Fix false negative for consider-using-augmented-assign on dicts

Assignments on dictionaries which used the same subscripts were not
generating `consider-using-augmented-assign` messages. This has been
fixed.

Closes pylint-dev#8959.

doc/whatsnew/fragments/8959.false_negative

@@ -0,0 +1,3 @@
+``consider-using-augmented-assign`` is now applied to dictionaries as well.
+
+Closes #8959.

pylint/checkers/utils.py

@@ -2041,6 +2041,26 @@ def is_hashable(node: nodes.NodeNG) -> bool:
         return True
 
 
+def subscript_chain_is_equal(left: nodes.Subscript, right: nodes.Subscript) -> bool:
+    while isinstance(left, nodes.Subscript) and isinstance(right, nodes.Subscript):
+        try:
+            if (
+                get_subscript_const_value(left).value
+                != get_subscript_const_value(right).value
+            ):
+                return False
+
+            left = left.value
+            right = right.value
+        except (AttributeError, InferredTypeError):
+            return False
+
+    try:
+        return left.name == right.name  # type: ignore[no-any-return]
+    except AttributeError:
+        return False
+
+
 def _is_target_name_in_binop_side(
     target: nodes.AssignName | nodes.AssignAttr, side: nodes.NodeNG | None
 ) -> bool:
@@ -2051,6 +2071,9 @@ def _is_target_name_in_binop_side(
         return False
     if isinstance(side, nodes.Attribute) and isinstance(target, nodes.AssignAttr):
         return target.as_string() == side.as_string()  # type: ignore[no-any-return]
+    if isinstance(side, nodes.Subscript) and isinstance(target, nodes.Subscript):
+        return subscript_chain_is_equal(side, target)
+
     return False
 
 
@@ -2065,7 +2088,7 @@ def is_augmented_assign(node: nodes.Assign) -> tuple[bool, str]:
     binop = node.value
     target = node.targets[0]
 
-    if not isinstance(target, (nodes.AssignName, nodes.AssignAttr)):
+    if not isinstance(target, (nodes.AssignName, nodes.AssignAttr, nodes.Subscript)):
         return False, ""
 
     # We don't want to catch x = "1" + x or x = "%s" % x

tests/functional/ext/code_style/cs_consider_using_augmented_assign.py

@@ -120,6 +120,15 @@ def return_str() -> str:
 x = x <= 3
 x = 3 <= x
 
+# Should also apply to dictionaries when subscripts are the same
+my_dict = {"count": 5}
+my_dict["count"] = my_dict["count"] + 2  # [consider-using-augmented-assign]
+my_dict["apples"] = my_dict["count"] + 1
+
+my_dict = {"msg": {"title": "Hello"}}
+my_dict["msg"]["title"] = my_dict["msg"]["title"] + " world!"  # [consider-using-augmented-assign]
+my_dict["msg"]["body"] = my_dict["msg"]["title"] + " everyone, this should not raise messages"
+
 
 # https://github.com/pylint-dev/pylint/issues/8086
 # consider-using-augmented-assign should only be flagged

tests/functional/ext/code_style/cs_consider_using_augmented_assign.txt

@@ -24,4 +24,6 @@ consider-using-augmented-assign:104:0:104:9::Use '&=' to do an augmented assign
 consider-using-augmented-assign:105:0:105:9::Use '&=' to do an augmented assign directly:INFERENCE
 consider-using-augmented-assign:108:0:108:9::Use '|=' to do an augmented assign directly:INFERENCE
 consider-using-augmented-assign:109:0:109:9::Use '|=' to do an augmented assign directly:INFERENCE
-consider-using-augmented-assign:134:8:134:27:A.test:Use '+=' to do an augmented assign directly:INFERENCE
+consider-using-augmented-assign:125:0:125:39::Use '+=' to do an augmented assign directly:INFERENCE
+consider-using-augmented-assign:129:0:129:61::Use '+=' to do an augmented assign directly:INFERENCE
+consider-using-augmented-assign:143:8:143:27:A.test:Use '+=' to do an augmented assign directly:INFERENCE