Function struct_default_target 

pub fn struct_default_target(
    path: &[SmolStr],
    args: &[Expr],
    type_args: &[TypeExpr],
    span: Span,
    ctx: Ctx,
    state: &mut State<'_>,
) -> Option<u16>

The struct S::default() names.

path is a struct (or a generic struct, instantiated at type_args) followed by default, and the call passes nothing. None leaves the path to the function lookups.