feat: treeshake for optional chaining (#4797)

antfu · lukastaegert · web-flow · commit ffc19b009126 · 2023-01-12T08:54:18.000+01:00
* feat: treeshake for optional chaining

* chore: typo

* chore: fix

* chore: clean up

* fix: improve coverage

* fix: remove solo

Co-authored-by: Lukas Taegert-Atkinson &lt;lukastaegert@users.noreply.github.com&gt;
diff --git a/src/ast/nodes/ChainExpression.ts b/src/ast/nodes/ChainExpression.ts
@@ -1,9 +1,42 @@
+import type { DeoptimizableEntity } from '../DeoptimizableEntity';
+import type { HasEffectsContext } from '../ExecutionContext';
+import { SHARED_RECURSION_TRACKER } from '../utils/PathTracker';
+import { EMPTY_PATH } from '../utils/PathTracker';
 import type CallExpression from './CallExpression';
 import type MemberExpression from './MemberExpression';
 import type * as NodeType from './NodeType';
+import type { LiteralValueOrUnknown } from './shared/Expression';
+import { UnknownValue } from './shared/Expression';
 import { NodeBase } from './shared/Node';
 
-export default class ChainExpression extends NodeBase {
+const unset = Symbol('unset');
+
+export default class ChainExpression extends NodeBase implements DeoptimizableEntity {
 	declare expression: CallExpression | MemberExpression;
 	declare type: NodeType.tChainExpression;
+	private objectValue: LiteralValueOrUnknown | typeof unset = unset;
+
+	deoptimizeCache(): void {
+		this.objectValue = UnknownValue;
+	}
+
+	getLiteralValueAtPath(): LiteralValueOrUnknown {
+		if (this.getObjectValue() == null) return undefined;
+		return UnknownValue;
+	}
+
+	hasEffects(context: HasEffectsContext): boolean {
+		if (this.getObjectValue() == null) return false;
+		return this.expression.hasEffects(context);
+	}
+
+	private getObjectValue() {
+		if (this.objectValue === unset) {
+			let object =
+				this.expression.type === 'CallExpression' ? this.expression.callee : this.expression.object;
+			if (object.type === 'MemberExpression') object = (object as MemberExpression).object;
+			this.objectValue = object.getLiteralValueAtPath(EMPTY_PATH, SHARED_RECURSION_TRACKER, this);
+		}
+		return this.objectValue;
+	}
 }
diff --git a/test/form/samples/tree-shake-optional-chaining-literal/_config.js b/test/form/samples/tree-shake-optional-chaining-literal/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'tree-shake expressions optional chaining with literal values'
+};
diff --git a/test/form/samples/tree-shake-optional-chaining-literal/_expected.js b/test/form/samples/tree-shake-optional-chaining-literal/_expected.js
@@ -0,0 +1,6 @@
+// remains
+exist?.foo?.();
+
+if (exist?.z) {
+  console.log("remains");
+}
diff --git a/test/form/samples/tree-shake-optional-chaining-literal/main.js b/test/form/samples/tree-shake-optional-chaining-literal/main.js
@@ -0,0 +1,23 @@
+undefined?.foo();
+undefined?.foo?.bar?.();
+undefined?.();
+
+if (undefined?.foo) {
+  console.log("shaked");
+}
+
+if (undefined?.foo?.bar || false) {
+  console.log("shaked");
+}
+
+(undefined || null)?.foo();
+(undefined ?? null ?? undefined?.bar)?.foo();
+
+null?.bar();
+
+// remains
+exist?.foo?.();
+
+if (exist?.z) {
+  console.log("remains")
+}

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+module.exports = {`
	`2`	`+ description: 'tree-shake expressions optional chaining with literal values'`
	`3`	`+};`