Ignore lambda calls with variadic arguments without a context.

Inferring variadic positional arguments and keyword arguments
will result into empty Tuples and Dicts, which can lead in
some cases to false positives with regard to no-value-for-parameter.
In order to avoid this, until we'll have support for call context
propagation, we're ignoring such cases if detected.
We already did that for function calls, but the previous fix
was not taking in consideration ``lambdas``

Close #2918

ChangeLog

@@ -7,6 +7,18 @@ What's New in Pylint 2.4.0?
 
 Release date: TBA
 
+* Ignore lambda calls with variadic arguments without a context.
+
+  Inferring variadic positional arguments and keyword arguments
+  will result into empty Tuples and Dicts, which can lead in
+  some cases to false positives with regard to no-value-for-parameter.
+  In order to avoid this, until we'll have support for call context
+  propagation, we're ignoring such cases if detected.
+  We already did that for function calls, but the previous fix
+  was not taking in consideration ``lambdas``
+
+  Close #2918
+
 * Added a new check, ``self-assigning-variable``
 
   This check is emitted when we detect that a variable is assigned

pylint/checkers/typecheck.py

@@ -510,44 +510,33 @@ def _has_parent_of_type(node, node_type, statement):
     return isinstance(parent, node_type)
 
 
-def _is_name_used_as_variadic(name, variadics):
-    """Check if the given name is used as a variadic argument."""
-    return any(
-        variadic.value == name or variadic.value.parent_of(name)
-        for variadic in variadics
-    )
-
-
-def _no_context_variadic_keywords(node):
+def _no_context_variadic_keywords(node, scope):
     statement = node.statement()
-    scope = node.scope()
     variadics = ()
 
-    if not isinstance(scope, astroid.FunctionDef):
-        return False
-
-    if isinstance(statement, (astroid.Return, astroid.Expr)) and isinstance(
-        statement.value, astroid.Call
-    ):
-        call = statement.value
-        variadics = list(call.keywords or []) + call.kwargs
+    if isinstance(scope, astroid.Lambda) and not isinstance(scope, astroid.FunctionDef):
+        variadics = list(node.keywords or []) + node.kwargs
+    else:
+        if isinstance(statement, (astroid.Return, astroid.Expr)) and isinstance(
+            statement.value, astroid.Call
+        ):
+            call = statement.value
+            variadics = list(call.keywords or []) + call.kwargs
 
     return _no_context_variadic(node, scope.args.kwarg, astroid.Keyword, variadics)
 
 
-def _no_context_variadic_positional(node):
-    statement = node.statement()
-    scope = node.scope()
+def _no_context_variadic_positional(node, scope):
     variadics = ()
-
-    if not isinstance(scope, astroid.FunctionDef):
-        return False
-
-    if isinstance(statement, (astroid.Expr, astroid.Return)) and isinstance(
-        statement.value, astroid.Call
-    ):
-        call = statement.value
-        variadics = call.starargs + call.kwargs
+    if isinstance(scope, astroid.Lambda) and not isinstance(scope, astroid.FunctionDef):
+        variadics = node.starargs + node.kwargs
+    else:
+        statement = node.statement()
+        if isinstance(statement, (astroid.Expr, astroid.Return)) and isinstance(
+            statement.value, astroid.Call
+        ):
+            call = statement.value
+            variadics = call.starargs + call.kwargs
 
     return _no_context_variadic(node, scope.args.vararg, astroid.Starred, variadics)
 
@@ -563,6 +552,10 @@ def _no_context_variadic(node, variadic_name, variadic_type, variadics):
     This can lead pylint to believe that a function call receives
     too few arguments.
     """
+    scope = node.scope()
+    is_in_lambda_scope = not isinstance(scope, astroid.FunctionDef) and isinstance(
+        scope, astroid.Lambda
+    )
     statement = node.statement()
     for name in statement.nodes_of_class(astroid.Name):
         if name.name != variadic_name:
@@ -576,10 +569,19 @@ def _no_context_variadic(node, variadic_name, variadic_type, variadics):
         else:
             continue
 
-        inferred_statement = inferred.statement()
-        if not length and isinstance(inferred_statement, astroid.FunctionDef):
+        if is_in_lambda_scope and isinstance(inferred.parent, astroid.Arguments):
+            # The statement of the variadic will be the assignment itself,
+            # so we need to go the lambda instead
+            inferred_statement = inferred.parent.parent
+        else:
+            inferred_statement = inferred.statement()
+
+        if not length and isinstance(inferred_statement, astroid.Lambda):
             is_in_starred_context = _has_parent_of_type(node, variadic_type, statement)
-            used_as_starred_argument = _is_name_used_as_variadic(name, variadics)
+            used_as_starred_argument = any(
+                variadic.value == name or variadic.value.parent_of(name)
+                for variadic in variadics
+            )
             if is_in_starred_context or used_as_starred_argument:
                 return True
     return False
@@ -1120,9 +1122,14 @@ def visit_call(self, node):
         keyword_args = list(call_site.keyword_arguments.keys())
 
         # Determine if we don't have a context for our call and we use variadics.
-        if isinstance(node.scope(), astroid.FunctionDef):
-            has_no_context_positional_variadic = _no_context_variadic_positional(node)
-            has_no_context_keywords_variadic = _no_context_variadic_keywords(node)
+        node_scope = node.scope()
+        if isinstance(node_scope, (astroid.Lambda, astroid.FunctionDef)):
+            has_no_context_positional_variadic = _no_context_variadic_positional(
+                node, node_scope
+            )
+            has_no_context_keywords_variadic = _no_context_variadic_keywords(
+                node, node_scope
+            )
         else:
             has_no_context_positional_variadic = (
                 has_no_context_keywords_variadic

tests/functional/arguments.py

@@ -1,5 +1,5 @@
 # pylint: disable=too-few-public-methods, no-absolute-import,missing-docstring,import-error,wrong-import-position
-# pylint: disable=wrong-import-order, useless-object-inheritance
+# pylint: disable=wrong-import-order, useless-object-inheritance,unnecessary-lambda
 
 def decorator(fun):
     """Decorator"""
@@ -235,3 +235,10 @@ def mutated_function(arg):
 
 mutated_function(do_something=False)
 mutated_function()
+
+
+def func(one, two, three):
+    return one + two + three
+
+
+CALL = lambda *args: func(*args)