From 89024cea9b5ff45e1ba8af84a959d51d7bca9902 Mon Sep 17 00:00:00 2001
From: Floriel <Ffloriel@users.noreply.github.com>
Date: Tue, 12 Nov 2024 16:11:23 +0100
Subject: [PATCH] fix: fix issue where pseudo classes like :where, :not, :is
 were always removed at root level

#1282 #978
---
 .../purgecss/__tests__/pseudo-class.test.ts   | 38 +++++++++++++------
 .../test_examples/pseudo-class/is.css         |  8 ++++
 packages/purgecss/src/index.ts                | 33 +++++++++++++++-
 3 files changed, 65 insertions(+), 14 deletions(-)

diff --git a/packages/purgecss/__tests__/pseudo-class.test.ts b/packages/purgecss/__tests__/pseudo-class.test.ts
index 87da3584..6a55e230 100644
--- a/packages/purgecss/__tests__/pseudo-class.test.ts
+++ b/packages/purgecss/__tests__/pseudo-class.test.ts
@@ -1,5 +1,5 @@
 import { PurgeCSS } from "./../src/index";
-import { ROOT_TEST_EXAMPLES } from "./utils";
+import { findInCSS, ROOT_TEST_EXAMPLES } from "./utils";
 
 describe(":not pseudo class", () => {
   let purgedCSS: string;
@@ -116,13 +116,18 @@ describe(":where pseudo class", () => {
 
   it("removes unused selectors", () => {
     expect(purgedCSS.includes(".unused")).toBe(false);
-    expect(purgedCSS.includes(".root :where(.a) .c {")).toBe(true);
-    expect(purgedCSS.includes(".root:where(.a) .c {")).toBe(true);
-    expect(
-      purgedCSS.includes(
+  });
+
+  it("keeps used selectors", () => {
+    findInCSS(
+      expect,
+      [
+        ".root :where(.a) .c {",
+        ".root:where(.a) .c {",
         ".\\[\\&\\:where\\(\\.a\\)\\]\\:text-black:where(.a) {",
-      ),
-    ).toBe(true);
+      ],
+      purgedCSS,
+    );
   });
 });
 
@@ -141,10 +146,19 @@ describe(":is pseudo class", () => {
 
   it("removes unused selectors", () => {
     expect(purgedCSS.includes(".unused")).toBe(false);
-    expect(purgedCSS.includes(".root :is(.a) .c {")).toBe(true);
-    expect(purgedCSS.includes(".root:is(.a) .c {")).toBe(true);
-    expect(
-      purgedCSS.includes(".\\[\\&\\:is\\(\\.a\\)\\]\\:text-black:is(.a) {"),
-    ).toBe(true);
+    expect(purgedCSS.includes(":is(.unused)")).toBe(false);
+  });
+
+  it("keeps used selectors", () => {
+    findInCSS(
+      expect,
+      [
+        ".root :is(.a) .c {",
+        ".root:is(.a) .c {",
+        ".\\[\\&\\:is\\(\\.a\\)\\]\\:text-black:is(.a) {",
+        ":is(.b)",
+      ],
+      purgedCSS,
+    );
   });
 });
diff --git a/packages/purgecss/__tests__/test_examples/pseudo-class/is.css b/packages/purgecss/__tests__/test_examples/pseudo-class/is.css
index 31b86954..fc612af6 100644
--- a/packages/purgecss/__tests__/test_examples/pseudo-class/is.css
+++ b/packages/purgecss/__tests__/test_examples/pseudo-class/is.css
@@ -25,4 +25,12 @@
 
 .\[\&\:is\(\.a\)\]\:text-black:is(.a) {
   color: black;
+}
+
+:is(.b) {
+  color: black;
+}
+
+:is(.unused) {
+  color: chartreuse;
 }
\ No newline at end of file
diff --git a/packages/purgecss/src/index.ts b/packages/purgecss/src/index.ts
index dcd8a0fe..0c8e02c5 100644
--- a/packages/purgecss/src/index.ts
+++ b/packages/purgecss/src/index.ts
@@ -303,6 +303,33 @@ function isInPseudoClassWhereOrIs(selector: selectorParser.Node): boolean {
   );
 }
 
+/**
+ * Returns true if the selector is a pseudo class at the root level
+ * Pseudo classes checked: :where, :is, :has, :not
+ * @param selector - selector
+ */
+function isPseudoClassAtRootLevel(selector: selectorParser.Node): boolean {
+  let result = false;
+  if (
+    selector.type === "selector" &&
+    selector.parent?.type === "root" &&
+    selector.nodes.length === 1
+  ) {
+    selector.walk((node) => {
+      if (
+        node.type === "pseudo" &&
+        (node.value === ":where" ||
+          node.value === ":is" ||
+          node.value === ":has" ||
+          node.value === ":not")
+      ) {
+        result = true;
+      }
+    });
+  }
+  return result;
+}
+
 function isPostCSSAtRule(node?: postcss.Node): node is postcss.AtRule {
   return node?.type === "atrule";
 }
@@ -531,7 +558,6 @@ class PurgeCSS {
     }
 
     const selectorsRemovedFromRule: string[] = [];
-
     // selector transformer, walk over the list of the parsed selectors twice.
     // First pass will remove the unused selectors. It goes through
     // pseudo-classes like :where() and :is() and remove the unused
@@ -543,7 +569,6 @@ class PurgeCSS {
         if (selector.type !== "selector") {
           return;
         }
-
         const keepSelector = this.shouldKeepSelector(selector, selectors);
 
         if (!keepSelector) {
@@ -864,6 +889,10 @@ class PurgeCSS {
       return true;
     }
 
+    if (isPseudoClassAtRootLevel(selector)) {
+      return true;
+    }
+
     // if there is any greedy safelist pattern, run all the selector parts through them
     // if there is any match, return true
     if (this.options.safelist.greedy.length > 0) {