C compiler error when unwrapping Optional in an array

[louis77]

V version: V 0.4.9 63f5f4a, press to see full `v doctor` output

V full version	V 0.4.9 7af8faf.63f5f4a
OS	macos, macOS, 15.2, 24C101
Processor	8 cpus, 64bit, little endian, Apple M2
Memory	0.06GB/16GB
V executable	/Users/louis/Git/nv/v
V last modified time	2025-01-10 15:29:47
V home dir	OK, value: /Users/louis/Git/nv
VMODULES	OK, value: /Users/louis/.vmodules
VTMP	OK, value: /tmp/v_501
Current working dir	OK, value: /Users/louis/Git/v_staleworker
Git version	git version 2.39.5 (Apple Git-154)
V git status	weekly.2025.1-29-g63f5f4a6-dirty (8 commit(s) behind V master)
.git/config present	true
cc version	Apple clang version 16.0.0 (clang-1600.0.26.4)
gcc version	Apple clang version 16.0.0 (clang-1600.0.26.4)
clang version	Homebrew clang version 18.1.8
tcc version	tcc version 0.9.28rc 2024-02-05 HEAD@105d70f7 (AArch64 Darwin)
tcc git status	thirdparty-macos-arm64 713692d4
emcc version	N/A
glibc version	N/A

What did you do?
./v -g -o vdbg cmd/v && ./vdbg src/main_test.v && src/main_test

module main

fn make_option() ?string {
	return "abc"
}

fn test_rows() {
	cols := [make_option()]
	if col := cols[0] {
		println("I made it")
	}
}

What did you see?

================== C compilation error (from cc): ==============
cc: /tmp/v_501/main_test.01JHB9CM93FXXWM4QG45C2FYHY.tmp.c:13055:6: error: use of undeclared identifier '_t1'
cc:  13055 |         if (_t1.state == 0) {
cc:        |             ^
cc: /tmp/v_501/main_test.01JHB9CM93FXXWM4QG45C2FYHY.tmp.c:13056:10: error: initializing 'string' (aka 'struct string') with an expression of incompatible type '_option_string' (aka 'struct _option_string')
cc:  13056 |                 string col = (*(_option_string*)array_get(cols, 0));
cc:        |                        ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc: 2 errors generated.
================================================================
(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?

I expected this code to compile. cols[0] is a ?string and it should be unwrapped by if val := col[0]. I stumbled across this bug while using the Row type from db.pg library.

Note

You can use the 👍 reaction to increase the issue's priority for developers.

Please note that only the 👍 reaction to the issue itself counts as a vote.
Other reactions and those to comments will not be taken into account.

[JalonSolov]

Using latest V, V 0.4.9 81b421b, I put your example in a file named x.v and tried it with v -g run x.v. I got this:

x.v:9:5: warning: unused variable: `col`
    7 | fn test_rows() {
    8 |     cols := [make_option()]
    9 |     if col := cols[0] {
      |        ~~~
   10 |         println("I made it")
   11 |     }

No failures, nothing else. You need to do v up and try again.

[louis77]

Ok, I pulled the latest commit but still get the same error:

% ~/Git/nv/v test src/main_test.v
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 FAIL     0.000 ms /Users/louis/Git/v_staleworker/src/main_test.v
>> compilation failed:
================== C compilation error (from cc): ==============
cc: /tmp/v_501/tsession_1ed3b0240_01JHBAFTBGQ8X3YGM1KJQY8JRH/main_test.01JHBAFV4X475V943FF2SXJGZW.tmp.c:12973:6: error: use of undeclared identifier '_t1'
cc:  12973 |         if (_t1.state == 0) {
cc:        |             ^
cc: /tmp/v_501/tsession_1ed3b0240_01JHBAFTBGQ8X3YGM1KJQY8JRH/main_test.01JHBAFV4X475V943FF2SXJGZW.tmp.c:12974:10: error: initializing 'string' (aka 'struct string') with an expression of incompatible type '_option_string' (aka 'struct _option_string')
cc:  12974 |                 string col = (*(_option_string*)array_get(cols, 0));
cc:        |                        ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc: 2 errors generated.
================================================================
(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 .

V doctor:

% ~/Git/nv/v doctor              
|V full version      |V 0.4.9 7af8faf.81b421b
|:-------------------|:-------------------
|OS                  |macos, macOS, 15.2, 24C101
|Processor           |8 cpus, 64bit, little endian, Apple M2
|Memory              |0.14GB/16GB
|                    |
|V executable        |/Users/louis/Git/nv/v
|V last modified time|2025-01-11 18:35:28
|                    |
|V home dir          |OK, value: /Users/louis/Git/nv
|VMODULES            |OK, value: /Users/louis/.vmodules
|VTMP                |OK, value: /tmp/v_501
|Current working dir |OK, value: /Users/louis/Git/v_staleworker
|                    |
|Git version         |git version 2.39.5 (Apple Git-154)
|V git status        |weekly.2025.1-35-g81b421bb-dirty
|.git/config present |true
|                    |
|cc version          |Apple clang version 16.0.0 (clang-1600.0.26.4)
|gcc version         |Apple clang version 16.0.0 (clang-1600.0.26.4)
|clang version       |Homebrew clang version 18.1.8
|tcc version         |tcc version 0.9.28rc 2024-02-05 HEAD@105d70f7 (AArch64 Darwin)
|tcc git status      |thirdparty-macos-arm64 713692d4
|emcc version        |N/A
|glibc version       |N/A

[JalonSolov]

Ah... I missed that it was a test file... renaming to x_test.v, and trying with v -g test x_test.v, I see this:

---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 FAIL     0.000 ms /tmp/x_test.v
>> compilation failed:
/tmp/v_1000/tsession_7d6955be5740_01JHBB0KDSGJRY0ERV68ZVEW82/../../../../../../tmp/x_test.v:9: error: '_t1' undeclared
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 .

--------------------------------------------------------------------------------------------------------------------------------------------
To reproduce just failure 1 run:    '/home/jalon/git/v/v' -g '/tmp/x_test.v'
Summary for all V _test.v files: 1 failed, 1 total. Elapsed time: 826 ms, on 1 job. Comptime: 750 ms. Runtime: 0 ms.

[JalonSolov]

So the bug only happens when the test option is used. Exact same source only gives the unused variable warning if compiled.

[huly-for-github]

Connected to Huly®: V_0.6-21869