Runtime memory access error I can't explain

[einar-hjortdal]

Describe the bug

When running this test, this line causes no issue, but this line causes a runtime memory access error. I believe this is a compiler bug.

Reproduction Steps

1. clone
2. git checkout c8db48b55eae20f3c9308ea70dc42127cba45780
3. v run peony_test.v

Expected Behavior

Both println should output the same string

Current Behavior

second println causes runtime memory access error

Possible Solution

No response

Additional Information/Context

Looks like this bug causes the database to receive bad parameters too: instead of returning the expected result of 1, it returns 0. That is because it doesn't receive the string provided but something else, however I can't output what that something else is, because of the memory bounds violation.

V version

V 0.5.0 cab281f

Environment details (OS name and version, etc.)

V full version	V 0.5.0 e3b915d.cab281f
OS	linux, "openmamba release 2025.12.1 for x86_64 (rolling)"
Processor	8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz
Memory	10.07GB/31.16GB
V executable	/home/einar/.local/lib64/v/v
V last modified time	2026-01-08 14:54:14
V home dir	OK, value: /home/einar/.local/lib64/v
VMODULES	OK, value: /home/einar/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/einar/Documents/projects/vlang/active/peony
Git version	git version 2.52.0
V git status	weekly.2025.38-682-gcab281ff
.git/config present	true
cc version	cc (GCC) 15.2.1 20251019
gcc version	gcc (GCC) 15.2.1 20251019
clang version	N/A
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 (GNU libc) 2.42

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[einar-hjortdal]

Minimal repro:

module main

import arrays

interface Value {}

fn generate_params(s string) (string, []Value) {
	mut conditions := []string{}
	mut params := []Value{}

	if s != '' {
		conditions = arrays.concat(conditions, 'email = ?')
		params = arrays.concat(params, s)
	}

	println(params) // [Value('info@peony.com')]
	return conditions.str(), params
}

fn main() {
	_, params := generate_params('info@peony.com')
	println(params)
// 0x7f313783c170: at ???: RUNTIME ERROR: invalid memory access
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:4717: by builtin__string_clone
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:4807: by builtin__string_str
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:1361: by indent_main__Value_str
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:1345: by indent_Array_main__Value_str
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:1339: by Array_main__Value_str
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:5551: by main__main
// /tmp/v_1000/26293.01KEF99BW0NNS6WZTSG2PVCY4F.tmp.c:5579: by main
}

[einar-hjortdal]

Even more minimal: sometimes this does not actually panic.

module main

import arrays

interface Value {}

fn generate_params(s string) []Value {
	mut params := []Value{}
	params = arrays.concat(params, s)
	println(params)
	return params
}

fn main() {
	params := generate_params('info@peony.com')
	println(params)
}

Output when panic:

$v run ./26293b.v 
[Value('info@peony.com')]
0x7f7f457f9150: at ???: RUNTIME ERROR: invalid memory access
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:4673: by builtin__string_clone
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:4763: by builtin__string_str
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:1350: by indent_main__Value_str
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:1334: by indent_Array_main__Value_str
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:1328: by Array_main__Value_str
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:5498: by main__main
/tmp/v_1000/26293b.01KEF9CQ3RE9VZ0JVANBGNRCQF.tmp.c:5526: by main

Output when it does not panic: still wrong output.

$v run ./26293b.v 
[Value('info@peony.com')]
[Value('')]

[einar-hjortdal]

module main

interface Value {}

fn generate_params(s string) []Value {
	mut params := [Value(s)]
	println(params)
	return params
}

fn main() {
	params := generate_params('info@peony.com')
	println(params)
}

This does not panic, and the output is as expected:

$v run ./26293b.v 
[Value('info@peony.com')]
[Value('info@peony.com')]

This is not a workaround, just my observation trying to repro the issue