Add propagate_inbounds to new getindex method

[jakobnissen]

MWE:

struct TextKmerIterator
    data::Vector{UInt8}
    stop::UInt # inclusive
end

function foo(x::TextKmerIterator)
    kmer, i, k = UInt(0), UInt(1), UInt(0)
    @inbounds while i ≤ x.stop
        byte = x.data[i]
        k += one(UInt)
        i += 1
        kmer = ((kmer << 2) & UInt(0x3f)) | 0x01
        if k == 3
            return kmer, (kmer, i, k-one(UInt))
        end
    end
    return nothing
end

And then

julia> it = TextKmerIterator(collect(codeunits("T")), 4)
Main.TextKmerIterator(UInt8[0x54], 0x0000000000000004)

julia> foo(it)
ERROR: BoundsError: attempt to access 1-element Vector{UInt8} at index [2]

According to Nicholas Bauer on Slack, the culprit is

julia/base/abstractarray.jl

Line 1051 in 0b55425

getindex(A::Array, i1::Integer, I::Integer...) = A[to_indices(A, (i1, I...))...]

added in #36427 which lacks propagate inbounds.

[simeonschaub]

Ah, that looks like it was missed. Note however that reading arrays out of bounds should always be avoided nevertheless and can lead to segfaults.

[sanjibansg]

I would like to contribute to this issue. Do guide me on approaching this @simeonschaub @jakobnissen

[jakobnissen]

@Kahanikaar Nice! You would need to clone the Julia repo. Then go to the relevant file and add @_propagate_inbounds_meta right before the function call. I think that should do the trick.

To verify it worked, you can run my test code. If you don't see a BoundsError, it probably worked. To be sure, you can run @code_native foo(it) and check that there is no boundschecking branch.

[sanjibansg]

Initial PR made. Do review. @jakobnissen @simeonschaub

[KristofferC]

Closed by #40281?

[jakobnissen]

Yes, looks like it! Thanks for your PR anyway, @Kahanikaar