config: Do not fail if a warning filter category cannot be imported

AUTHORS

@@ -201,6 +201,7 @@ Ilya Konstantinov
 Ionuț Turturică
 Isaac Virshup
 Israel Fruchter
+Israël Hallé
 Itxaso Aizpurua
 Iwan Briquemont
 Jaap Broekhuizen

changelog/13732.improvement.rst

@@ -0,0 +1 @@
+Previously, when filtering warnings, pytest would fail if the filter referenced a class that could not be imported. Now, this only outputs a message indicating the problem.

src/_pytest/config/__init__.py

@@ -1965,6 +1965,8 @@ def parse_warning_filter(
         raise UsageError(error_template.format(error=str(e))) from None
     try:
         category: type[Warning] = _resolve_warning_category(category_)
+    except ImportError:
+        raise
     except Exception:
         exc_info = ExceptionInfo.from_current()
         exception_text = exc_info.getrepr(style="native")
@@ -2023,7 +2025,19 @@ def apply_warning_filters(
     # Filters should have this precedence: cmdline options, config.
     # Filters should be applied in the inverse order of precedence.
     for arg in config_filters:
-        warnings.filterwarnings(*parse_warning_filter(arg, escape=False))
+        try:
+            warnings.filterwarnings(*parse_warning_filter(arg, escape=False))
+        except ImportError as e:
+            warnings.warn(
+                f"Failed to import filter module '{e.name}': {arg}", PytestConfigWarning
+            )
+            continue
 
     for arg in cmdline_filters:
-        warnings.filterwarnings(*parse_warning_filter(arg, escape=True))
+        try:
+            warnings.filterwarnings(*parse_warning_filter(arg, escape=True))
+        except ImportError as e:
+            warnings.warn(
+                f"Failed to import filter module '{e.name}': {arg}", PytestConfigWarning
+            )
+            continue

testing/test_config.py

@@ -2400,8 +2400,6 @@ def test_parse_warning_filter(
         ":" * 5,
         # Invalid action.
         "FOO::",
-        # ImportError when importing the warning class.
-        "::test_parse_warning_filter_failure.NonExistentClass::",
         # Class is not a Warning subclass.
         "::list::",
         # Negative line number.

testing/test_warnings.py

@@ -424,6 +424,33 @@ def test():
     result.stdout.fnmatch_lines(["* 1 failed in*"])
 
 
+def test_accept_unknown_category(pytester: Pytester) -> None:
+    """Category types that can't be imported don't cause failure (#13732)."""
+    pytester.makeini(
+        """
+        [pytest]
+        filterwarnings =
+            always:Failed to import filter module.*:pytest.PytestConfigWarning
+            ignore::foobar.Foobar
+    """
+    )
+    pytester.makepyfile(
+        """
+        def test():
+            pass
+    """
+    )
+    result = pytester.runpytest("-W", "ignore::bizbaz.Bizbaz")
+    result.stdout.fnmatch_lines(
+        [
+            f"*== {WARNINGS_SUMMARY_HEADER} ==*",
+            "*PytestConfigWarning: Failed to import filter module 'foobar': ignore::foobar.Foobar",
+            "*PytestConfigWarning: Failed to import filter module 'bizbaz': ignore::bizbaz.Bizbaz",
+            "* 1 passed, * warning*",
+        ]
+    )
+
+
 class TestDeprecationWarningsByDefault:
     """
     Note: all pytest runs are executed in a subprocess so we don't inherit warning filters