From 9295f8122d366137c8cace79cf4b163f586028d3 Mon Sep 17 00:00:00 2001
From: Samuel Colvin <s@muelcolvin.com>
Date: Fri, 24 Mar 2023 15:46:49 +0000
Subject: [PATCH] stop panic on to_string, report using write_unraisable
 instead

---
 newsfragments/3062.fixed.md |  1 +
 src/gil.rs                  |  8 ++++++++
 src/marker.rs               |  8 ++++++++
 src/types/mod.rs            | 11 +++++++++--
 4 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 newsfragments/3062.fixed.md

diff --git a/newsfragments/3062.fixed.md b/newsfragments/3062.fixed.md
new file mode 100644
index 00000000000..9738978f7b4
--- /dev/null
+++ b/newsfragments/3062.fixed.md
@@ -0,0 +1 @@
+Stop panic on `fmt::Display`, instead return `"<unprintable object>"` string and report error via `sys.unraisablehook()`
diff --git a/src/gil.rs b/src/gil.rs
index aa4ed2e7825..5e3aa4d33ff 100644
--- a/src/gil.rs
+++ b/src/gil.rs
@@ -463,6 +463,14 @@ pub(crate) fn ensure_gil_unchecked() -> EnsureGIL {
     }
 }
 
+/// Yields access to the GIL only if it is already held
+pub(crate) fn try_ensure_gil() -> Option<EnsureGIL> {
+    if gil_is_acquired() {
+        Some(EnsureGIL(None))
+    } else {
+        None
+    }
+}
 /// Struct used internally which avoids acquiring the GIL where it's not necessary.
 pub(crate) struct EnsureGIL(Option<GILGuard>);
 
diff --git a/src/marker.rs b/src/marker.rs
index bd30d3c3396..7f93d27a1bc 100644
--- a/src/marker.rs
+++ b/src/marker.rs
@@ -354,6 +354,14 @@ impl Python<'_> {
     {
         f(gil::ensure_gil_unchecked().python())
     }
+
+    /// Similar to [`Self::with_gil`] but only provides access to the GIL if it is already held.
+    pub fn try_with_gil<F, R>(f: F) -> Option<R>
+    where
+        F: for<'py> FnOnce(Python<'py>) -> R,
+    {
+        gil::try_ensure_gil().map(|gil| f(unsafe { gil.python() }))
+    }
 }
 
 impl<'py> Python<'py> {
diff --git a/src/types/mod.rs b/src/types/mod.rs
index 8d3e2714383..235093dfa93 100644
--- a/src/types/mod.rs
+++ b/src/types/mod.rs
@@ -99,8 +99,15 @@ macro_rules! pyobject_native_type_base(
             fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>)
                    -> ::std::result::Result<(), ::std::fmt::Error>
             {
-                let s = self.str().or(::std::result::Result::Err(::std::fmt::Error))?;
-                f.write_str(&s.to_string_lossy())
+                match self.str() {
+                    ::std::result::Result::Ok(s) => return f.write_str(&s.to_string_lossy()),
+                    ::std::result::Result::Err(err) => err.write_unraisable(self.py(), ::std::option::Option::Some(self)),
+                }
+
+                match self.get_type().name() {
+                    ::std::result::Result::Ok(name) => ::std::write!(f, "<unprintable {} object>", name),
+                    ::std::result::Result::Err(_err) => f.write_str("<unprintable object>"),
+                }
             }
         }