How should I declare StructArray field type in type-stable manner?

There are a lot of Any inferred types in this example:

struct Foo
    x::StructVector{NamedTuple{(:a, :b), Tuple{Int64, Float64}}}
end

f = Foo(StructVector(a=[1,2,3], b=[0.1, 0.2, 0.3]))

function first_prod(f::Foo)
    f.x.a[1] * f.x.b[1]
end

@code_typed first_prod(f)

outputs:

CodeInfo(
1 ─ %1 = Base.getfield(f, :x)::StructVector{NamedTuple{(:a, :b), Tuple{Int64, Float64}}}
│   %2 = StructArrays.getfield(%1, :components)::Union{Tuple, NamedTuple}
│   %3 = StructArrays.getfield(%2, :a)::Any
│   %4 = Base.getindex(%3, 1)::Any
│   %5 = Base.getfield(f, :x)::StructVector{NamedTuple{(:a, :b), Tuple{Int64, Float64}}}
│   %6 = StructArrays.getfield(%5, :components)::Union{Tuple, NamedTuple}
│   %7 = StructArrays.getfield(%6, :b)::Any
│   %8 = Base.getindex(%7, 1)::Any
│   %9 = (%4 * %8)::Any
└──      return %9
) => Any

The issue names no repository files or tests; begin by reproducing the Julia example with StructVector and running @code_typed on first_prod. Investigate how the declared StructVector field type and component access produce the shown Any inferences; done means establishing a type-stable declaration or documenting why one is not available.