Segmentation fault with typo in iterate(x, n)

[dalum]

Note the typo in Base.iterate(a, n) = iterate(a.data) (missing n on the right hand side):

julia> struct MyType{N,T}
       data::NTuple{N,T}
       end

julia> Base.iterate(a::MyType) = iterate(a.data)

julia> Base.iterate(a::MyType, n) = iterate(a.data)

julia> Base.length(a::MyType) = length(a.data)

julia> a = MyType((0., 0.))
MyType{2,Float64}(^P(0.0, 0.0))

julia> b = MyType((1., 0.))
MyType{2,Float64}((1.0, 0.0))

julia> MyType(Tuple(x + y for (x,y) in zip(a, b)))

signal (11): Segmentation fault
in expression starting at no file:0
jl_gc_pool_alloc at /home/dalum/Projects/julia/src/gc.c:963
jl_gc_alloc_ at /home/dalum/Projects/julia/src/julia_internal.h:274 [inlined]
jl_gc_alloc at /home/dalum/Projects/julia/src/gc.c:2668
_new_array_ at /home/dalum/Projects/julia/src/array.c:100 [inlined]
_new_array at /home/dalum/Projects/julia/src/array.c:158 [inlined]
jl_alloc_array_1d at /home/dalum/Projects/julia/src/array.c:418
Type at ./boot.jl:394 [inlined]
Type at ./boot.jl:413 [inlined]
_reformat_bt at ./error.jl:61
jl_apply_generic at /home/dalum/Projects/julia/src/gf.c:2184
catch_backtrace at ./error.jl:91
eval_user_input at /home/dalum/Projects/julia/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:97
macro expansion at /home/dalum/Projects/julia/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:117 [inlined]
#28 at ./task.jl:259
jl_apply_generic at /home/dalum/Projects/julia/src/gf.c:2184
jl_apply at /home/dalum/Projects/julia/src/julia.h:1537 [inlined]
start_task at /home/dalum/Projects/julia/src/task.c:268
unknown function (ip: 0xffffffffffffffff)
Allocations: 919274 (Pool: 919020; Big: 254); GC: 1
fish: “~/Projects/julia/julia” terminated by signal SIGSEGV (Address boundary error)

[martinholters]

Simpler reproduction:

struct Foo end

Base.iterate(::Foo) = (0, 0)
Base.iterate(::Foo, n) = n < 1000000 ? (0, n+1) : nothing
Base.length(::Foo) = 10

collect(i for i in Foo())

collect(::Generator) assumes the iterator not to lie about its length. The @inbounds annotations here:

julia/base/array.jl

Lines 655 to 669 in 1968b23

	while true
	y = iterate(itr, st)
	y === nothing && break
	el, st = y
	if el isa T || typeof(el) === T
	@inbounds dest[i] = el::T
	i += 1
	else
	R = promote_typejoin(T, typeof(el))
	new = similar(dest, R)
	copyto!(new,1, dest,1, i-1)
	@inbounds new[i] = el
	return collect_to!(new, itr, i+1, st)
	end
	end

assume the dest array to be large enough to hold all generated elements, but it is allocated based on the length. I guess we could just replace the while true with while i <= lastindex(dest)? Then we would just produce the first length elements, which seems ok.

[martinholters]

Ref. #29458 which should hopefully be made to also fix this.

[KristofferC]

Dup of #28763