parser, checker, pref: allow getting notified about unused function params

[ttytm]

The PR should implement #22875 as desired.

Example:

NOTE: the v-analyzer hints won't work until this is on by default. For now, when compiling with -check-unused-fn-args you'll get:

fn (unused_receiver Foo) method(unused_param int) {}

fn func(unused_param int) {}

❯ v -check-unused-fn-args run vlib/v/checker/tests/unused_param.vv
vlib/v/checker/tests/unused_param.vv:5:33: notice: unused parameter: `unused_param`
    3 | struct Foo {}
    4 | 
    5 | fn (unused_receiver Foo) method(unused_param int) {}
      |                                 ~~~~~~~~~~~~
    6 | 
    7 | fn func(unused_param int) {}
vlib/v/checker/tests/unused_param.vv:7:9: notice: unused parameter: `unused_param`
    5 | fn (unused_receiver Foo) method(unused_param int) {}
    6 | 
    7 | fn func(unused_param int) {}
      |         ~~~~~~~~~~~~
    8 | 
    9 | pub fn pub_func(unused_param int) {}

_{Huly®: V_0.6-21322}

[StunxFS]

It would be great if v fmt could detect unused parameters and use _ instead, thus automatically fixing all code with unused parameters.

Or, that there was a command, something like v fix, that could fix that problem automatically.

[ttytm]

It would be great if v fmt could detect unused parameters and use _ instead, thus automatically fixing all code with unused parameters.

With this I see some situations where a format on save would replace the param name that is not in use yet but I want to use a few moments later.

[StunxFS]

It would be great if v fmt could detect unused parameters and use _ instead, thus automatically fixing all code with unused parameters.

With this I see some situations where a format on save would replace the param name that is not in use yet but I want to use a few moments later.

So it would be better to have a special command for automatic fixes: v fix, and when the compiler finds a problem that can be fixed using v fix, it would recommend using it.

[medvednikov]

So it would be better to have a special command for automatic fixes: v fix, and when the compiler finds a problem that can be fixed using v fix, it would recommend using it.

That's a great idea, I've always wanted something like that. Can fix mut params as well etc

[spytheman]

Excellent work.