Fixed warn_on_error() not showing the actual line of the type violation

docs/versionhistory.rst

@@ -3,6 +3,10 @@ Version history
 
 This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-versioning-200>`_.
 
+**UNRELEASED**
+
+- Fixed ``warn_on_error()`` not showing where the type violation actually occurred
+
 **3.0.1** (2023-03-16)
 
 - Improved the documentation

src/typeguard/_functions.py

@@ -280,7 +280,7 @@ def warn_on_error(exc: TypeCheckError, memo: TypeCheckMemo) -> None:
     :attr:`TypeCheckConfiguration.typecheck_fail_callback`.
 
     """
-    warnings.warn(TypeCheckWarning(str(exc)))
+    warnings.warn(TypeCheckWarning(str(exc)), stacklevel=3)
 
 
 @contextmanager

tests/test_warn_on_error.py

@@ -0,0 +1,29 @@
+from typing import List
+
+import pytest
+
+from typeguard import TypeCheckWarning, check_type, config, typechecked, warn_on_error
+
+
+def test_check_type(monkeypatch, recwarn):
+    monkeypatch.setattr(config, "typecheck_fail_callback", warn_on_error)
+    with pytest.warns(TypeCheckWarning) as warning:
+        check_type(1, str)
+
+    assert len(warning.list) == 1
+    assert warning.list[0].filename == __file__
+    assert warning.list[0].lineno == test_check_type.__code__.co_firstlineno + 3
+
+
+def test_typechecked(monkeypatch, recwarn):
+    @typechecked
+    def foo() -> List[int]:
+        return ["aa"]  # type: ignore[list-item]
+
+    monkeypatch.setattr(config, "typecheck_fail_callback", warn_on_error)
+    with pytest.warns(TypeCheckWarning) as warning:
+        foo()
+
+    assert len(warning.list) == 1
+    assert warning.list[0].filename == __file__
+    assert warning.list[0].lineno == foo.__code__.co_firstlineno + 1