Inconsistent C function naming for generic struct methods

[kbkpbot]

Describe the bug

I've encountered an inconsistency in the C function naming convention for generic struct methods.

This inconsistency causes issues during compiler development, particularly when implementing features like auto_str() that automatically generate string conversion functions for types. The inconsistent naming makes it difficult to reliably locate and call these generated methods.

This may related to PR #25857

Reproduction Steps

Consider the following V code:
f.v

module main

struct MyS[T] {
mut:
        a T
}

fn (mut m MyS[T]) add(val T) {          // a `generic` method
        m.a += val
}

fn (mut m MyS[int]) sub(val int) {      // a `concrete` method?
        m.a -= val
}

fn main() {
        mut x := MyS[int]{}

        x.add(100)
        x.sub(50)
        dump(x)
}

The generated C code shows different naming patterns for the add and sub methods:

VV_LOC void main__MyS_T_int_add_T_int(main__MyS_T_int* m, int val) {
        m->a += val;
}
VV_LOC void main__MyS_T_int_sub(main__MyS_T_int* m, int val) {
        m->a -= val;
}
VV_LOC void main__main(void) {
        main__MyS_T_int x = ((main__MyS_T_int){.a = 0,});
        main__MyS_T_int_add_T_int(&x, 100);
        main__MyS_T_int_sub(&x, 50);
         _v_dump_expr_main__MyS_T_int(_S("f.v"), 21, _S("x"), x);
}

Expected Behavior

Standardize the naming convention to be consistent for both generic and concrete methods. A possible approach could be to always do not include the parameter type in the function name for consistency. e.g. :

        main__MyS_T_int_add(&x, 100);
        main__MyS_T_int_sub(&x, 50);

Current Behavior

        main__MyS_T_int_add_T_int(&x, 100);
        main__MyS_T_int_sub(&x, 50);

Possible Solution

Fix cgen

Additional Information/Context

No response

V version

V 0.4.12 3caa1b7

Environment details (OS name and version, etc.)

V full version	V 0.4.12 3caa1b7
OS	linux, Ubuntu 24.04.3 LTS
Processor	8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz
Memory	10.88GB/15.51GB
V executable	/media/HD/github/kbkpbot/v/v
V last modified time	2025-12-02 12:47:59
V home dir	OK, value: /media/HD/github/kbkpbot/v
VMODULES	OK, value: /home/mars/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/mars/v/bug/autostr
Git version	git version 2.43.0
V git status	weekly.2025.46-126-gc54edf65-dirty
.git/config present	true
cc version	cc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
gcc version	gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
clang version	Ubuntu clang version 18.1.3 (1ubuntu1)
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 2.39-0ubuntu8.6) 2.39

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[kbkpbot]

For example, a auto_str function look like this:

module main
import strings

@[markused]
pub fn (it MyS[int]) str() string { return it.indent_str(0) }
@[markused]
pub fn (it MyS[int]) indent_str(indent_count int) string {
        mut res := strings.new_builder(128)
        indents := '    '.repeat(indent_count)
        res.write_string('MyS[int]{')
        res.write_string('\n')
        res.write_string('${indents}    a: ${it.a}\n')
        res.write_string('${indents}    b: ${it.b}\n')
        res.write_string('${indents}}')
        return res.str()
}

which will generate a C code naming main__MyS_T_int_str, but cgen will like to call main__MyS_T_int_str_T_int....

[kbkpbot]

It seems need the parameter type in the function name:

fn (mut m MyS[T]) add(val T) => main__MyS_T_int_add_T_int
fn (mut m MyS[int]) sub(val int) => main__MyS_T_int_sub
fn (mut m MyT) add[T](val T) => main__MyT_add_T_int