Make return expressions of pure functions pure

docs/999-big-list-of-options.md

@@ -1712,12 +1712,14 @@ Allows to manually define a list of function names that should always be conside
 
 This can not only help with dead code removal, but can also improve JavaScript chunk generation especially when using [`experimentalMinChunkSize`](guide/en/#experimentalminchunksize).
 
+Besides any functions matching that name, any properties on a pure function and any functions returned from a pure functions will also be considered pure.
+
 ```js
 // rollup.config.js
 export default {
   treeshake: {
     preset: 'smallest',
-    manualPureFunctions: ['styled.div', 'local']
+    manualPureFunctions: ['styled', 'local']
   }
   // ...
 };
@@ -1731,8 +1733,8 @@ styled.div`
   color: blue;
 `; // removed
 styled?.div(); // removed
-styled(); // not removed
-styled.h1(); // not removed
+styled()(); // removed
+styled().div(); // removed
 ```
 
 **treeshake.moduleSideEffects**<br> Type: `boolean | "no-external" | string[] | (id: string, external: boolean) => boolean`<br> CLI: `--treeshake.moduleSideEffects`/`--no-treeshake.moduleSideEffects`/`--treeshake.moduleSideEffects no-external`<br> Default: `true`

src/ast/nodes/Identifier.ts

@@ -133,12 +133,14 @@ export default class Identifier extends NodeBase implements PatternNode {
 		recursionTracker: PathTracker,
 		origin: DeoptimizableEntity
 	): [expression: ExpressionEntity, isPure: boolean] {
-		return this.getVariableRespectingTDZ()!.getReturnExpressionWhenCalledAtPath(
-			path,
-			interaction,
-			recursionTracker,
-			origin
-		);
+		const [expression, isPure] =
+			this.getVariableRespectingTDZ()!.getReturnExpressionWhenCalledAtPath(
+				path,
+				interaction,
+				recursionTracker,
+				origin
+			);
+		return [expression, isPure || this.isPureFunction(path)];
 	}
 
 	hasEffects(context: HasEffectsContext): boolean {
@@ -149,6 +151,7 @@ export default class Identifier extends NodeBase implements PatternNode {
 		return (
 			(this.context.options.treeshake as NormalizedTreeshakingOptions).unknownGlobalSideEffects &&
 			this.variable instanceof GlobalVariable &&
+			!this.isPureFunction(EMPTY_PATH) &&
 			this.variable.hasEffectsOnInteractionAtPath(
 				EMPTY_PATH,
 				NODE_INTERACTION_UNKNOWN_ACCESS,
@@ -301,7 +304,7 @@ export default class Identifier extends NodeBase implements PatternNode {
 				return false;
 			}
 		}
-		return currentPureFunction?.[PureFunctionKey];
+		return currentPureFunction?.[PureFunctionKey] as boolean;
 	}
 }
 

src/ast/nodes/shared/CallExpressionBase.ts

@@ -53,7 +53,6 @@ export default abstract class CallExpressionBase extends NodeBase implements Deo
 		recursionTracker: PathTracker
 	): void {
 		const [returnExpression, isPure] = this.getReturnExpression(recursionTracker);
-		// TODO Lukas test
 		if (isPure) return;
 		if (returnExpression === UNKNOWN_EXPRESSION) {
 			interaction.thisArg.deoptimizePath(UNKNOWN_PATH);
@@ -96,21 +95,22 @@ export default abstract class CallExpressionBase extends NodeBase implements Deo
 		recursionTracker: PathTracker,
 		origin: DeoptimizableEntity
 	): [expression: ExpressionEntity, isPure: boolean] {
-		const [returnExpression] = this.getReturnExpression(recursionTracker);
-		if (returnExpression === UNKNOWN_EXPRESSION) {
-			return UNKNOWN_RETURN_EXPRESSION;
+		const returnExpression = this.getReturnExpression(recursionTracker);
+		if (returnExpression[0] === UNKNOWN_EXPRESSION) {
+			return returnExpression;
 		}
 		return recursionTracker.withTrackedEntityAtPath(
 			path,
 			returnExpression,
 			() => {
 				this.deoptimizableDependentExpressions.push(origin);
-				return returnExpression.getReturnExpressionWhenCalledAtPath(
+				const [expression, isPure] = returnExpression[0].getReturnExpressionWhenCalledAtPath(
 					path,
 					interaction,
 					recursionTracker,
 					origin
 				);
+				return [expression, isPure || returnExpression[1]];
 			},
 			UNKNOWN_RETURN_EXPRESSION
 		);
@@ -141,7 +141,11 @@ export default abstract class CallExpressionBase extends NodeBase implements Deo
 		) {
 			return false;
 		}
-		return this.getReturnExpression()[0].hasEffectsOnInteractionAtPath(path, interaction, context);
+		const [returnExpression, isPure] = this.getReturnExpression();
+		return (
+			(type === INTERACTION_ASSIGNED || !isPure) &&
+			returnExpression.hasEffectsOnInteractionAtPath(path, interaction, context)
+		);
 	}
 
 	protected abstract getReturnExpression(

test/form/samples/manual-pure-functions/_config.js

@@ -1,9 +1,6 @@
 module.exports = {
-	solo: true,
 	description: 'allows to manually declare functions as pure by name',
 	options: {
 		treeshake: { manualPureFunctions: ['foo', 'bar.a'] }
 	}
 };
-// TODO Lukas also tagged templates
-// TODO Lukas also check "this" or arguments are not deoptimized

test/form/samples/manual-pure-functions/_expected.js

@@ -1,11 +1,15 @@
-const lib = () => console.log();
-lib.a = () => {
-	console.log();
-	const result = () => console.log();
-	result.c = console.log;
-	return result;
+const lib = {
+	a: () => {
+		console.log();
+		return () => {
+			console.log();
+			return () => {
+				console.log();
+				return console.log;
+			}
+		}
+	}
 };
-lib.a.b = () => console.log();
 
 lib(); // not removed
 lib.b(); // not removed

test/form/samples/manual-pure-functions/main.js

@@ -1,11 +1,27 @@
 import { lib as bar } from './other';
-const foo = console.log;
 
+foo; // removed
 foo(); // removed
-bar.a(); // removed
-bar?.a(); // removed
+foo.a; // removed
+foo.a(); // removed
+foo.a()(); // removed
+foo.a().a; // removed
+foo.a().a(); // removed
+foo.a().a()(); // removed
+foo.a().a().a; // removed
+foo.a().a().a(); // removed
 
 bar(); // not removed
 bar.b(); // not removed
 
-bar.a.b(); // removed
+bar.a(); // removed
+bar?.a(); // removed
+bar.a.a; // removed
+bar.a.a(); // removed
+bar.a()(); //removed
+bar.a().a; //removed
+bar.a().a(); //removed
+bar.a()()(); //removed
+bar.a()().a; //removed
+bar.a()().a(); //removed
+

test/form/samples/manual-pure-functions/other.js

@@ -1,8 +1,12 @@
-export const lib = () => console.log();
-lib.a = () => {
-	console.log();
-	const result = () => console.log();
-	result.c = console.log;
-	return result;
+export const lib = {
+	a: () => {
+		console.log();
+		return () => {
+			console.log();
+			return () => {
+				console.log();
+				return console.log;
+			}
+		}
+	}
 };
-lib.a.b = () => console.log();