Add populate_all feature

Closes #16

README.rst

@@ -112,6 +112,8 @@ Below is the full listing of options::
                             this only triggers if there is only one star import in
                             the file; this is skipped if there are any uses of
                             `__all__` or `del` in the file
+      --populate-all        populate `__all__` with unused import found in the
+                            code.
       --remove-all-unused-imports
                             remove all unused imports (not just those from the
                             standard library)

autoflake.py

@@ -294,7 +294,8 @@ def break_up_import(line):
 def filter_code(source, additional_imports=None,
                 expand_star_imports=False,
                 remove_all_unused_imports=False,
-                remove_unused_variables=False):
+                remove_unused_variables=False,
+                populate_all=False):
     """Yield code with unused imports removed."""
     imports = SAFE_IMPORTS
     if additional_imports:
@@ -335,6 +336,10 @@ def filter_code(source, additional_imports=None,
     else:
         marked_variable_line_numbers = frozenset()
 
+    if populate_all:
+        marked_import_line_numbers = frozenset()
+        source = populate_all_with_modules(source, marked_unused_module)
+
     sio = io.StringIO(source)
     previous_line = ''
     for line_number, line in enumerate(sio.readlines(), start=1):
@@ -478,6 +483,43 @@ def filter_useless_pass(source):
             yield line
 
 
+def populate_all_with_modules(source, marked_unused_module):
+    all_syntax = re.search('^__all__(.)+\]', source, flags=re.MULTILINE)
+    if all_syntax:
+        # If there are existing `__all__`, parse it and append to it
+        insert_position = all_syntax.span()[0]
+        end_position = all_syntax.span()[1]
+        all_modules = all_syntax.group().split('=')[1].strip()
+        all_modules = ast.literal_eval(all_modules)
+    else:
+        # If no existing `__all__`, always append in EOF
+        insert_position = len(source)
+        end_position = -1
+        all_modules = []
+
+    for modules in marked_unused_module.values():
+        # Get the imported name, `a.b.Foo` -> Foo
+        all_modules += [get_imported_name(name) for name in modules]
+
+    new_all_syntax = '__all__ = ' + str(all_modules)
+    source = source[:insert_position] + new_all_syntax + source[end_position:]
+    return source
+
+
+def get_imported_name(module):
+    """
+    Return only imported name from pyflakes full module path
+
+    Example:
+    - `a.b.Foo` -> `Foo`
+    - `a as b` -> b
+    """
+    if '.' in module:
+        return module.split('.')[-1]
+    elif ' as ' in module:
+        return module.split(' as ')[-1]
+    return module
+
 def get_indentation(line):
     """Return leading whitespace."""
     if line.strip():
@@ -497,7 +539,8 @@ def get_line_ending(line):
 
 
 def fix_code(source, additional_imports=None, expand_star_imports=False,
-             remove_all_unused_imports=False, remove_unused_variables=False):
+             remove_all_unused_imports=False, remove_unused_variables=False,
+             populate_all=False):
     """Return code with all filtering run on it."""
     if not source:
         return source
@@ -515,9 +558,10 @@ def fix_code(source, additional_imports=None, expand_star_imports=False,
                     additional_imports=additional_imports,
                     expand_star_imports=expand_star_imports,
                     remove_all_unused_imports=remove_all_unused_imports,
-                    remove_unused_variables=remove_unused_variables))))
+                    remove_unused_variables=remove_unused_variables,
+                    populate_all=populate_all))))
 
-        if filtered_source == source:
+        if filtered_source == source or populate_all:
             break
         source = filtered_source
 
@@ -537,7 +581,9 @@ def fix_file(filename, args, standard_out):
         additional_imports=args.imports.split(',') if args.imports else None,
         expand_star_imports=args.expand_star_imports,
         remove_all_unused_imports=args.remove_all_unused_imports,
-        remove_unused_variables=args.remove_unused_variables)
+        remove_unused_variables=args.remove_unused_variables,
+        populate_all=args.populate_all,
+    )
 
     if original_source != filtered_source:
         if args.in_place:
@@ -692,6 +738,9 @@ def _main(argv, standard_out, standard_error):
                              'one star import in the file; this is skipped if '
                              'there are any uses of `__all__` or `del` in the '
                              'file')
+    parser.add_argument('--populate-all', action='store_true',
+                        help='populate `__all__` with unused import found in '
+                        'the code.')
     parser.add_argument('--remove-all-unused-imports', action='store_true',
                         help='remove all unused imports (not just those from '
                              'the standard library)')

test_autoflake.py

@@ -485,6 +485,49 @@ def foo():
 """
         self.assertEqual(line, ''.join(autoflake.filter_code(line)))
 
+    def test_filter_code_populate_all(self):
+        self.assertEqual("""
+import math
+import sys
+__all__ = ['math', 'sys']
+""", ''.join(autoflake.filter_code("""
+import math
+import sys
+""", populate_all=True)))
+
+    def test_filter_code_populate_all_appending(self):
+        self.assertEqual("""
+import math
+import sys
+__all__ = ['math', 'sys']
+""", ''.join(autoflake.filter_code("""
+import math
+import sys
+__all__ = ['math']
+""", populate_all=True)))
+
+    def test_filter_code_populate_all_ignore_comment(self):
+        self.assertEqual("""
+import math
+import sys
+# __all__ = ['math']
+__all__ = ['math', 'sys']
+""", ''.join(autoflake.filter_code("""
+import math
+import sys
+# __all__ = ['math']
+""", populate_all=True)))
+
+    def test_filter_code_populate_all_from_import(self):
+        self.assertEqual("""
+from a.b import Foo
+from a.c import Bar
+__all__ = ['Foo', 'Bar']
+""", ''.join(autoflake.filter_code("""
+from a.b import Foo
+from a.c import Bar
+""", populate_all=True)))
+
     def test_fix_code(self):
         self.assertEqual(
             """\