implement CSS pruning for array/object expressions

Author: dummdidumm

packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js

@@ -731,7 +731,7 @@ function attribute_matches(node, name, expected_value, operator, case_insensitiv
 		/** @type {string[]} */
 		let prev_values = [];
 		for (const chunk of chunks) {
-			const current_possible_values = get_possible_values(chunk);
+			const current_possible_values = get_possible_values(chunk, name === 'class');
 
 			// impossible to find out all combinations
 			if (!current_possible_values) return true;

packages/svelte/src/compiler/phases/2-analyze/css/utils.js

@@ -4,30 +4,54 @@ const UNKNOWN = {};
 
 /**
  * @param {Node} node
+ * @param {boolean} is_class
  * @param {Set<any>} set
  */
-function gather_possible_values(node, set) {
+function gather_possible_values(node, is_class, set) {
 	if (node.type === 'Literal') {
 		set.add(String(node.value));
 	} else if (node.type === 'ConditionalExpression') {
-		gather_possible_values(node.consequent, set);
-		gather_possible_values(node.alternate, set);
+		gather_possible_values(node.consequent, is_class, set);
+		gather_possible_values(node.alternate, is_class, set);
+	} else if (is_class && node.type === 'ArrayExpression') {
+		for (const entry of node.elements) {
+			if (entry) {
+				gather_possible_values(entry, is_class, set);
+			} else {
+				set.add(UNKNOWN);
+			}
+		}
+	} else if (is_class && node.type === 'ObjectExpression') {
+		for (const property of node.properties) {
+			if (
+				property.type === 'Property' &&
+				!property.computed &&
+				(property.key.type === 'Identifier' || property.key.type === 'Literal')
+			) {
+				set.add(
+					property.key.type === 'Identifier' ? property.key.name : String(property.key.value)
+				);
+			} else {
+				set.add(UNKNOWN);
+			}
+		}
 	} else {
 		set.add(UNKNOWN);
 	}
 }
 
 /**
  * @param {AST.Text | AST.ExpressionTag} chunk
+ * @param {boolean} is_class
  * @returns {Set<string> | null}
  */
-export function get_possible_values(chunk) {
+export function get_possible_values(chunk, is_class) {
 	const values = new Set();
 
 	if (chunk.type === 'Text') {
 		values.add(chunk.data);
 	} else {
-		gather_possible_values(chunk.expression, values);
+		gather_possible_values(chunk.expression, is_class, values);
 	}
 
 	if (values.has(UNKNOWN)) return null;

packages/svelte/tests/css/samples/clsx-can-prune/_config.js

@@ -0,0 +1,20 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector ".unused"\nhttps://svelte.dev/e/css_unused_selector',
+			start: {
+				line: 15,
+				column: 1,
+				character: 325
+			},
+			end: {
+				line: 15,
+				column: 8,
+				character: 332
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/clsx-can-prune/expected.css

@@ -0,0 +1,9 @@
+
+	.used1.svelte-xyz { color: green; }
+	.used2.svelte-xyz { color: green; }
+	.used3.svelte-xyz { color: green; }
+	.used4.svelte-xyz { color: green; }
+	.used5.svelte-xyz { color: green; }
+	.used6.svelte-xyz { color: green; }
+
+	/* (unused) .unused { color: red; }*/

packages/svelte/tests/css/samples/clsx-can-prune/input.svelte

@@ -0,0 +1,16 @@
+<p class={['used1']}></p>
+<p class={[{ used2: true }]}></p>
+<p class={{ used3: true }}></p>
+<p class={{ 'used4 used5': true }}></p>
+<p class={{ used6 }}></p>
+
+<style>
+	.used1 { color: green; }
+	.used2 { color: green; }
+	.used3 { color: green; }
+	.used4 { color: green; }
+	.used5 { color: green; }
+	.used6 { color: green; }
+
+	.unused { color: red; }
+</style>

packages/svelte/tests/css/samples/clsx-cannot-prune-1/expected.css

@@ -0,0 +1,2 @@
+
+	.x.svelte-xyz { color: green; }

packages/svelte/tests/css/samples/clsx-cannot-prune-1/input.svelte

@@ -0,0 +1,5 @@
+<h1 class={[foo]}>hello world</h1>
+
+<style>
+	.x { color: green; }
+</style>

packages/svelte/tests/css/samples/clsx-cannot-prune-2/expected.css

@@ -0,0 +1,2 @@
+
+	.x.svelte-xyz { color: green; }

packages/svelte/tests/css/samples/clsx-cannot-prune-2/input.svelte

@@ -0,0 +1,5 @@
+<h1 class={{ foo: true, ...rest }}>hello world</h1>
+
+<style>
+	.x { color: green; }
+</style>

packages/svelte/tests/css/samples/clsx-cannot-prune-3/expected.css

@@ -0,0 +1,2 @@
+
+	.x.svelte-xyz { color: green; }