Invalid syntax cause a crash in Julia 1.0

[inkydragon]

background

Somebody in Chinese Julia community wants to implement a STMonad in Julia, and he found this bug.

And I found that this code in julia 0.6.4 only cause a error, Julia also suggest that this code use a deprecated syntax. But in Julia 1.0 this cause a crash.

Error info

v 1.0.0

minimal reproducible example

struct STMonad{A,B}
	function STMonad()
		new{S,Ref{S}}() where S
	end
end

STMonad()

Julia info

julia> versioninfo()
Julia Version 1.0.0
Commit 5d4eaca0c9 (2018-08-08 20:58 UTC)
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, broadwell)

output

PS C:\Users\woclass\Desktop\`del> C:\Users\woclass\AppData\Local\Julia-1.0.0\bin\julia.exe .\STMonad.jl

Please submit a bug report with steps to reproduce this fault, and any error messages that follow (in their entirety). Thanks.
Exception: EXCEPTION_ACCESS_VIOLATION at 0x6b5cf117 -- jl_new_structv at /home/Administrator/buildbot/worker/package_win64/build/src\datatype.c:774
in expression starting at C:\Users\woclass\Desktop\`del\STMonad.jl:7
jl_set_nth_field at /home/Administrator/buildbot/worker/package_win64/build/src\datatype.c:889 [inlined]
jl_new_structv at /home/Administrator/buildbot/worker/package_win64/build/src\datatype.c:781
Type at C:\Users\woclass\Desktop\`del\STMonad.jl:3
jl_fptr_trampoline at /home/Administrator/buildbot/worker/package_win64/build/src\gf.c:1829
jl_apply_generic at /home/Administrator/buildbot/worker/package_win64/build/src\gf.c:2182
do_call at /home/Administrator/buildbot/worker/package_win64/build/src\interpreter.c:324
eval_value at /home/Administrator/buildbot/worker/package_win64/build/src\interpreter.c:428
eval_stmt_value at /home/Administrator/buildbot/worker/package_win64/build/src\interpreter.c:363 [inlined]
eval_body at /home/Administrator/buildbot/worker/package_win64/build/src\interpreter.c:682
jl_interpret_toplevel_thunk_callback at /home/Administrator/buildbot/worker/package_win64/build/src\interpreter.c:799
unknown function (ip: FFFFFFFFFFFFFFFE)
unknown function (ip: 000000000EB4522F)
unknown function (ip: FFFFFFFFFFFFFFFF)
jl_toplevel_eval_flex at /home/Administrator/buildbot/worker/package_win64/build/src\toplevel.c:787
jl_parse_eval_all at /home/Administrator/buildbot/worker/package_win64/build/src\ast.c:838
jl_load at /home/Administrator/buildbot/worker/package_win64/build/src\toplevel.c:821 [inlined]
jl_load_ at /home/Administrator/buildbot/worker/package_win64/build/src\toplevel.c:828
include at .\boot.jl:317 [inlined]
include_relative at .\loading.jl:1038
include at .\sysimg.jl:29
jl_apply_generic at /home/Administrator/buildbot/worker/package_win64/build/src\gf.c:2182
exec_options at .\client.jl:229
_start at .\client.jl:421
jl_apply_generic at /home/Administrator/buildbot/worker/package_win64/build/src\gf.c:2182
jl_apply at /home/Administrator/buildbot/worker/package_win64/build/src\julia.h:1536 [inlined]
true_main at /home/Administrator/buildbot/worker/package_win64/build/ui\repl.c:112
wmain at /home/Administrator/buildbot/worker/package_win64/build/ui\repl.c:233
__tmainCRTStartup at /usr/src/debug/mingw64-x86_64-runtime-5.0.3-1/crt\crtexe.c:329
mainCRTStartup at /usr/src/debug/mingw64-x86_64-runtime-5.0.3-1/crt\crtexe.c:212
BaseThreadInitThunk at C:\WINDOWS\System32\KERNEL32.DLL (unknown line)
RtlUserThreadStart at C:\WINDOWS\SYSTEM32\ntdll.dll (unknown line)
Allocations: 5974 (Pool: 5964; Big: 10); GC: 0

v 0.6.4

And in Juliua 0.6.4 this code just cause a MethodError, not a crash.

julia> struct STMonad{A, B}
           function STMonad()
               new{S, Ref{S}}() where S
           end
       end

WARNING: deprecated syntax "inner constructor STMonad(...) around REPL[1]:3".
Use "STMonad{A,B}(...) where {A,B}" instead.

julia> STMonad()
ERROR: MethodError: no method matching STMonad()

[yuyichao]

The deprecated syntax isn't an issue (it got a new meaning on 1.0 and isn't deprecated anymore).

new{S, Ref{S}}() where S is invalid code and that's what's causing the crash.

[JeffBezanson]

Correct; that new expression basically expands to _allocate(STMonad{S,Ref{S}}) where S which is invalid for two reasons:

1. The type has free variables and so cannot be constructed (this should give an error).
2. The body of where S needs to be a type, but instead would be this (invalid) instance of STMonad. If you fix the deprecation warning on 0.6 you get:

julia> struct STMonad{A,B}
           function (::Type{STMonad})()
               new{S, Ref{S}}() where S
           end
       end

julia> STMonad()
ERROR: TypeError: UnionAll: expected Type, got STMonad{S,Ref{S}}
Stacktrace:
 [1] UnionAll(::TypeVar, ::Any) at ./boot.jl:263
 [2] STMonad() at ./REPL[1]:3