merge upstream changes from anyhow (#10)

Cargo.toml

@@ -15,10 +15,14 @@ default = ["std"]
 std = []
 
 [dev-dependencies]
-futures = "0.3"
+futures = { version = "0.3", default-features = false }
 rustversion = "1.0"
 thiserror = "1.0"
 trybuild = { version = "1.0.19", features = ["diff"] }
 
 [dependencies]
 indenter = "^0.1.1"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+rustdoc-args = ["--cfg", "doc_cfg"]

README.md

@@ -199,9 +199,21 @@ type Result<T, E = eyre::Report<MyContext>> = core::result::Result<T, E>;
   }
   ```
 
-- A backtrace is captured and printed with the error if the underlying error
-  type does not already provide its own. In order to see backtraces, the
-  `RUST_LIB_BACKTRACE=1` environment variable must be defined.
+- If using the nightly channel, a backtrace is captured and printed with the
+  error if the underlying error type does not already provide its own. In order
+  to see backtraces, they must be enabled through the environment variables
+  described in [`std::backtrace`]:
+
+  - If you want panics and errors to both have backtraces, set
+    `RUST_BACKTRACE=1`;
+  - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;
+  - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
+    `RUST_LIB_BACKTRACE=0`.
+
+  The tracking issue for this feature is [rust-lang/rust#53487].
+
+  [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables
+  [rust-lang/rust#53487]: https://github.com/rust-lang/rust/issues/53487
 
 - Eyre works with any error type that has an impl of `std::error::Error`,
   including ones defined in your crate. We do not bundle a `derive(Error)` macro

src/error.rs

@@ -26,6 +26,7 @@ where
     /// If the error type does not provide a backtrace, a backtrace will be
     /// created here to ensure that a backtrace exists.
     #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
     pub fn new<E>(error: E) -> Self
     where
         E: StdError + Send + Sync + 'static,
@@ -266,11 +267,19 @@ where
     /// Backtraces are only available on the nightly channel. Tracking issue:
     /// [rust-lang/rust#53487][tracking].
     ///
-    /// In order for the backtrace to be meaningful, the environment variable
-    /// `RUST_LIB_BACKTRACE=1` must be defined. Backtraces are somewhat
+    /// In order for the backtrace to be meaningful, one of the two environment
+    /// variables `RUST_LIB_BACKTRACE=1` or `RUST_BACKTRACE=1` must be defined
+    /// and `RUST_LIB_BACKTRACE` must not be `0`. Backtraces are somewhat
     /// expensive to capture in Rust, so we don't necessarily want to be
     /// capturing them all over the place all the time.
     ///
+    /// - If you want panics and errors to both have backtraces, set
+    ///   `RUST_BACKTRACE=1`;
+    /// - If you want only errors to have backtraces, set
+    ///   `RUST_LIB_BACKTRACE=1`;
+    /// - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
+    ///   `RUST_LIB_BACKTRACE=0`.
+    ///
     /// [tracking]: https://github.com/rust-lang/rust/issues/53487
     #[cfg(backtrace)]
     pub fn backtrace(&self) -> &Backtrace {

src/lib.rs

@@ -250,9 +250,21 @@
 //!   # ;
 //!   ```
 //!
-//! - A backtrace is captured and printed with the error if the underlying error
-//!   type does not already provide its own. In order to see backtraces, the
-//!   `RUST_LIB_BACKTRACE=1` environment variable must be defined.
+//! - If using the nightly channel, a backtrace is captured and printed with the
+//!   error if the underlying error type does not already provide its own. In
+//!   order to see backtraces, they must be enabled through the environment
+//!   variables described in [`std::backtrace`]:
+//!
+//!   - If you want panics and errors to both have backtraces, set
+//!     `RUST_BACKTRACE=1`;
+//!   - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;
+//!   - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
+//!     `RUST_LIB_BACKTRACE=0`.
+//!
+//!   The tracking issue for this feature is [rust-lang/rust#53487].
+//!
+//!   [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables
+//!   [rust-lang/rust#53487]: https://github.com/rust-lang/rust/issues/53487
 //!
 //! - Eyre works with any error type that has an impl of `std::error::Error`,
 //!   including ones defined in your crate. We do not bundle a `derive(Error)`
@@ -316,6 +328,7 @@
 
 #![doc(html_root_url = "https://docs.rs/eyre/0.3.8")]
 #![cfg_attr(backtrace, feature(backtrace))]
+#![cfg_attr(doc_cfg, feature(doc_cfg))]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![allow(
     clippy::needless_doctest_main,