feat: optimize in checks on namespaces to keep them treeshake-able (#6029)

cyyynthia · lukastaegert · web-flow · commit 9a8614f3b516 · 2025-07-27T06:10:50.000Z
* feat: optimize `in` checks on namespaces

* fix: remove bad leftovers

* fix: set renderedLiteralValue to UnknownValue on deopt for BinaryExpression

* Adapt test for changed traceExport signature

---------

Co-authored-by: Lukas Taegert-Atkinson &lt;lukastaegert@users.noreply.github.com&gt;
Co-authored-by: Lukas Taegert-Atkinson &lt;lukas.taegert-atkinson@tngtech.com&gt;
diff --git a/src/ast/nodes/BinaryExpression.ts b/src/ast/nodes/BinaryExpression.ts
@@ -12,11 +12,22 @@ import {
 	SHARED_RECURSION_TRACKER,
 	UNKNOWN_PATH
 } from '../utils/PathTracker';
+import { getRenderedLiteralValue } from '../utils/renderLiteralValue';
+import type NamespaceVariable from '../variables/NamespaceVariable';
 import ExpressionStatement from './ExpressionStatement';
 import type { LiteralValue } from './Literal';
 import type * as NodeType from './NodeType';
-import { type LiteralValueOrUnknown, UnknownValue } from './shared/Expression';
-import { doNotDeoptimize, type ExpressionNode, NodeBase } from './shared/Node';
+import {
+	type InclusionOptions,
+	type LiteralValueOrUnknown,
+	UnknownValue
+} from './shared/Expression';
+import {
+	doNotDeoptimize,
+	type ExpressionNode,
+	type IncludeChildren,
+	NodeBase
+} from './shared/Node';
 
 type Operator =
 	| '!='
@@ -71,13 +82,18 @@ const binaryOperators: Partial<
 	// instanceof: () => UnknownValue,
 };
 
+const UNASSIGNED = Symbol('Unassigned');
+
 export default class BinaryExpression extends NodeBase implements DeoptimizableEntity {
 	declare left: ExpressionNode;
 	declare operator: keyof typeof binaryOperators;
 	declare right: ExpressionNode;
 	declare type: NodeType.tBinaryExpression;
+	renderedLiteralValue: string | typeof UnknownValue | typeof UNASSIGNED = UNASSIGNED;
 
-	deoptimizeCache(): void {}
+	deoptimizeCache(): void {
+		this.renderedLiteralValue = UnknownValue;
+	}
 
 	getLiteralValueAtPath(
 		path: ObjectPath,
@@ -88,6 +104,13 @@ export default class BinaryExpression extends NodeBase implements DeoptimizableE
 		const leftValue = this.left.getLiteralValueAtPath(EMPTY_PATH, recursionTracker, origin);
 		if (typeof leftValue === 'symbol') return UnknownValue;
 
+		// Optimize `'export' in namespace`
+		if (this.operator === 'in' && this.right.variable?.isNamespace) {
+			return (
+				(this.right.variable as NamespaceVariable).context.traceExport(String(leftValue))[0] != null
+			);
+		}
+
 		const rightValue = this.right.getLiteralValueAtPath(EMPTY_PATH, recursionTracker, origin);
 		if (typeof rightValue === 'symbol') return UnknownValue;
 
@@ -97,6 +120,16 @@ export default class BinaryExpression extends NodeBase implements DeoptimizableE
 		return operatorFunction(leftValue, rightValue);
 	}
 
+	getRenderedLiteralValue() {
+		// Only optimize `'export' in ns`
+		if (this.operator !== 'in' || !this.right.variable?.isNamespace) return UnknownValue;
+
+		if (this.renderedLiteralValue !== UNASSIGNED) return this.renderedLiteralValue;
+		return (this.renderedLiteralValue = getRenderedLiteralValue(
+			this.getLiteralValueAtPath(EMPTY_PATH, SHARED_RECURSION_TRACKER, this)
+		));
+	}
+
 	hasEffects(context: HasEffectsContext): boolean {
 		// support some implicit type coercion runtime errors
 		if (
@@ -113,9 +146,20 @@ export default class BinaryExpression extends NodeBase implements DeoptimizableE
 		return type !== INTERACTION_ACCESSED || path.length > 1;
 	}
 
+	include(
+		context: InclusionContext,
+		includeChildrenRecursively: IncludeChildren,
+		_options?: InclusionOptions
+	) {
+		this.included = true;
+		if (typeof this.getRenderedLiteralValue() === 'symbol') {
+			super.include(context, includeChildrenRecursively, _options);
+		}
+	}
+
 	includeNode(context: InclusionContext) {
 		this.included = true;
-		if (this.operator === 'in') {
+		if (this.operator === 'in' && typeof this.getRenderedLiteralValue() === 'symbol') {
 			this.right.includePath(UNKNOWN_PATH, context);
 		}
 	}
@@ -129,8 +173,13 @@ export default class BinaryExpression extends NodeBase implements DeoptimizableE
 		options: RenderOptions,
 		{ renderedSurroundingElement }: NodeRenderOptions = BLANK
 	): void {
-		this.left.render(code, options, { renderedSurroundingElement });
-		this.right.render(code, options);
+		const renderedLiteralValue = this.getRenderedLiteralValue();
+		if (typeof renderedLiteralValue !== 'symbol') {
+			code.overwrite(this.start, this.end, renderedLiteralValue);
+		} else {
+			this.left.render(code, options, { renderedSurroundingElement });
+			this.right.render(code, options);
+		}
 	}
 }
 
diff --git a/src/ast/nodes/UnaryExpression.ts b/src/ast/nodes/UnaryExpression.ts
@@ -10,6 +10,7 @@ import {
 	type ObjectPath,
 	SHARED_RECURSION_TRACKER
 } from '../utils/PathTracker';
+import { getRenderedLiteralValue } from '../utils/renderLiteralValue';
 import Identifier from './Identifier';
 import type { LiteralValue } from './Literal';
 import type * as NodeType from './NodeType';
@@ -142,33 +143,4 @@ export default class UnaryExpression extends NodeBase {
 
 const CHARACTERS_THAT_DO_NOT_REQUIRE_SPACE = /[\s([=%&*+-/<>^|,?:;]/;
 
-function getRenderedLiteralValue(value: unknown) {
-	if (value === undefined) {
-		// At the moment, the undefined only happens when the operator is void
-		return 'void 0';
-	}
-	if (typeof value === 'boolean') {
-		return String(value);
-	}
-	if (typeof value === 'string') {
-		return JSON.stringify(value);
-	}
-	if (typeof value === 'number') {
-		return getSimplifiedNumber(value);
-	}
-	return UnknownValue;
-}
-
-function getSimplifiedNumber(value: number) {
-	if (Object.is(-0, value)) {
-		return '-0';
-	}
-	const exp = value.toExponential();
-	const [base, exponent] = exp.split('e');
-	const floatLength = base.split('.')[1]?.length || 0;
-	const finalizedExp = `${base.replace('.', '')}e${parseInt(exponent) - floatLength}`;
-	const stringifiedValue = String(value).replace('+', '');
-	return finalizedExp.length < stringifiedValue.length ? finalizedExp : stringifiedValue;
-}
-
 UnaryExpression.prototype.includeNode = onlyIncludeSelf;
diff --git a/src/ast/utils/renderLiteralValue.ts b/src/ast/utils/renderLiteralValue.ts
@@ -0,0 +1,29 @@
+import { UnknownValue } from '../nodes/shared/Expression';
+
+export function getRenderedLiteralValue(value: unknown) {
+	if (value === undefined) {
+		return 'void 0';
+	}
+	if (typeof value === 'boolean') {
+		return String(value);
+	}
+	if (typeof value === 'string') {
+		return JSON.stringify(value);
+	}
+	if (typeof value === 'number') {
+		return getSimplifiedNumber(value);
+	}
+	return UnknownValue;
+}
+
+function getSimplifiedNumber(value: number) {
+	if (Object.is(-0, value)) {
+		return '-0';
+	}
+	const exp = value.toExponential();
+	const [base, exponent] = exp.split('e');
+	const floatLength = base.split('.')[1]?.length || 0;
+	const finalizedExp = `${base.replace('.', '')}e${parseInt(exponent) - floatLength}`;
+	const stringifiedValue = String(value).replace('+', '');
+	return finalizedExp.length < stringifiedValue.length ? finalizedExp : stringifiedValue;
+}
diff --git a/test/form/samples/namespace-optimization-in-operator/_config.js b/test/form/samples/namespace-optimization-in-operator/_config.js
@@ -0,0 +1,8 @@
+module.exports = defineTest({
+	description:
+		'it does static optimization of internal namespaces when checking whether an export exists',
+	expectedWarnings: [
+		// That's a bit of an annoyance that Rollup still complains despite the if gate...
+		'MISSING_EXPORT'
+	]
+});
diff --git a/test/form/samples/namespace-optimization-in-operator/_expected.js b/test/form/samples/namespace-optimization-in-operator/_expected.js
@@ -0,0 +1,3 @@
+function c() {}
+
+console.log(c());
diff --git a/test/form/samples/namespace-optimization-in-operator/foo.js b/test/form/samples/namespace-optimization-in-operator/foo.js
@@ -0,0 +1,3 @@
+export function a() {}
+export function b() {}
+export function c() {}
diff --git a/test/form/samples/namespace-optimization-in-operator/main.js b/test/form/samples/namespace-optimization-in-operator/main.js
@@ -0,0 +1,4 @@
+import * as foo from './foo';
+
+if ('d' in foo) console.log(foo.d())
+if ('c' in foo) console.log(foo.c())

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+function c() {}`
	`2`	`+`
	`3`	`+console.log(c());`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+export function a() {}`
	`2`	`+export function b() {}`
	`3`	`+export function c() {}`