Description

A converter registered from a source annotation that isinstance rejects could not be used. The
converter compared the registered source type against the incoming data with a raw isinstance:

decomposed_from = DecomposedType(convert_from_type)
check_type = convert_from_type if decomposed_from.is_union else decomposed_from.root
if isinstance(data, check_type):

isinstance rejects several valid annotations:

The same applies to the target side (TypeConverter._convert and is_instance) and to the
indirect path, which had its own union special case.

Fix

• Both matching paths now use DecomposedType.is_instance, the safe check this file already
  documents for parameterized generics ("Use DecomposedType for safe isinstance check with
  parameterized generics"), and the one the target side already uses. The ad-hoc union branches
  are removed; a union is resolved member by member inside is_instance.
• DecomposedType.is_instance is made safe for the same constructs:
  • Literal[...] constrains the value, not the class, so it is matched against its literal
    arguments with a type check (True does not satisfy Literal[1], and vice versa).
  • Any other construct whose root is not a class matches nothing instead of raising.

Tests

• test_converter.py: sources registered from Any, Literal["a"] (match and no-match), and
  dict[str, int] | None (both members, direct and through an indirect chain), plus targets of
  Any and Literal. All of these fail before the change.
• test_type_utils.py: is_instance with Literal (including the bool / int distinction) and
  with constructs that keep a non-class root (NoReturn, Final[int]).

Verification: test_converter.py + test_type_utils.py → 93 passed (87 before); reverting the
source change fails exactly the 6 new tests. yapf --style ./pyproject.toml and ruff check
(versions pinned in .pre-commit-config.yaml) are clean.

Note: this branch is based on develop before #2309, which also touches type_utils.py
(is_subtype). The two changes are in different methods; I will rebase if #2309 lands first.

Summary by CodeRabbit

• Bug Fixes
  • Improved converter matching for unions, generic types, Any, and Literal annotations.
  • Literal matching now requires both the value and its exact type to match, so values such as True do not match Literal[1].
  • Unsupported type constructs no longer cause matching errors.