How does PostCSS's Processor.normalize() use its return value internally?

[kimjh0813]

In PostCSS 8.0.1, the condition order in normalize() caused plugin containers like { postcssPlugin, plugins: [...] } to pass through.
This broke TailwindCSS in some environments (Turbopack).
In 8.0.2, the condition order was changed, and now only plugin functions are included.
I'm trying to understand: how and where does the Processor class use the normalized plugin list, and what plugin structure does it expect for execution?

8.0.1 normalize function in lib/processor.js

      if (typeof i === 'object' && i.postcssPlugin) {
        normalized.push(i)
      } else if (typeof i === 'object' && Array.isArray(i.plugins)) {
        normalized = normalized.concat(i.plugins)
      } else if (typeof i === 'function') {
        normalized.push(i)
      } ....

8.0.2 normalize function in lib/processor.js

      if (typeof i === 'object' && Array.isArray(i.plugins)) {
        normalized = normalized.concat(i.plugins)
      } else if (typeof i === 'object' && i.postcssPlugin) {
        normalized.push(i)
      } else if (typeof i === 'function') {
        normalized.push(i)
      } ....

[ai]

I'm trying to understand: how and where does the Processor class use the normalized plugin list

We copy plugins to LazyResult

postcss/lib/lazy-result.js

Line 179 in 94b5260

this.plugins = this.processor.plugins.map(plugin => {

and then we are suing them here for new event-based API

postcss/lib/lazy-result.js

Line 254 in 94b5260

for (let plugin of this.plugins) {

And here for olds API:

postcss/lib/lazy-result.js

Line 288 in 94b5260

for (let i = 0; i < this.plugins.length; i++) {

or

postcss/lib/lazy-result.js

Line 398 in 94b5260

for (let plugin of this.plugins) {

what plugin structure does it expect for execution?

I think we can use TS types for that https://github.com/postcss/postcss/blob/main/lib/postcss.d.ts#L219-L227

[kimjh0813]

Thanks for the response!
They really helped me understand the PostCSS codebase more clearly.