Only remove trailing comma if the last alias is removed (Instagram#334)

libcst/codemod/commands/tests/test_remove_unused_imports.py

@@ -83,3 +83,10 @@ def test_access_in_assignment(self) -> None:
             b(0)[x] = False
         """
         self.assertCodemod(before, before)
+
+    def test_no_formatting_if_no_unused_imports(self) -> None:
+        before = """
+            from m import (a, b,)
+            a(b, 'look at these ugly quotes')
+        """
+        self.assertCodemod(before, before)

libcst/codemod/visitors/_remove_imports.py

@@ -343,17 +343,22 @@ def leave_Import(
                 names_to_keep.append(import_alias)
                 continue
 
+        # no changes
+        if names_to_keep == original_node.names:
+            return updated_node
+
         # Now, either remove this statement or remove the imports we are
         # deleting from this statement.
         if len(names_to_keep) == 0:
             return cst.RemoveFromParent()
-        else:
+
+        if names_to_keep[-1] != original_node.names[-1]:
             # Remove trailing comma in order to not mess up import statements.
             names_to_keep = [
                 *names_to_keep[:-1],
                 names_to_keep[-1].with_changes(comma=cst.MaybeSentinel.DEFAULT),
             ]
-            return updated_node.with_changes(names=names_to_keep)
+        return updated_node.with_changes(names=names_to_keep)
 
     def leave_ImportFrom(
         self, original_node: cst.ImportFrom, updated_node: cst.ImportFrom
@@ -399,14 +404,19 @@ def leave_ImportFrom(
                 names_to_keep.append(import_alias)
                 continue
 
+        # no changes
+        if names_to_keep == names:
+            return updated_node
+
         # Now, either remove this statement or remove the imports we are
         # deleting from this statement.
         if len(names_to_keep) == 0:
             return cst.RemoveFromParent()
-        else:
+
+        if names_to_keep[-1] != names[-1]:
             # Remove trailing comma in order to not mess up import statements.
             names_to_keep = [
                 *names_to_keep[:-1],
                 names_to_keep[-1].with_changes(comma=cst.MaybeSentinel.DEFAULT),
             ]
-            return updated_node.with_changes(names=names_to_keep)
+        return updated_node.with_changes(names=names_to_keep)

libcst/codemod/visitors/tests/test_remove_imports.py

@@ -797,3 +797,17 @@ def visit_ImportFrom(self, node: cst.ImportFrom) -> None:
             after,
             RemoveImportTransformer(CodemodContext()).transform_module(module).code,
         )
+
+    def test_remove_comma(self) -> None:
+        """
+        Trailing commas should be removed if and only if the last alias is removed.
+        """
+        before = """
+            from m import (a, b,)
+            import x, y
+        """
+        after = """
+            from m import (b,)
+            import x
+        """
+        self.assertCodemod(before, after, [("m", "a", None), ("y", None, None)])