feat: tree-shake deterministic dynamic imports

src/Module.ts

@@ -716,6 +716,27 @@ export default class Module {
 		this.includeAllExports(false);
 	}
 
+	includeExportsByNames(names: readonly string[], includeNamespaceMembers: boolean): void {
+		if (!this.isExecuted) {
+			markModuleAndImpureDependenciesAsExecuted(this);
+			this.graph.needsTreeshakingPass = true;
+		}
+
+		for (const name of names) {
+			const variable = this.getVariableForExportName(name)[0];
+			if (variable) {
+				variable.deoptimizePath(UNKNOWN_PATH);
+				if (!variable.included) {
+					this.includeVariable(variable);
+				}
+			}
+		}
+
+		if (includeNamespaceMembers) {
+			this.namespace.setMergedNamespaces(this.includeAndGetAdditionalMergedNamespaces());
+		}
+	}
+
 	isIncluded(): boolean | null {
 		// Modules where this.ast is missing have been loaded via this.load and are
 		// not yet fully processed, hence they cannot be included.
@@ -1218,9 +1239,19 @@ export default class Module {
 				resolution: string | Module | ExternalModule | undefined;
 			}
 		).resolution;
+
 		if (resolution instanceof Module) {
 			resolution.includedDynamicImporters.push(this);
-			resolution.includeAllExports(true);
+
+			const importedNames = this.options.treeshake
+				? node.getDeterministicImportedNames()
+				: undefined;
+
+			if (importedNames) {
+				resolution.includeExportsByNames(importedNames, true);
+			} else {
+				resolution.includeAllExports(true);
+			}
 		}
 	}
 

src/ast/nodes/ImportExpression.ts

@@ -3,6 +3,7 @@ import ExternalModule from '../../ExternalModule';
 import type Module from '../../Module';
 import type { GetInterop, NormalizedOutputOptions } from '../../rollup/types';
 import type { PluginDriver } from '../../utils/PluginDriver';
+import { EMPTY_ARRAY } from '../../utils/blank';
 import type { GenerateCodeSnippets } from '../../utils/generateCodeSnippets';
 import {
 	INTEROP_NAMESPACE_DEFAULT_ONLY_VARIABLE,
@@ -12,8 +13,17 @@ import { findFirstOccurrenceOutsideComment, type RenderOptions } from '../../uti
 import type { InclusionContext } from '../ExecutionContext';
 import type ChildScope from '../scopes/ChildScope';
 import type NamespaceVariable from '../variables/NamespaceVariable';
+import ArrowFunctionExpression from './ArrowFunctionExpression';
+import AwaitExpression from './AwaitExpression';
+import CallExpression from './CallExpression';
+import ExpressionStatement from './ExpressionStatement';
+import FunctionExpression from './FunctionExpression';
+import Identifier from './Identifier';
+import MemberExpression from './MemberExpression';
 import type * as NodeType from './NodeType';
 import type ObjectExpression from './ObjectExpression';
+import ObjectPattern from './ObjectPattern';
+import VariableDeclarator from './VariableDeclarator';
 import {
 	type ExpressionNode,
 	type GenericEsTreeNode,
@@ -45,6 +55,100 @@ export default class ImportExpression extends NodeBase {
 		this.source.bind();
 	}
 
+	/**
+	 * Get imported variables for deterministic usage, valid cases are:
+	 *
+	 * - `const { foo } = await import('bar')`.
+	 * - `(await import('bar')).foo`
+	 * - `import('bar').then(({ foo }) => {})`
+	 *
+	 * Returns empty array if it's side-effect only import.
+	 * Returns undefined if it's not fully deterministic.
+	 */
+	getDeterministicImportedNames(): readonly string[] | undefined {
+		const parent1 = this.parent;
+
+		// Side-effect only: import('bar')
+		if (parent1 instanceof ExpressionStatement) {
+			return EMPTY_ARRAY;
+		}
+
+		if (parent1 instanceof AwaitExpression) {
+			const parent2 = parent1.parent;
+
+			// Side-effect only: await import('bar')
+			if (parent2 instanceof ExpressionStatement) {
+				return EMPTY_ARRAY;
+			}
+
+			// Case 1: const { foo } = await import('bar')
+			if (parent2 instanceof VariableDeclarator) {
+				const declaration = parent2.id;
+				return declaration instanceof ObjectPattern
+					? getDeterministicObjectDestructure(declaration)
+					: undefined;
+			}
+
+			// Case 2: (await import('bar')).foo
+			if (parent2 instanceof MemberExpression) {
+				const id = parent2.property;
+				if (!parent2.computed && id instanceof Identifier) {
+					return [id.name];
+				}
+			}
+
+			return;
+		}
+
+		// Case 3: import('bar').then(({ foo }) => {})
+		if (parent1 instanceof MemberExpression) {
+			const callExpression = parent1.parent;
+			const property = parent1.property;
+
+			if (!(callExpression instanceof CallExpression) || !(property instanceof Identifier)) {
+				return;
+			}
+
+			const memberName = property.name;
+
+			// side-effect only, when only chaining .catch or .finally
+			if (
+				callExpression.parent instanceof ExpressionStatement &&
+				['catch', 'finally'].includes(memberName)
+			) {
+				return EMPTY_ARRAY;
+			}
+
+			if (memberName !== 'then') return;
+
+			// Side-effect only: import('bar').then()
+			if (callExpression.arguments.length === 0) {
+				return EMPTY_ARRAY;
+			}
+
+			const argument = callExpression.arguments[0];
+
+			if (
+				callExpression.arguments.length !== 1 ||
+				!(argument instanceof ArrowFunctionExpression || argument instanceof FunctionExpression)
+			) {
+				return;
+			}
+
+			// Side-effect only: import('bar').then(() => {})
+			if (argument.params.length === 0) {
+				return EMPTY_ARRAY;
+			}
+
+			const declaration = argument.params[0];
+			if (argument.params.length === 1 && declaration instanceof ObjectPattern) {
+				return getDeterministicObjectDestructure(declaration);
+			}
+
+			return;
+		}
+	}
+
 	hasEffects(): boolean {
 		return true;
 	}
@@ -296,3 +400,15 @@ const accessedImportGlobals: Record<string, string[]> = {
 	cjs: ['require'],
 	system: ['module']
 };
+
+function getDeterministicObjectDestructure(objectPattern: ObjectPattern): string[] | undefined {
+	const variables: string[] = [];
+
+	for (const property of objectPattern.properties) {
+		if (property.type === 'RestElement' || property.computed || property.key.type !== 'Identifier')
+			return;
+		variables.push((property.key as Identifier).name);
+	}
+
+	return variables;
+}

src/ast/variables/NamespaceVariable.ts

@@ -133,8 +133,9 @@ export default class NamespaceVariable extends Variable {
 			snippets: { _, cnst, getObject, getPropertyAccess, n, s }
 		} = options;
 		const memberVariables = this.getMemberVariables();
-		const members: [key: string | null, value: string][] = Object.entries(memberVariables).map(
-			([name, original]) => {
+		const members: [key: string | null, value: string][] = Object.entries(memberVariables)
+			.filter(([_, variable]) => variable.included)
+			.map(([name, original]) => {
 				if (this.referencedEarly || original.isReassigned) {
 					return [
 						null,
@@ -143,8 +144,7 @@ export default class NamespaceVariable extends Variable {
 				}
 
 				return [name, original.getName(getPropertyAccess)];
-			}
-		);
+			});
 		members.unshift([null, `__proto__:${_}null`]);
 
 		let output = getObject(members, { lineBreakIndent: { base: '', t } });

test/chunking-form/samples/deprecated/dynamic-import-inlining-object/_expected/amd/entry.js

@@ -1,13 +1,10 @@
 define(['exports'], (function (exports) { 'use strict';
 
 	const bar = 2;
-	Promise.resolve().then(function () { return foo$1; });
+	Promise.resolve().then(function () { return foo; });
 
-	const foo = 1;
-
-	var foo$1 = /*#__PURE__*/Object.freeze({
-		__proto__: null,
-		foo: foo
+	var foo = /*#__PURE__*/Object.freeze({
+		__proto__: null
 	});
 
 	exports.bar = bar;

test/chunking-form/samples/deprecated/dynamic-import-inlining-object/_expected/cjs/entry.js

@@ -1,13 +1,10 @@
 'use strict';
 
 const bar = 2;
-Promise.resolve().then(function () { return foo$1; });
+Promise.resolve().then(function () { return foo; });
 
-const foo = 1;
-
-var foo$1 = /*#__PURE__*/Object.freeze({
-	__proto__: null,
-	foo: foo
+var foo = /*#__PURE__*/Object.freeze({
+	__proto__: null
 });
 
 exports.bar = bar;

test/chunking-form/samples/deprecated/dynamic-import-inlining-object/_expected/es/entry.js

@@ -1,11 +1,8 @@
 const bar = 2;
-Promise.resolve().then(function () { return foo$1; });
+Promise.resolve().then(function () { return foo; });
 
-const foo = 1;
-
-var foo$1 = /*#__PURE__*/Object.freeze({
-	__proto__: null,
-	foo: foo
+var foo = /*#__PURE__*/Object.freeze({
+	__proto__: null
 });
 
 export { bar };

test/chunking-form/samples/deprecated/dynamic-import-inlining-object/_expected/system/entry.js

@@ -4,13 +4,10 @@ System.register([], (function (exports) {
 		execute: (function () {
 
 			const bar = exports('bar', 2);
-			Promise.resolve().then(function () { return foo$1; });
+			Promise.resolve().then(function () { return foo; });
 
-			const foo = 1;
-
-			var foo$1 = /*#__PURE__*/Object.freeze({
-				__proto__: null,
-				foo: foo
+			var foo = /*#__PURE__*/Object.freeze({
+				__proto__: null
 			});
 
 		})

test/chunking-form/samples/dynamic-import-inlining-object/_expected/amd/entry.js

@@ -1,13 +1,10 @@
 define(['exports'], (function (exports) { 'use strict';
 
 	const bar = 2;
-	Promise.resolve().then(function () { return foo$1; });
+	Promise.resolve().then(function () { return foo; });
 
-	const foo = 1;
-
-	var foo$1 = /*#__PURE__*/Object.freeze({
-		__proto__: null,
-		foo: foo
+	var foo = /*#__PURE__*/Object.freeze({
+		__proto__: null
 	});
 
 	exports.bar = bar;

test/chunking-form/samples/dynamic-import-inlining-object/_expected/cjs/entry.js

@@ -1,13 +1,10 @@
 'use strict';
 
 const bar = 2;
-Promise.resolve().then(function () { return foo$1; });
+Promise.resolve().then(function () { return foo; });
 
-const foo = 1;
-
-var foo$1 = /*#__PURE__*/Object.freeze({
-	__proto__: null,
-	foo: foo
+var foo = /*#__PURE__*/Object.freeze({
+	__proto__: null
 });
 
 exports.bar = bar;

test/chunking-form/samples/dynamic-import-inlining-object/_expected/es/entry.js

@@ -1,11 +1,8 @@
 const bar = 2;
-Promise.resolve().then(function () { return foo$1; });
+Promise.resolve().then(function () { return foo; });
 
-const foo = 1;
-
-var foo$1 = /*#__PURE__*/Object.freeze({
-	__proto__: null,
-	foo: foo
+var foo = /*#__PURE__*/Object.freeze({
+	__proto__: null
 });
 
 export { bar };

test/chunking-form/samples/dynamic-import-inlining-object/_expected/system/entry.js

@@ -4,13 +4,10 @@ System.register([], (function (exports) {
 		execute: (function () {
 
 			const bar = exports('bar', 2);
-			Promise.resolve().then(function () { return foo$1; });
+			Promise.resolve().then(function () { return foo; });
 
-			const foo = 1;
-
-			var foo$1 = /*#__PURE__*/Object.freeze({
-				__proto__: null,
-				foo: foo
+			var foo = /*#__PURE__*/Object.freeze({
+				__proto__: null
 			});
 
 		})

test/chunking-form/samples/resolve-dynamic-import/_expected/amd/main.js

@@ -24,12 +24,10 @@ define(['require', './direct-relative-external', 'to-indirect-relative-external'
 	new Promise(function (resolve, reject) { require(['direct-absolute-external'], function (m) { resolve(/*#__PURE__*/_interopNamespaceDefault(m)); }, reject); });
 	new Promise(function (resolve, reject) { require(['to-indirect-absolute-external'], function (m) { resolve(/*#__PURE__*/_interopNamespaceDefault(m)); }, reject); });
 
-	const value = 'existing';
 	console.log('existing');
 
 	var existing = /*#__PURE__*/Object.freeze({
-		__proto__: null,
-		value: value
+		__proto__: null
 	});
 
 	//main

test/chunking-form/samples/resolve-dynamic-import/_expected/cjs/main.js

@@ -12,12 +12,10 @@ import('to-indirect-relative-external');
 import('direct-absolute-external');
 import('to-indirect-absolute-external');
 
-const value = 'existing';
 console.log('existing');
 
 var existing = /*#__PURE__*/Object.freeze({
-	__proto__: null,
-	value: value
+	__proto__: null
 });
 
 //main

test/chunking-form/samples/resolve-dynamic-import/_expected/es/main.js

@@ -10,12 +10,10 @@ import('to-indirect-relative-external');
 import('direct-absolute-external');
 import('to-indirect-absolute-external');
 
-const value = 'existing';
 console.log('existing');
 
 var existing = /*#__PURE__*/Object.freeze({
-	__proto__: null,
-	value: value
+	__proto__: null
 });
 
 //main