Swap assignment not working in closure

[elliotchance]

Describe the bug

Cannot use a, b = b, a in a closure.

Reproduction Steps

module main

fn main() {
	f := foo()
	f()
}

fn foo() fn () {
	return fn () {
		mut left := 1
		mut right := 2

		left, right = right, left

		println('${left} ${right}')
	}
}

Expected Behavior

No compiler error.

Current Behavior

Produces a C compiler error:

==================
/tmp/v_501/bug.3024684967219090772.tmp.c:2081:17: error: use of undeclared identifier '_V_closure_ctx'
        int _var_114 = _V_closure_ctx->left;
                       ^
/tmp/v_501/bug.3024684967219090772.tmp.c:2082:17: error: use of undeclared identifier '_V_closure_ctx'
        int _var_120 = _V_closure_ctx->right;
                       ^
2 errors generated.
...
==================
(Use `v -cg` to print the entire error message)

builder error: 
==================
C error. This should never happen.

Possible Solution

You can work around this with a temporary variable:

tmp := left
left = right
right = left

Additional Information/Context

No response

V version

V 0.4.2 4bc9a8f.48a1d6c

Environment details (OS name and version, etc.)

V full version: V 0.4.2 4bc9a8f.48a1d6c
OS: macos, macOS, 12.6, 21G115
Processor: 10 cpus, 64bit, little endian, Apple M1 Max

getwd: /Users/elliot
vexe: /Users/elliot/Downloads/v-5/v
vexe mtime: 2023-10-21 03:59:08

vroot: OK, value: /Users/elliot/Downloads/v-5
VMODULES: OK, value: /Users/elliot/.vmodules
VTMP: OK, value: /tmp/v_501

Git version: git version 2.37.0 (Apple Git-136)
Git vroot status: weekly.2023.42-19-g48a1d6cc (94 commit(s) behind V master)
.git/config present: true

CC version: Apple clang version 14.0.0 (clang-1400.0.29.102)
thirdparty/tcc status: thirdparty-macos-amd64 46662e20

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