error code

Author: hauntsaninja

mypy/errorcodes.py

@@ -215,6 +215,9 @@ def __hash__(self) -> int:
     "General",
     default_enabled=False,
 )
+STR_UNPACK: Final[ErrorCode] = ErrorCode(
+    "str-unpack", "Warn about expressions that unpack str", "General"
+)
 NAME_MATCH: Final = ErrorCode(
     "name-match", "Check that type definition has consistent naming", "General"
 )

mypy/messages.py

@@ -1144,7 +1144,7 @@ def wrong_number_values_to_unpack(
             )
 
     def unpacking_strings_disallowed(self, context: Context) -> None:
-        self.fail("Unpacking a string is disallowed", context)
+        self.fail("Unpacking a string is disallowed", context, code=codes.STR_UNPACK)
 
     def type_not_iterable(self, type: Type, context: Context) -> None:
         self.fail(f"{format_type(type, self.options)} object is not iterable", context)

test-data/unit/check-expressions.test

@@ -2492,3 +2492,20 @@ x + T  # E: Unsupported left operand type for + ("int")
 T()  # E: "TypeVar" not callable
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]
+
+[case testStringDisallowedUnpacking]
+d: dict[str, str]
+
+for a1, b1 in d: # E: Unpacking a string is disallowed
+    reveal_type(a1)  # E: Cannot determine type of "a1" \
+                     # N: Revealed type is "Any"
+    reveal_type(b1)  # E: Cannot determine type of "b1" \
+                     # N: Revealed type is "Any"
+
+s = "foo"
+a2, b2 = s # E: Unpacking a string is disallowed
+reveal_type(a2)  # E: Cannot determine type of "a2" \
+                 # N: Revealed type is "Any"
+reveal_type(b2)  # E: Cannot determine type of "b2" \
+                 # N: Revealed type is "Any"
+[builtins fixtures/dict.pyi]

test-data/unit/check-unions.test

@@ -729,20 +729,6 @@ reveal_type(x) # N: Revealed type is "Any"
 reveal_type(y) # N: Revealed type is "Any"
 [out]
 
-[case testStringDisallowedUnpacking]
-from typing import Dict
-
-d: Dict[str, str]
-
-for a, b in d: # E: Unpacking a string is disallowed
-    pass
-
-s = "foo"
-a, b = s # E: Unpacking a string is disallowed
-
-[builtins fixtures/dict.pyi]
-[out]
-
 [case testUnionAlwaysTooMany]
 from typing import Union, Tuple
 bad: Union[Tuple[int, int, int], Tuple[str, str, str]]