From 4a90464619146ba074c8dc9de12615ed113221cd Mon Sep 17 00:00:00 2001
From: Bianca Nenciu <nbianca@users.noreply.github.com>
Date: Tue, 7 Jul 2020 18:51:19 +0300
Subject: [PATCH] FIX: Do not highlight large code blocks (#10125)

---
 .../discourse/app/lib/highlight-syntax.js     |  5 +++++
 .../components/highlighted-code-test.js       | 21 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/app/assets/javascripts/discourse/app/lib/highlight-syntax.js b/app/assets/javascripts/discourse/app/lib/highlight-syntax.js
index 48543dcd1df..404e73cadcc 100644
--- a/app/assets/javascripts/discourse/app/lib/highlight-syntax.js
+++ b/app/assets/javascripts/discourse/app/lib/highlight-syntax.js
@@ -14,6 +14,11 @@ export default function highlightSyntax($elem) {
   }
 
   $(selector, $elem).each(function(i, e) {
+    // Large code blocks can cause crashes or slowdowns
+    if (e.innerHTML.length > 30000) {
+      return;
+    }
+
     $(e).removeClass("lang-auto");
     loadScript(path).then(() => {
       customHighlightJSLanguages();
diff --git a/test/javascripts/components/highlighted-code-test.js b/test/javascripts/components/highlighted-code-test.js
index 38b0f2d6316..27cfe5696d3 100644
--- a/test/javascripts/components/highlighted-code-test.js
+++ b/test/javascripts/components/highlighted-code-test.js
@@ -1,5 +1,7 @@
 import componentTest from "helpers/component-test";
 
+const LONG_CODE_BLOCK = "puts a\n".repeat(15000);
+
 moduleForComponent("highlighted-code", { integration: true });
 
 componentTest("highlighting code", {
@@ -20,3 +22,22 @@ componentTest("highlighting code", {
     );
   }
 });
+
+componentTest("large code blocks are not highlighted", {
+  template: "{{highlighted-code lang='ruby' code=code}}",
+
+  beforeEach() {
+    Discourse.HighlightJSPath =
+      "assets/highlightjs/highlight-test-bundle.min.js";
+    this.set("code", LONG_CODE_BLOCK);
+  },
+
+  async test(assert) {
+    assert.equal(
+      find("code")
+        .text()
+        .trim(),
+      LONG_CODE_BLOCK.trim()
+    );
+  }
+});