Remove limit on max parallel file ops (#5986)

Author: lukastaegert

docs/configuration-options/index.md

@@ -637,9 +637,9 @@ Note that when a relative path is directly marked as "external" using the [`exte
 | -------: | :------------------------------ |
 |    Type: | `number`                        |
 |     CLI: | `--maxParallelFileOps <number>` |
-| Default: | 20                              |
+| Default: | `Infinity`                      |
 
-Limits the number of files rollup will open in parallel when reading modules or writing chunks. Without a limit or with a high enough value, builds can fail with an "EMFILE: too many open files". This depends on how many open file handles the operating system allows.
+Limits the number of files rollup will open in parallel when reading modules or writing chunks. Without a limit or with a high enough value, builds can fail with an "EMFILE: too many open files". This depends on how many open file handles the operating system allows. If you set the limit too low and use plugins that rely on the [`this.load`](../plugin-development/index.md#this-load) context function, such as the `commonjs` plugin, then it can happen that builds stall without an error message as it limits the number of parallel `load` calls.
 
 ### onLog
 

src/utils/options/normalizeInputOptions.ts

@@ -176,11 +176,8 @@ const getMaxParallelFileOps = (
 	config: InputOptions
 ): NormalizedInputOptions['maxParallelFileOps'] => {
 	const maxParallelFileOps = config.maxParallelFileOps;
-	if (typeof maxParallelFileOps === 'number') {
-		if (maxParallelFileOps <= 0) return Infinity;
-		return maxParallelFileOps;
-	}
-	return 20;
+	if (typeof maxParallelFileOps !== 'number' || maxParallelFileOps <= 0) return Infinity;
+	return maxParallelFileOps;
 };
 
 const getModuleContext = (

test/function/samples/options-hook/_config.js

@@ -11,8 +11,9 @@ module.exports = defineTest({
 				name: 'test-plugin',
 				buildStart(options) {
 					// The fs option is not json stringifiable
-					const { fs, ...restOptions } = options;
+					const { fs, maxParallelFileOps, ...restOptions } = options;
 					assert.ok(fs);
+					assert.strictEqual(maxParallelFileOps, Infinity);
 					assert.deepStrictEqual(JSON.parse(JSON.stringify(restOptions)), {
 						context: 'undefined',
 						experimentalCacheExpiry: 10,
@@ -21,7 +22,6 @@ module.exports = defineTest({
 						jsx: false,
 						logLevel: 'info',
 						makeAbsoluteExternalsRelative: 'ifRelativeSource',
-						maxParallelFileOps: 20,
 						perf: false,
 						plugins: [
 							{