Batch reading content files to prevent too many open files error (#12079)

* Refactor

* Refactor

* Batch content file reads in Node into groups of 500

We shouldn’t need to do this for our Rust code because it utilizes Rayon’s default thread pool for parallelism. This threadpool has roughly the number of cores as the number of available threads except when overridden. This generally is much, much lower than 500 and can be explicitly overridden via an env var to work around potential issues with open file descriptors if anyone ever runs into that.

* Fix sequential/parallel flip

* Update changelog

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix incorrectly generated CSS when using square brackets inside arbitrary properties ([#11709](https://github.com/tailwindlabs/tailwindcss/pull/11709))
 - Make `content` optional for presets in TypeScript types ([#11730](https://github.com/tailwindlabs/tailwindcss/pull/11730))
 - Handle variable colors that have variable fallback values ([#12049](https://github.com/tailwindlabs/tailwindcss/pull/12049))
+- Batch reading content files to prevent `too many open files` error ([#12079](https://github.com/tailwindlabs/tailwindcss/pull/12079))
 
 ## [3.3.3] - 2023-07-13
 

src/lib/expandTailwindAtRules.js

@@ -145,14 +145,26 @@ export default function expandTailwindAtRules(context) {
       //   getClassCandidatesOxide(file, transformer(content), extractor, candidates, seen)
       // }
     } else {
-      await Promise.all(
-        context.changedContent.map(async ({ file, content, extension }) => {
-          let transformer = getTransformer(context.tailwindConfig, extension)
-          let extractor = getExtractor(context, extension)
-          content = file ? await fs.promises.readFile(file, 'utf8') : content
-          getClassCandidates(transformer(content), extractor, candidates, seen)
-        })
-      )
+      /** @type {[item: {file?: string, content?: string}, meta: {transformer: any, extractor: any}][]} */
+      let regexParserContent = []
+
+      for (let item of context.changedContent) {
+        let transformer = getTransformer(context.tailwindConfig, item.extension)
+        let extractor = getExtractor(context, item.extension)
+        regexParserContent.push([item, { transformer, extractor }])
+      }
+
+      const BATCH_SIZE = 500
+
+      for (let i = 0; i < regexParserContent.length; i += BATCH_SIZE) {
+        let batch = regexParserContent.slice(i, i + BATCH_SIZE)
+        await Promise.all(
+          batch.map(async ([{ file, content }, { transformer, extractor }]) => {
+            content = file ? await fs.promises.readFile(file, 'utf8') : content
+            getClassCandidates(transformer(content), extractor, candidates, seen)
+          })
+        )
+      }
     }
 
     env.DEBUG && console.timeEnd('Reading changed files')