Add a new check `dict-init-mutate` (#7794)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/pylint/extensions/dict_init_mutate.py b/pylint/extensions/dict_init_mutate.py
new file mode 100644
index 000000000..fb4c83647
--- /dev/null
+++ b/pylint/extensions/dict_init_mutate.py
@@ -0,0 +1,66 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
+# Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt
+
+"""Check for use of dictionary mutation after initialization."""
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from astroid import nodes
+
+from pylint.checkers import BaseChecker
+from pylint.checkers.utils import only_required_for_messages
+from pylint.interfaces import HIGH
+
+if TYPE_CHECKING:
+    from pylint.lint.pylinter import PyLinter
+
+
+class DictInitMutateChecker(BaseChecker):
+    name = "dict-init-mutate"
+    msgs = {
+        "C3401": (
+            "Declare all known key/values when initializing the dictionary.",
+            "dict-init-mutate",
+            "Dictionaries can be initialized with a single statement "
+            "using dictionary literal syntax.",
+        )
+    }
+
+    @only_required_for_messages("dict-init-mutate")
+    def visit_assign(self, node: nodes.Assign) -> None:
+        """
+        Detect dictionary mutation immediately after initialization.
+
+        At this time, detecting nested mutation is not supported.
+        """
+        if not isinstance(node.value, nodes.Dict):
+            return
+
+        dict_name = node.targets[0]
+        if len(node.targets) != 1 or not isinstance(dict_name, nodes.AssignName):
+            return
+
+        first_sibling = node.next_sibling()
+        if (
+            not first_sibling
+            or not isinstance(first_sibling, nodes.Assign)
+            or len(first_sibling.targets) != 1
+        ):
+            return
+
+        sibling_target = first_sibling.targets[0]
+        if not isinstance(sibling_target, nodes.Subscript):
+            return
+
+        sibling_name = sibling_target.value
+        if not isinstance(sibling_name, nodes.Name):
+            return
+
+        if sibling_name.name == dict_name.name:
+            self.add_message("dict-init-mutate", node=node, confidence=HIGH)
+
+
+def register(linter: PyLinter) -> None:
+    linter.register_checker(DictInitMutateChecker(linter))