Fix hook tracing with specced mocks

changelog/792.bugfix.rst

@@ -0,0 +1 @@
+Fix hook tracing raising ``TypeError`` for specced mocks passed as hook arguments or returned from first-result hooks.

src/pluggy/_tracing.py

@@ -9,6 +9,7 @@
 import enum
 import os
 from typing import Any
+from typing import cast
 
 
 _Writer = Callable[[str], object]
@@ -60,10 +61,12 @@ def _format_block(indent: str, lines: list[str]) -> list[str]:
 
 def _render_value(obj: object) -> str:
     """Render a traced value, adding detail only where ``str`` is ambiguous."""
+    obj_type = type(obj)
     # Before the str check: a StrEnum member is a str whose str() drops the name.
-    if isinstance(obj, (enum.Enum, os.PathLike)):
+    if issubclass(obj_type, (enum.Enum, os.PathLike)):
         return _safe_repr(obj)
-    if isinstance(obj, str):
+    if issubclass(obj_type, str):
+        obj = cast(str, obj)
         if len(obj.splitlines()) > 1:
             return _safe_str(obj)
         if _is_plain_token(obj):
@@ -94,8 +97,8 @@ def get(self, name: str) -> TagTracerSub:
         return TagTracerSub(self, (name,))
 
     def _format_message(self, tags: Sequence[str], args: Sequence[object]) -> str:
-        if isinstance(args[-1], dict):
-            extra = args[-1]
+        if issubclass(type(args[-1]), dict):
+            extra = cast(dict[object, object], args[-1])
             args = args[:-1]
         else:
             extra = {}

testing/test_tracer.py

@@ -1,6 +1,7 @@
 import enum
 import os
 import pathlib
+from unittest.mock import Mock
 
 import pytest
 
@@ -164,6 +165,32 @@ def hello_again(self, arg):
     ]
 
 
+@pytest.mark.parametrize("spec", [str, dict])
+def test_plugin_tracing_with_mock(pm: PluginManager, spec: type) -> None:
+    class Api:
+        @hookspec(firstresult=True)
+        def hello(self, arg: object) -> object:
+            "Return the argument."
+
+    class Plugin:
+        @hookimpl
+        def hello(self, arg: object) -> object:
+            return arg
+
+    pm.add_hookspecs(Api)
+    pm.register(Plugin())
+    trace_out: list[str] = []
+    pm.trace.root.setwriter(trace_out.append)
+    pm.enable_tracing()
+
+    value = Mock(spec=spec)
+    assert pm.hook.hello(arg=value) is value
+    assert trace_out == [
+        f"  hello [hook]\n      arg: {value}\n",
+        f"  finish hello --> {value} [hook]\n",
+    ]
+
+
 class BrokenRepr:
     def __repr__(self) -> str:
         raise RuntimeError("repr is broken")