checker.py: Add support for list concatenation

This adds support for when '__all__'
is defined from concatenated lists.
However, because pyflakes is not an
interpreter, this only applies to
certain reduced test cases.

Fixes https://github.com/PyCQA/pyflakes/issues/276

2 files changed, 27 insertions, 16 deletions

diff --git a/pyflakes/checker.py b/pyflakes/checker.py
index 2060ce4..3dd968d 100644
--- a/pyflakes/checker.py
+++ b/pyflakes/checker.py
@@ -390,10 +390,10 @@ class ExportBinding(Binding):
     can be determined statically, they will be treated as names for export and
     additional checking applied to them.
 
-    The only C{__all__} assignment that can be recognized is one which takes
-    the value of a literal list containing literal strings.  For example::
+    The only recognized C{__all__} assignment via list concatenation is in the
+    following format:
 
-        __all__ = ["foo", "bar"]
+        __all__ = ['a'] + ['b'] + ['c']
 
     Names which are imported and not otherwise used but appear in the value of
     C{__all__} will not have an unused import warning reported for them.
@@ -405,9 +405,25 @@ class ExportBinding(Binding):
         else:
             self.names = []
         if isinstance(source.value, (ast.List, ast.Tuple)):
-            for node in source.value.elts:
-                if isinstance(node, ast.Str):
-                    self.names.append(node.s)
+            self.names += ast.literal_eval(source.value)
+        # If concatenating lists
+        elif isinstance(source.value, ast.BinOp):
+            currentValue = source.value
+            while isinstance(currentValue.right, ast.List):
+                left = currentValue.left
+                right = currentValue.right
+                self.names += ast.literal_eval(right)
+                # If more lists are being added
+                if isinstance(left, ast.BinOp):
+                    currentValue = left
+                # If just two lists are being added
+                elif isinstance(left, ast.List):
+                    self.names += ast.literal_eval(left)
+                    # All lists accounted for - done
+                    break
+                # If not list concatenation
+                else:
+                    break
         super(ExportBinding, self).__init__(name, source)
 
 
diff --git a/pyflakes/test/test_imports.py b/pyflakes/test/test_imports.py
index 86e1d37..f83e77e 100644
--- a/pyflakes/test/test_imports.py
+++ b/pyflakes/test/test_imports.py
@@ -1068,19 +1068,14 @@ class TestSpecialAll(TestCase):
             __all__ += ['c', 'd']
         ''', m.UndefinedExport, m.UndefinedExport)
 
-    def test_unrecognizable(self):
+    def test_concatenationAssignment(self):
         """
-        If C{__all__} is defined in a way that can't be recognized statically,
-        it is ignored.
+        The C{__all__} variable is defined through list concatenation.
         """
         self.flakes('''
-        import foo
-        __all__ = ["f" + "oo"]
-        ''', m.UnusedImport)
-        self.flakes('''
-        import foo
-        __all__ = [] + ["foo"]
-        ''', m.UnusedImport)
+        import sys
+        __all__ = ['a'] + ['b'] + ['c']
+        ''', m.UndefinedExport, m.UndefinedExport, m.UndefinedExport, m.UnusedImport)
 
     def test_unboundExported(self):
         """