Improve size calculation

docs/configuration-options/index.md

@@ -2345,7 +2345,7 @@ Set a minimal chunk size target in Byte for code-splitting setups. When this val
 
 Larger values will try to merge any chunk below the limit into other chunks. In that case, it is accepted that entries may load some unnecessary code. The algorithm always tries to merge in a way that minimizes the amount of unnecessary code, though.
 
-Unfortunately, due to the way chunking works, chunk size is measured before any chunk rendering plugins like minifiers ran, which means you should use a high enough limit to take this into account.
+Unfortunately, due to the way chunking works, chunk size is measured before any chunk rendering plugins like minifiers ran, which means you should use a high enough limit to take this into account. When calculating the size, it will take tree-shaking of top-level statements into account, though.
 
 ### perf
 

src/Module.ts

@@ -401,6 +401,17 @@ export default class Module {
 		return error(properties);
 	}
 
+	// sum up the length of all ast nodes that are included
+	estimateSize(): number {
+		let size = 0;
+		for (const node of this.ast!.body) {
+			if (node.included) {
+				size += node.end - node.start;
+			}
+		}
+		return size;
+	}
+
 	getAllExportNames(): Set<string> {
 		if (this.allExportNames) {
 			return this.allExportNames;

src/utils/chunkAssignment.ts

@@ -583,7 +583,9 @@ function getPartitionedChunks(
 			// rendering did not happen yet, but we can detect empty modules
 			if (module.isIncluded()) {
 				pure &&= !module.hasEffects();
-				size += module.originalCode.length;
+				// we use a trivial size for the default minChunkSize to improve
+				// performance
+				size += minChunkSize > 1 ? module.estimateSize() : 1;
 			}
 		}
 		chunkDescription.pure = pure;
@@ -613,7 +615,6 @@ function getPartitionedChunks(
 	};
 }
 
-// TODO Lukas improve size calculation
 function addChunkDependenciesAndAtomsAndGetSideEffectAtoms(
 	chunkLists: ChunkDescription[][],
 	chunkByModule: Map<Module, ChunkDescription>,
@@ -652,8 +653,6 @@ function addChunkDependenciesAndAtomsAndGetSideEffectAtoms(
 			}
 			const { containedAtoms } = chunk;
 			for (const entryIndex of dependentEntries) {
-				// containedAtoms is mutated after destructuring
-				// eslint-disable-next-line unicorn/consistent-destructuring
 				atomsByEntry[entryIndex] |= containedAtoms;
 			}
 		}

test/chunking-form/samples/min-chunk-size/tree-shaking/_config.js

@@ -0,0 +1,9 @@
+module.exports = defineTest({
+	description: 'takes tree-shaking into account and ignores top-level comments',
+	options: {
+		input: ['main1.js', 'main2.js'],
+		output: {
+			experimentalMinChunkSize: 100
+		}
+	}
+});

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/amd/main1.js

@@ -0,0 +1,9 @@
+define(['exports'], (function (exports) { 'use strict';
+
+   console.log('shared');
+
+   const main = 'main';
+
+   exports.main = main;
+
+}));

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/amd/main2.js

@@ -0,0 +1,5 @@
+define(['./main1'], (function (main1) { 'use strict';
+
+	console.log('other');
+
+}));

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/cjs/main1.js

@@ -0,0 +1,7 @@
+'use strict';
+
+console.log('shared');
+
+const main = 'main';
+
+exports.main = main;

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/cjs/main2.js

@@ -0,0 +1,5 @@
+'use strict';
+
+require('./main1.js');
+
+console.log('other');

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/es/main1.js

@@ -0,0 +1,5 @@
+console.log('shared');
+
+const main = 'main';
+
+export { main };

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/es/main2.js

@@ -0,0 +1,3 @@
+import './main1.js';
+
+console.log('other');

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/system/main1.js

@@ -0,0 +1,12 @@
+System.register([], (function (exports) {
+   'use strict';
+   return {
+      execute: (function () {
+
+         console.log('shared');
+
+         const main = exports('main', 'main');
+
+      })
+   };
+}));

test/chunking-form/samples/min-chunk-size/tree-shaking/_expected/system/main2.js

@@ -0,0 +1,11 @@
+System.register(['./main1.js'], (function () {
+	'use strict';
+	return {
+		setters: [null],
+		execute: (function () {
+
+			console.log('other');
+
+		})
+	};
+}));

test/chunking-form/samples/min-chunk-size/tree-shaking/main1.js

@@ -0,0 +1,4 @@
+export const main = 'main';
+/* a very long comment exceeding 100 characters
+   -------------------------------------------- */
+import './shared';

test/chunking-form/samples/min-chunk-size/tree-shaking/main2.js

@@ -0,0 +1,2 @@
+import './shared';
+console.log('other');

test/chunking-form/samples/min-chunk-size/tree-shaking/shared.js

@@ -0,0 +1,4 @@
+console.log('shared');
+/* a very long comment exceeding 100 characters
+   -------------------------------------------- */
+export const unused = 'also very long and very unused';

test/cli/samples/empty-chunk-multiple/_config.js

@@ -4,5 +4,5 @@ module.exports = defineTest({
 	description: 'shows warning when multiple chunks empty',
 	command: 'rollup -c',
 	error: () => true,
-	stderr: stderr => assertIncludes(stderr, '(!) Generated empty chunks\n"a" and "b"')
+	stderr: stderr => assertIncludes(stderr, '(!) Generated empty chunks\n"main1" and "main2"')
 });

test/cli/samples/empty-chunk-multiple/rollup.config.js

@@ -1,5 +1,5 @@
 module.exports = {
-	input: 'main.js',
+	input: ['main1.js', 'main2.js'],
 	output: {
 		format: 'cjs'
 	}

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

@@ -28,7 +28,7 @@ module.exports = defineTest({
 					entryFileNames: '[name].js',
 					esModule: 'if-default-prop',
 					experimentalDeepDynamicChunkOptimization: false,
-					experimentalMinChunkSize: 0,
+					experimentalMinChunkSize: 1,
 					exports: 'auto',
 					extend: false,
 					externalImportAssertions: true,