refactor(core): improve dev perf, fine-grained site reloads - part1

[slorber]

Motivation

Adding a single character to a Markdown doc leads to a huge amount of useless CPU/IO work.

Even on a Macbook Pro M3 it's significant:

[PERF] Load - loadPlugins: 422.472ms
[PERF] Load - loadClientModules: 0.117ms
[PERF] Load - loadHtmlTags: 0.338ms
[PERF] Load - loadRoutes: 5.879ms
[PERF] Load - load codeTranslations: 26.732ms
[PERF] Load - loadSiteMetadata: 6.05ms
[PERF] Load - codegen: 22.853ms
[PERF] Loading site: 557.539ms

[PERF] Load - loadPlugins: 465.051ms
[PERF] Load - loadClientModules: 0.055ms
[PERF] Load - loadHtmlTags: 0.177ms
[PERF] Load - loadRoutes: 5.83ms
[PERF] Load - load codeTranslations: 4.533ms
[PERF] Load - loadSiteMetadata: 175.073ms
[PERF] Load - codegen: 2.892ms
[PERF] Loading site: 688.203ms

[PERF] Load - loadPlugins: 907.536ms
[PERF] Load - loadClientModules: 0.057ms
[PERF] Load - loadHtmlTags: 0.135ms
[PERF] Load - loadRoutes: 5.784ms
[PERF] Load - load codeTranslations: 52.264ms
[PERF] Load - loadSiteMetadata: 6.597ms
[PERF] Load - codegen: 2.834ms
[PERF] Loading site: 1.024s

We should optimize and only reload what is necessary.

This is also the opportunity to refactor and clean a bit our mess + instrument code to debug perf issues more easily in the future

Ideally:

• Only a plugin should reload if a plugin file gets updated
• Only a docs version should reload if a docs version file gets updated
• We should bail-out from the reload process early if deepEqual(previousContent,newContent)
• A markdown change not affecting front matter should likely not trigger any site/plugin reload, and be handled only by the Webpack dev server
• We should avoid rewriting files that are exactly the same file as before

Note: the full optimization is going to happen in multiple PRs, and this one only implements the initial setup + the most simple optimization (still leading to great perf improvements when editing md files)

Test Plan

Unit tests + local + dogfood

The start.ts code is quite difficult to test unfortunately 😅 lots of IO/file watchers

Test links

https://deploy-preview-9903--docusaurus-2.netlify.app/

[netlify]

✅ [V2]

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🔨 Latest commit	841c7d6
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/65e0d5aaf32ae00008d3a342
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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 60	🟢 98	🟢 96	🟢 100	🟠 88	Report
/docs/installation	🟠 59	🟢 96	🟢 100	🟢 100	🟠 88	Report
/docs/category/getting-started	🟠 76	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog	🟠 69	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 68	🟢 96	🟢 100	🟢 100	🟠 88	Report
/blog/tags/release	🟠 69	🟢 100	🟢 100	🟠 80	🟠 88	Report
/blog/tags	🟠 76	🟢 100	🟢 100	🟢 90	🟠 88	Report

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	92d68f2
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/65eaf3b789ec4b00083f0938
😎 Deploy Preview	https://deploy-preview-9903--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

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[github-actions]

Size Change: 0 B

Total Size: 992 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	75.4 kB
website/build/assets/css/styles.********.css	114 kB
website/build/assets/js/main.********.js	765 kB
website/build/index.html	37.9 kB

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