C error: `json.decode` fails for Option when `json.encode` was not called previously

[jorgeluismireles]

V version: V 0.4.11 708c73b, press to see full `v doctor` output

V full version	V 0.4.11 7dc3889.708c73b
OS	linux, Ubuntu 22.04.5 LTS
Processor	4 cpus, 64bit, little endian, Intel(R) Core(TM) i3-4150 CPU @ 3.50GHz
Memory	0.53GB/3.7GB
V executable	/home/jorge/v/v
V last modified time	2025-07-22 18:55:18
V home dir	OK, value: /home/jorge/v
VMODULES	OK, value: /home/jorge/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/jorge/bugs
Git version	git version 2.34.1
V git status	weekly.2025.16-464-g708c73b4
.git/config present	true
cc version	cc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
gcc version	gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
clang version	Ubuntu clang version 14.0.0-1ubuntu1.1
tcc version	tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 696c1d84
emcc version	emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.5 ()
glibc version	ldd (Ubuntu GLIBC 2.35-0ubuntu3.10) 2.35

What did you do?
./v -g -o vdbg cmd/v && ./vdbg 250722b.v && 250722b

import json

struct Base {
	time ?i64 @[omitempy]
}

fn main() {

	//_ := json.encode(Base{}) // workaround

	d1 := json.decode(Base, '{}')!
	dump(d1)
}

What did you see?

================== C compilation error (from tcc): ==============
cc: /tmp/v_1000/250722b.01K0T434TZZNP93QRFWPMC5BE2.tmp.c:2122: warning: implicit declaration of function '_option_ok'
cc: /home/jorge/v/thirdparty/tcc/lib/libgc.a: error: 'GC_noop1_ptr' defined twice
cc: tcc: error: undefined symbol '_option_ok'
=================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).
builder error: 
==================
C error found. It should never happen, when compiling pure V code.
This is a V compiler bug, please report it using `v bug file.v`,
or goto https://github.com/vlang/v/issues/new/choose .
You can also use #help on Discord: https://discord.gg/vlang .

What did you expect to see?

Compile.

Workaround

Call previously json.encode(Base{}) it should be over same struct Base:

fn main() {
	_ := json.encode(Base{}) // workaround
	d1 := json.decode(Base, '{}')!
	dump(d1)
}

[250722b.v:10] d1: Base{
    time: Option(none)
}

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[huly-for-github]

Connected to Huly®: V_0.6-23430

[jorgeluismireles]

Another workaround is import json2 even as not used:

import json
import x.json2 as _

struct Base {
	time ?i64 @[omitempy]
}

fn main() {
	d1 := json.decode(Base, '{}')!
	dump(d1)
}

[code.v:10] d1: Base{
    time: Option(none)
}

[jorgeluismireles]

Importing time also fixes the problem (json2 does it):

import json
import time as _

struct Base {
	time ?i64 @[omitempy]
}

fn main() {
	d1 := json.decode(Base, '{}')!
	dump(d1)
}

[code.v:10] d1: Base{
    time: Option(none)
}

[jorgeluismireles]

Also rand:

import json
import rand as _

struct Base {
	time ?i64 @[omitempy]
}

fn main() {
	d1 := json.decode(Base, '{}')!
	dump(d1)
}

[jorgeluismireles]

Last I found it fixes is import strings.textscanner as _. No idea why.

[spytheman]

It is imho a -skip-unused issue (markused is now more aggressive). Importing the other modules, masks the problem, because they have constructs that use options.

[spytheman]

After ae1fa8a , markused is more precise, and on latest master, the code sample in the issue compiles fine for me.

@jorgeluismireles can you please check if after v up you still have the problem?

[felipensp]

Yeah, it's already fixed by latest changes on markused. 👍🏻

[jorgeluismireles]

Yes, is working now with V 0.4.11 bf03add.