[libcalamares] Deal with deprecations in XML QDomDocument

Introduce some Calamares helpers in the compat/ headers
space to help Xml-wrangling (i18n support tools, GeoIP)
avoid compiler warnings about deprecated API.

It's cleaner this way anyway, with a nice value returned
from setting a document's contents, rather than a bunch
of pointer arguments.

lang/CMakeLists.txt

@@ -19,6 +19,9 @@ find_package(${qtname} COMPONENTS Xml)
 if(TARGET ${qtname}::Xml)
     add_executable(txload txload.cpp)
     target_link_libraries(txload ${qtname}::Xml)
+    # Special-case, needs compatibility-header for XML-handling,
+    # but doesn't want all of libcalamares.
+    target_include_directories(txload PRIVATE ${CMAKE_SOURCE_DIR}/src/libcalamares)
 endif()
 
 install_calamares_gettext_translations(python

lang/txload.cpp

@@ -18,6 +18,8 @@
  * differences in translation are.
  */
 
+#include "compat/Xml.h"
+
 #include <QCoreApplication>
 #include <QDebug>
 #include <QFile>
@@ -39,8 +41,6 @@ bool
 load_file( const char* filename, QDomDocument& doc )
 {
     QFile file( filename );
-    QString err;
-    int err_line, err_column;
     if ( !file.open( QIODevice::ReadOnly ) )
     {
         qDebug() << "Could not open" << filename;
@@ -49,9 +49,10 @@ load_file( const char* filename, QDomDocument& doc )
     QByteArray ba( file.read( 1024 * 1024 ) );
     qDebug() << "Read" << ba.length() << "bytes from" << filename;
 
-    if ( !doc.setContent( ba, &err, &err_line, &err_column ) )
+    auto p = Calamares::setXmlContent( doc, ba );
+    if ( !p.errorMessage.isEmpty() )
     {
-        qDebug() << "Could not read" << filename << ':' << err_line << ':' << err_column << ' ' << err;
+        qDebug() << "Could not read" << filename << ':' << p.errorLine << ':' << p.errorColumn << ' ' << p.errorMessage;
         file.close();
         return false;
     }
@@ -177,10 +178,12 @@ merge_into( QDomDocument& originDocument, QDomDocument& alternateDocument )
         {
             QDomElement e = n.toElement();
             if ( e.tagName() == "context" )
+            {
                 if ( !merge_into( originDocument, e ) )
                 {
                     return false;
                 }
+            }
         }
         n = n.nextSibling();
     }

src/libcalamares/compat/Xml.h

@@ -0,0 +1,42 @@
+/* === This file is part of Calamares - <https://calamares.io> ===
+ *
+ *   SPDX-FileCopyrightText: 2024 Adriaan de Groot <groot@kde.org>
+ *   SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ *   Calamares is Free Software: see the License-Identifier above.
+ *
+ *
+ */
+#ifndef CALAMARES_COMPAT_XML_H
+#define CALAMARES_COMPAT_XML_H
+
+#include <QDomDocument>
+
+namespace Calamares
+{
+#if QT_VERSION < QT_VERSION_CHECK( 6, 6, 0 )
+struct ParseResult
+{
+    QString errorMessage;
+    int errorLine = -1;
+    int errorColumn = -1;
+}
+
+[[nodiscard]] inline ParseResult
+setXmlContent( QDomDocument& doc, const QByteArray& ba )
+{
+    ParseResult p;
+    const bool r = doc.setContent( ba, &p.errorMessage, &p.errorLine, &p.errorColumn );
+    return r ? ParseResult {} : p;
+}
+#else
+[[nodiscard]] inline QDomDocument::ParseResult
+setXmlContent( QDomDocument& doc, const QByteArray& ba )
+{
+    return doc.setContent( ba );
+}
+#endif
+
+}  // namespace Calamares
+
+#endif

src/libcalamares/geoip/GeoIPXML.cpp

@@ -9,6 +9,7 @@
 
 #include "GeoIPXML.h"
 
+#include "compat/Xml.h"
 #include "utils/Logger.h"
 
 #include <QtXml/QDomDocument>
@@ -28,11 +29,9 @@ getElementTexts( const QByteArray& data, const QString& tag )
 {
     QStringList elements;
 
-    QString domError;
-    int errorLine, errorColumn;
-
     QDomDocument doc;
-    if ( doc.setContent( data, false, &domError, &errorLine, &errorColumn ) )
+    const auto p = Calamares::setXmlContent( doc, data );
+    if ( p.errorMessage.isEmpty() )
     {
         const auto tzElements = doc.elementsByTagName( tag );
         cDebug() << "GeoIP found" << tzElements.length() << "elements";
@@ -48,7 +47,8 @@ getElementTexts( const QByteArray& data, const QString& tag )
     }
     else
     {
-        cWarning() << "GeoIP XML data error:" << domError << "(line" << errorLine << errorColumn << ')';
+        cWarning() << "GeoIP XML data error:" << p.errorMessage << "(line" << p.errorLine << ':' << p.errorColumn
+                   << ')';
     }
 
     if ( elements.count() < 1 )