Add type_hint_literal macro

[bschoenmaeckers]

This adds a macro to make Literal type hints less verbose.

[Tpt]

Nice! I am a bit scared by this added complexity: do we have actual usescases where it will be useful?

[bschoenmaeckers]

Nice! I am a bit scared by this added complexity: do we have actual usescases where it will be useful?

My usecase is a local project that implements a FromPyObject for a rust enum. As it looks very verbose it moved me to create a macro for this.

pub enum Period {
    Daily,
    Weekly,
    Monthly,
    Quarterly,
    SemiAnnually,
    Yearly,
}

impl FromPyObject<'_, '_> for Period {
    type Error = PyErr;

    const INPUT_TYPE: PyStaticExpr = pyo3::type_hint_subscript!(
        pyo3::type_hint_identifier!("typing", "Literal"),
        PyStaticExpr::Constant {
            value: PyStaticConstant::Str("D")
        },
        PyStaticExpr::Constant {
            value: PyStaticConstant::Str("W")
        },
        PyStaticExpr::Constant {
            value: PyStaticConstant::Str("M")
        },
        PyStaticExpr::Constant {
            value: PyStaticConstant::Str("Q")
        },
        PyStaticExpr::Constant {
            value: PyStaticConstant::Str("S")
        },
        PyStaticExpr::Constant {
            value: PyStaticConstant::Str("Y")
        }
    );
}

This looks to my like a common pattern and other users may benefit from this.

[Tpt]

@bschoenmaeckers Make sense! Thank you!

[Tpt]

It hits the compiler recursion limit in macros

[bschoenmaeckers]

Interesting, I do not see this failure locally...

[jorenham]

float isn't valid as Literal value: https://typing.python.org/en/latest/spec/literal.html#legal-and-illegal-parameterizations