refactor: extract type aliases to _types.py to fix import cycle (#13)

Move JSONObject, JSONValue, JSONArray, JSONPrimitive, Key, KeyElement,
and KeySpecifier type aliases to a new _types.py module. This breaks
the circular import between _exceptions.py, _json.py, and _keys.py.

The cycle existed because _exceptions.py needed type annotations from
_json.py and _keys.py, but those modules import exceptions.

Author: tbhb

pyproject.toml

@@ -208,6 +208,9 @@ ignore-variadic-names = true
   "S101",    # assert statements in tests
   "PLR2004", # magic values in assertions in tests
 ]
+"src/jsonlt/_exceptions.py" = [
+  "TC001",  # direct imports from _types.py to break circular import cycle
+]
 
 [tool.uv.build-backend]
 module-name = "jsonlt"

src/jsonlt/_exceptions.py

@@ -4,14 +4,9 @@
 following the specification's error categories.
 """
 
-# pyright: reportImportCycles=false
-
-from typing import TYPE_CHECKING
 from typing_extensions import override
 
-if TYPE_CHECKING:
-    from ._json import JSONObject
-    from ._keys import Key
+from ._types import JSONObject, Key
 
 
 class JSONLTError(Exception):

src/jsonlt/_json.py

@@ -9,20 +9,17 @@
 
 import json
 from json import JSONDecodeError
-from typing import TYPE_CHECKING, TypeAlias, cast
+from typing import TYPE_CHECKING, cast
 
 from ._constants import MIN_NESTING_DEPTH
 from ._exceptions import LimitError, ParseError
+from ._types import JSONArray, JSONObject, JSONPrimitive, JSONValue
 
 if TYPE_CHECKING:
     from collections.abc import Mapping, Sequence
 
-# JSON type definitions per RFC 8259
-# Using string annotations for forward references to avoid runtime | issues
-JSONPrimitive: TypeAlias = "str | int | float | bool | None"
-JSONArray: TypeAlias = "list[JSONValue]"
-JSONObject: TypeAlias = "dict[str, JSONValue]"
-JSONValue: TypeAlias = "JSONPrimitive | JSONArray | JSONObject"
+# Re-export type aliases for backwards compatibility
+__all__ = ["JSONArray", "JSONObject", "JSONPrimitive", "JSONValue"]
 
 
 def json_nesting_depth(value: object) -> int:

src/jsonlt/_keys.py

@@ -6,7 +6,7 @@
 
 import json
 from collections.abc import Sequence
-from typing import TYPE_CHECKING, TypeAlias
+from typing import TYPE_CHECKING
 
 from ._constants import (
     MAX_INTEGER_KEY,
@@ -16,30 +16,14 @@
 )
 from ._exceptions import InvalidKeyError, LimitError
 from ._json import utf8_byte_length
+from ._types import Key, KeyElement, KeySpecifier
 
 if TYPE_CHECKING:
     from typing import TypeGuard
     from typing_extensions import TypeIs
 
-KeyElement: TypeAlias = "str | int"
-"""A key element is a string or integer that may appear in a tuple key."""
-
-Key: TypeAlias = "str | int | tuple[str | int, ...]"
-"""A key identifies a record within a table.
-
-A key is one of:
-- A string
-- An integer in the range [-(2^53)+1, (2^53)-1]
-- A tuple of key elements (non-empty, max 16 elements)
-"""
-
-KeySpecifier: TypeAlias = "str | tuple[str, ...]"
-"""A key specifier defines how to extract a key from a record.
-
-A key specifier is one of:
-- A string naming a single field
-- A tuple of strings naming multiple fields (for compound keys)
-"""
+# Re-export type aliases for backwards compatibility
+__all__ = ["Key", "KeyElement", "KeySpecifier"]
 
 
 def is_valid_key_element(value: object) -> "TypeIs[str | int]":

src/jsonlt/_types.py

@@ -0,0 +1,48 @@
+"""Type aliases for JSONLT.
+
+This module contains ONLY TypeAlias definitions for JSON and key types.
+It exists to break circular imports between _exceptions.py, _json.py, and _keys.py:
+- _exceptions.py needs JSONObject and Key for ConflictError
+- _json.py needs ParseError, LimitError from _exceptions.py
+- _keys.py needs InvalidKeyError, LimitError from _exceptions.py
+
+By placing the type aliases here with no dependencies on other JSONLT modules,
+all modules can safely import from _types.py.
+"""
+
+from typing import TypeAlias
+
+# JSON type definitions per RFC 8259
+# Using string annotations for forward references to avoid runtime | issues
+JSONPrimitive: TypeAlias = "str | int | float | bool | None"
+"""A JSON primitive value: string, number, boolean, or null."""
+
+JSONArray: TypeAlias = "list[JSONValue]"
+"""A JSON array containing any JSON values."""
+
+JSONObject: TypeAlias = "dict[str, JSONValue]"
+"""A JSON object mapping string keys to JSON values."""
+
+JSONValue: TypeAlias = "JSONPrimitive | JSONArray | JSONObject"
+"""Any JSON value: primitive, array, or object."""
+
+# Key type definitions per JSONLT specification
+KeyElement: TypeAlias = "str | int"
+"""A key element is a string or integer that may appear in a tuple key."""
+
+Key: TypeAlias = "str | int | tuple[str | int, ...]"
+"""A key identifies a record within a table.
+
+A key is one of:
+- A string
+- An integer in the range [-(2^53)+1, (2^53)-1]
+- A tuple of key elements (non-empty, max 16 elements)
+"""
+
+KeySpecifier: TypeAlias = "str | tuple[str, ...]"
+"""A key specifier defines how to extract a key from a record.
+
+A key specifier is one of:
+- A string naming a single field
+- A tuple of strings naming multiple fields (for compound keys)
+"""