[mypyc] Support attributes that override properties (#14377)

Code like this is now supported by mypyc:
```
class B:
    @Property
    def x(self) -> int:
        return 0

class C(B):
    x: int = 0  # Attribute overrides a property
```

The implementation generates implicit getter/setter methods for
attributes as needed and puts them in the vtable. I had to change both
the irbuild "prepare" pass (where we generate declarations), irbuild
main pass (where we generate implicit accessor IRs), and codegen (where
implicit properties aren't visible externally to CPython).

Also fix a minor mypy bug related to overriding properties and multiple
inheritance that I encountered.

This doesn't handle glue methods yet.

Author: JukkaL

mypy/checker.py

@@ -2498,8 +2498,13 @@ class C(B, A[int]): ...  # this is unsafe because...
             ok = is_equivalent(first_type, second_type)
             if not ok:
                 second_node = base2[name].node
-                if isinstance(second_node, Decorator) and second_node.func.is_property:
-                    ok = is_subtype(first_type, cast(CallableType, second_type).ret_type)
+                if (
+                    isinstance(second_type, FunctionLike)
+                    and second_node is not None
+                    and is_property(second_node)
+                ):
+                    second_type = get_property_type(second_type)
+                    ok = is_subtype(first_type, second_type)
         else:
             if first_type is None:
                 self.msg.cannot_determine_type_in_base(name, base1.name, ctx)

mypyc/codegen/emitclass.py

@@ -824,7 +824,10 @@ def generate_getseter_declarations(cl: ClassIR, emitter: Emitter) -> None:
                 )
             )
 
-    for prop in cl.properties:
+    for prop, (getter, setter) in cl.properties.items():
+        if getter.decl.implicit:
+            continue
+
         # Generate getter declaration
         emitter.emit_line("static PyObject *")
         emitter.emit_line(
@@ -834,7 +837,7 @@ def generate_getseter_declarations(cl: ClassIR, emitter: Emitter) -> None:
         )
 
         # Generate property setter declaration if a setter exists
-        if cl.properties[prop][1]:
+        if setter:
             emitter.emit_line("static int")
             emitter.emit_line(
                 "{}({} *self, PyObject *value, void *closure);".format(
@@ -854,11 +857,13 @@ def generate_getseters_table(cl: ClassIR, name: str, emitter: Emitter) -> None:
                 )
             )
             emitter.emit_line(" NULL, NULL},")
-    for prop in cl.properties:
+    for prop, (getter, setter) in cl.properties.items():
+        if getter.decl.implicit:
+            continue
+
         emitter.emit_line(f'{{"{prop}",')
         emitter.emit_line(f" (getter){getter_name(cl, prop, emitter.names)},")
 
-        setter = cl.properties[prop][1]
         if setter:
             emitter.emit_line(f" (setter){setter_name(cl, prop, emitter.names)},")
             emitter.emit_line("NULL, NULL},")
@@ -878,6 +883,9 @@ def generate_getseters(cl: ClassIR, emitter: Emitter) -> None:
             if i < len(cl.attributes) - 1:
                 emitter.emit_line("")
     for prop, (getter, setter) in cl.properties.items():
+        if getter.decl.implicit:
+            continue
+
         rtype = getter.sig.ret_type
         emitter.emit_line("")
         generate_readonly_getter(cl, prop, rtype, getter, emitter)

mypyc/ir/class_ir.py

@@ -278,10 +278,18 @@ def name_prefix(self, names: NameGenerator) -> str:
     def struct_name(self, names: NameGenerator) -> str:
         return f"{exported_name(self.fullname)}Object"
 
-    def get_method_and_class(self, name: str) -> tuple[FuncIR, ClassIR] | None:
+    def get_method_and_class(
+        self, name: str, *, prefer_method: bool = False
+    ) -> tuple[FuncIR, ClassIR] | None:
         for ir in self.mro:
             if name in ir.methods:
-                return ir.methods[name], ir
+                func_ir = ir.methods[name]
+                if not prefer_method and func_ir.decl.implicit:
+                    # This is an implicit accessor, so there is also an attribute definition
+                    # which the caller prefers. This happens if an attribute overrides a
+                    # property.
+                    return None
+                return func_ir, ir
 
         return None
 

mypyc/ir/func_ir.py

@@ -139,6 +139,7 @@ def __init__(
         kind: int = FUNC_NORMAL,
         is_prop_setter: bool = False,
         is_prop_getter: bool = False,
+        implicit: bool = False,
     ) -> None:
         self.name = name
         self.class_name = class_name
@@ -155,7 +156,11 @@ def __init__(
             else:
                 self.bound_sig = sig.bound_sig()
 
-        # this is optional because this will be set to the line number when the corresponding
+        # If True, not present in the mypy AST and must be synthesized during irbuild
+        # Currently only supported for property getters/setters
+        self.implicit = implicit
+
+        # This is optional because this will be set to the line number when the corresponding
         # FuncIR is created
         self._line: int | None = None
 
@@ -198,6 +203,7 @@ def serialize(self) -> JsonDict:
             "kind": self.kind,
             "is_prop_setter": self.is_prop_setter,
             "is_prop_getter": self.is_prop_getter,
+            "implicit": self.implicit,
         }
 
     # TODO: move this to FuncIR?
@@ -219,6 +225,7 @@ def deserialize(cls, data: JsonDict, ctx: DeserMaps) -> FuncDecl:
             data["kind"],
             data["is_prop_setter"],
             data["is_prop_getter"],
+            data["implicit"],
         )
 
 

mypyc/irbuild/classdef.py

@@ -25,6 +25,7 @@
     is_class_var,
 )
 from mypy.types import ENUM_REMOVED_PROPS, Instance, UnboundType, get_proper_type
+from mypyc.common import PROPSET_PREFIX
 from mypyc.ir.class_ir import ClassIR, NonExtClassInfo
 from mypyc.ir.func_ir import FuncDecl, FuncSignature
 from mypyc.ir.ops import (
@@ -53,7 +54,13 @@
     object_rprimitive,
 )
 from mypyc.irbuild.builder import IRBuilder
-from mypyc.irbuild.function import handle_ext_method, handle_non_ext_method, load_type
+from mypyc.irbuild.function import (
+    gen_property_getter_ir,
+    gen_property_setter_ir,
+    handle_ext_method,
+    handle_non_ext_method,
+    load_type,
+)
 from mypyc.irbuild.util import dataclass_type, get_func_def, is_constant, is_dataclass_decorator
 from mypyc.primitives.dict_ops import dict_new_op, dict_set_item_op
 from mypyc.primitives.generic_ops import py_hasattr_op, py_setattr_op
@@ -151,6 +158,24 @@ def transform_class_def(builder: IRBuilder, cdef: ClassDef) -> None:
         else:
             builder.error("Unsupported statement in class body", stmt.line)
 
+    # Generate implicit property setters/getters
+    for name, decl in ir.method_decls.items():
+        if decl.implicit and decl.is_prop_getter:
+            getter_ir = gen_property_getter_ir(builder, decl, cdef)
+            builder.functions.append(getter_ir)
+            ir.methods[getter_ir.decl.name] = getter_ir
+
+            setter_ir = None
+            setter_name = PROPSET_PREFIX + name
+            if setter_name in ir.method_decls:
+                setter_ir = gen_property_setter_ir(builder, ir.method_decls[setter_name], cdef)
+                builder.functions.append(setter_ir)
+                ir.methods[setter_name] = setter_ir
+
+            ir.properties[name] = (getter_ir, setter_ir)
+            # TODO: Generate glue method if needed?
+            # TODO: Do we need interpreted glue methods? Maybe not?
+
     cls_builder.finalize(ir)
 
 

mypyc/irbuild/function.py

@@ -28,7 +28,7 @@
     Var,
 )
 from mypy.types import CallableType, get_proper_type
-from mypyc.common import LAMBDA_NAME, SELF_NAME
+from mypyc.common import LAMBDA_NAME, PROPSET_PREFIX, SELF_NAME
 from mypyc.ir.class_ir import ClassIR, NonExtClassInfo
 from mypyc.ir.func_ir import (
     FUNC_CLASSMETHOD,
@@ -1026,3 +1026,34 @@ def get_native_impl_ids(builder: IRBuilder, singledispatch_func: FuncDef) -> dic
     """
     impls = builder.singledispatch_impls[singledispatch_func]
     return {impl: i for i, (typ, impl) in enumerate(impls) if not is_decorated(builder, impl)}
+
+
+def gen_property_getter_ir(builder: IRBuilder, func_decl: FuncDecl, cdef: ClassDef) -> FuncIR:
+    """Generate an implicit trivial property getter for an attribute.
+
+    These are used if an attribute can also be accessed as a property.
+    """
+    name = func_decl.name
+    builder.enter(name)
+    self_reg = builder.add_argument("self", func_decl.sig.args[0].type)
+    value = builder.builder.get_attr(self_reg, name, func_decl.sig.ret_type, -1)
+    builder.add(Return(value))
+    args, _, blocks, ret_type, fn_info = builder.leave()
+    return FuncIR(func_decl, args, blocks)
+
+
+def gen_property_setter_ir(builder: IRBuilder, func_decl: FuncDecl, cdef: ClassDef) -> FuncIR:
+    """Generate an implicit trivial property setter for an attribute.
+
+    These are used if an attribute can also be accessed as a property.
+    """
+    name = func_decl.name
+    builder.enter(name)
+    self_reg = builder.add_argument("self", func_decl.sig.args[0].type)
+    value_reg = builder.add_argument("value", func_decl.sig.args[1].type)
+    assert name.startswith(PROPSET_PREFIX)
+    attr_name = name[len(PROPSET_PREFIX) :]
+    builder.add(SetAttr(self_reg, attr_name, value_reg, -1))
+    builder.add(Return(builder.none()))
+    args, _, blocks, ret_type, fn_info = builder.leave()
+    return FuncIR(func_decl, args, blocks)