QUiLoader, QAbstractFormBuilder: Introduce errorString().

Introduce errorString() to be able to obtain load errors
in Qt Designer. Remove automatic Qt 3 form conversion
from Qt Designer (since uic3 no longer exists) and move
all form load error checking logic including language
check into QAbstractFormBuilder.
Make language accessible in FormBuilderExtra in case
Jambi is revived.

Reviewed-by: hjk

src/uitools/quiloader.cpp

@@ -653,7 +653,7 @@ QUiLoader::~QUiLoader()
     Loads a form from the given \a device and creates a new widget with the
     given \a parentWidget to hold its contents.
 
-    \sa createWidget()
+    \sa createWidget(), errorString()
 */
 QWidget *QUiLoader::load(QIODevice *device, QWidget *parentWidget)
 {
@@ -936,6 +936,19 @@ bool QUiLoader::isTranslationEnabled() const
     return d->builder.trEnabled;
 }
 
+/*!
+    Returns a human-readable description of the last error occurred in load().
+
+    \since 5.0
+    \sa load()
+*/
+
+QString QUiLoader::errorString() const
+{
+    Q_D(const QUiLoader);
+    return d->builder.errorString();
+}
+
 QT_END_NAMESPACE
 
 #include "quiloader.moc"

src/uitools/quiloader.h

@@ -90,6 +90,8 @@ public:
     void setTranslationEnabled(bool enabled);
     bool isTranslationEnabled() const;
 
+    QString errorString() const;
+
 private:
     QScopedPointer<QUiLoaderPrivate> d_ptr;
     Q_DECLARE_PRIVATE(QUiLoader)

tools/uilib/abstractformbuilder.cpp

@@ -52,6 +52,7 @@
 #include <QtCore/QDir>
 #include <QtCore/QQueue>
 #include <QtCore/QHash>
+#include <QtCore/QPair>
 #include <QtCore/qdebug.h>
 #include <QtCore/QCoreApplication>
 
@@ -177,44 +178,97 @@ QAbstractFormBuilder::~QAbstractFormBuilder()
 {
 }
 
+// Return UI file version from attribute 'version="4.0"'
+static QPair<int, int> uiVersion(const QString &attr)
+{
+    const QStringList versions = attr.split(QLatin1Char('.'), QString::SkipEmptyParts);
+    if (versions.size() >= 2) {
+        bool okMajor, okMinor;
+        const int majorVersion = versions.at(0).toInt(&okMajor);
+        const int minorVersion = versions.at(1).toInt(&okMinor);
+        if (okMajor &&  okMinor)
+            return QPair<int, int>(majorVersion, minorVersion);
+    }
+    return QPair<int, int>(-1, -1);
+}
+
+static inline QString msgXmlError(const QXmlStreamReader &reader)
+{
+    return QCoreApplication::translate("QAbstractFormBuilder", "An error has occurred while reading the UI file at line %1, column %2: %3")
+                                       .arg(reader.lineNumber()).arg(reader.columnNumber()).arg(reader.errorString());
+}
+
+// Read and check the  version and the (optional) language attribute
+// of an <ui> element and leave reader positioned at <ui>.
+static bool inline readUiAttributes(QXmlStreamReader &reader, const QString &language, QString *errorMessage)
+{
+    const QString uiElement = QLatin1String("ui");
+    // Read up to first element
+    while (!reader.atEnd()) {
+        switch (reader.readNext()) {
+        case QXmlStreamReader::Invalid:
+            *errorMessage = msgXmlError(reader);
+            return false;
+        case QXmlStreamReader::StartElement:
+            if (reader.name().compare(uiElement, Qt::CaseInsensitive) == 0) {
+                const QString versionAttribute = QLatin1String("version");
+                const QString languageAttribute = QLatin1String("language");
+                const QXmlStreamAttributes attributes = reader.attributes();
+                if (attributes.hasAttribute(versionAttribute)) {
+                    const QString versionString = attributes.value(versionAttribute).toString();
+                    if (uiVersion(versionString).first < 4) {
+                        *errorMessage = QCoreApplication::translate("QAbstractFormBuilder", "This file was created using Designer from Qt-%1 and cannot be read.")
+                                .arg(versionString);
+                        return false;
+                    } // version error
+                }     // has version
+                if (attributes.hasAttribute(languageAttribute)) {
+                    // Check on optional language (Jambi)
+                    const QString formLanguage = attributes.value(languageAttribute).toString();
+                    if (!formLanguage.isEmpty() && formLanguage.compare(language, Qt::CaseInsensitive)) {
+                        *errorMessage = QCoreApplication::translate("QAbstractFormBuilder", "This file cannot be read because it was created using %1.").arg(formLanguage);
+                        return false;
+                    } // language error
+                }    // has language
+                return true;
+            }  // <ui> matched
+            break;
+        default:
+            break;
+        }
+    }
+    // No <ui> found.
+    *errorMessage = QCoreApplication::translate("QAbstractFormBuilder",  "Invalid UI file: The root element <ui> is missing.");
+    return false;
+}
+
 /*!
     \fn QWidget *QAbstractFormBuilder::load(QIODevice *device, QWidget *parent)
 
     Loads an XML representation of a widget from the given \a device,
     and constructs a new widget with the specified \a parent.
 
-    \sa save()
+    \sa save(), errorString()
 */
 QWidget *QAbstractFormBuilder::load(QIODevice *dev, QWidget *parentWidget)
 {
-    QXmlStreamReader reader;
-    reader.setDevice(dev);
+    QXmlStreamReader reader(dev);
+    d->m_errorString.clear();
+    if (!readUiAttributes(reader, d->m_language, &d->m_errorString)) {
+        uiLibWarning(d->m_errorString);
+        return false;
+    }
     DomUI ui;
-    bool initialized = false;
-
-    const QString uiElement = QLatin1String("ui");
-    while (!reader.atEnd()) {
-        if (reader.readNext() == QXmlStreamReader::StartElement) {
-            if (reader.name().compare(uiElement, Qt::CaseInsensitive) == 0) {
-                ui.read(reader);
-                initialized = true;
-            } else {
-                reader.raiseError(QCoreApplication::translate("QAbstractFormBuilder", "Unexpected element <%1>").arg(reader.name().toString()));
-            }
-        }
-    }
+    ui.read(reader);
     if (reader.hasError()) {
-        uiLibWarning(QCoreApplication::translate("QAbstractFormBuilder", "An error has occurred while reading the UI file at line %1, column %2: %3")
-                                .arg(reader.lineNumber()).arg(reader.columnNumber())
-                                .arg(reader.errorString()));
-        return 0;
-    }
-    if (!initialized) {
-        uiLibWarning(QCoreApplication::translate("QAbstractFormBuilder", "Invalid UI file: The root element <ui> is missing."));
+        d->m_errorString = msgXmlError(reader);
+        uiLibWarning(d->m_errorString);
         return 0;
     }
 
     QWidget *widget = create(&ui, parentWidget);
+    if (!widget && d->m_errorString.isEmpty())
+        d->m_errorString = QCoreApplication::translate("QAbstractFormBuilder", "Invalid UI file");
     return widget;
 }
 
@@ -3119,4 +3173,16 @@ bool QAbstractFormBuilder::isScriptingEnabled() const
 #endif
 }
 
+/*!
+    Returns a human-readable description of the last error occurred in load().
+
+    \since 5.0
+    \sa load()
+*/
+
+QString QAbstractFormBuilder::errorString() const
+{
+    return d->m_errorString;
+}
+
 QT_END_NAMESPACE

tools/uilib/abstractformbuilder.h

@@ -127,6 +127,8 @@ public:
     void setScriptingEnabled(bool enabled);
     bool isScriptingEnabled() const;
 
+    QString errorString() const;
+
 protected:
 //
 // load

tools/uilib/formbuilderextra.cpp

@@ -87,6 +87,7 @@ QFormBuilderExtra::CustomWidgetData::CustomWidgetData(const DomCustomWidget *dcw
 QFormBuilderExtra::QFormBuilderExtra() :
     m_defaultMargin(INT_MIN),
     m_defaultSpacing(INT_MIN),
+    m_language(QLatin1String("c++")),
     m_layoutWidget(false),
     m_resourceBuilder(0),
     m_textBuilder(0)

tools/uilib/formbuilderextra_p.h

@@ -180,6 +180,8 @@ public:
     int m_defaultMargin;
     int m_defaultSpacing;
     QDir m_workingDirectory;
+    QString m_errorString;
+    QString m_language;
 
 private:
     void clearResourceBuilder();