From 31f93c3e07d7dedcff9cce075c2290a41b79dd98 Mon Sep 17 00:00:00 2001
From: Nolan Lawson <nlawson@salesforce.com>
Date: Thu, 29 Feb 2024 09:30:56 -0800
Subject: [PATCH] refactor: move fragment cache-busting to Karma-only (#4025)

Co-authored-by: Will Harney <62956339+wjhsf@users.noreply.github.com>
---
 .../engine-core/src/framework/template.ts     | 30 +++++++++++++++----
 .../legacy-scope-tokens/index.spec.js         |  3 ++
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/packages/@lwc/engine-core/src/framework/template.ts b/packages/@lwc/engine-core/src/framework/template.ts
index 6e0bf34b29..2cb85f6815 100644
--- a/packages/@lwc/engine-core/src/framework/template.ts
+++ b/packages/@lwc/engine-core/src/framework/template.ts
@@ -13,6 +13,8 @@ import {
     isTrue,
     isUndefined,
     KEY__SCOPED_CSS,
+    keys,
+    noop,
     toString,
 } from '@lwc/shared';
 
@@ -111,7 +113,26 @@ function validateLightDomTemplate(template: Template, vm: VM) {
 const enum FragmentCache {
     HAS_SCOPED_STYLE = 1 << 0,
     SHADOW_MODE_SYNTHETIC = 1 << 1,
-    HAS_LEGACY_SCOPE_TOKEN = 1 << 2,
+}
+
+// This should be a no-op outside of LWC's Karma tests, where it's not needed
+let registerFragmentCache: (fragmentCache: any) => void = noop;
+
+// Only used in LWC's Karma tests
+if (process.env.NODE_ENV === 'test-karma-lwc') {
+    // Keep track of fragmentCaches, so we can clear them in LWC's Karma tests
+    const fragmentCaches: any[] = [];
+    registerFragmentCache = (fragmentCache: any) => {
+        fragmentCaches.push(fragmentCache);
+    };
+
+    (window as any).__lwcResetFragmentCaches = () => {
+        for (const fragmentCache of fragmentCaches) {
+            for (const key of keys(fragmentCache)) {
+                delete fragmentCache[key];
+            }
+        }
+    };
 }
 
 function buildParseFragmentFn(
@@ -120,6 +141,8 @@ function buildParseFragmentFn(
     return (strings: string[], ...keys: number[]) => {
         const cache = create(null);
 
+        registerFragmentCache(cache);
+
         return function (): Element {
             const {
                 context: { hasScopedStyles, stylesheetToken, legacyStylesheetToken },
@@ -138,11 +161,6 @@ function buildParseFragmentFn(
             if (hasStyleToken && isSyntheticShadow) {
                 cacheKey |= FragmentCache.SHADOW_MODE_SYNTHETIC;
             }
-            if (hasLegacyToken) {
-                // This isn't strictly required for prod, but it's required for our karma tests
-                // since the lwcRuntimeFlag may change over time
-                cacheKey |= FragmentCache.HAS_LEGACY_SCOPE_TOKEN;
-            }
 
             if (!isUndefined(cache[cacheKey])) {
                 return cache[cacheKey];
diff --git a/packages/@lwc/integration-karma/test/rendering/legacy-scope-tokens/index.spec.js b/packages/@lwc/integration-karma/test/rendering/legacy-scope-tokens/index.spec.js
index 5b67ac70d3..56478d91de 100644
--- a/packages/@lwc/integration-karma/test/rendering/legacy-scope-tokens/index.spec.js
+++ b/packages/@lwc/integration-karma/test/rendering/legacy-scope-tokens/index.spec.js
@@ -11,6 +11,9 @@ describe('legacy scope tokens', () => {
 
             afterEach(() => {
                 setFeatureFlagForTest('ENABLE_LEGACY_SCOPE_TOKENS', false);
+                // We keep a cache of parsed static fragments; these need to be reset
+                // since they can vary based on whether we use the legacy scope token or not.
+                window.__lwcResetFragmentCaches();
             });
 
             function getAttributes(elm) {