crate: add features to switch Error backend

Allows end users to choose between anyhow and eyre.

Co-Authored-By: Jacob Rothstein <hi@jbr.me>

Cargo.toml

@@ -16,24 +16,26 @@ features = ["docs"]
 rustdoc-args = ["--cfg", "feature=\"docs\""]
 
 [features]
-default = ["fs", "cookie-secure"]
+default = ["error_anyhow", "fs", "cookie-secure"]
 docs = ["unstable"]
+error_anyhow = ["anyhow"]
+error_eyre = ["eyre", "stable-eyre"]
 unstable = []
 hyperium_http = ["http"]
 async_std = ["fs"]
 cookie-secure = ["cookie/secure"]
 fs = ["async-std"]
 
 [dependencies]
+# features: error_anyhow
+anyhow = { version = "1.0.26", optional = true }
 # features: async_std
 async-std = { version = "1.6.0", optional = true }
 futures-lite = "1.11.1"
 async-channel = "1.5.1"
 
 # features: hyperium/http
 http = { version = "0.2.0", optional = true }
-
-anyhow = "1.0.26"
 cookie = { version = "0.14.0", features = ["percent-encode"] }
 infer = "0.2.3"
 pin-project-lite = "0.1.0"
@@ -44,6 +46,11 @@ serde_urlencoded = "0.7.0"
 rand = "0.7.3"
 serde_qs = "0.7.0"
 base64 = "0.13.0"
+backtrace = "0.3.50"
+
+# features: error_anyhow
+eyre = { version = "0.6.1", optional = true }
+stable-eyre = { version = "0.2.1", optional = true }
 
 [dev-dependencies]
 http = "0.2.0"

src/error.rs

@@ -1,10 +1,18 @@
 //! HTTP error types
 
+use std::convert::TryInto;
 use std::error::Error as StdError;
 use std::fmt::{self, Debug, Display};
 
 use crate::StatusCode;
-use std::convert::TryInto;
+
+#[cfg(all(not(backtrace), feature = "error_eyre"))]
+use stable_eyre::BacktraceExt;
+
+#[cfg(feature = "error_anyhow")]
+use anyhow::Error as BaseError;
+#[cfg(feature = "error_eyre")]
+use eyre::Report as BaseError;
 
 /// A specialized `Result` type for HTTP operations.
 ///
@@ -14,7 +22,7 @@ pub type Result<T> = std::result::Result<T, Error>;
 
 /// The error type for HTTP operations.
 pub struct Error {
-    error: anyhow::Error,
+    error: BaseError,
     status: crate::StatusCode,
     type_name: Option<&'static str>,
 }
@@ -29,7 +37,7 @@ impl Error {
     where
         S: TryInto<StatusCode>,
         S::Error: Debug,
-        E: Into<anyhow::Error>,
+        E: Into<BaseError>,
     {
         Self {
             status: status
@@ -51,7 +59,7 @@ impl Error {
             status: status
                 .try_into()
                 .expect("Could not convert into a valid `StatusCode`"),
-            error: anyhow::Error::msg(msg),
+            error: BaseError::msg(msg),
             type_name: None,
         }
     }
@@ -96,7 +104,7 @@ impl Error {
     /// compiled on a toolchain that does not support backtraces, or
     /// if executed without backtraces enabled with
     /// `RUST_LIB_BACKTRACE=1`.
-    #[cfg(backtrace)]
+    #[cfg(all(backtrace, feature = "error_anyhow"))]
     pub fn backtrace(&self) -> Option<&std::backtrace::Backtrace> {
         let backtrace = self.error.backtrace();
         if let std::backtrace::BacktraceStatus::Captured = backtrace.status() {
@@ -106,12 +114,24 @@ impl Error {
         }
     }
 
-    #[cfg(not(backtrace))]
+    #[cfg(all(not(backtrace), feature = "error_anyhow"))]
     #[allow(missing_docs)]
     pub fn backtrace(&self) -> Option<()> {
         None
     }
 
+    #[cfg(all(backtrace, feature = "error_eyre"))]
+    #[allow(missing_docs)]
+    pub fn backtrace(&self) -> Option<&std::backtrace::Backtrace> {
+        self.error.backtrace()
+    }
+
+    #[cfg(all(not(backtrace), feature = "error_eyre"))]
+    #[allow(missing_docs)]
+    pub fn backtrace(&self) -> Option<&backtrace::Backtrace> {
+        self.error.backtrace()
+    }
+
     /// Attempt to downcast the error object to a concrete type.
     pub fn downcast<E>(self) -> std::result::Result<E, Self>
     where
@@ -158,7 +178,7 @@ impl Debug for Error {
     }
 }
 
-impl<E: Into<anyhow::Error>> From<E> for Error {
+impl<E: Into<BaseError>> From<E> for Error {
     fn from(error: E) -> Self {
         Self::new(StatusCode::InternalServerError, error)
     }

tests/error.rs

@@ -71,6 +71,19 @@ fn option_ext() {
     assert_eq!(err.status(), StatusCode::NotFound);
 }
 
+#[cfg(feature = "error_eyre")]
+#[test]
+fn eyre_error_into_http_types_error() {
+    let eyre_error = eyre::Error::new(std::io::Error::new(std::io::ErrorKind::Other, "irrelevant"));
+    let http_types_error: Error = eyre_error.into();
+    assert_eq!(http_types_error.status(), StatusCode::InternalServerError);
+
+    let eyre_error = eyre::Error::new(std::io::Error::new(std::io::ErrorKind::Other, "irrelevant"));
+    let http_types_error: Error = Error::new(StatusCode::ImATeapot, eyre_error);
+    assert_eq!(http_types_error.status(), StatusCode::ImATeapot);
+}
+
+#[cfg(feature = "error_anyhow")]
 #[test]
 fn anyhow_error_into_http_types_error() {
     let anyhow_error =