SIGSEGV and StackOverflow from dispatching on ::Type{T}, ::Array{Union{T,Missing},N})

[oxinabox]

EDIT: MWE from below

 julia> typeintersect((Tuple{Type{T},Array{Union{T,Missing},N}} where {T,N}),
                     (Tuple{Type{T},Array{Union{T,Nothing},N}} where {T,N}))
ERROR: StackOverflowError

Original text:

If I do

for U in (:(Union{T, Missing}), :(Union{T, Nothing}),)
    @eval function bar(::Type{T}, xs::Array{$U,N}) where {T,N}
        T
    end
end

Then julia SIGSEGV's (Address boundary error)

When I do:

@eval function bazz(::Type{T}, xs::Array{Union{T,Missing},N}) where {T,N}
   T
end

I get a StackOverflowError

When I do:

function bazz(::Type{T}, xs::Array{Union{T,Missing},N}) where {T,N}
   T
end

I am back to crashing out with SIGSEGV's (Address boundary error)

But if i do:

function bazz(::Type{<:T},xs::Array{Union{T,Missing},N}) where {T,N}
   T
end

then it is fine.
But that is a different expression

as is

function bazz(::Type{T},xs::Array{<:Union{T,Missing},N}) where {T,N}
   T
end

This is on Version 1.6.0-DEV.184 (2020-06-06)

[MasonProtter]

On 1.5.0-beta1, I don't get any SIGSEVs, but I do get StackOverflowErrors. The eval appears to be unrelated to the error so far as I can tell. I get the same error with or without eval.

julia> for U in (:(Union{T, Missing}), :(Union{T, Nothing}),)
           @eval function bar(::Type{T}, xs::Array{$U,N}) where {T,N}
               T
           end
       end
ERROR: StackOverflowError:
Stacktrace:
 [1] top-level scope at none:1
 [2] eval(::Module, ::Any) at ./boot.jl:331
 [3] top-level scope at REPL[4]:2

julia> @eval function bazz(::Type{T}, xs::Array{Union{T,Missing},N}) where {T,N}
          T
       end
bazz (generic function with 1 method)

julia> @eval function bar(::Type{T}, xs::Array{Union{T,Nothing},N}) where {T,N}
          T
       end
ERROR: StackOverflowError:
Stacktrace:
 [1] top-level scope at none:1
 [2] eval(::Module, ::Any) at ./boot.jl:331
 [3] top-level scope at REPL[6]:1

julia> function bar(::Type{T}, xs::Array{Union{T,Nothing},N}) where {T,N}
          T
       end
ERROR: StackOverflowError:
Stacktrace:
 [1] top-level scope at REPL[7]:1

julia> versioninfo()
Julia Version 1.5.0-beta1.0
Commit 6443f6c95a* (2020-05-28 17:42 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: AMD Ryzen 5 2600 Six-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-9.0.1 (ORCJIT, znver1)
Environment:
  JULIA_NUM_THREADS = 6

[JeffBezanson]

Seems to be a stack overflow in type intersection:

julia> typeintersect((Tuple{Type{T},Array{Union{T,Missing},N}} where {T,N}),
                     (Tuple{Type{T},Array{Union{T,Nothing},N}} where {T,N}))
ERROR: StackOverflowError:

The SEGV is probably just the usual issue with stack overflow (on mac os?).

[oxinabox]

Correct I am on MacOS

[KlausC]

Interestingly, the stack overflow (on v1.4.1 on Linux) does not prevent the correct methods to be defined:

julia> for U in (:(Union{T, Missing}), :(Union{T, Nothing}),)
           @eval function bar(::Type{T}, xs::Array{$U,N}) where {T,N}
               T
           end
       end
ERROR: StackOverflowError:
Stacktrace:
 [1] top-level scope at REPL[1]:1
 [2] eval(::Module, ::Any) at ./boot.jl:331
 [3] top-level scope at REPL[1]:2

julia> methods(bar)
# 2 methods for generic function "bar":
[1] bar(::Type{T}, xs::Array{Union{Missing, T},N}) where {T, N} in Main at REPL[1]:3
[2] bar(::Type{T}, xs::Array{Union{Nothing, T},N}) where {T, N} in Main at REPL[1]:3
julia> bar(Float64, [nothing, 1.5])
Float64
julia> typeof([nothing, 1.5])
Array{Union{Nothing, Float64},1}

[OkonSamuel]

I can also reproduce this issue on my PC. But i just thought i should note that

for U in (:(Union{T, Missing}), :(Union{T, Nothing}),)
           @eval function bar(xs::Array{$U,N}, ::Type{T}) where {T,N}
               T
           end
       end

works.

julia> bar(Union{Int, Missing}[1,2,3], Int)
Int64

julia> versioninfo()
Julia Version 1.4.2
Commit 44fa15b150* (2020-05-23 18:35 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i3-5005U CPU @ 2.00GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-8.0.1 (ORCJIT, broadwell)

[ViralBShah]

I tried a few of the things that should have segfaulted, but don't seem to. I wonder if the segfaults got fixed in the linked PRs and if this issue can be closed.

[vtjnash]

The MWE still fails in typeintersection