subtyping covariance issue with Union{<:AbstractMatrix{P},P}}

[projekter]

After getting a "unreachable reached", I was able to construct the following MWE that reproduces the error:

struct Problem{P}
    item::AbstractVector{<:Union{P,<:AbstractMatrix{P}}}

    function Problem{P}(item::AbstractVector{<:Union{P,<:AbstractMatrix{P}}}) where {P}
        return new{P}(item)
    end
end

struct Container
    el::Problem
end

struct Failure
    function Failure(cnt::Container)
        element = cnt.el
        return typeof(element)(element.item)
    end
end

prob = Problem{Int}(Int[])
cnt = Container(prob)
Failure(cnt)

The construction of Failure in the last line triggers the error. Notably, only on Windows (Julia 1.7.3 x64), when running on Linux (Ubuntu WSL 1.7.3 x64), the code passes through. Of course, using the Debugger where everything is interpreted also works fine.
Some observations:

• If I delete the constructor for Problem, the problem vanishes. Unfortunately, the actual constructor does a bit of work, so that this is not an option.
• If I change Failure to accept a Problem directly, without the Container, the problem vanishes.
• If the item is of a more simple type - e.g., replacing the Union by either P or <:AbstractMatrix{P} - the problem vanishes.
• I was very surprised when I ended up with this MWE, since a construction like this (with a type like item, a container, a typeof-constructor call, the internal constructor like this) has been part of my code for weeks now and always worked. I did some other changes completely unrelated to this, which somehow ended up raising this error. Unfortunately, I cannot say what was responsible, since I mainly tested on WSL in the last days, where everything works.

julia> versioninfo()
Julia Version 1.7.3
Commit 742b9abb4d (2022-05-06 12:58 UTC)
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 11th Gen Intel(R) Core(TM) i7-11800H @ 2.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, tigerlake)

julia> Failure(cnt)

Unreachable reached at 000000005f78134d

Please submit a bug report with steps to reproduce this fault, and any error messages that follow (in their entirety). Thanks.
Exception: EXCEPTION_ILLEGAL_INSTRUCTION at 0x5f78134d -- Failure at .\REPL[3]:4
in expression starting at REPL[6]:1
Failure at .\REPL[3]:4
unknown function (ip: 000000005f78139c)
jl_apply at /cygdrive/c/buildbot/worker/package_win64/build/src\julia.h:1788 [inlined]
do_call at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:126
eval_value at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:215
eval_stmt_value at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:166 [inlined]
eval_body at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:583
jl_interpret_toplevel_thunk at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:731
jl_toplevel_eval_flex at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:885
jl_toplevel_eval_flex at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:830
jl_toplevel_eval at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:894 [inlined]
jl_toplevel_eval_in at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:944
eval at .\boot.jl:373 [inlined]
eval_user_input at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.7\REPL\src\REPL.jl:150
repl_backend_loop at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.7\REPL\src\REPL.jl:246
start_repl_backend at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.7\REPL\src\REPL.jl:231
#run_repl#47 at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.7\REPL\src\REPL.jl:364
run_repl at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.7\REPL\src\REPL.jl:351
#936 at .\client.jl:394
jfptr_YY.936_22652.clone_1 at C:\Users\Benjamin\AppData\Local\Programs\Julia-1.7.3\lib\julia\sys.dll (unknown line)
jl_apply at /cygdrive/c/buildbot/worker/package_win64/build/src\julia.h:1788 [inlined]
jl_f__call_latest at /cygdrive/c/buildbot/worker/package_win64/build/src\builtins.c:757
#invokelatest#2 at .\essentials.jl:716 [inlined]
invokelatest at .\essentials.jl:714 [inlined]
run_main_repl at .\client.jl:379
exec_options at .\client.jl:309
_start at .\client.jl:495
jfptr__start_34800.clone_1 at C:\Users\Benjamin\AppData\Local\Programs\Julia-1.7.3\lib\julia\sys.dll (unknown line)
jl_apply at /cygdrive/c/buildbot/worker/package_win64/build/src\julia.h:1788 [inlined]
true_main at /cygdrive/c/buildbot/worker/package_win64/build/src\jlapi.c:559
jl_repl_entrypoint at /cygdrive/c/buildbot/worker/package_win64/build/src\jlapi.c:701
mainCRTStartup at /cygdrive/c/buildbot/worker/package_win64/build/cli\loader_exe.c:42
BaseThreadInitThunk at C:\WINDOWS\System32\KERNEL32.DLL (unknown line)
RtlUserThreadStart at C:\WINDOWS\SYSTEM32\ntdll.dll (unknown line)
Allocations: 2722 (Pool: 2711; Big: 11); GC: 0

[vtjnash]

MWE:

julia> T = Tuple{Type{Val{P}} where P, AbstractVector{<:Union{P, <:AbstractMatrix{P}}} where P}
Tuple{Type{Val{P}} where P, AbstractVector{<:Union{P, var"#s4"} where var"#s4"<:AbstractMatrix{P}} where P}

julia> S = Tuple{Type{Val{P}}, AbstractVector{<:Union{P, <:AbstractMatrix{P}}}} where P
Tuple{Type{Val{P}}, AbstractVector{<:Union{P, var"#s4"} where var"#s4"<:AbstractMatrix{P}}} where P

julia> S<:T
true # returns `false` on Windows

[vtjnash]

everywhere else MWE:

julia> T = Tuple{Type{Val{P}} where P, AbstractVector{<:Union{<:AbstractMatrix{P},P}} where P}
Tuple{Type{Val{P}} where P, AbstractVector{<:Union{var"#s2", P} where var"#s2"<:AbstractMatrix{P}} where P}

julia> S = Tuple{Type{Val{P}}, AbstractVector{<:Union{<:AbstractMatrix{P},P}}} where P
Tuple{Type{Val{P}}, AbstractVector{<:Union{var"#s1", P} where var"#s1"<:AbstractMatrix{P}}} where P

julia> S<:T
false # returns `true` on Windows

[vtjnash]

perhaps related or similar?

julia> S = Pair{Val{P}, AbstractVector{<:Union{P,<:AbstractMatrix{P}}}} where P
Pair{Val{P}, AbstractVector{<:Union{P, var"#s1"} where var"#s1"<:AbstractMatrix{P}}} where P

julia> T = Pair{Val{R}, AbstractVector{<:Union{P,<:AbstractMatrix{P}}}} where {P,R}
Pair{Val{R}, AbstractVector{<:Union{P, var"#s1"} where var"#s1"<:AbstractMatrix{P}}} where {P, R}

julia> S<:T
false # should be true?

julia> typeintersect(S,T)
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