Deoptimize awaited expressions (#4162)

Author: lukastaegert

src/ast/ExecutionContext.ts

@@ -7,7 +7,7 @@ interface ExecutionContextIgnore {
 	breaks: boolean;
 	continues: boolean;
 	labels: Set<string>;
-	returnAwaitYield: boolean;
+	returnYield: boolean;
 }
 
 export const BROKEN_FLOW_NONE = 0;
@@ -51,7 +51,7 @@ export function createHasEffectsContext(): HasEffectsContext {
 			breaks: false,
 			continues: false,
 			labels: new Set(),
-			returnAwaitYield: false
+			returnYield: false
 		},
 		includedLabels: new Set(),
 		instantiated: new DiscriminatedPathTracker(),

src/ast/nodes/ArrowFunctionExpression.ts

@@ -83,7 +83,7 @@ export default class ArrowFunctionExpression extends NodeBase {
 			breaks: false,
 			continues: false,
 			labels: new Set(),
-			returnAwaitYield: true
+			returnYield: true
 		};
 		if (this.body.hasEffects(context)) return true;
 		context.ignore = ignore;

src/ast/nodes/AwaitExpression.ts

@@ -1,6 +1,5 @@
-import { NormalizedTreeshakingOptions } from '../../rollup/types';
-import { NO_ARGS } from '../CallOptions';
-import { HasEffectsContext, InclusionContext } from '../ExecutionContext';
+import { InclusionContext } from '../ExecutionContext';
+import { UNKNOWN_PATH } from '../utils/PathTracker';
 import ArrowFunctionExpression from './ArrowFunctionExpression';
 import * as NodeType from './NodeType';
 import FunctionNode from './shared/FunctionNode';
@@ -9,25 +8,15 @@ import { ExpressionNode, IncludeChildren, Node, NodeBase } from './shared/Node';
 export default class AwaitExpression extends NodeBase {
 	argument!: ExpressionNode;
 	type!: NodeType.tAwaitExpression;
+	protected deoptimized = false;
 
-	hasEffects(context: HasEffectsContext): boolean {
-		const { propertyReadSideEffects } = this.context.options
-			.treeshake as NormalizedTreeshakingOptions;
-		return (
-			!context.ignore.returnAwaitYield ||
-			this.argument.hasEffects(context) ||
-			this.argument.hasEffectsWhenCalledAtPath(
-				['then'],
-				{ args: NO_ARGS, thisParam: null, withNew: false },
-				context
-			) ||
-			(propertyReadSideEffects &&
-				(propertyReadSideEffects === 'always' ||
-					this.argument.hasEffectsWhenAccessedAtPath(['then'], context)))
-		);
+	hasEffects(): boolean {
+		if (!this.deoptimized) this.applyDeoptimizations();
+		return true;
 	}
 
 	include(context: InclusionContext, includeChildrenRecursively: IncludeChildren): void {
+		if (!this.deoptimized) this.applyDeoptimizations();
 		if (!this.included) {
 			this.included = true;
 			checkTopLevelAwait: if (!this.context.usesTopLevelAwait) {
@@ -41,4 +30,9 @@ export default class AwaitExpression extends NodeBase {
 		}
 		this.argument.include(context, includeChildrenRecursively);
 	}
+
+	protected applyDeoptimizations(): void {
+		this.deoptimized = true;
+		this.argument.deoptimizePath(UNKNOWN_PATH);
+	}
 }

src/ast/nodes/ReturnStatement.ts

@@ -15,7 +15,7 @@ export default class ReturnStatement extends StatementBase {
 
 	hasEffects(context: HasEffectsContext): boolean {
 		if (
-			!context.ignore.returnAwaitYield ||
+			!context.ignore.returnYield ||
 			(this.argument !== null && this.argument.hasEffects(context))
 		)
 			return true;

src/ast/nodes/YieldExpression.ts

@@ -14,8 +14,7 @@ export default class YieldExpression extends NodeBase {
 	hasEffects(context: HasEffectsContext): boolean {
 		if (!this.deoptimized) this.applyDeoptimizations();
 		return (
-			!context.ignore.returnAwaitYield ||
-			(this.argument !== null && this.argument.hasEffects(context))
+			!context.ignore.returnYield || (this.argument !== null && this.argument.hasEffects(context))
 		);
 	}
 

src/ast/nodes/shared/FunctionNode.ts

@@ -114,7 +114,7 @@ export default class FunctionNode extends NodeBase {
 			breaks: false,
 			continues: false,
 			labels: new Set(),
-			returnAwaitYield: true
+			returnYield: true
 		};
 		if (this.body.hasEffects(context)) return true;
 		context.brokenFlow = brokenFlow;

test/form/samples/async-function-effects/main.js

@@ -77,14 +77,6 @@
 	return { then() {} };
 })();
 
-// removed
-(async function () {
-	await {
-		then: function () {}
-	};
-	return { then() {} };
-})();
-
 (async function () {
 	await {
 		get then() {
@@ -104,16 +96,6 @@
 	return { then() {} };
 })();
 
-// removed
-(async function () {
-	await {
-		get then() {
-			return () => {};
-		}
-	};
-	return { then() {} };
-})();
-
 (async function () {
 	await await {
 		then(resolve) {

test/form/samples/ignore-property-access-side-effects/main.js

@@ -38,13 +38,3 @@ const foo7 = (async () => ({
 		return () => {};
 	}
 }))();
-
-const foo8 = (async function () {
-	await {
-		get then() {
-			console.log('effect');
-			return () => {};
-		}
-	};
-	return { then() {} };
-})();

test/function/samples/track-awaited-object/_config.js

@@ -0,0 +1,10 @@
+const assert = require('assert');
+
+module.exports = {
+	description: 'tracks object mutations through await',
+	async exports(exports) {
+		assert.strictEqual(exports.toggled, false);
+		await exports.test();
+		assert.strictEqual(exports.toggled, true);
+	}
+};

test/function/samples/track-awaited-object/main.js

@@ -0,0 +1,19 @@
+function fn() {
+	const obj = {
+		test() {
+			if (typeof obj.testfn === 'function') {
+				obj.testfn();
+			}
+		}
+	};
+
+	return obj;
+}
+
+export let toggled = false;
+
+export const test = async function () {
+	const obj = await fn();
+	obj.testfn = () => (toggled = true);
+	obj.test();
+};