From 0f06b07552e80f3438cb85d30ec407a2cd8995e8 Mon Sep 17 00:00:00 2001
From: Konrad Borowski <konrad@borowski.pw>
Date: Fri, 12 Aug 2022 15:02:34 +0000
Subject: [PATCH] Implement UnwindSafe and RefUnwindSafe for Backtrace

Backtrace doesn't have visible mutable state.
---
 library/std/src/backtrace.rs       | 3 ++-
 library/std/src/backtrace/tests.rs | 7 +++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/library/std/src/backtrace.rs b/library/std/src/backtrace.rs
index f0e199fac73..e7110aebdea 100644
--- a/library/std/src/backtrace.rs
+++ b/library/std/src/backtrace.rs
@@ -92,6 +92,7 @@
 use crate::env;
 use crate::ffi::c_void;
 use crate::fmt;
+use crate::panic::UnwindSafe;
 use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed};
 use crate::sync::LazyLock;
 use crate::sys_common::backtrace::{lock, output_filename};
@@ -427,7 +428,7 @@ fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
     }
 }
 
-type LazyResolve = impl (FnOnce() -> Capture) + Send + Sync;
+type LazyResolve = impl (FnOnce() -> Capture) + Send + Sync + UnwindSafe;
 
 fn lazy_resolve(mut capture: Capture) -> LazyResolve {
     move || {
diff --git a/library/std/src/backtrace/tests.rs b/library/std/src/backtrace/tests.rs
index ef419806dcc..73543a3af54 100644
--- a/library/std/src/backtrace/tests.rs
+++ b/library/std/src/backtrace/tests.rs
@@ -1,4 +1,5 @@
 use super::*;
+use crate::panic::{RefUnwindSafe, UnwindSafe};
 
 fn generate_fake_frames() -> Vec<BacktraceFrame> {
     vec![
@@ -91,3 +92,9 @@ fn test_frames() {
 
     assert!(iter.all(|(f, e)| format!("{f:#?}") == *e));
 }
+
+#[test]
+fn backtrace_unwind_safe() {
+    fn assert_unwind_safe<T: UnwindSafe + RefUnwindSafe>() {}
+    assert_unwind_safe::<Backtrace>();
+}