fix(perf): avoid superfluous timer wrappings in watch mode

[ZhengLiu2825]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

In watch mode, every time bundle starts, inputOptions.plugins will be wrapped in another layer of timer, which will cause incorrect performance timings.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
rollup	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 10, 2023 5:09am

[codecov]

Codecov Report

Merging #5114 (d3af65f) into master (e9fef3f) will decrease coverage by 0.02%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #5114      +/-   ##
==========================================
- Coverage   98.94%   98.93%   -0.02%     
==========================================
  Files         226      226              
  Lines        8429     8431       +2     
  Branches     2314     2315       +1     
==========================================
+ Hits         8340     8341       +1     
  Misses         32       32              
- Partials       57       58       +1     

Files Changed	Coverage Δ
src/utils/timers.ts	91.07% <50.00%> (-1.53%)	⬇️

[lukastaegert]

Thank you for spotting is. The only issue I see with your implementation is that isWithTimers now is global state, which means that completely unrelated runs will now also influence each other. Basically if you have a config file with an array of configs, only the plugins in the first config will be instrumented.
Maybe a cleaner approach would be to leave a flag on each instrumented plugin in getPluginWithTimers, e.g.

function getPluginWithTimers(plugin: any, index: number): Plugin {
	if (plugin._hasTimedHooks) return plugin;
	plugin._hasTimedHooks = true;
	for (const hook of TIMED_PLUGIN_HOOKS) {
		if (hook in plugin) {

One could also use a Symbol to hide the flag, or keep a Set<Plugin> of instrumented plugins as global state. What do you think?

[lukastaegert]

I changed your code as I suggested and will merge it now.

[rollup-bot]

This PR has been released as part of rollup@3.29.1. You can test it via npm install rollup.