Preserve subscript index reads during method inlining

CHANGELOG.md

@@ -1,6 +1,7 @@
 # **Upcoming release**
 
 - ...
+- Fix inlining parameters used as indices in subscript assignments (#827).
 
 # Release 1.15.0
 

rope/base/worder.py

@@ -486,6 +486,12 @@ def get_assignment_type(self, offset):
         if double not in ("==", "<=", ">=", "!="):
             for op in [single, double, triple]:
                 if op.endswith("="):
+                    for end in range(next_char, next_char + len(op) - 1):
+                        if self.code[end] in ")]":
+                            # A subscript index is read, unlike an unpacking target.
+                            parens_start = self._find_parens_start(end)
+                            if self._find_primary_start(end) < parens_start:
+                                return None
                     return op
 
     def get_primary_range(self, offset):

ropetest/codeanalyzetest.py

@@ -387,6 +387,56 @@ def test_is_assigned_here_for_not_equal_test(self):
         word_finder = worder.Worder(code)
         self.assertFalse(word_finder.is_assigned_here(0))
 
+    def test_subscript_assignment_does_not_assign_its_index(self):
+        for code in (
+            "get_registry()[name] = value\n",
+            "registry[name]=value\n",
+            "registry[name]+=value\n",
+            "registry[(name)]=value\n",
+            "registry[left + name] = value\n",
+            "registry[:name] = value\n",
+            "registry[name:]=value\n",
+            "registry[registry[name]]=value\n",
+            "[registry[name]]=values\n",
+        ):
+            with self.subTest(code=code):
+                word_finder = worder.Worder(code)
+                self.assertFalse(word_finder.is_assigned_here(code.index("name")))
+
+    def test_grouped_and_list_assignment_targets_are_assigned(self):
+        for code in (
+            "(name)=value\n",
+            "(name) = value\n",
+            "[name]=value\n",
+            "[name] = value\n",
+            "[(name)]=value\n",
+            "([name])=value\n",
+        ):
+            with self.subTest(code=code):
+                word_finder = worder.Worder(code)
+                self.assertTrue(word_finder.is_assigned_here(code.index("name")))
+
+    def test_assignment_operator_types(self):
+        for operator in (
+            "=", "+=", "-=", "*=", "/=", "//=", "%=", "**=", "@=",
+            "&=", "|=", "^=", "<<=", ">>=", ":=",
+        ):
+            code = "name " + operator + " value\n"
+            if operator == ":=":
+                code = "(" + code.rstrip() + ")\n"
+            with self.subTest(operator=operator):
+                word_finder = worder.Worder(code)
+                self.assertEqual(
+                    operator, word_finder.get_assignment_type(code.index("name"))
+                )
+
+    def test_comparison_operators_do_not_assign(self):
+        for operator in ("==", "!=", "<=", ">="):
+            code = "name " + operator + " value\n"
+            with self.subTest(operator=operator):
+                word_finder = worder.Worder(code)
+                self.assertFalse(word_finder.is_assigned_here(0))
+
     # XXX: is_assigned_here should work for tuple assignments
     def xxx_test_is_assigned_here_for_tuple_assignment(self):
         code = "a, b = (1, 2)\n"

ropetest/refactor/inlinetest.py

@@ -354,6 +354,26 @@ def a_func(param):
         self._inline2(self.mod, self.mod.read().index("a_func") + 1)
         self.assertEqual("print(1)\n", self.mod.read())
 
+    def test_parameters_used_as_subscript_assignment_indices(self):
+        code = dedent("""\
+            registry = {}
+            def get_registry():
+                return registry
+            def register(name, value):
+                get_registry()[name] = value
+            register("cache", 42)
+        """)
+        refactored = self._inline(code, code.index("register") + 1)
+        self.assertEqual(
+            dedent("""\
+                registry = {}
+                def get_registry():
+                    return registry
+                get_registry()["cache"] = 42
+            """),
+            refactored,
+        )
+
     def test_parameters_renaming_for_passed_statements(self):
         self.mod.write(dedent("""\
             def a_func(param):