stubtest: get better signatures for __init__ of C classes

When an __init__ method has the generic C-class signature,
check the underlying class for a better signature.

Author: tungol

mypy/stubtest.py

@@ -7,13 +7,15 @@
 from __future__ import annotations
 
 import argparse
+import ast
 import collections.abc
 import copy
 import enum
 import functools
 import importlib
 import importlib.machinery
 import inspect
+import itertools
 import os
 import pkgutil
 import re
@@ -1526,7 +1528,202 @@ def is_read_only_property(runtime: object) -> bool:
     return isinstance(runtime, property) and runtime.fset is None
 
 
+def _signature_fromstr(
+    cls: type[inspect.Signature], obj: Any, s: str, skip_bound_arg: bool = True
+) -> inspect.Signature:
+    """Private helper to parse content of '__text_signature__'
+    and return a Signature based on it.
+
+    This is a copy of inspect._signature_fromstr from 3.13, which we need
+    for python/cpython#115270, an important fix for working with
+    built-in instance methods.
+    """
+    Parameter = cls._parameter_cls  # type: ignore[attr-defined]
+
+    if sys.version_info >= (3, 12):
+        clean_signature, self_parameter = inspect._signature_strip_non_python_syntax(s)  # type: ignore[attr-defined]
+    else:
+        clean_signature, self_parameter, last_positional_only = inspect._signature_strip_non_python_syntax(s)  # type: ignore[attr-defined]
+
+    program = "def foo" + clean_signature + ": pass"
+
+    try:
+        module_ast = ast.parse(program)
+    except SyntaxError:
+        module_ast = None
+
+    if not isinstance(module_ast, ast.Module):
+        raise ValueError("{!r} builtin has invalid signature".format(obj))
+
+    f = module_ast.body[0]
+    assert isinstance(f, ast.FunctionDef)
+
+    parameters = []
+    empty = Parameter.empty
+
+    module = None
+    module_dict: dict[str, Any] = {}
+
+    module_name = getattr(obj, "__module__", None)
+    if not module_name:
+        objclass = getattr(obj, "__objclass__", None)
+        module_name = getattr(objclass, "__module__", None)
+
+    if module_name:
+        module = sys.modules.get(module_name, None)
+        if module:
+            module_dict = module.__dict__
+    sys_module_dict = sys.modules.copy()
+
+    def parse_name(node: ast.arg) -> str:
+        assert isinstance(node, ast.arg)
+        if node.annotation is not None:
+            raise ValueError("Annotations are not currently supported")
+        return node.arg
+
+    def wrap_value(s: str) -> ast.Constant:
+        try:
+            value = eval(s, module_dict)
+        except NameError:
+            try:
+                value = eval(s, sys_module_dict)
+            except NameError:
+                raise ValueError
+
+        if isinstance(value, (str, int, float, bytes, bool, type(None))):
+            return ast.Constant(value)
+        raise ValueError
+
+    class RewriteSymbolics(ast.NodeTransformer):
+        def visit_Attribute(self, node: ast.Attribute) -> Any:
+            a = []
+            n: ast.expr = node
+            while isinstance(n, ast.Attribute):
+                a.append(n.attr)
+                n = n.value
+            if not isinstance(n, ast.Name):
+                raise ValueError
+            a.append(n.id)
+            value = ".".join(reversed(a))
+            return wrap_value(value)
+
+        def visit_Name(self, node: ast.Name) -> Any:
+            if not isinstance(node.ctx, ast.Load):
+                raise ValueError()
+            return wrap_value(node.id)
+
+        def visit_BinOp(self, node: ast.BinOp) -> Any:
+            # Support constant folding of a couple simple binary operations
+            # commonly used to define default values in text signatures
+            left = self.visit(node.left)
+            right = self.visit(node.right)
+            if not isinstance(left, ast.Constant) or not isinstance(right, ast.Constant):
+                raise ValueError
+            if isinstance(node.op, ast.Add):
+                return ast.Constant(left.value + right.value)
+            elif isinstance(node.op, ast.Sub):
+                return ast.Constant(left.value - right.value)
+            elif isinstance(node.op, ast.BitOr):
+                return ast.Constant(left.value | right.value)
+            raise ValueError
+
+    def p(name_node: ast.arg, default_node: Any, default: Any = empty) -> None:
+        name = parse_name(name_node)
+        if default_node and default_node is not inspect._empty:
+            try:
+                default_node = RewriteSymbolics().visit(default_node)
+                default = ast.literal_eval(default_node)
+            except ValueError:
+                raise ValueError("{!r} builtin has invalid signature".format(obj)) from None
+        parameters.append(Parameter(name, kind, default=default, annotation=empty))
+
+    # non-keyword-only parameters
+    if sys.version_info >= (3, 12):
+        total_non_kw_args = len(f.args.posonlyargs) + len(f.args.args)
+        required_non_kw_args = total_non_kw_args - len(f.args.defaults)
+        defaults = itertools.chain(itertools.repeat(None, required_non_kw_args), f.args.defaults)
+
+        kind = Parameter.POSITIONAL_ONLY
+        for name, default in zip(f.args.posonlyargs, defaults):
+            p(name, default)
+
+        kind = Parameter.POSITIONAL_OR_KEYWORD
+        for name, default in zip(f.args.args, defaults):
+            p(name, default)
+
+    else:
+        args = reversed(f.args.args)
+        defaults = reversed(f.args.defaults)
+        iter = itertools.zip_longest(args, defaults, fillvalue=None)
+        if last_positional_only is not None:
+            kind = Parameter.POSITIONAL_ONLY
+        else:
+            kind = Parameter.POSITIONAL_OR_KEYWORD
+        for i, (name, default) in enumerate(reversed(list(iter))):
+            p(name, default)
+            if i == last_positional_only:
+                kind = Parameter.POSITIONAL_OR_KEYWORD
+
+    # *args
+    if f.args.vararg:
+        kind = Parameter.VAR_POSITIONAL
+        p(f.args.vararg, empty)
+
+    # keyword-only arguments
+    kind = Parameter.KEYWORD_ONLY
+    for name, default in zip(f.args.kwonlyargs, f.args.kw_defaults):
+        p(name, default)
+
+    # **kwargs
+    if f.args.kwarg:
+        kind = Parameter.VAR_KEYWORD
+        p(f.args.kwarg, empty)
+
+    if self_parameter is not None:
+        # Possibly strip the bound argument:
+        #    - We *always* strip first bound argument if
+        #      it is a module.
+        #    - We don't strip first bound argument if
+        #      skip_bound_arg is False.
+        assert parameters
+        _self = getattr(obj, "__self__", None)
+        self_isbound = _self is not None
+        self_ismodule = inspect.ismodule(_self)
+        if self_isbound and (self_ismodule or skip_bound_arg):
+            parameters.pop(0)
+        else:
+            # for builtins, self parameter is always positional-only!
+            p = parameters[0].replace(kind=Parameter.POSITIONAL_ONLY)
+            parameters[0] = p
+
+    return cls(parameters, return_annotation=cls.empty)
+
+
 def safe_inspect_signature(runtime: Any) -> inspect.Signature | None:
+    if (
+        hasattr(runtime, "__name__")
+        and runtime.__name__ == "__init__"
+        and hasattr(runtime, "__text_signature__")
+        and runtime.__text_signature__ == "($self, /, *args, **kwargs)"
+        and hasattr(runtime, "__objclass__")
+        and runtime.__objclass__ is not object
+        and hasattr(runtime.__objclass__, "__text_signature__")
+        and runtime.__objclass__.__text_signature__ is not None
+    ):
+        # This is an __init__ method with the generic C-class signature.
+        # In this case, the underlying class usually has a better signature,
+        # which we can convert into an __init__ signature by adding $self
+        # at the start. If we hit an error, failover to the normal
+        # path without trying to recover.
+        if "/" in runtime.__objclass__.__text_signature__:
+            new_sig = f"($self, {runtime.__objclass__.__text_signature__[1:]}"
+        else:
+            new_sig = f"($self, /, {runtime.__objclass__.__text_signature__[1:]}"
+        try:
+            return _signature_fromstr(inspect.Signature, runtime, new_sig)
+        except Exception:
+            pass
+
     try:
         try:
             return inspect.signature(runtime)