Fix --trace for parametrized tests

Without this, the second time it tries to stop in a parametrized
function it raises instead:

`ValueError: --trace can't be used with a fixture named func!`

> RonnyPfannschmidt
>
>practically this belongs to the FunctionDefininition (and should only happen once at that)
>unfortunately with the current design that's not exposed and we have a hack instead
>
>the ""correct" fix is not to have more than one place where this is added, but that's for after FunctionDefinition lands

Co-Authored-By: Ronny Pfannschmidt <opensource@ronnypfannschmidt.de>

changelog/6099.bugfix.rst

@@ -0,0 +1 @@
+Fix ``--trace`` when used with parametrized functions.

src/_pytest/debugging.py

@@ -275,12 +275,15 @@ def _test_pytest_function(pyfuncitem):
     _pdb = pytestPDB._init_pdb("runcall")
     testfunction = pyfuncitem.obj
     pyfuncitem.obj = _pdb.runcall
-    if "func" in pyfuncitem._fixtureinfo.argnames:  # pragma: no branch
+    if "func" in pyfuncitem.funcargs:  # pragma: no branch
         raise ValueError("--trace can't be used with a fixture named func!")
     pyfuncitem.funcargs["func"] = testfunction
-    new_list = list(pyfuncitem._fixtureinfo.argnames)
-    new_list.append("func")
-    pyfuncitem._fixtureinfo.argnames = tuple(new_list)
+    if "func" not in pyfuncitem._fixtureinfo.argnames:
+        # TODO: when using parameterized tests, the _fixtureinfo is shared
+        # that needs to move to FunctionDefinition
+        new_list = list(pyfuncitem._fixtureinfo.argnames)
+        new_list.append("func")
+        pyfuncitem._fixtureinfo.argnames = tuple(new_list)
 
 
 def _enter_pdb(node, excinfo, rep):

testing/test_pdb.py

@@ -1025,6 +1025,34 @@ def test_3():
         assert "Exit: Quitting debugger" not in child.before.decode("utf8")
         TestPDB.flush(child)
 
+    def test_trace_with_parametrize_handles_shared_fixtureinfo(self, testdir):
+        p1 = testdir.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.parametrize('myparam', [1,2])
+            def test_1(myparam):
+                assert True
+            """
+        )
+        child = testdir.spawn_pytest("--trace " + str(p1))
+        child.expect_exact("> PDB runcall (IO-capturing turned off) >")
+        child.expect_exact("test_1")
+        child.expect_exact("Pdb")
+        child.sendline("args")
+        child.expect_exact("myparam = 1\r\n")
+        child.sendline("c")
+        child.expect_exact("Pdb")
+        child.sendline("args")
+        child.expect_exact("myparam = 2\r\n")
+        child.sendline("c")
+        rest = child.read().decode("utf8")
+        assert "2 passed in" in rest
+        assert "reading from stdin while output" not in rest
+        # Only printed once - not on stderr.
+        assert "Exit: Quitting debugger" not in child.before.decode("utf8")
+        TestPDB.flush(child)
+
 
 def test_trace_after_runpytest(testdir):
     """Test that debugging's pytest_configure is re-entrant."""