Small corrections to array slice parsing

rewrite/rewrite/python/_parser_visitor.py

@@ -1743,14 +1743,22 @@ def visit_SetComp(self, node):
 
     def visit_Slice(self, node):
         prefix = self.__whitespace()
-        if node.lower:
-            lower = self.__pad_right(self.__convert(node.lower), self.__source_before(':'))
-        else:
-            lower = self.__pad_right(j.Empty(random_id(), Space.EMPTY, Markers.EMPTY), self.__source_before(':'))
-        upper = self.__pad_right(
-            self.__convert(node.upper) if node.upper else j.Empty(random_id(), Space.EMPTY, Markers.EMPTY),
-            self.__source_before(':') if node.step else self.__whitespace('\n'))
-        step = self.__pad_right(self.__convert(node.step), self.__whitespace('\n')) if node.step else None
+
+        lower_expr = self.__convert(node.lower) if node.lower else None
+        right_padding = self.__whitespace(':')
+        lower = self.__pad_right(lower_expr, right_padding) if lower_expr else None
+        self._cursor += 1
+
+        upper_expr = self.__convert(node.upper) if node.upper else None
+        right_padding = self.__whitespace()
+        has_step = self.__cursor_at(':')
+        upper = self.__pad_right(upper_expr if node.upper else j.Empty(random_id(), self.__whitespace(), Markers.EMPTY), right_padding)
+        self._cursor += 1
+
+        step = self.__pad_right(
+            self.__convert(node.step) if node.step else j.Empty(random_id(), Space.EMPTY, Markers.EMPTY),
+            self.__whitespace(']')) if node.step or has_step else None
+
         return py.Slice(
             random_id(),
             prefix,

rewrite/tests/python/all/array_test.py

@@ -26,6 +26,16 @@ def test_array_slice_no_upper():
     rewrite_run(python("a = [1, 2][0:]"))
 
 
+def test_array_slice_all_empty():
+    # language=python
+    rewrite_run(python("a = [1, 2][ :  :   ]"))
+
+
+def test_array_slice_empty_upper_and_step():
+    # language=python
+    rewrite_run(python("a = [1, 2][0::]"))
+
+
 def test_array_slice_no_lower():
     # language=python
     rewrite_run(python("a = [1, 2][:1]"))