C compilation bug

[mobiuscog]

V doctor:

V full version: V 0.4.9 7b9b3dd.5eecd04
OS: macos, macOS, 15.2, 24C101
Processor: 20 cpus, 64bit, little endian, Apple M1 Ultra

getwd: /Volumes/Data/code/v/test/src
vexe: /Volumes/Data/code/v/v/v
vexe mtime: 2025-01-03 18:03:15

vroot: OK, value: /Volumes/Data/code/v/v
VMODULES: OK, value: /Users/mobius/.vmodules
VTMP: OK, value: /tmp/v_501

Git version: git version 2.39.5 (Apple Git-154)
Git vroot status: weekly.2024.53-18-g5eecd04e
.git/config present: true

CC version: Apple clang version 16.0.0 (clang-1600.0.26.6)
emcc version: N/A
thirdparty/tcc: N/A

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

module main

const image_width = 800
const image_height = 400


struct Colour {
	r u8
	g u8
	b u8
}
const buffer_size = image_width * image_height * sizeof[Colour]()
// Declare a type so we don't have to keep passing the size around
type ImageBuffer = [buffer_size]Colour

fn main() {
	println('Hello World!')
}

What did you see?

================== C compilation error (from cc): ==============
cc: /tmp/v_501/main.01JGPNDXBD2EJD25JFEWYY6MYB.tmp.c:1092:9: error: unknown type name 'Array_fixed_main__Colour_0'
cc:  1092 | typedef Array_fixed_main__Colour_0 main__ImageBuffer;
cc:       |         ^
cc: 1 error 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?

No errors

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_{Huly®: V_0.6-21787}

[jorgeluismireles]

At least there is a C error problem here because [x]Colour needs x to be a constant without pre-calculations.
Next program works:

struct Colour{}
//const x = 800*1000*3
const x = 2_400_000
type ImageBuffer = [x]Colour

But if we uncomment the const x = 800*1000*3 line we got this error:

Running code...
Can't run code. The server returned an error:
/tmp/v_60000/code.01JGPQSKYVJQNSJQDRXP1P8VGT.tmp.c:1088: error: ';' expected (got "main__ImageBuffer")
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 .
Exited with error status 1
Please try again.

See https://play.vlang.io/p/f29d3067b2

[JalonSolov]

The problem (with the current compiler) is that the size of a fixed array must be known at compile time. Calculating const values doesn't happen until runtime (specifically, in the _vinit() routine).

Values such as those shown above are reduced at compile time, but not until the TRANSFORM step, which is long after the compile time evaluation has been done.

So this particular issue brings up 2 things:

1. V should give a clean error message, instead of allowing it to fall through to a C error.

2. V should be able to do this type of simple transformation before the value is used for something like a fixed array size.

[jorgeluismireles]

2. V should be able to do this type of simple transformation before the value is used
   for something like a fixed array size.

Or used for example to set the values of an enum

const x = 1*2
const y = 1*2
enum Num {
	x = x
	y = y
}
println('${Num.x:d} ${Num.y:d}') // prints 2 2