From c08766abf2267f4eeda159c5688309d22d319722 Mon Sep 17 00:00:00 2001
From: Magdalena Stojek <magdalena.stojek@qt.io>
Date: Thu, 8 May 2025 12:36:56 +0200
Subject: [PATCH] QXmlStreamWriter: Refactor writeEscaped() to use switch

The character escaping logic in writeEscaped() previously relied on a
long if/else cascade to handle escaping and error detection.
This change replaces the cascade with a switch statement, improving the
control flow. The loop now exits when a non-null replacement is set.
To support this, cases that previously raised an error without assigning
a replacement now assign an empty, non-null string to trigger the break.

Fixes: QTBUG-136681
Change-Id: I4a584738bcda741f881712547af12abd35e2fd0a
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
---
 src/corelib/serialization/qxmlstream.cpp | 56 ++++++++++++++----------
 1 file changed, 33 insertions(+), 23 deletions(-)

diff --git a/src/corelib/serialization/qxmlstream.cpp b/src/corelib/serialization/qxmlstream.cpp
index 99a99273ade..9949da2d3af 100644
--- a/src/corelib/serialization/qxmlstream.cpp
+++ b/src/corelib/serialization/qxmlstream.cpp
@@ -3208,43 +3208,53 @@ void QXmlStreamWriterPrivate::writeEscaped(QAnyStringView s, bool escapeWhitespa
             while (it != end) {
                 auto next_it = it;
                 auto [uc, encodingError] = decoder(next_it, end);
-                if (uc == u'<') {
+                switch (uc) {
+                case u'<':
                     replacement = "&lt;"_L1;
                     break;
-                } else if (uc == u'>') {
+                case u'>':
                     replacement = "&gt;"_L1;
                     break;
-                } else if (uc == u'&') {
+                case u'&':
                     replacement = "&amp;"_L1;
                     break;
-                } else if (uc == u'\"') {
+                case u'\"':
                     replacement = "&quot;"_L1;
                     break;
-                } else if (uc == u'\t') {
-                    if (escapeWhitespace) {
+                case u'\t':
+                    if (escapeWhitespace)
                         replacement = "&#9;"_L1;
-                        break;
-                    }
-                } else if (uc == u'\n') {
-                    if (escapeWhitespace) {
-                        replacement = "&#10;"_L1;
-                        break;
-                    }
-                } else if (uc == u'\v' || uc == u'\f') {
-                    raiseError(QXmlStreamWriter::Error::InvalidCharacter);
                     break;
-                } else if (uc == u'\r') {
-                    if (escapeWhitespace) {
+                case u'\n':
+                    if (escapeWhitespace)
+                        replacement = "&#10;"_L1;
+                    break;
+                case u'\r':
+                    if (escapeWhitespace)
                         replacement = "&#13;"_L1;
+                    break;
+                case u'\v':
+                case u'\f':
+                    raiseError(QXmlStreamWriter::Error::InvalidCharacter);
+                    replacement = ""_L1;
+                    Q_ASSERT(!replacement.isNull());
+                    break;
+                default:
+                    if (uc > 0x1F)
                         break;
-                    }
-                } else if (uc <= u'\x1F' || uc == u'\uFFFE' || uc == u'\uFFFF') {
-                    if (encodingError)
-                        raiseError(QXmlStreamWriter::Error::EncodingError);
-                    else
-                        raiseError(QXmlStreamWriter::Error::InvalidCharacter);
+                    // ASCII control characters
+                    Q_FALLTHROUGH();
+                case 0xFFFE:
+                case 0xFFFF:
+                    raiseError(encodingError
+                                       ? QXmlStreamWriter::Error::EncodingError
+                                       : QXmlStreamWriter::Error::InvalidCharacter);
+                    replacement = ""_L1;
+                    Q_ASSERT(!replacement.isNull());
                     break;
                 }
+                if (!replacement.isNull())
+                    break;
                 it = next_it;
             }