
+            message,
+            debug,
+            source,
+        }
+    }
+}
+
+impl fmt::Display for ChainedFrameError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.message)
+    }
+}
+
+impl fmt::Debug for ChainedFrameError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.debug)
+    }
+}
+
+impl std::error::Error for ChainedFrameError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        self.source.as_ref().map(|s| s.as_ref() as &(dyn std::error::Error + 'static))
+    }
+}
+
+/// Extension trait to convert to `anyhow::Error`.
+pub trait IntoAnyhow {
+    /// Convert into an `anyhow::Error`, flattening the error tree into a source chain.
+    fn into_anyhow(self) -> anyhow::Error;
+}
+
+/// Convert `Exn<E>` to `anyhow::Error`, flattening the error tree into a source chain.
+impl<E> IntoAnyhow for Exn<E>
+where
+    E: std::error::Error + Send + Sync + 'static,
+{
+    fn into_anyhow(self) -> anyhow::Error {
+        let chained = ChainedFrameError::from_frame(self.as_frame());
+        anyhow::Error::new(chained)
+    }
+}
+
+/// Convert `Error` to `anyhow::Error`, flattening the error tree into a source chain.
+impl IntoAnyhow for Error {
+    fn into_anyhow(self) -> anyhow::Error {
+        let frame = self.into_frame();
+        let chained = ChainedFrameError::from_frame(&frame);
+        anyhow::Error::new(chained)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{ErrorExt, ResultExt};
+
+    #[derive(Debug)]
+    struct TestError1(&'static str);
+    impl fmt::Display for TestError1 {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(f, "TestError1: {}", self.0)
+        }
+    }
+    impl std::error::Error for TestError1 {}
+
+    #[derive(Debug)]
+    struct TestError2(&'static str);
+    impl fmt::Display for TestError2 {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(f, "TestError2: {}", self.0)
+        }
+    }
+    impl std::error::Error for TestError2 {}
+
+    #[derive(Debug)]
+    struct TestError3(&'static str);
+    impl fmt::Display for TestError3 {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(f, "TestError3: {}", self.0)
+        }
+    }
+    impl std::error::Error for TestError3 {}
+
+    #[test]
+    fn test_exn_to_anyhow_simple() {
+        let err: Exn<TestError1> = TestError1("base error").raise();
+        let anyhow_err = err.into_anyhow();
+
+        let error_chain = format!("{:?}", anyhow_err);
+        assert!(error_chain.contains("TestError1: base error"));
+    }
+
+    #[test]
+    fn test_exn_to_anyhow_chain() {
+        let result: Result<(), TestError3> = Err(TestError3("lowest error"));
+        let result = result.or_raise(|| TestError2("middle error"));
+        let result = result.or_raise(|| TestError1("top error"));
+
+        let err = result.unwrap_err();
+        let anyhow_err = err.into_anyhow();
+
+        // Verify the error chain is preserved
+        let error_chain = format!("{:?}", anyhow_err);
+        assert!(error_chain.contains("TestError1: top error"));
+
+        // Check that sources are accessible - should have all three levels
+        let mut source = anyhow_err.source();
+        assert!(source.is_some(), "Should have first source");
+
+        // Verify middle error is in the chain
+        if let Some(err) = source {
+            let s = format!("{}", err);
+            assert!(s.contains("TestError2: middle error"), "Second level should be middle error, got: {}", s);
+            source = err.source();
+        }
+
+        // Verify lowest error is in the chain
+        assert!(source.is_some(), "Should have third source");
+        if let Some(err) = source {
+            let s = format!("{}", err);
+            assert!(s.contains("TestError3: lowest error"), "Third level should be lowest error, got: {}", s);
+        }
+    }
+
+    #[test]
+    fn test_error_to_anyhow() {
+        let exn: Exn<TestError1> = TestError1("base error").raise();
+        let error: Error = exn.into();
+        let anyhow_err = error.into_anyhow();
+
+        let error_chain = format!("{:?}", anyhow_err);
+        assert!(error_chain.contains("TestError1: base error"));
+    }
+
+    #[test]
+    fn test_anyhow_error_chain_prints() {
+        // Create a chain of errors
+        let result: Result<(), TestError3> = Err(TestError3("IO failed"));
+        let result = result.or_raise(|| TestError2("failed to read file"));
+        let result = result.or_raise(|| TestError1("operation failed"));
+
+        let err = result.unwrap_err();
+        let anyhow_err = err.into_anyhow();
+
+        // Print the error to verify it displays as a chain
+        // This would normally print:
+        // Error: TestError1: operation failed
+        //
+        // Caused by:
+        //    0: TestError2: failed to read file
+        //    1: TestError3: IO failed
+        let display = format!("{}", anyhow_err);
+        assert!(display.contains("TestError1: operation failed"));
+
+        // Also test debug format
+        let debug = format!("{:?}", anyhow_err);
+        assert!(debug.contains("TestError1: operation failed"));
+    }
+}

gix-error/src/error.rs

@@ -11,6 +11,14 @@ impl Error {
         }
         current.as_error_send_sync()
     }
+
+    /// Return the inner frame.
+    #[cfg(feature = "anyhow")]
+    pub(crate) fn into_frame(self) -> Box<exn::Frame> {
+        match self.inner {
+            Inner::ExnAsError(frame) | Inner::Exn(frame) => frame,
+        }
+    }
     //
     // /// Return an iterator over all sources, i.e. the linear chain.
     // pub fn iter_sources(&self) -> ErrorIter<'_> {

gix-error/src/lib.rs

@@ -13,6 +13,12 @@
 /// A result type to hide the [Exn] error wrapper.
 mod exn;
 
+#[cfg(feature = "anyhow")]
+mod anyhow;
+
+#[cfg(feature = "anyhow")]
+pub use self::anyhow::IntoAnyhow;
+
 pub use exn::{ErrorExt, Exn, Frame, OptionExt, ResultExt, Something, Untyped};
 
 /// An error type that wraps an inner type-erased boxed `std::error::Error` or an `Exn` frame.