Avoid duplicate function arguments when --showlocals is enabled

changelog/5675.improvement.rst

@@ -0,0 +1 @@
+When `--showlocals` is enabled, function arguments are no longer displayed in a separate block because they are already included in the locals output.

src/_pytest/_code/code.py

@@ -1483,7 +1483,8 @@ def toterminal(self, tw: TerminalWriter) -> None:
                 self.reprlocals.toterminal(tw, indent=" " * 8)
             return
 
-        if self.reprfuncargs:
+        # Locals already include the arguments; skip the separate block.
+        if self.reprfuncargs and self.reprlocals is None:
             self.reprfuncargs.toterminal(tw)
 
         self._write_entry_lines(tw)

testing/test_terminal.py

@@ -1227,6 +1227,33 @@ def test_showlocals_short():
             ]
         )
 
+    def test_showlocals_no_duplicate_funcargs(self, pytester: Pytester) -> None:
+        """Helper params must not render twice with --showlocals (#5675)."""
+        p1 = pytester.makepyfile(
+            """
+            class LargeRepr:
+                def __repr__(self):
+                    return "X" * 10000
+
+            def helper(data, flag):
+                assert flag is False
+
+            def test_failure():
+                helper(LargeRepr(), True)
+            """
+        )
+        # Without --showlocals the funcargs block stays (truncated).
+        result = pytester.runpytest(p1)
+        result.stdout.fnmatch_lines(["data = X*"])
+        # With --showlocals params show once, in the padded locals block.
+        result = pytester.runpytest(p1, "--showlocals")
+        result.stdout.no_fnmatch_line("data = X*")
+        result.stdout.fnmatch_lines(["data  *= X*"])
+        # Same at higher verbosity; locals keep their existing behavior.
+        result = pytester.runpytest(p1, "--showlocals", "-vv")
+        result.stdout.no_fnmatch_line("data = X*")
+        result.stdout.fnmatch_lines(["data  *= X*"])
+
     @pytest.fixture
     def verbose_testfile(self, pytester: Pytester) -> Path:
         return pytester.makepyfile(