Add stable backtrace feature

.github/workflows/ci.yml

@@ -20,6 +20,15 @@ jobs:
           toolchain: ${{matrix.rust}}
       - run: cargo test
       - run: cargo check --no-default-features
+      - run: cargo check --features backtrace
+
+  backtrace:
+    name: Rust 1.42.0
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dtolnay/rust-toolchain@1.42.0
+      - run: cargo check --features backtrace
 
   nostd:
     name: Rust 1.36.0
@@ -37,6 +46,14 @@ jobs:
       - uses: dtolnay/rust-toolchain@1.34.0
       - run: cargo check
 
+  windows:
+    name: Windows
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo check --features backtrace
+
   clippy:
     name: Clippy
     runs-on: ubuntu-latest

Cargo.toml

@@ -14,6 +14,9 @@ categories = ["rust-patterns"]
 default = ["std"]
 std = []
 
+[dependencies]
+backtrace = { version = "0.3", optional = true }
+
 [dev-dependencies]
 futures = { version = "0.3", default-features = false }
 rustversion = "1.0"

build.rs

@@ -4,6 +4,11 @@ use std::path::Path;
 use std::process::{Command, ExitStatus, Stdio};
 use std::str;
 
+#[cfg(all(feature = "backtrace", not(feature = "std")))]
+compile_error! {
+    "`backtrace` feature without `std` feature is not supported"
+}
+
 // This code exercises the surface area that we expect of the std Backtrace
 // type. If the current toolchain is able to compile it, we go ahead and use
 // backtrace in anyhow.