missing compilation message for `fn f(x u8) {} f(9999)`, where the literal is clearly > 255

[spytheman]

V version: V 0.5.0 edd4a71, press to see full `v doctor` output

V full version	V 0.5.0 b29ac57.edd4a71
OS	linux, Ubuntu 20.04.6 LTS
Processor	4 cpus, 64bit, little endian, Intel(R) Core(TM) i3-3225 CPU @ 3.30GHz
Memory	2.54GB/15.42GB
V executable	/home/delian/v/v
V last modified time	2026-02-12 07:32:06
V home dir	OK, value: /home/delian/v
VMODULES	OK, value: /home/delian/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/delian/v
env VFLAGS	"-no-parallel"
Git version	git version 2.50.0
V git status	weekly.2026.07-22-gedd4a712
.git/config present	true
cc version	cc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
gcc version	gcc (Ubuntu 10.5.0-1ubuntu1~20.04) 10.5.0
clang version	Ubuntu clang version 18.1.8 (11~20.04.2)
tcc version	tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 696c1d84
emcc version	N/A
glibc version	ldd (Ubuntu GLIBC 2.31-0ubuntu9.18) 2.31

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

fn f(a u8, c u8, m u8, xn u8) int {
	return int(a) + int(c) + int(m) + int(xn)
}

println(f(1256, 256, 256, 0xFFFFFFFF))

What did you see?

487

What did you expect to see?

Either a notice or a warning or an error at compile time, since 1256 and 256 and 0xFFFFFFFF are > 255, which is the maximum value for u8.

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[spytheman]

Potentially linked to #26584 too.

[spytheman]

Note: avoiding number literals, works correctly.
For example:

fn f(a u8, c u8, m u8, xn u8) int {
        return int(a) + int(c) + int(m) + int(xn)
}

a := 999
c := 256
m := 5
xn := u16(0xFFFF)
dump(f(a, c, m, xn))

produces:

#0 10:59:53 ^ master ~/v>v run /home/delian/code/misc/2026_02_12__10/y.v
/home/delian/code/misc/2026_02_12__10/y.v:9:8: error: cannot use `int` as `u8` in argument 1 to `f`
    7 | m := 5
    8 | xn := u16(0xFFFF)
    9 | dump(f(a, c, m, xn))
      |        ^
/home/delian/code/misc/2026_02_12__10/y.v:9:11: error: cannot use `int` as `u8` in argument 2 to `f`
    7 | m := 5
    8 | xn := u16(0xFFFF)
    9 | dump(f(a, c, m, xn))
      |           ^
/home/delian/code/misc/2026_02_12__10/y.v:9:14: error: cannot use `int` as `u8` in argument 3 to `f`
    7 | m := 5
    8 | xn := u16(0xFFFF)
    9 | dump(f(a, c, m, xn))
      |              ^
/home/delian/code/misc/2026_02_12__10/y.v:9:17: error: cannot use `u16` as `u8` in argument 4 to `f`
    7 | m := 5
    8 | xn := u16(0xFFFF)
    9 | dump(f(a, c, m, xn))
      |                 ~~
#1 10:59:57 ^ master ~/v>

[jorgeluismireles]

As a reference, Golang not gives a warning but prevents compiling next code:

package main

import "fmt"

func f(a uint8) {
	fmt.Printf("a=%d", a)
}

func main() {
	f(257)
}

/prog.go:10:4: cannot use 257 (untyped int constant) as uint8 value in argument to f (overflows)

Go build failed.

But is flexible enough to let passing (not casted) number 255 since can be converted to a valid u8 value.

IMO the question is if V should issue a warning or prevent compile this at all:

fn f(a u8) {
	dump('${a}')
}

f(257)

Right now prints 1.

[JalonSolov]

V should give the same message for literals as it does for variables.