Refactoring: make the type of fullname str instead of Bogus[str] (#14435)

The type Bogus[X] is treated as Any when the code is compiled with
mypyc, while it's equivalent to X when only type checking. They are
sometimes used when X is not actually the real type of a value, but
changing it to the correct type would be complicated.

Bogus[str] types are pretty awkward, since we are lying to the type
checker and mypyc only sees Any types.

An empty fullname is now represented by "" instead of None, so we no
longer need a Bogus[str] type.

This might break some plugins, so we should document this in release
notes and the relevant issue that tracks plugin incompatibilities.

(Various small optimizations, including this, together netted a 6%
performance improvement in self check.)

Author: JukkaL

mypy/checker.py

@@ -2178,7 +2178,7 @@ def visit_class_def(self, defn: ClassDef) -> None:
                     temp = self.temp_node(sig, context=decorator)
                     fullname = None
                     if isinstance(decorator, RefExpr):
-                        fullname = decorator.fullname
+                        fullname = decorator.fullname or None
 
                     # TODO: Figure out how to have clearer error messages.
                     # (e.g. "class decorator must be a function that accepts a type."
@@ -4598,7 +4598,7 @@ def visit_decorator(self, e: Decorator) -> None:
             temp = self.temp_node(sig, context=e)
             fullname = None
             if isinstance(d, RefExpr):
-                fullname = d.fullname
+                fullname = d.fullname or None
             # if this is a expression like @b.a where b is an object, get the type of b
             # so we can pass it the method hook in the plugins
             object_type: Type | None = None

mypy/checkexpr.py

@@ -216,8 +216,8 @@ def extract_refexpr_names(expr: RefExpr) -> set[str]:
     Note that currently, the only two subclasses of RefExpr are NameExpr and
     MemberExpr."""
     output: set[str] = set()
-    while isinstance(expr.node, MypyFile) or expr.fullname is not None:
-        if isinstance(expr.node, MypyFile) and expr.fullname is not None:
+    while isinstance(expr.node, MypyFile) or expr.fullname:
+        if isinstance(expr.node, MypyFile) and expr.fullname:
             # If it's None, something's wrong (perhaps due to an
             # import cycle or a suppressed error).  For now we just
             # skip it.
@@ -228,7 +228,7 @@ def extract_refexpr_names(expr: RefExpr) -> set[str]:
             if isinstance(expr.node, TypeInfo):
                 # Reference to a class or a nested class
                 output.update(split_module_names(expr.node.module_name))
-            elif expr.fullname is not None and "." in expr.fullname and not is_suppressed_import:
+            elif "." in expr.fullname and not is_suppressed_import:
                 # Everything else (that is not a silenced import within a class)
                 output.add(expr.fullname.rsplit(".", 1)[0])
             break
@@ -526,7 +526,7 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
             # There are two special cases where plugins might act:
             # * A "static" reference/alias to a class or function;
             #   get_function_hook() will be invoked for these.
-            fullname = e.callee.fullname
+            fullname = e.callee.fullname or None
             if isinstance(e.callee.node, TypeAlias):
                 target = get_proper_type(e.callee.node.target)
                 if isinstance(target, Instance):
@@ -536,7 +536,7 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
             #   get_method_hook() and get_method_signature_hook() will
             #   be invoked for these.
             if (
-                fullname is None
+                not fullname
                 and isinstance(e.callee, MemberExpr)
                 and self.chk.has_type(e.callee.expr)
             ):
@@ -605,7 +605,7 @@ def method_fullname(self, object_type: Type, method_name: str) -> str | None:
         elif isinstance(object_type, TupleType):
             type_name = tuple_fallback(object_type).type.fullname
 
-        if type_name is not None:
+        if type_name:
             return f"{type_name}.{method_name}"
         else:
             return None
@@ -5489,7 +5489,7 @@ def type_info_from_type(typ: Type) -> TypeInfo | None:
 
 
 def is_operator_method(fullname: str | None) -> bool:
-    if fullname is None:
+    if not fullname:
         return False
     short_name = fullname.split(".")[-1]
     return (

mypy/nodes.py

@@ -25,7 +25,6 @@
 from mypy_extensions import trait
 
 import mypy.strconv
-from mypy.bogus_type import Bogus
 from mypy.util import short_type
 from mypy.visitor import ExpressionVisitor, NodeVisitor, StatementVisitor
 
@@ -247,12 +246,10 @@ class SymbolNode(Node):
     def name(self) -> str:
         pass
 
-    # fullname can often be None even though the type system
-    # disagrees. We mark this with Bogus to let mypyc know not to
-    # worry about it.
+    # Fully qualified name
     @property
     @abstractmethod
-    def fullname(self) -> Bogus[str]:
+    def fullname(self) -> str:
         pass
 
     @abstractmethod
@@ -294,7 +291,7 @@ class MypyFile(SymbolNode):
     __match_args__ = ("name", "path", "defs")
 
     # Fully qualified module name
-    _fullname: Bogus[str]
+    _fullname: str
     # Path to the file (empty string if not known)
     path: str
     # Top-level definitions and statements
@@ -361,7 +358,7 @@ def name(self) -> str:
         return "" if not self._fullname else self._fullname.split(".")[-1]
 
     @property
-    def fullname(self) -> Bogus[str]:
+    def fullname(self) -> str:
         return self._fullname
 
     def accept(self, visitor: NodeVisitor[T]) -> T:
@@ -526,16 +523,15 @@ def __init__(self) -> None:
         self.is_static = False
         self.is_final = False
         # Name with module prefix
-        # TODO: Type should be Optional[str]
-        self._fullname = cast(Bogus[str], None)
+        self._fullname = ""
 
     @property
     @abstractmethod
     def name(self) -> str:
         pass
 
     @property
-    def fullname(self) -> Bogus[str]:
+    def fullname(self) -> str:
         return self._fullname
 
 
@@ -871,7 +867,7 @@ def name(self) -> str:
         return self.func.name
 
     @property
-    def fullname(self) -> Bogus[str]:
+    def fullname(self) -> str:
         return self.func.fullname
 
     @property
@@ -967,7 +963,7 @@ def __init__(self, name: str, type: mypy.types.Type | None = None) -> None:
         super().__init__()
         self._name = name  # Name without module prefix
         # TODO: Should be Optional[str]
-        self._fullname = cast("Bogus[str]", None)  # Name with module prefix
+        self._fullname = ""  # Name with module prefix
         # TODO: Should be Optional[TypeInfo]
         self.info = VAR_NO_INFO
         self.type: mypy.types.Type | None = type  # Declared or inferred type, or None
@@ -1019,7 +1015,7 @@ def name(self) -> str:
         return self._name
 
     @property
-    def fullname(self) -> Bogus[str]:
+    def fullname(self) -> str:
         return self._fullname
 
     def accept(self, visitor: NodeVisitor[T]) -> T:
@@ -1057,7 +1053,7 @@ class ClassDef(Statement):
 
     __slots__ = (
         "name",
-        "fullname",
+        "_fullname",
         "defs",
         "type_vars",
         "base_type_exprs",
@@ -1075,7 +1071,7 @@ class ClassDef(Statement):
     __match_args__ = ("name", "defs")
 
     name: str  # Name of the class without module prefix
-    fullname: Bogus[str]  # Fully qualified name of the class
+    _fullname: str  # Fully qualified name of the class
     defs: Block
     type_vars: list[mypy.types.TypeVarLikeType]
     # Base class expressions (not semantically analyzed -- can be arbitrary expressions)
@@ -1102,7 +1098,7 @@ def __init__(
     ) -> None:
         super().__init__()
         self.name = name
-        self.fullname = None  # type: ignore[assignment]
+        self._fullname = ""
         self.defs = defs
         self.type_vars = type_vars or []
         self.base_type_exprs = base_type_exprs or []
@@ -1117,6 +1113,14 @@ def __init__(
         self.deco_line: int | None = None
         self.removed_statements = []
 
+    @property
+    def fullname(self) -> str:
+        return self._fullname
+
+    @fullname.setter
+    def fullname(self, v: str) -> None:
+        self._fullname = v
+
     def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_class_def(self)
 
@@ -1725,7 +1729,7 @@ class RefExpr(Expression):
     __slots__ = (
         "kind",
         "node",
-        "fullname",
+        "_fullname",
         "is_new_def",
         "is_inferred_def",
         "is_alias_rvalue",
@@ -1739,7 +1743,7 @@ def __init__(self) -> None:
         # Var, FuncDef or TypeInfo that describes this
         self.node: SymbolNode | None = None
         # Fully qualified name (or name if not global)
-        self.fullname: str | None = None
+        self._fullname = ""
         # Does this define a new name?
         self.is_new_def = False
         # Does this define a new name with inferred type?
@@ -1752,6 +1756,14 @@ def __init__(self) -> None:
         # Cache type guard from callable_type.type_guard
         self.type_guard: mypy.types.Type | None = None
 
+    @property
+    def fullname(self) -> str:
+        return self._fullname
+
+    @fullname.setter
+    def fullname(self, v: str) -> None:
+        self._fullname = v
+
 
 class NameExpr(RefExpr):
     """Name expression
@@ -2806,7 +2818,7 @@ class is generic then it will be a type constructor of higher kind.
         "self_type",
     )
 
-    _fullname: Bogus[str]  # Fully qualified name
+    _fullname: str  # Fully qualified name
     # Fully qualified name for the module this type was defined in. This
     # information is also in the fullname, but is harder to extract in the
     # case of nested class definitions.
@@ -3023,7 +3035,7 @@ def name(self) -> str:
         return self.defn.name
 
     @property
-    def fullname(self) -> Bogus[str]:
+    def fullname(self) -> str:
         return self._fullname
 
     def is_generic(self) -> bool:
@@ -3739,11 +3751,7 @@ def serialize(self, prefix: str, name: str) -> JsonDict:
             if prefix is not None:
                 fullname = self.node.fullname
                 if (
-                    # See the comment above SymbolNode.fullname -- fullname can often be None,
-                    # but for complex reasons it's annotated as being `Bogus[str]` instead of `str | None`,
-                    # meaning mypy erroneously thinks the `fullname is not None` check here is redundant
-                    fullname is not None  # type: ignore[redundant-expr]
-                    and "." in fullname
+                    "." in fullname
                     and fullname != prefix + "." + name
                     and not (isinstance(self.node, Var) and self.node.from_module_getattr)
                 ):

mypy/partially_defined.py

@@ -287,7 +287,7 @@ def is_undefined(self, name: str) -> bool:
 
 
 def refers_to_builtin(o: RefExpr) -> bool:
-    return o.fullname is not None and o.fullname.startswith("builtins.")
+    return o.fullname.startswith("builtins.")
 
 
 class Loop:

mypy/semanal.py

@@ -3022,13 +3022,13 @@ def analyze_lvalues(self, s: AssignmentStmt) -> None:
     def apply_dynamic_class_hook(self, s: AssignmentStmt) -> None:
         if not isinstance(s.rvalue, CallExpr):
             return
-        fname = None
+        fname = ""
         call = s.rvalue
         while True:
             if isinstance(call.callee, RefExpr):
                 fname = call.callee.fullname
             # check if method call
-            if fname is None and isinstance(call.callee, MemberExpr):
+            if not fname and isinstance(call.callee, MemberExpr):
                 callee_expr = call.callee.expr
                 if isinstance(callee_expr, RefExpr) and callee_expr.fullname:
                     method_name = call.callee.name
@@ -4624,7 +4624,7 @@ def bind_name_expr(self, expr: NameExpr, sym: SymbolTableNode) -> None:
         else:
             expr.kind = sym.kind
             expr.node = sym.node
-            expr.fullname = sym.fullname
+            expr.fullname = sym.fullname or ""
 
     def visit_super_expr(self, expr: SuperExpr) -> None:
         if not self.type and not expr.call.args:
@@ -4849,7 +4849,7 @@ def visit_member_expr(self, expr: MemberExpr) -> None:
                     self.process_placeholder(expr.name, "attribute", expr)
                     return
                 expr.kind = sym.kind
-                expr.fullname = sym.fullname
+                expr.fullname = sym.fullname or ""
                 expr.node = sym.node
         elif isinstance(base, RefExpr):
             # This branch handles the case C.bar (or cls.bar or self.bar inside
@@ -4881,7 +4881,7 @@ def visit_member_expr(self, expr: MemberExpr) -> None:
                     if not n:
                         return
                     expr.kind = n.kind
-                    expr.fullname = n.fullname
+                    expr.fullname = n.fullname or ""
                     expr.node = n.node
 
     def visit_op_expr(self, expr: OpExpr) -> None:
@@ -5341,7 +5341,7 @@ def is_overloaded_item(self, node: SymbolNode, statement: Statement) -> bool:
         return False
 
     def is_defined_in_current_module(self, fullname: str | None) -> bool:
-        if fullname is None:
+        if not fullname:
             return False
         return module_prefix(self.modules, fullname) == self.cur_mod_id
 

mypy/server/aststrip.py

@@ -230,7 +230,7 @@ def visit_op_expr(self, node: OpExpr) -> None:
     def strip_ref_expr(self, node: RefExpr) -> None:
         node.kind = None
         node.node = None
-        node.fullname = None
+        node.fullname = ""
         node.is_new_def = False
         node.is_inferred_def = False
 

mypy/server/deps.py

@@ -289,13 +289,9 @@ def visit_decorator(self, o: Decorator) -> None:
             # all call sites, making them all `Any`.
             for d in o.decorators:
                 tname: str | None = None
-                if isinstance(d, RefExpr) and d.fullname is not None:
+                if isinstance(d, RefExpr) and d.fullname:
                     tname = d.fullname
-                if (
-                    isinstance(d, CallExpr)
-                    and isinstance(d.callee, RefExpr)
-                    and d.callee.fullname is not None
-                ):
+                if isinstance(d, CallExpr) and isinstance(d.callee, RefExpr) and d.callee.fullname:
                     tname = d.callee.fullname
                 if tname is not None:
                     self.add_dependency(make_trigger(tname), make_trigger(o.func.fullname))
@@ -500,7 +496,7 @@ def visit_assignment_stmt(self, o: AssignmentStmt) -> None:
             if (
                 isinstance(rvalue, CallExpr)
                 and isinstance(rvalue.callee, RefExpr)
-                and rvalue.callee.fullname is not None
+                and rvalue.callee.fullname
             ):
                 fname: str | None = None
                 if isinstance(rvalue.callee.node, TypeInfo):
@@ -510,7 +506,7 @@ def visit_assignment_stmt(self, o: AssignmentStmt) -> None:
                         fname = init.node.fullname
                 else:
                     fname = rvalue.callee.fullname
-                if fname is None:
+                if not fname:
                     return
                 for lv in o.lvalues:
                     if isinstance(lv, RefExpr) and lv.fullname and lv.is_new_def:
@@ -638,7 +634,7 @@ def visit_del_stmt(self, o: DelStmt) -> None:
     # Expressions
 
     def process_global_ref_expr(self, o: RefExpr) -> None:
-        if o.fullname is not None:
+        if o.fullname:
             self.add_dependency(make_trigger(o.fullname))
 
         # If this is a reference to a type, generate a dependency to its

mypy/strconv.py

@@ -367,7 +367,7 @@ def pretty_name(
             id = ""
         if isinstance(target_node, mypy.nodes.MypyFile) and name == fullname:
             n += id
-        elif kind == mypy.nodes.GDEF or (fullname != name and fullname is not None):
+        elif kind == mypy.nodes.GDEF or (fullname != name and fullname):
             # Append fully qualified name for global references.
             n += f" [{fullname}{id}]"
         elif kind == mypy.nodes.LDEF:

mypy/stubtest.py

@@ -1147,7 +1147,7 @@ def apply_decorator_to_funcitem(
     ) -> nodes.FuncItem | None:
         if not isinstance(decorator, nodes.RefExpr):
             return None
-        if decorator.fullname is None:
+        if not decorator.fullname:
             # Happens with namedtuple
             return None
         if (