From b6a960c96cfc9acb12684ac44d956be90f127995 Mon Sep 17 00:00:00 2001
From: Jonathan Kew <jkew@mozilla.com>
Date: Sat, 24 Feb 2024 08:56:43 +0000
Subject: [PATCH] Bug 1880996 - Check for zero-length text in
 nsBidiPresUtils::ProcessSimpleRun. r=dholbert

In the example here, failing to check for an empty string was resulting
in lots of extra work to set up for drawing a shadow, etc., even though
nothing ends up being rendered. Just bail out early if there's no text.

Differential Revision: https://phabricator.services.mozilla.com/D202630
---
 layout/base/nsBidiPresUtils.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/layout/base/nsBidiPresUtils.cpp b/layout/base/nsBidiPresUtils.cpp
index ad085edbb12f..b1215972c243 100644
--- a/layout/base/nsBidiPresUtils.cpp
+++ b/layout/base/nsBidiPresUtils.cpp
@@ -2363,6 +2363,12 @@ void nsBidiPresUtils::ProcessSimpleRun(const char16_t* aText, size_t aLength,
                                        nsBidiPositionResolve* aPosResolve,
                                        int32_t aPosResolveCount,
                                        nscoord* aWidth) {
+  if (!aLength) {
+    if (aWidth) {
+      *aWidth = 0;
+    }
+    return;
+  }
   // Get bidi class from the first (or only) character.
   uint32_t ch = aText[0];
   if (aLength > 1 && NS_IS_HIGH_SURROGATE(ch) &&