fix: handle ParamSpec args/kwargs subscripts like tuple/dict (#1693)

Summary:
Fixes #1692

Pull Request resolved: #1693

Reviewed By: ndmitchell

Differential Revision: D87946959

Pulled By: yangdanny97

fbshipit-source-id: c4aea136fac746462ea6e1667ead912b9d47b9c1

Author: gvozdvmozgu

pyrefly/lib/alt/expr.rs

@@ -2074,6 +2074,34 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                         Some(&context),
                     )
                 }
+                Type::Args(_) => {
+                    let tuple = Tuple::Unbounded(Box::new(self.stdlib.object().clone().to_type()));
+                    self.infer_tuple_subscript(
+                        tuple,
+                        slice,
+                        range,
+                        errors,
+                        Some(&|| ErrorContext::Index(self.for_display(base.clone()))),
+                    )
+                }
+                Type::Kwargs(_) => {
+                    let kwargs_ty = self
+                        .stdlib
+                        .dict(
+                            self.stdlib.str().clone().to_type(),
+                            self.stdlib.object().clone().to_type(),
+                        )
+                        .to_type();
+                    self.call_method_or_error(
+                        &kwargs_ty,
+                        &dunder::GETITEM,
+                        range,
+                        &[CallArg::expr(slice)],
+                        &[],
+                        errors,
+                        Some(&|| ErrorContext::Index(self.for_display(base.clone()))),
+                    )
+                }
                 Type::ClassType(ref cls) | Type::SelfType(ref cls)
                     if let Some(tuple) = self.as_tuple(cls) =>
                 {

pyrefly/lib/module/typeshed.rs

@@ -15,7 +15,6 @@ use std::sync::LazyLock;
 use anyhow::anyhow;
 use dupe::Dupe;
 use pyrefly_bundled::bundled_typeshed;
-use pyrefly_config::error::ErrorDisplayConfig;
 use pyrefly_config::error_kind::ErrorKind;
 use pyrefly_config::error_kind::Severity;
 use pyrefly_python::module_name::ModuleName;

pyrefly/lib/test/paramspec.rs

@@ -300,6 +300,25 @@ def decorator(f: Callable[P, int]) -> Callable[P, None]:
 "#,
 );
 
+testcase!(
+    test_paramspec_args_kwargs_subscriptable,
+    r#"
+from typing import Callable, ParamSpec, TypeVar, assert_type
+
+FP = ParamSpec('FP')
+FR = TypeVar('FR')
+
+def decorate(f: Callable[FP, FR]) -> Callable[FP, FR]:
+  def wrapper(*args: FP.args, **kwargs: FP.kwargs) -> FR:
+    if len(args) > 0:
+      assert_type(args[0], object)
+    if 'foo' in kwargs:
+      assert_type(kwargs['foo'], object)
+    return f(*args, **kwargs)
+  return wrapper
+"#,
+);
+
 testcase!(
     test_paramspec_named_arguments_concatenate,
     r#"