Tree-shake unused declarations while keeping initializer side-effects

src/ast/nodes/ForInStatement.ts

@@ -49,7 +49,7 @@ export default class ForInStatement extends StatementBase {
 
 	include(context: InclusionContext, includeChildrenRecursively: IncludeChildren) {
 		this.included = true;
-		this.left.includeWithAllDeclaredVariables(includeChildrenRecursively, context);
+		this.left.includeWithAllDeclaredVariables(context, includeChildrenRecursively);
 		this.left.deoptimizePath(EMPTY_PATH);
 		this.right.include(context, includeChildrenRecursively);
 		const { brokenFlow } = context;

src/ast/nodes/ForOfStatement.ts

@@ -34,7 +34,7 @@ export default class ForOfStatement extends StatementBase {
 
 	include(context: InclusionContext, includeChildrenRecursively: IncludeChildren) {
 		this.included = true;
-		this.left.includeWithAllDeclaredVariables(includeChildrenRecursively, context);
+		this.left.includeWithAllDeclaredVariables(context, includeChildrenRecursively);
 		this.left.deoptimizePath(EMPTY_PATH);
 		this.right.include(context, includeChildrenRecursively);
 		const { brokenFlow } = context;

src/ast/nodes/VariableDeclaration.ts

@@ -33,7 +33,7 @@ function areAllDeclarationsIncludedAndNotExported(
 	exportNamesByVariable: Map<Variable, string[]>
 ): boolean {
 	for (const declarator of declarations) {
-		if (!declarator.included) return false;
+		if (!declarator.id.included) return false;
 		if (declarator.id.type === NodeType.Identifier) {
 			if (exportNamesByVariable.has(declarator.id.variable!)) return false;
 		} else {
@@ -69,12 +69,13 @@ export default class VariableDeclaration extends NodeBase {
 	}
 
 	includeWithAllDeclaredVariables(
-		includeChildrenRecursively: IncludeChildren,
-		context: InclusionContext
-	) {
+		context: InclusionContext,
+		includeChildrenRecursively: IncludeChildren
+	): void {
 		this.included = true;
 		for (const declarator of this.declarations) {
-			declarator.include(context, includeChildrenRecursively);
+			declarator.id.included = true;
+			declarator.includeWithAllDeclaredVariables(context, includeChildrenRecursively);
 		}
 	}
 
@@ -158,11 +159,7 @@ export default class VariableDeclaration extends NodeBase {
 			this.end - (code.original.charCodeAt(this.end - 1) === 59 /*";"*/ ? 1 : 0)
 		);
 		let actualContentEnd: number | undefined, renderedContentEnd: number;
-		if (/\n\s*$/.test(code.slice(this.start, separatedNodes[0].start))) {
-			renderedContentEnd = this.start + this.kind.length;
-		} else {
-			renderedContentEnd = separatedNodes[0].start;
-		}
+		renderedContentEnd = findNonWhiteSpace(code.original, this.start + this.kind.length);
 		let lastSeparatorPos = renderedContentEnd - 1;
 		code.remove(this.start, lastSeparatorPos);
 		let isInDeclaration = false;
@@ -187,11 +184,12 @@ export default class VariableDeclaration extends NodeBase {
 			leadingString = '';
 			nextSeparatorString = '';
 			if (
-				node.id instanceof Identifier &&
-				isReassignedExportsMember(
-					(node.id as IdentifierWithVariable).variable,
-					options.exportNamesByVariable
-				)
+				!node.id.included ||
+				(node.id instanceof Identifier &&
+					isReassignedExportsMember(
+						(node.id as IdentifierWithVariable).variable,
+						options.exportNamesByVariable
+					))
 			) {
 				if (hasRenderedContent) {
 					separatorString += ';';

src/ast/nodes/VariableDeclarator.ts

@@ -1,7 +1,15 @@
+import MagicString from 'magic-string';
+import { BLANK } from '../../utils/blank';
+import {
+	findFirstOccurrenceOutsideComment,
+	findNonWhiteSpace,
+	RenderOptions
+} from '../../utils/renderHelpers';
+import { HasEffectsContext, InclusionContext } from '../ExecutionContext';
 import { ObjectPath } from '../utils/PathTracker';
 import { UNDEFINED_EXPRESSION } from '../values';
 import * as NodeType from './NodeType';
-import { ExpressionNode, NodeBase } from './shared/Node';
+import { ExpressionNode, IncludeChildren, NodeBase } from './shared/Node';
 import { PatternNode } from './shared/Pattern';
 
 export default class VariableDeclarator extends NodeBase {
@@ -16,4 +24,46 @@ export default class VariableDeclarator extends NodeBase {
 	deoptimizePath(path: ObjectPath) {
 		this.id.deoptimizePath(path);
 	}
+
+	hasEffects(context: HasEffectsContext): boolean {
+		return this.id.hasEffects(context) || (this.init !== null && this.init.hasEffects(context));
+	}
+
+	include(context: InclusionContext, includeChildrenRecursively: IncludeChildren) {
+		this.included = true;
+		if (includeChildrenRecursively || this.id.shouldBeIncluded(context)) {
+			this.id.include(context, includeChildrenRecursively);
+		}
+		if (this.init) {
+			this.init.include(context, includeChildrenRecursively);
+		}
+	}
+
+	includeWithAllDeclaredVariables(
+		context: InclusionContext,
+		includeChildrenRecursively: IncludeChildren
+	): void {
+		this.included = true;
+		this.id.include(context, includeChildrenRecursively);
+		if (this.init) {
+			this.init.include(context, includeChildrenRecursively);
+		}
+	}
+
+	render(code: MagicString, options: RenderOptions) {
+		const renderId = this.id.included;
+		if (renderId) {
+			this.id.render(code, options);
+		} else {
+			const operatorPos = findFirstOccurrenceOutsideComment(code.original, '=', this.id.end);
+			code.remove(this.start, findNonWhiteSpace(code.original, operatorPos + 1));
+		}
+		if (this.init) {
+			this.init.render(
+				code,
+				options,
+				renderId ? BLANK : { renderedParentType: NodeType.ExpressionStatement }
+			);
+		}
+	}
 }

src/ast/nodes/shared/Node.ts

@@ -73,8 +73,8 @@ export interface Node extends Entity {
 	 * for for-loops that do not use a declared loop variable.
 	 */
 	includeWithAllDeclaredVariables(
-		includeChildrenRecursively: IncludeChildren,
-		context: InclusionContext
+		context: InclusionContext,
+		includeChildrenRecursively: IncludeChildren
 	): void;
 	render(code: MagicString, options: RenderOptions, nodeRenderOptions?: NodeRenderOptions): void;
 
@@ -216,9 +216,9 @@ export class NodeBase implements ExpressionNode {
 	}
 
 	includeWithAllDeclaredVariables(
-		includeChildrenRecursively: IncludeChildren,
-		context: InclusionContext
-	) {
+		context: InclusionContext,
+		includeChildrenRecursively: IncludeChildren
+	): void {
 		this.include(context, includeChildrenRecursively);
 	}
 

test/chunking-form/samples/preserve-entry-signatures/false/_expected/amd/main.js

@@ -2,7 +2,7 @@ define(['require', 'exports'], function (require, exports) { 'use strict';
 
 	const shared = 'shared';
 
-	const dynamic = new Promise(function (resolve, reject) { require(['./generated-dynamic'], resolve, reject) });
+	new Promise(function (resolve, reject) { require(['./generated-dynamic'], resolve, reject) });
 
 	globalThis.sharedStatic = shared;
 

test/chunking-form/samples/preserve-entry-signatures/false/_expected/cjs/main.js

@@ -4,7 +4,7 @@ Object.defineProperty(exports, '__esModule', { value: true });
 
 const shared = 'shared';
 
-const dynamic = Promise.resolve().then(function () { return require('./generated-dynamic.js'); });
+Promise.resolve().then(function () { return require('./generated-dynamic.js'); });
 
 globalThis.sharedStatic = shared;
 

test/chunking-form/samples/preserve-entry-signatures/false/_expected/es/main.js

@@ -1,6 +1,6 @@
 const shared = 'shared';
 
-const dynamic = import('./generated-dynamic.js');
+import('./generated-dynamic.js');
 
 globalThis.sharedStatic = shared;
 

test/chunking-form/samples/preserve-entry-signatures/false/_expected/system/main.js

@@ -5,7 +5,7 @@ System.register([], function (exports, module) {
 
 			const shared = exports('s', 'shared');
 
-			const dynamic = module.import('./generated-dynamic.js');
+			module.import('./generated-dynamic.js');
 
 			globalThis.sharedStatic = shared;
 

test/form/samples/builtin-prototypes/array-expression/_expected.js

@@ -1,19 +1,19 @@
-const map2 = [ 1 ].map( x => console.log( 1 ) );
-const map4 = [ 1 ].map( x => x ).map( x => console.log( 1 ) );
-const map5 = [ 1 ].map( x => console.log( 1 ) ).map( x => x );
-const map7 = [ 1 ].map( x => x ).map( x => x ).map( x => console.log( 1 ) );
-const map8 = [ 1 ].map( x => x ).map( x => console.log( 1 ) ).map( x => x );
+[ 1 ].map( x => console.log( 1 ) );
+[ 1 ].map( x => x ).map( x => console.log( 1 ) );
+[ 1 ].map( x => console.log( 1 ) ).map( x => x );
+[ 1 ].map( x => x ).map( x => x ).map( x => console.log( 1 ) );
+[ 1 ].map( x => x ).map( x => console.log( 1 ) ).map( x => x );
 
 []();
-const _everyEffect = [ 1 ].every( () => console.log( 1 ) || true );
-const _filterEffect = [ 1 ].filter( () => console.log( 1 ) || true );
-const _findEffect = [ 1 ].find( () => console.log( 1 ) || true );
-const _findIndexEffect = [ 1 ].findIndex( () => console.log( 1 ) || true );
-const _forEachEffect = [ 1 ].forEach( () => console.log( 1 ) || true );
-const _mapEffect = [ 1 ].map( () => console.log( 1 ) || 1 );
-const _reduceEffect = [ 1 ].reduce( () => console.log( 1 ) || 1, 1 );
-const _reduceRightEffect = [ 1 ].reduceRight( () => console.log( 1 ) || 1, 1 );
-const _someEffect = [ 1 ].some( () => console.log( 1 ) || true );
+[ 1 ].every( () => console.log( 1 ) || true );
+[ 1 ].filter( () => console.log( 1 ) || true );
+[ 1 ].find( () => console.log( 1 ) || true );
+[ 1 ].findIndex( () => console.log( 1 ) || true );
+[ 1 ].forEach( () => console.log( 1 ) || true );
+[ 1 ].map( () => console.log( 1 ) || 1 );
+[ 1 ].reduce( () => console.log( 1 ) || 1, 1 );
+[ 1 ].reduceRight( () => console.log( 1 ) || 1, 1 );
+[ 1 ].some( () => console.log( 1 ) || true );
 
 // mutator methods
 const exported = [ 1 ];
@@ -23,7 +23,7 @@ exported.pop();
 exported.push( 0 );
 exported.reverse();
 exported.shift();
-const _sortEffect = [ 1 ].sort( () => console.log( 1 ) || 0 );
+[ 1 ].sort( () => console.log( 1 ) || 0 );
 exported.sort();
 exported.splice( 0 );
 exported.unshift( 0 );

test/form/samples/builtin-prototypes/literal/_expected.js

@@ -1,9 +1,9 @@
-const _replaceEffect = 'ab'.replace( 'a', () => console.log( 1 ) || 'b' );
+'ab'.replace( 'a', () => console.log( 1 ) || 'b' );
 
 // deep property access is forbidden
-const deepBoolean = true.x.y;
-const deepNumber = (1).x.y;
-const deepString = 'ab'.x.y;
+true.x.y;
+(1).x.y;
+'ab'.x.y;
 
 // due to strict mode, extension is forbidden
 true.x = 1;

test/form/samples/builtin-prototypes/object-expression/_expected.js

@@ -1,11 +1,11 @@
 const object = {};
-const propertyIsEnumerable1 = object.propertyIsEnumerable( 'toString' );
-const propertyIsEnumerable2 = {}.propertyIsEnumerable( 'toString' );
-const propertyIsEnumerable3 = {}.propertyIsEnumerable( 'toString' ).valueOf();
+object.propertyIsEnumerable( 'toString' );
+{}.propertyIsEnumerable( 'toString' );
+{}.propertyIsEnumerable( 'toString' ).valueOf();
 
-const _hasOwnProperty = {}.hasOwnProperty( 'toString' ).valueOf();
-const _isPrototypeOf = {}.isPrototypeOf( {} ).valueOf();
-const _propertyIsEnumerable = {}.propertyIsEnumerable( 'toString' ).valueOf();
-const _toLocaleString = {}.toLocaleString().trim();
-const _toString = {}.toString().trim();
-const _valueOf = {}.valueOf();
+{}.hasOwnProperty( 'toString' ).valueOf();
+{}.isPrototypeOf( {} ).valueOf();
+{}.propertyIsEnumerable( 'toString' ).valueOf();
+{}.toLocaleString().trim();
+{}.toString().trim();
+{}.valueOf();

test/form/samples/conditional-expression-paths/_expected.js

@@ -4,24 +4,24 @@ var bar = { x: () => {}, y: {} };
 var baz = { x: () => console.log('effect') };
 
 // unknown branch without side-effects
-var a1 = (unknownValue ? foo : bar).y.z;
-var b1 = (unknownValue ? foo : bar).x();
+(unknownValue ? foo : bar).y.z;
+(unknownValue ? foo : bar).x();
 
 // unknown branch with side-effect
-var a2 = (unknownValue ? foo : baz).y.z;
-var b2 = (unknownValue ? foo : baz).x();
+(unknownValue ? foo : baz).y.z;
+(unknownValue ? foo : baz).x();
 
 // known branch without side-effects
-var a3 = ( foo ).y.z;
-var b3 = ( foo).y.z;
-var c3 = ( foo ).x();
-var d3 = ( foo).x();
+( foo ).y.z;
+( foo).y.z;
+( foo ).x();
+( foo).x();
 
 // known branch with side-effect
-var a4 = ( baz ).y.z;
-var b4 = ( baz).y.z;
-var c4 = ( baz ).x();
-var d4 = ( baz).x();
+( baz ).y.z;
+( baz).y.z;
+( baz ).x();
+( baz).x();
 var baz3 = {};
 ( baz3 ).y.z = 1;
 ( baz3).y.z = 1;

test/form/samples/conditional-expression/_expected.js

@@ -0,0 +1,17 @@
+// side-effect in condition
+foo() ? 1 : 2;
+
+var unknownValue = bar();
+
+// unknown branch with side-effect
+unknownValue ? foo() : 2;
+unknownValue ? 1 : foo();
+(unknownValue ? function () {} : function () {this.x = 1;})();
+
+// known side-effect
+ foo() ;
+( function () {this.x = 1;} )();
+( () => () => console.log( 'effect' ) )()();
+ foo();
+( function () {this.x = 1;})();
+( () => () => console.log( 'effect' ))()();