Add dot prefix if file makefile extension is invalid for pathlib (#8222)

AUTHORS

@@ -40,6 +40,7 @@ Aron Curzon
 Aviral Verma
 Aviv Palivoda
 Barney Gale
+Ben Gartner
 Ben Webb
 Benjamin Peterson
 Bernard Pratz

changelog/8192.bugfix.rst

@@ -0,0 +1,3 @@
+``testdir.makefile` now silently accepts values which don't start with ``.`` to maintain backward compatibility with older pytest versions.
+
+``pytester.makefile`` now issues a clearer error if the ``.`` is missing in the ``ext`` argument.

src/_pytest/pytester.py

@@ -64,6 +64,7 @@ from _pytest.reports import TestReport
 from _pytest.tmpdir import TempPathFactory
 from _pytest.warning_types import PytestWarning
 
+
 if TYPE_CHECKING:
     from typing_extensions import Literal
 
@@ -750,6 +751,11 @@ class Pytester:
     ) -> Path:
         items = list(files.items())
 
+        if ext and not ext.startswith("."):
+            raise ValueError(
+                f"pytester.makefile expects a file extension, try .{ext} instead of {ext}"
+            )
+
         def to_text(s: Union[Any, bytes]) -> str:
             return s.decode(encoding) if isinstance(s, bytes) else str(s)
 
@@ -1559,6 +1565,14 @@ class Testdir:
 
     def makefile(self, ext, *args, **kwargs) -> py.path.local:
         """See :meth:`Pytester.makefile`."""
+        if ext and not ext.startswith("."):
+            # pytester.makefile is going to throw a ValueError in a way that
+            # testdir.makefile did not, because
+            # pathlib.Path is stricter suffixes than py.path
+            # This ext arguments is likely user error, but since testdir has
+            # allowed this, we will prepend "." as a workaround to avoid breaking
+            # testdir usage that worked before
+            ext = "." + ext
         return py.path.local(str(self._pytester.makefile(ext, *args, **kwargs)))
 
     def makeconftest(self, source) -> py.path.local:

testing/test_pytester.py

@@ -17,6 +17,7 @@ from _pytest.pytester import LineMatcher
 from _pytest.pytester import Pytester
 from _pytest.pytester import SysModulesSnapshot
 from _pytest.pytester import SysPathsSnapshot
+from _pytest.pytester import Testdir
 
 
 def test_make_hook_recorder(pytester: Pytester) -> None:
@@ -816,3 +817,33 @@ def test_makefile_joins_absolute_path(pytester: Pytester) -> None:
 def test_testtmproot(testdir) -> None:
     """Check test_tmproot is a py.path attribute for backward compatibility."""
     assert testdir.test_tmproot.check(dir=1)
+
+
+def test_testdir_makefile_dot_prefixes_extension_silently(
+    testdir: Testdir,
+) -> None:
+    """For backwards compat #8192"""
+    p1 = testdir.makefile("foo.bar", "")
+    assert ".foo.bar" in str(p1)
+
+
+def test_pytester_makefile_dot_prefixes_extension_with_warning(
+    pytester: Pytester,
+) -> None:
+    with pytest.raises(
+        ValueError,
+        match="pytester.makefile expects a file extension, try .foo.bar instead of foo.bar",
+    ):
+        pytester.makefile("foo.bar", "")
+
+
+def test_testdir_makefile_ext_none_raises_type_error(testdir) -> None:
+    """For backwards compat #8192"""
+    with pytest.raises(TypeError):
+        testdir.makefile(None, "")
+
+
+def test_testdir_makefile_ext_empty_string_makes_file(testdir) -> None:
+    """For backwards compat #8192"""
+    p1 = testdir.makefile("", "")
+    assert "test_testdir_makefile" in str(p1)