Prevent ASI errors for conditional expressions

src/ast/nodes/ConditionalExpression.ts

@@ -1,6 +1,7 @@
 import MagicString from 'magic-string';
 import { BLANK } from '../../utils/blank';
 import {
+	findFirstLineBreakOutsideComment,
 	findFirstOccurrenceOutsideComment,
 	NodeRenderOptions,
 	RenderOptions
@@ -151,20 +152,30 @@ export default class ConditionalExpression extends NodeBase implements Deoptimiz
 	render(
 		code: MagicString,
 		options: RenderOptions,
-		{ renderedParentType, isCalleeOfRenderedParent }: NodeRenderOptions = BLANK
+		{ renderedParentType, isCalleeOfRenderedParent, preventASI }: NodeRenderOptions = BLANK
 	) {
 		if (!this.test.included) {
 			const colonPos = findFirstOccurrenceOutsideComment(code.original, ':', this.consequent.end);
+			const inclusionStart =
+				(this.consequent.included
+					? findFirstOccurrenceOutsideComment(code.original, '?', this.test.end)
+					: colonPos) + 1;
+			if (preventASI) {
+				const branchStart = (this.usedBranch as ExpressionNode).start;
+				let lineBreakPos = inclusionStart;
+				do {
+					lineBreakPos = findFirstLineBreakOutsideComment(code.original, lineBreakPos);
+					if (lineBreakPos >= 0 && lineBreakPos < branchStart) {
+						code.remove(lineBreakPos, lineBreakPos + 1);
+						lineBreakPos++;
+					} else {
+						lineBreakPos = -1;
+					}
+				} while (lineBreakPos >= 0);
+			}
+			code.remove(this.start, inclusionStart);
 			if (this.consequent.included) {
-				const questionmarkPos = findFirstOccurrenceOutsideComment(
-					code.original,
-					'?',
-					this.test.end
-				);
-				code.remove(this.start, questionmarkPos + 1);
 				code.remove(colonPos, this.end);
-			} else {
-				code.remove(this.start, colonPos + 1);
 			}
 			removeAnnotations(this, code);
 			(this.usedBranch as ExpressionNode).render(code, options, {

src/ast/nodes/ReturnStatement.ts

@@ -22,7 +22,7 @@ export default class ReturnStatement extends StatementBase {
 
 	render(code: MagicString, options: RenderOptions) {
 		if (this.argument) {
-			this.argument.render(code, options);
+			this.argument.render(code, options, { preventASI: true });
 			if (this.argument.start === this.start + 6 /* 'return'.length */) {
 				code.prependLeft(this.start + 6, ' ');
 			}

src/utils/renderHelpers.ts

@@ -17,6 +17,7 @@ export interface NodeRenderOptions {
 	isCalleeOfRenderedParent?: boolean;
 	isNoStatement?: boolean;
 	isShorthandProperty?: boolean;
+	preventASI?: boolean;
 	renderedParentType?: string; // also serves as a flag if the rendered parent is different from the actual parent
 	start?: number;
 }

test/form/samples/keep-tree-shaking-comments-no-asi/_config.js

@@ -0,0 +1,4 @@
+module.exports = {
+	description:
+		'always keep leading comments when tree-shaking and no automatic semicolons are inserted'
+};

test/form/samples/keep-tree-shaking-comments-no-asi/_expected.js

@@ -0,0 +1,7 @@
+console.log(
+	/* keep me */
+	'expected');
+
+console.log(
+	/* keep me */
+	'expected' );

test/form/samples/keep-tree-shaking-comments-no-asi/main.js

@@ -0,0 +1,9 @@
+console.log(false ?
+	'unexpected' :
+	/* keep me */
+	'expected');
+
+console.log(true ?
+	/* keep me */
+	'expected' :
+	'unexpected');

test/function/samples/prevent-tree-shaking-asi/_config.js

@@ -0,0 +1,9 @@
+const assert = require('assert');
+
+module.exports = {
+	description: 'prevent automatic semicolon insertion from changing behaviour when tree-shaking',
+	exports(exports) {
+		assert.strictEqual(exports.test1(), 'expected');
+		assert.strictEqual(exports.test2(), 'expected');
+	}
+};

test/function/samples/prevent-tree-shaking-asi/main.js

@@ -0,0 +1,15 @@
+export function test1() {
+	return true ?
+
+
+		'expected' :
+		'unexpected';
+}
+
+export function test2() {
+	return false ?
+		'unexpected' :
+
+
+		'expected';
+}