Merge pull request #333 from dtolnay/stablebacktrace

Turn on cfg(std_backtrace) on new enough stable rustc

build.rs

@@ -46,13 +46,15 @@ const PROBE: &str = r#"
 "#;
 
 fn main() {
+    let mut error_generic_member_access = false;
     if cfg!(feature = "std") {
         println!("cargo:rerun-if-env-changed=RUSTC_BOOTSTRAP");
 
         match compile_probe() {
             Some(status) if status.success() => {
                 println!("cargo:rustc-cfg=std_backtrace");
                 println!("cargo:rustc-cfg=error_generic_member_access");
+                error_generic_member_access = true;
             }
             _ => {}
         }
@@ -78,6 +80,12 @@ fn main() {
         // https://github.com/rust-lang/rust/issues/71668
         println!("cargo:rustc-cfg=anyhow_no_unsafe_op_in_unsafe_fn_lint");
     }
+
+    if !error_generic_member_access && cfg!(feature = "std") && rustc >= 65 {
+        // std::backtrace::Backtrace
+        // https://blog.rust-lang.org/2022/11/03/Rust-1.65.0.html#stabilized-apis
+        println!("cargo:rustc-cfg=std_backtrace");
+    }
 }
 
 fn compile_probe() -> Option<ExitStatus> {