rspec/rules/S6794/python/rule.adoc

This rule raises an issue when a type alias is declared outside of a `type` statement.

== Why is this an issue?

Since Python 3.12 the keyword `type` is used to defined type aliases. 
It replaces the following construct:

[source,python]
----
from typing import TypeAlias, TypeVar

_T = TypeVar("_T")

MyTypeAlias: TypeAlias = set[_T]
----

Using the `type` statement to define type aliases allows for a more concise code and thus better readability.
This also makes it possible to declutter the code, as imports from the `typing` module (`TypeAlias` and `TyperVar`) can be removed.

[source,python]
----
type MyTypeAlias[T] = set[T]
----

=== Exceptions

This rule will only raise an issue when the Python version of the analyzed project is set to 3.12 or higher.

== How to fix it

Use a `type` statement to declare the `TypeAlias` instead of using a regular assignment.

=== Code examples

==== Noncompliant code example

[source,python,diff-id=1,diff-type=noncompliant]
----
from typing import TypeAlias

MyStringAlias: TypeAlias = str # Noncompliant: this TypeAlias can be more concise with the help of the type statement.

_T = TypeVar("_T")
MyGenericAlias: TypeAlias = list[_T]  # Noncompliant: the type statement can help replace both the TypeVar and the TypeAlias statements.
----

==== Compliant solution

[source,python,diff-id=1,diff-type=compliant]
----
type MyStringAlias = str # Compliant

type MyGenericAlias[T] = list[T]  # Compliant
----


== Resources
=== Documentation

* Python Documentation - https://docs.python.org/3.12/reference/simple_stmts.html#type[The type statement]
* Python 3.12 Release Notes - https://docs.python.org/3.12/whatsnew/3.12.html#pep-695-type-parameter-syntax[PEP 695: Type Parameter Syntax]

ifdef::env-github,rspecator-view[]

'''

== Implementation Specification
=== Message
(visible only on this page)

Use a `type` statement instead of this `TypeAlias`.

'''
endif::env-github,rspecator-view[]