Fix overzealous `arguments-differ` for variadics

No message is emitted if the overriding function provides positional or
keyword variadics in its signature that can feasibly accept and pass on
all parameters given by the overridden function.

Closes #1482
Closes #1553

1 files changed, 25 insertions, 15 deletions

diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index c1628a117..d4aa8393e 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -281,11 +281,30 @@ def _different_parameters(original, overridden, dummy_parameter_regex):
     original_parameters = _positional_parameters(original)
     overridden_parameters = _positional_parameters(overridden)
 
+    # Copy kwonlyargs list so that we don't affect later function linting
+    original_kwonlyargs = [v for v in original.args.kwonlyargs]
+
+    # Allow positional/keyword variadic in overridden to match against any
+    # positional/keyword argument in original.
+    # Keep any arguments that are found seperately in overridden to satisfy
+    # later tests
+    if overridden.args.vararg:
+        overidden_names = [v.name for v in overridden_parameters]
+        original_parameters = [
+            v for v in original_parameters if v.name in overidden_names
+        ]
+
+    if overridden.args.kwarg:
+        overidden_names = [v.name for v in overridden.args.kwonlyargs]
+        original_kwonlyargs = [
+            v for v in original.args.kwonlyargs if v.name in overidden_names
+        ]
+
     different_positional = _has_different_parameters(
         original_parameters, overridden_parameters, dummy_parameter_regex
     )
     different_kwonly = _has_different_parameters(
-        original.args.kwonlyargs, overridden.args.kwonlyargs, dummy_parameter_regex
+        original_kwonlyargs, overridden.args.kwonlyargs, dummy_parameter_regex
     )
     if original.name in PYMETHODS:
         # Ignore the difference for special methods. If the parameter
@@ -295,21 +314,12 @@ def _different_parameters(original, overridden, dummy_parameter_regex):
         # be used as keyword arguments anyway.
         different_positional = different_kwonly = False
 
-    # Both or none should have extra variadics, otherwise the method
-    # loses or gains capabilities that are not reflected into the parent method,
-    # leading to potential inconsistencies in the code.
-    different_kwarg = (
-        sum(1 for param in (original.args.kwarg, overridden.args.kwarg) if not param)
-        == 1
-    )
-    different_vararg = (
-        sum(1 for param in (original.args.vararg, overridden.args.vararg) if not param)
-        == 1
-    )
+    # Arguments will only violate LSP if there are variadics in the original
+    # that are then removed from the overridden
+    kwarg_lost = original.args.kwarg and not overridden.args.kwarg
+    vararg_lost = original.args.vararg and not overridden.args.vararg
 
-    return any(
-        (different_positional, different_kwarg, different_vararg, different_kwonly)
-    )
+    return any((different_positional, kwarg_lost, vararg_lost, different_kwonly))
 
 
 def _is_invalid_base_class(cls):