Add a new error, 'star-needs-assignment-target'.

This error is emitted on Python 3 when a Starred expression (*x) is
not used in an assignment target. This is not caught when parsing the
AST on Python 3, so it needs to be a separate check.

5 files changed, 28 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 745cb18..4e53733 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -192,6 +192,10 @@ ChangeLog for Pylint
       which is used when a star import is detected in another scope than the
       module level, which is an error on Python 3. Using this will emit a
       SyntaxWarning on Python 2.
+
+    * Add a new error, 'star-needs-assignment-target', emitted on Python 3 when
+      a Starred expression (*x) is not used in an assignment target. This is not
+      caught when parsing the AST on Python 3, so it needs to be a separate check.      
       
 
 
diff --git a/pylint/checkers/base.py b/pylint/checkers/base.py
index 75f8ad7..e70f428 100644
--- a/pylint/checkers/base.py
+++ b/pylint/checkers/base.py
@@ -317,6 +317,11 @@ class BasicErrorChecker(_BasicChecker):
                   'Emitted when a star expression is used as a starred '
                   'assignment target.',
                   {'minversion': (3, 0)}),
+        'E0114': ('Can use starred expression only in assignment target',
+                  'star-needs-assignment-target',
+                  'Emitted when a star expression is not used in an '
+                  'assignment target.',
+                  {'minversion': (3, 0)}),
         }
 
     @check_messages('function-redefined')
@@ -326,14 +331,24 @@ class BasicErrorChecker(_BasicChecker):
     @check_messages('too-many-star-expressions',
                     'invalid-star-assignment-target')
     def visit_assign(self, node):
-        starred = node.targets[0].nodes_of_class(astroid.Starred)
-        if len(list(starred)) > 1:
+        starred = list(node.targets[0].nodes_of_class(astroid.Starred))
+        if len(starred) > 1:
             self.add_message('too-many-star-expressions', node=node)
 
         # Check *a = b
         if isinstance(node.targets[0], astroid.Starred):
             self.add_message('invalid-star-assignment-target', node=node)
 
+    @check_messages('star-needs-assignment-target')
+    def visit_starred(self, node):
+        """Check that a Starred expression is used in an assignment target."""
+        stmt = node.statement()
+        if not isinstance(stmt, astroid.Assign):
+            return
+
+        if stmt.value is node or stmt.value.parent_of(node):
+            self.add_message('star-needs-assignment-target', node=node)
+
     @check_messages('init-is-generator', 'return-in-init',
                     'function-redefined', 'return-arg-in-generator',
                     'duplicate-argument-name')
diff --git a/pylint/test/functional/star_needs_assignment_target.py b/pylint/test/functional/star_needs_assignment_target.py
new file mode 100644
index 0000000..5421c22
--- /dev/null
+++ b/pylint/test/functional/star_needs_assignment_target.py
@@ -0,0 +1,4 @@
+"""Test for a = *b"""

+

+FIRST = *[1, 2]  # [star-needs-assignment-target]

+*THIRD, FOURTH = [1, 2, 3,]

diff --git a/pylint/test/functional/star_needs_assignment_target.rc b/pylint/test/functional/star_needs_assignment_target.rc
new file mode 100644
index 0000000..c093be2
--- /dev/null
+++ b/pylint/test/functional/star_needs_assignment_target.rc
@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.0
diff --git a/pylint/test/functional/star_needs_assignment_target.txt b/pylint/test/functional/star_needs_assignment_target.txt
new file mode 100644
index 0000000..b66975c
--- /dev/null
+++ b/pylint/test/functional/star_needs_assignment_target.txt
@@ -0,0 +1 @@
+star-needs-assignment-target:3::Can use starred expression only in assignment target