v.debug: implement tracing hook feature

[felipensp]

This PR adds a feature to v.debug to allow tracing fn call. Activated by -d trace V flag.

debug.add_before_call(HookFnCall) HookFnCall

Adds a new hook fn that will be called before each fn call and return its idx

debug.add_after_call(HookFnCall) HookFnCall

Adds a new hook fn that will be called after each fn call and return its idx

debug.remove_before_call(HookFnCall)

Remove a hook fn from before hook list

debug.remove_after_call(HookFnCall)

Remove a hook fn from after hook list

Example

import time
import v.debug

@[heap]
struct Profiler {
mut:
	fn_map map[string]time.StopWatch
}

fn (mut p Profiler) trace_after(fn_name string) {
	println('>>> called after ${fn_name} - ${p.fn_map[fn_name].elapsed()}')
}

fn (mut p Profiler) trace_before(fn_name string) {
	p.fn_map[fn_name] = time.new_stopwatch()
	println('>>> called before ${fn_name}')
}

fn test_call() {
	println('${@FN} got called')
	time.sleep(100)
}

fn main() {
	mut myprofiler := Profiler{}
	debug.add_after_call(myprofiler.trace_after)
	debug.add_before_call(myprofiler.trace_before)
	test_call()
}

$ v -d trace run trace.v
>>> called before main.test_call
test_call got called
>>> called before time.sleep
>>> called after time.sleep - 35.800us
>>> called after main.test_call - 137.600us

[spytheman]

Why is it still draft, do you plan to add more features/bug fixes in the same PR?

[felipensp]

Why is it still draft, do you plan to add more features/bug fixes in the same PR?

No. I was just waiting for some feedback/tip/comment about to improved something on It.