Macro __impl_alt_from_data 

#[doc(hidden)]
macro_rules! __impl_alt_from_data {
    ($ty:ty, $methods:ident, $inferbase:ident, $flavor:ident $(($elem:ty))?) => { ... };
    ($ty:ty, $methods:ident, $inferbase:ident, $flavor:ident $(($elem:ty))?, serialize) => { ... };
    ({$($gen:tt)*} $ty:ty {$($whr:tt)*}, $methods:ident, $inferbase:ident, $flavor:ident $(($elem:ty))?) => { ... };
    ({$($gen:tt)*} $ty:ty {$($whr:tt)*}, $methods:ident, $inferbase:ident, $flavor:ident $(($elem:ty))?, serialize) => { ... };
}

Internal macro: canonical ALTREP emission.

Generates the standard ALTREP trait implementations (Altrep base, AltVec flavor, family-specific methods, InferBase) for a given type. The two arms differ only in serialization support on the Altrep base impl.