Fix unsafe default return values in NodeVisitor methods (#18536)

Raise NotImplementedError by default in NodeVisitor visit methods.

mypy/checker.py

@@ -77,6 +77,7 @@
     FuncBase,
     FuncDef,
     FuncItem,
+    GlobalDecl,
     IfStmt,
     Import,
     ImportAll,
@@ -92,6 +93,7 @@
     MypyFile,
     NameExpr,
     Node,
+    NonlocalDecl,
     OperatorAssignmentStmt,
     OpExpr,
     OverloadedFuncDef,
@@ -7876,6 +7878,17 @@ def warn_deprecated_overload_item(
                     if candidate == target:
                         self.warn_deprecated(item.func, context)
 
+    # leafs
+
+    def visit_pass_stmt(self, o: PassStmt, /) -> None:
+        return None
+
+    def visit_nonlocal_decl(self, o: NonlocalDecl, /) -> None:
+        return None
+
+    def visit_global_decl(self, o: GlobalDecl, /) -> None:
+        return None
+
 
 class CollectArgTypeVarTypes(TypeTraverserVisitor):
     """Collects the non-nested argument types in a set."""

mypy/semanal.py

@@ -97,10 +97,12 @@
     AwaitExpr,
     Block,
     BreakStmt,
+    BytesExpr,
     CallExpr,
     CastExpr,
     ClassDef,
     ComparisonExpr,
+    ComplexExpr,
     ConditionalExpr,
     Context,
     ContinueStmt,
@@ -114,6 +116,7 @@
     Expression,
     ExpressionStmt,
     FakeExpression,
+    FloatExpr,
     ForStmt,
     FuncBase,
     FuncDef,
@@ -126,6 +129,7 @@
     ImportBase,
     ImportFrom,
     IndexExpr,
+    IntExpr,
     LambdaExpr,
     ListComprehension,
     ListExpr,
@@ -193,6 +197,7 @@
     MappingPattern,
     OrPattern,
     SequencePattern,
+    SingletonPattern,
     StarredPattern,
     ValuePattern,
 )
@@ -7529,6 +7534,34 @@ def parse_dataclass_transform_field_specifiers(self, arg: Expression) -> tuple[s
             names.append(specifier.fullname)
         return tuple(names)
 
+    # leafs
+    def visit_int_expr(self, o: IntExpr, /) -> None:
+        return None
+
+    def visit_str_expr(self, o: StrExpr, /) -> None:
+        return None
+
+    def visit_bytes_expr(self, o: BytesExpr, /) -> None:
+        return None
+
+    def visit_float_expr(self, o: FloatExpr, /) -> None:
+        return None
+
+    def visit_complex_expr(self, o: ComplexExpr, /) -> None:
+        return None
+
+    def visit_ellipsis(self, o: EllipsisExpr, /) -> None:
+        return None
+
+    def visit_temp_node(self, o: TempNode, /) -> None:
+        return None
+
+    def visit_pass_stmt(self, o: PassStmt, /) -> None:
+        return None
+
+    def visit_singleton_pattern(self, o: SingletonPattern, /) -> None:
+        return None
+
 
 def replace_implicit_first_type(sig: FunctionLike, new: Type) -> FunctionLike:
     if isinstance(sig, CallableType):

mypy/traverser.py

@@ -58,6 +58,7 @@
     OverloadedFuncDef,
     ParamSpecExpr,
     PassStmt,
+    PromoteExpr,
     RaiseStmt,
     ReturnStmt,
     RevealExpr,
@@ -67,6 +68,7 @@
     StarExpr,
     StrExpr,
     SuperExpr,
+    TempNode,
     TryStmt,
     TupleExpr,
     TypeAlias,
@@ -77,6 +79,7 @@
     TypeVarExpr,
     TypeVarTupleExpr,
     UnaryExpr,
+    Var,
     WhileStmt,
     WithStmt,
     YieldExpr,
@@ -415,6 +418,85 @@ def visit_import_from(self, o: ImportFrom, /) -> None:
         for a in o.assignments:
             a.accept(self)
 
+    # leaf nodes
+    def visit_name_expr(self, o: NameExpr, /) -> None:
+        return None
+
+    def visit_str_expr(self, o: StrExpr, /) -> None:
+        return None
+
+    def visit_int_expr(self, o: IntExpr, /) -> None:
+        return None
+
+    def visit_float_expr(self, o: FloatExpr, /) -> None:
+        return None
+
+    def visit_bytes_expr(self, o: BytesExpr, /) -> None:
+        return None
+
+    def visit_ellipsis(self, o: EllipsisExpr, /) -> None:
+        return None
+
+    def visit_var(self, o: Var, /) -> None:
+        return None
+
+    def visit_continue_stmt(self, o: ContinueStmt, /) -> None:
+        return None
+
+    def visit_pass_stmt(self, o: PassStmt, /) -> None:
+        return None
+
+    def visit_break_stmt(self, o: BreakStmt, /) -> None:
+        return None
+
+    def visit_temp_node(self, o: TempNode, /) -> None:
+        return None
+
+    def visit_nonlocal_decl(self, o: NonlocalDecl, /) -> None:
+        return None
+
+    def visit_global_decl(self, o: GlobalDecl, /) -> None:
+        return None
+
+    def visit_import_all(self, o: ImportAll, /) -> None:
+        return None
+
+    def visit_type_var_expr(self, o: TypeVarExpr, /) -> None:
+        return None
+
+    def visit_paramspec_expr(self, o: ParamSpecExpr, /) -> None:
+        return None
+
+    def visit_type_var_tuple_expr(self, o: TypeVarTupleExpr, /) -> None:
+        return None
+
+    def visit_type_alias_expr(self, o: TypeAliasExpr, /) -> None:
+        return None
+
+    def visit_type_alias(self, o: TypeAlias, /) -> None:
+        return None
+
+    def visit_namedtuple_expr(self, o: NamedTupleExpr, /) -> None:
+        return None
+
+    def visit_typeddict_expr(self, o: TypedDictExpr, /) -> None:
+        return None
+
+    def visit_newtype_expr(self, o: NewTypeExpr, /) -> None:
+        return None
+
+    def visit__promote_expr(self, o: PromoteExpr, /) -> None:
+        return None
+
+    def visit_complex_expr(self, o: ComplexExpr, /) -> None:
+        return None
+
+    def visit_enum_call_expr(self, o: EnumCallExpr, /) -> None:
+        return None
+
+    def visit_singleton_pattern(self, o: SingletonPattern, /) -> None:
+        return None
+
 
 class ExtendedTraverserVisitor(TraverserVisitor):
     """This is a more flexible traverser.