Problematic interaction between Stateful and map

[lbilli]

When trying the following code:

v = split("abcd", "")
it = Iterators.Stateful(Iterators.map(identity, v))
popfirst!(it)
popfirst!(it)
collect(Iterators.take(it, 2))

in Julia 1.6.2 and 1.7.0-beta4:

signal (11): Segmentation fault
in expression starting at none:0
jl_gc_pool_alloc at /buildworker/worker/package_linux64/build/src/gc.c:1211
jl_gc_alloc_ at /buildworker/worker/package_linux64/build/src/julia_internal.h:336 [inlined]
jl_gc_alloc at /buildworker/worker/package_linux64/build/src/gc.c:3278
jl_gc_alloc_buf at /buildworker/worker/package_linux64/build/src/julia_internal.h:370 [inlined]
[...]

whereas in Julia 1.8.0-DEV.486 a simple error (still not the right answer):

ERROR: BoundsError: attempt to access 1-element Vector{SubString{String}} at index [2]
Stacktrace:
 [1] setindex!
   @ ./array.jl:946 [inlined]
 [2] collect_to!
   @ ./array.jl:829 [inlined]
 [3] collect_to_with_first!
   @ ./array.jl:803 [inlined]
 [4] _collect(c::UnitRange{Int64}, itr::Base.Iterators.Take{Base.Iterators.Stateful{Base.Generator{Vector{SubString{String}}, typeof(identity)}, Union{Nothing, Tuple{SubString{String}, Int64}}}}, #unused#::Base.EltypeUnknown, isz::Base.HasLength)
   @ Base ./array.jl:797
 [5] collect(itr::Base.Iterators.Take{Base.Iterators.Stateful{Base.Generator{Vector{SubString{String}}, typeof(identity)}, Union{Nothing, Tuple{SubString{String}, Int64}}}})
   @ Base ./array.jl:694
 [6] top-level scope
   @ REPL[4]:1

Might be related to #35530 and #41919