changes + test

src/_pytest/recwarn.py

@@ -329,9 +329,12 @@ def found_str() -> str:
             for w in self:
                 if not self.matches(w):
                     module = next(
-                        k
-                        for k, v in sys.modules.items()
-                        if getattr(v, "__file__", None) == w.filename
+                        (
+                            k
+                            for k, v in sys.modules.items()
+                            if getattr(v, "__file__", None) == w.filename
+                        ),
+                        None,
                     )
                     warnings.warn_explicit(
                         message=w.message,

testing/test_recwarn.py

@@ -545,6 +545,38 @@ def test_it():
         result.assert_outcomes()
 
 
+def test_re_emit_uses_correct_module(pytester: Pytester) -> None:
+    warning_module_code = """
+import warnings
+
+def trigger_warning(msg):
+    warnings.warn(msg, UserWarning)
+"""
+    pytester.makepyfile(module_a=warning_module_code)
+    pytester.makepyfile(module_b=warning_module_code)
+
+    test_code = """
+        import pytest
+    import warnings
+    from module_a import trigger_warning as trigger_warning_a
+    from module_b import trigger_warning as trigger_warning_b
+
+    def test_ignore_warning_from_module_a():
+        with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):
+            with pytest.warns(UserWarning, match="module A.") as outer:
+                warnings.filterwarnings("ignore", category=UserWarning, module="module_a")
+                with pytest.warns(UserWarning, match="module B.") as inner: # re-emit the module A warning
+                    trigger_warning_a("module A.")
+                    trigger_warning_b("module B.")
+        """
+    # Write the test to a new file called 'test_re_emit.py'
+    pytester.makepyfile(test_re_emit=test_code)
+
+    # Run the test and assert that it passed
+    result = pytester.runpytest()
+    result.assert_outcomes(passed=1)
+
+
 def test_raise_type_error_on_invalid_warning() -> None:
     """Check pytest.warns validates warning messages are strings (#10865) or
     Warning instances (#11959)."""