Support converting between anyhow::Error and eyre::Report automatically with ?

Cargo.toml

@@ -18,6 +18,7 @@ indenter = "0.3.0"
 once_cell = "1.18.0"
 owo-colors = "4.0"
 autocfg = "1.0"
+anyhow = "1.0"
 
 [profile.dev.package.backtrace]
 opt-level = 3

eyre/Cargo.toml

@@ -13,26 +13,26 @@ readme = { workspace = true }
 rust-version = { workspace = true }
 
 [features]
-default = ["anyhow", "auto-install", "track-caller"]
-anyhow = []
+default = [ "auto-install", "track-caller"]
 auto-install = []
 track-caller = []
 
 [dependencies]
 indenter = { workspace = true }
 once_cell = { workspace = true }
 pyo3 = { version = "0.20", optional = true, default-features = false }
+anyhow = { workspace = true, optional = true, default-features = false }
 
 [build-dependencies]
 autocfg = { workspace = true }
 
 [dev-dependencies]
+anyhow = { workspace = true, default-features = true }
 futures = { version = "0.3", default-features = false }
 rustversion = "1.0"
 thiserror = "1.0"
 trybuild = { version = "=1.0.89", features = ["diff"] } # pinned due to MSRV
 backtrace = "0.3.46"
-anyhow = "1.0.28"
 syn = { version = "2.0", features = ["full"] }
 pyo3 = { version = "0.20", default-features = false, features = ["auto-initialize"] }
 

eyre/src/backtrace.rs

@@ -17,13 +17,16 @@ macro_rules! capture_backtrace {
         None
     };
 }
+
 /// Capture a backtrace iff there is not already a backtrace in the error chain
 #[cfg(generic_member_access)]
 macro_rules! backtrace_if_absent {
     ($err:expr) => {
         match std::error::request_ref::<std::backtrace::Backtrace>($err as &dyn std::error::Error) {
-            Some(_) => None,
-            None => capture_backtrace!(),
+            Some(v) => None,
+            None => {
+                capture_backtrace!()
+            }
         }
     };
 }

eyre/src/context.rs

@@ -150,6 +150,11 @@ impl<D> StdError for ContextError<D, Report>
 where
     D: Display,
 {
+    #[cfg(generic_member_access)]
+    fn provide<'a>(&'a self, request: &mut std::error::Request<'a>) {
+        self.error.provide(request)
+    }
+
     fn source(&self) -> Option<&(dyn StdError + 'static)> {
         Some(ErrorImpl::error(self.error.inner.as_ref()))
     }

eyre/src/error.rs

@@ -8,6 +8,7 @@
 use core::ptr::{self, NonNull};
 
 use core::ops::{Deref, DerefMut};
+use std::any::Any;
 
 impl Report {
     /// Create a new error object from any error type.
@@ -488,6 +489,7 @@
     }
 }
 
+#[cfg(not(feature = "anyhow"))]
 impl<E> From<E> for Report
 where
     E: StdError + Send + Sync + 'static,
@@ -498,6 +500,27 @@
     }
 }
 
+#[cfg(feature = "anyhow")]
+impl<E> From<E> for Report
+where
+    E: 'static + Into<anyhow::Error>,
+    Result<(), E>: anyhow::Context<(), E>,
+{
+    #[cfg_attr(track_caller, track_caller)]
+    fn from(value: E) -> Self {
+        let mut value = Some(value);
+        let e = &mut value as &mut dyn Any;
+
+        if let Some(e) = e.downcast_mut::<Option<anyhow::Error>>() {
+            let e: Box<dyn StdError + Send + Sync> = e.take().unwrap().into();
+            Report::from_boxed(e)
+        } else {
+            let e: Box<dyn StdError + Send + Sync> = value.take().unwrap().into().into();
+            Report::from_boxed(e)
+        }
+    }
+}
+
 impl Deref for Report {
     type Target = dyn StdError + Send + Sync + 'static;
 

eyre/src/lib.rs

@@ -381,7 +381,7 @@
 use crate::error::ErrorImpl;
 use core::fmt::{Debug, Display};
 
-use std::error::Error as StdError;
+use std::{any::Any, error::Error as StdError};
 
 pub use eyre as format_err;
 /// Compatibility re-export of `eyre` for interop with `anyhow`
@@ -779,6 +779,7 @@
     #[cfg_attr(not(feature = "auto-install"), allow(dead_code))]
     pub fn default_with(error: &(dyn StdError + 'static)) -> Box<dyn EyreHandler> {
         // Capture the backtrace if the source error did not already capture one
+        eprintln!("checking backtrace");
         let backtrace = backtrace_if_absent!(error);
 
         Box::new(Self {
@@ -848,7 +849,10 @@
             let backtrace = self
                 .backtrace
                 .as_ref()
-                .or_else(|| std::error::request_ref::<Backtrace>(error))
+                .or_else(|| {
+                    eprintln!("Requesting backtrace from underlying type");
+                    std::error::request_ref::<std::backtrace::Backtrace>(error)
+                })
                 .expect("backtrace capture failed");
 
             if let BacktraceStatus::Captured = backtrace.status() {

eyre/tests/test_anyhow.rs

@@ -0,0 +1,59 @@
+#![cfg(generic_member_access)]
+#![feature(error_generic_member_access)]
+
+use eyre::Report;
+use std::fmt::Display;
+
+#[derive(Debug)]
+struct RootError;
+
+impl Display for RootError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "RootError")
+    }
+}
+
+impl std::error::Error for RootError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        None
+    }
+}
+
+fn this_function_fails() -> anyhow::Result<()> {
+    use anyhow::Context;
+
+    Err(RootError).context("Ouch!").context("Anyhow context A")
+}
+
+fn test_failure() -> eyre::Result<()> {
+    use anyhow::Context;
+    this_function_fails().context("Anyhow context B")?;
+
+    Ok(())
+}
+
+#[test]
+fn anyhow_conversion() {
+    use eyre::WrapErr;
+    let error: Report = test_failure().wrap_err("Eyre context").unwrap_err();
+
+    eprintln!("Error: {:?}", error);
+
+    let chain = error.chain().map(ToString::to_string).collect::<Vec<_>>();
+    assert_eq!(
+        chain,
+        [
+            "Eyre context",
+            // Anyhow context
+            "Anyhow context B",
+            "Anyhow context A",
+            // Anyhow error
+            "Ouch!",
+            // Original concrete error, shows up in chain too
+            "RootError"
+        ]
+    );
+
+    let backtrace = std::error::request_ref::<std::backtrace::Backtrace>(&*error).unwrap();
+    dbg!(backtrace);
+}