Raises an error when a fixture conflict for the same file

changelog/12953.improvement.rst

@@ -0,0 +1 @@
+When creating a fixture with the same name in different ways in the same file, an error is now raised.

src/_pytest/fixtures.py

@@ -1728,6 +1728,20 @@ def _register_fixture(
         )
 
         faclist = self._arg2fixturedefs.setdefault(name, [])
+
+        by_plugin = fixture_def.baseid == ""
+
+        if not by_plugin and faclist:
+            # If the fixture from a plugin, no conflict detection is performed.
+            if faclist[-1].baseid == fixture_def.baseid:
+                # The same file may create two fixtures with the same name (#12952).
+                msg = (
+                    f"Fixture definition conflict: {name!r} has multiple implementations,"
+                    f"namely {faclist[-1].func!r} and {func}  (from: {nodeid!r})."
+                )
+                print(msg)
+                raise ValueError(msg)
+
         if fixture_def.has_location:
             faclist.append(fixture_def)
         else:

testing/python/fixtures.py

@@ -5009,3 +5009,26 @@ def test_result():
     )
     result = pytester.runpytest()
     assert result.ret == 0
+
+
+def test_fixture_name_conflict(pytester: Pytester) -> None:
+    """The same file may create two fixtures with the same name, but not override(#12952)."""
+    pytester.makepyfile(
+        """
+        import pytest
+
+        @pytest.fixture(name="cache")
+        def c1():  # Create first, but register later
+            return 1
+
+        @pytest.fixture(name="cache")  # Create later, but register first
+        def c0():
+            return 0
+
+        def test_value(cache):
+            assert cache == 0  # Failed, `cache` from c1
+    """
+    )
+
+    result = pytester.runpytest()
+    result.stdout.fnmatch_lines(["E   ValueError: Fixture definition conflict:*"])