Unicode encoding error

.coveragerc

@@ -2,6 +2,7 @@
 include =
   pluggy/*
   src/pluggy/*
+  pluggy/testing/*
   testing/*
   */lib/python*/site-packages/pluggy/*
   */pypy*/site-packages/pluggy/*

changelog/13750(pytest).bugfix.rst

@@ -0,0 +1,3 @@
+This change addresses an issue in pluggy that occured when running pytest with any pluggy tracing enabled when parametrized values contained surrogate escape characters.
+Before, pluggy attempted to write trace messages using UTF-8 enconding, which fails for lone surrogates. Tracing now encodes lone surrogates with errors="replace" in order
+to ensure that trace logging will not crash hook execution in the future.

src/pluggy/_tracing.py

@@ -41,7 +41,8 @@ def _format_message(self, tags: Sequence[str], args: Sequence[object]) -> str:
 
     def _processmessage(self, tags: tuple[str, ...], args: tuple[object, ...]) -> None:
         if self._writer is not None and args:
-            self._writer(self._format_message(tags, args))
+            msg = self._format_message(tags, args)
+            self._writer(msg.encode("utf-8", "replace").decode("utf-8"))
         try:
             processor = self._tags2proc[tags]
         except KeyError:

testing/test_tracer.py

@@ -75,3 +75,38 @@ def test_setprocessor(rootlogger: TagTracer) -> None:
     log2("seen")
     tags, args = l2[0]
     assert args == ("seen",)
+
+
+def test_unicode_surrogate_handling(rootlogger: TagTracer) -> None:
+    out: list[str] = []
+    rootlogger.setwriter(out.append)
+    log = rootlogger.get("pytest")
+    s = "hello \ud800 world"
+    log(s)
+    assert len(out) == 1
+    assert "\ud800" not in out
+    assert "hello ? world" in out[0]
+
+
+def test_unicode_surrogate_handling_2(rootlogger: TagTracer) -> None:
+    out: list[str] = []
+    rootlogger.setwriter(out.append)
+    log = rootlogger.get("pytest")
+
+    bad = b"\xed\xa0\x80".decode("utf-8", "surrogatepass")
+
+    log(bad)
+
+    assert len(out) == 1
+    assert "\ud800" not in out[0]
+    assert "?" in out[0]
+
+
+def test_unicode_surrogate_handling_normal(rootlogger: TagTracer) -> None:
+    out: list[str] = []
+    rootlogger.setwriter(out.append)
+    log = rootlogger.get("pytest")
+    s = "hello world"
+    log(s)
+    assert len(out) == 1
+    assert "hello world" in out[0]