cgen error when `-cc g++` is used for `const x = $if some_define? { [u8(1), 2, 3]! } $else { [u8(4), 5, 6]! }`

[spytheman]

V version: V 0.4.12 67b2ba9, press to see full `v doctor` output

V full version	V 0.4.12 caf7d41.67b2ba9
OS	linux, Ubuntu 20.04.6 LTS
Processor	4 cpus, 64bit, little endian, Intel(R) Core(TM) i3-3225 CPU @ 3.30GHz
Memory	1.01GB/15.05GB
V executable	/home/delian/v/v
V last modified time	2025-11-13 08:08:49
V home dir	OK, value: /home/delian/v
VMODULES	OK, value: /home/delian/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/delian/v
env VFLAGS	"-no-parallel"
Git version	git version 2.50.0
V git status	weekly.2025.46-10-g67b2ba92
.git/config present	true
cc version	cc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
gcc version	gcc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
clang version	Ubuntu clang version 18.1.8 (11~20.04.2)
tcc version	tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 696c1d84
emcc version	N/A
glibc version	ldd (Ubuntu GLIBC 2.31-0ubuntu9.18) 2.31

What did you do?
./v -g -o vdbg cmd/v && ./vdbg /home/delian/code/misc/2025_11_13__13/y.v && /home/delian/code/misc/2025_11_13__13/y

const my_fixed_bytes = $if some_define? { [u8(1), 2, 3]! } $else { [u8(4), 5, 6]! }
println(my_fixed_bytes)

What did you see?

[4, 5, 6]

What did you expect to see?

A compiled program, that produces the same result, even with -cc g++ .

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[spytheman]

#1 13:31:06 ^ builtin_closure_use_fixed_arrays_for_closure_thunk ~/v>v -cc gcc run /home/delian/code/misc/2025_11_13__13/y.v
[4, 5, 6]
#0 13:31:10 ^
#0 13:31:10 ^
#0 13:31:10 ^ builtin_closure_use_fixed_arrays_for_closure_thunk ~/v>v -cc g++ run /home/delian/code/misc/2025_11_13__13/y.v
================== C compilation error (from g++): ==============
cc: /tmp/v_1000/y.01K9YFQRMHN18TQS1WSDA1VQ61.tmp.c: In function ‘void _vinit(int, voidptr)’:
cc: /tmp/v_1000/y.01K9YFQRMHN18TQS1WSDA1VQ61.tmp.c:5458:33: error: taking address of temporary array
cc:  5458 |  memcpy(&_t1, (Array_fixed_u8_3){((u8)(4)), 5, 6} , sizeof(Array_fixed_u8_3));
cc:       |                                 ^~~~~~~~~~~~~~~~~
=================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).
#1 13:31:13 ^ builtin_closure_use_fixed_arrays_for_closure_thunk ~/v>

[spytheman]

Note, that this compiles and runs fine with both gcc and g++:

const my_bytes = [u8(1), 2, 3]!
println(my_bytes)

and generates:

static Array_fixed_u8_3 _const_main__my_bytes = {((u8)(1)), 2, 3}; // fixed array const

while g++ chokes on the generated:

Array_fixed_u8_3 _const_main__my_fixed_bytes; // inited later
...
Array_fixed_u8_3 _t1;
#if defined(CUSTOM_DEFINE_some_define)
#else
    memcpy(&_t1, (Array_fixed_u8_3){((u8)(4)), 5, 6}    , sizeof(Array_fixed_u8_3));
#endif
    memcpy(&_const_main__my_fixed_bytes, &_t1, sizeof(Array_fixed_u8_3));

[spytheman]

This could have worked with g++ as well:

Array_fixed_u8_3 _const_main__my_fixed_bytes; // inited later
...
#if defined(CUSTOM_DEFINE_some_define)
#else
    Array_fixed_u8_3 _t1 = {((u8)(4)), 5, 6};
#endif
    memcpy(&_const_main__my_fixed_bytes, &_t1, sizeof(Array_fixed_u8_3));