Undefined behavior if variable is out of scope when defer is called

[kravlad]

Describe the bug

if we define a defer block inside the loop with a variable that is in local scope we get undefined behavior when defer is being called.

Reproduction Steps

fn main() {
    for i in 1..4 {
	defer {
	    println('Deferred execution for $i')
	}
	println('Hello, World! $i')
    }
}

Expected Behavior

compile error?? (I don't know)

Current Behavior

output:

Hello, World! 1
Hello, World! 2
Hello, World! 3
Deferred execution for 49598448

Possible Solution

No response

Additional Information/Context

No response

V version

0.4.10 a91e2de

Environment details (OS name and version, etc.)

V full version	V 0.4.10 a91e2de
OS	macos, macOS, 15.5, 24F74
Processor	8 cpus, 64bit, little endian, Apple M1
Memory	0.3GB/16GB
V executable	/Users/user/dev/v/v
V last modified time	2025-06-05 15:14:14
V home dir	OK, value: /Users/user/dev/v
VMODULES	OK, value: /Users/user/.vmodules
VTMP	OK, value: /tmp/v_501
Current working dir	OK, value: /Users/user
Git version	git version 2.49.0
V git status	weekly.2025.14-315-ga91e2def
.git/config present	true
cc version	Apple clang version 17.0.0 (clang-1700.0.13.5)
gcc version	Apple clang version 17.0.0 (clang-1700.0.13.5)
clang version	Apple clang version 17.0.0 (clang-1700.0.13.5)
tcc version	tcc version 0.9.28rc 2024-02-05 HEAD@105d70f7 (AArch64 Darwin)
tcc git status	thirdparty-macos-arm64 e447816c
emcc version	N/A
glibc version	N/A

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[huly-for-github]

Connected to Huly®: V_0.6-23022

[kravlad]

For example, how it works in Go:

func main() {
    for i := range 3 {
        defer fmt.Println("Deferred execution for ", i)
	    fmt.Println("Hello, World! ", i)
        }
}

output:

Hello, World!  0
Hello, World!  1
Hello, World!  2
Deferred execution for  2
Deferred execution for  1
Deferred execution for  0

[felipensp]

VV_LOC void main__main(void) {
        bool main__main_defer_0 = false;
        int_literal i;
        for (int i = 1; i < 4; ++i) {
                main__main_defer_0 = true;
                println(str_intp(2, _MOV((StrIntpData[]){{_S("Hello, World! "), 0xfe07, {.d_i32 = i}}, {_SLIT0, 0, { .d_c = 0 }}})));
        }
// Defer begin
if (main__main_defer_0) {
        println(str_intp(2, _MOV((StrIntpData[]){{_S("Deferred execution for "), 0xfe07, {.d_i32 = i}}, {_SLIT0, 0, { .d_c = 0 }}})));
}
// Defer end
}

[felipensp]

Since it is not a local scoped defer it uses a i variable not initialized... hence the output looks random.