Cannot use optional in closure

[elliotchance]

Describe the bug

Using an optional in the closure bound variables results in a compiler error.

Reproduction Steps

module main

struct Foo {
	optional ?int
}

fn main() {
	f := Foo{45}
	if v := f.optional {
		func := fn [v] () {
			println(v)
		}
		func()
	}
}

Expected Behavior

No compiler error.

Current Behavior

V panic: sym: invalid type (typ=ast.Type(0x0 = 0) idx=0). Compiler bug. This should never happen. Please report the bug using `v bug file.v`.

v hash: 48a1d6c
0   v                                   0x0000000100382d71 v__ast__default_table_panic_handler + 33
1   v                                   0x0000000100382dc8 v__ast__Table_panic + 72
2   v                                   0x00000001002c9532 v__ast__Table_sym + 354
3   v                                   0x00000001003d4214 v__gen__c__Gen_gen_anon_fn_decl + 820
4   v                                   0x00000001003d0a8a v__gen__c__Gen_gen_anon_fn + 58
5   v                                   0x00000001003c7f14 v__gen__c__Gen_expr + 500
6   v                                   0x00000001003ea3d8 v__gen__c__Gen_assign_stmt + 10104
7   v                                   0x000000010043f6c3 v__gen__c__Gen_stmt + 467
8   v                                   0x000000010043f0d3 v__gen__c__Gen_stmts_with_tmp_var + 4355
9   v                                   0x00000001003e60dc v__gen__c__Gen_stmts + 92
10  v                                   0x00000001004760eb v__gen__c__Gen_if_expr + 11867
11  v                                   0x00000001003c9113 v__gen__c__Gen_expr + 5107
12  v                                   0x000000010043fc97 v__gen__c__Gen_stmt + 1959
13  v                                   0x000000010043f0d3 v__gen__c__Gen_stmts_with_tmp_var + 4355
14  v                                   0x00000001003e60dc v__gen__c__Gen_stmts + 92
15  v                                   0x00000001004a367a v__gen__c__Gen_gen_fn_decl + 14746
16  v                                   0x0000000100449d1b v__gen__c__Gen_fn_decl + 2683
17  v                                   0x000000010043fe1a v__gen__c__Gen_stmt + 2346
18  v                                   0x000000010043f0d3 v__gen__c__Gen_stmts_with_tmp_var + 4355
19  v                                   0x00000001003e60dc v__gen__c__Gen_stmts + 92
20  v                                   0x00000001004231f8 v__gen__c__Gen_gen_file + 504
21  v                                   0x0000000100422c87 v__gen__c__cgen_process_one_file_cb + 5543
22  v                                   0x0000000100366c4a sync__pool__process_in_thread + 122
23  v                                   0x00000001002c7554 sync__pool__process_in_thread_thread_wrapper + 36
24  libsystem_pthread.dylib             0x00007ff8144c14e1 _pthread_start + 125
25  libsystem_pthread.dylib             0x00007ff8144bcf6b thread_start + 15

Possible Solution

I can use a new variables to avoid this issue:

	if v := f.optional {
		v2 := v
		func := fn [v2] () {
			println(v2)
		}
		func()
	}

Additional Information/Context

No response

V version

V 0.4.2 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 (100 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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