fix(config): let webpack merge postcss plugins

[danielroe]

🔗 Linked issue

resolves #18814
resolves #18798

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Currently we normalize postcss options at config stage, but modules may modify them later, leaving the options in an impossible situation. This PR defers normalizing them until just before passing them to the webpack loader.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[HuuNghi]

When will you deploy this issues?

[danielroe]

Planning for this week - likely Friday.

[LirZeitouny]

When this fix will be deployed?

[Benyaminrmb]

should I update nuxt version to apply your fix?

[danielroe]

Indeed, this fix was released last week in 2.16.1.

[Benyaminrmb]

How can I update ^2.15.7 to 2.16.1?
by changing the package.json file only?
or should I change something in nuxt.config ?

  // Build Configuration: https://go.nuxtjs.dev/config-build
  build: {
    transpile: [
      'vue-upload-drop-images',
      'vee-validate/dist/rules',
      'vee-validate/dist/locale/fa',
      'vee-validate/dist/locale/en',
    ],
    postcss: {
      plugins: {
        tailwindcss: {},
        autoprefixer: {},
      },
    },
  },

I updated to new version of nuxt and recive this notice in cmd by running npm run dev command.

i @nuxt/postcss8 is disabled since nuxt has upgraded to postcss v8

[danielroe]

That's not a problem - it's just saying that the @nuxt/postcss8 module (which existed to enable PostCSS 8 support) is not enabled because your version of Nuxt has built-in PostCSS 8 support.

[Benyaminrmb]

First of all change package.json :

"nuxt": "2.16.1",

Then I added
postcss.config.js:

module.exports = {
  plugins: {
    tailwindcss: {},
    autoprefixer: {},
  },
}

And change
nuxt.config :

build: {
    postcssOptions: {
      plugins:{
        tailwindcss: {},
        autoprefixer: {},
      },
    },
    postcss: {
      postcssOptions: require('./postcss.config.js'),
    },
  },

It's fixed my problem ❤