Unreachable reached

[fatteneder]

MWE

struct Trait end

struct A
    x::Float32
end
struct B
    x::Vector{A}
end
hastrait(::Type{B}) = Trait
hastrait(t) = hastrait(typeof(t))

function totalsize(::Type{T}) where T
    if hastrait(T) !== Trait
        error("$T has no trait")
    end
    sum(fieldtypes(T), init=0) do t
        totalsize(t)
    end
end

totalsize(B)

The line hastrait(t) = hastrait(typeof(t)) is wrong and should be fixed with hastrait(::Type{T}) where T = nothing, but the crash should not happen.

• On v1.10.4 this crashes.
  Stack trace

julia> include("mwe.jl")
Unreachable reached at 0x7f0b91f13c45

[362153] signal (4.2): Illegal instruction
in expression starting at /home/florian/wd/graphics/VulkanTutorial/mwe.jl:45
totalsize at /home/florian/wd/graphics/VulkanTutorial/mwe.jl:37
unknown function (ip: 0x7f0b91f13c72)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
#1 at /home/florian/wd/graphics/VulkanTutorial/mwe.jl:41
MappingRF at ./reduce.jl:100 [inlined]
afoldl at ./operators.jl:544
unknown function (ip: 0x7f0b91f13bad)
_foldl_impl at ./reduce.jl:68 [inlined]
foldl_impl at ./reduce.jl:48
unknown function (ip: 0x7f0b91f13a0d)
mapfoldl_impl at ./reduce.jl:44
unknown function (ip: 0x7f0b91f138fd)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
#mapfoldl#298 at ./reduce.jl:175
unknown function (ip: 0x7f0b91f137d8)
mapfoldl at ./reduce.jl:175 [inlined]
#mapreduce#302 at ./reduce.jl:307 [inlined]
mapreduce at ./reduce.jl:307 [inlined]
#sum#305 at ./reduce.jl:535 [inlined]
sum at ./reduce.jl:535
unknown function (ip: 0x7f0b91f136b0)
totalsize at /home/florian/wd/graphics/VulkanTutorial/mwe.jl:40
unknown function (ip: 0x7f0b91f13572)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
jl_apply at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/julia.h:1982 [inlined]
do_call at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:126
eval_value at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:223
eval_stmt_value at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:174 [inlined]
eval_body at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:617
jl_interpret_toplevel_thunk at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:775
jl_toplevel_eval_flex at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:934
jl_toplevel_eval_flex at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:877
ijl_toplevel_eval_in at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:985
eval at ./boot.jl:385 [inlined]
include_string at ./loading.jl:2076
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
_include at ./loading.jl:2136
include at ./client.jl:489
unknown function (ip: 0x7f0b91f12e95)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
jl_apply at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/julia.h:1982 [inlined]
do_call at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:126
eval_value at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:223
eval_stmt_value at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:174 [inlined]
eval_body at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:617
jl_interpret_toplevel_thunk at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/interpreter.c:775
jl_toplevel_eval_flex at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:934
jl_toplevel_eval_flex at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:877
jl_toplevel_eval_flex at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:877
jl_toplevel_eval_flex at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:877
ijl_toplevel_eval_in at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/toplevel.c:985
eval at ./boot.jl:385 [inlined]
eval_user_input at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/usr/share/julia/stdlib/v1.10/REPL/src/REPL.jl:150
repl_backend_loop at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/usr/share/julia/stdlib/v1.10/REPL/src/REPL.jl:246
#start_repl_backend#46 at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/usr/share/julia/stdlib/v1.10/REPL/src/REPL.jl:231
start_repl_backend at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/usr/share/julia/stdlib/v1.10/REPL/src/REPL.jl:228
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
#run_repl#59 at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/usr/share/julia/stdlib/v1.10/REPL/src/REPL.jl:389
run_repl at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/usr/share/julia/stdlib/v1.10/REPL/src/REPL.jl:375
jfptr_run_repl_91737.1 at /home/florian/.julia/juliaup/julia-1.10.4+0.x64.linux.gnu/lib/julia/sys.so (unknown line)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
#1013 at ./client.jl:432
jfptr_YY.1013_82703.1 at /home/florian/.julia/juliaup/julia-1.10.4+0.x64.linux.gnu/lib/julia/sys.so (unknown line)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
jl_apply at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/julia.h:1982 [inlined]
jl_f__call_latest at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/builtins.c:812
#invokelatest#2 at ./essentials.jl:892 [inlined]
invokelatest at ./essentials.jl:889 [inlined]
run_main_repl at ./client.jl:416
exec_options at ./client.jl:333
_start at ./client.jl:552
jfptr__start_82729.1 at /home/florian/.julia/juliaup/julia-1.10.4+0.x64.linux.gnu/lib/julia/sys.so (unknown line)
_jl_invoke at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:2895 [inlined]
ijl_apply_generic at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/gf.c:3077
jl_apply at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/julia.h:1982 [inlined]
true_main at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/jlapi.c:582
jl_repl_entrypoint at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/src/jlapi.c:731
main at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-10/cli/loader_exe.c:58
__libc_start_call_main at /lib64/libc.so.6 (unknown line)
__libc_start_main at /lib64/libc.so.6 (unknown line)
unknown function (ip: 0x4010b8)
Allocations: 1392378 (Pool: 1391069; Big: 1309); GC: 2
[1]    362153 illegal hardware instruction (core dumped)  julia

rr trace uploaded to https://julialang-dumps.s3.amazonaws.com/reports/2024-06-16T10-41-10-fatteneder.tar.zst

• On v1.11 and nightly this gives a StackOverflowError.

---

julia> versioninfo()
Julia Version 1.10.1
Commit 7790d6f0641 (2024-02-13 20:41 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 8 × 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, tigerlake)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)
Environment:
  JULIA_PKG_SERVER = https://staging.pkg.julialang.org
  LD_PRELOAD = /usr/lib64/libstdc++.so.6

and installed with juliaup.

[aviatesk]

This actually seems to be a duplicate of https://github.com/JuliaLang/julia/issues/40009, and has been fixed by https://github.com/JuliaLang/julia/pull/52999 on the latest master.

[ctarn]

I don't think there's anything wrong with the crash. After calling totalsize(B), it will run into the sum loop, and call totalsize(Vector{A}), and then evaluate the if sentence. Then hastrait(Vector{A}) will call the second method, i.e., = hastrait(typeof(Vector{A})) = hastrait(DataType). However, typeof(DataType) also returns DataType, and thus the recursive call will never stop, and throws an error finally. It seems that everything makes sense and it's not a bug.

The case is slightly different to #40009, since the recursive will require incremental memory space and will crash, but the cases in #40009 not.