QXmlStreamWriter: Ensure correct newline handling with auto-formatting

Previously, QXmlStreamWriter would incorrectly insert a newline before
the first token when writeStartDocument() was not used, while
auto-formatting was enabled.
This fix ensures that the first token is written inline without an extra
leading newline, while preserving expected formatting for subsequent
tokens.

To achieve this, two new flags have been introduced:
- didWriteStartDocument: Tracks whether writeStartDocument() was called.
- didWriteAnyToken: Ensures that at least one token has been written
before allowing newlines.

Fixes: QTBUG-28721
Pick-to: 6.9 6.8
Change-Id: I8be7e8fc6ac0e63304359d24c6c8372e5ba42bb4
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/serialization/qxmlstream.cpp

@@ -2913,6 +2913,8 @@ public:
     uint hasIoError :1;
     uint hasEncodingError :1;
     uint autoFormatting :1;
+    uint didWriteStartDocument :1;
+    uint didWriteAnyToken :1;
     std::string autoFormattingIndent;
     NamespaceDeclaration emptyNamespace;
     qsizetype lastNamespaceDeclaration;
@@ -2946,6 +2948,8 @@ QXmlStreamWriterPrivate::QXmlStreamWriterPrivate(QXmlStreamWriter *q)
     lastNamespaceDeclaration = 1;
     autoFormatting = false;
     namespacePrefixCount = 0;
+    didWriteStartDocument = false;
+    didWriteAnyToken = false;
 }
 
 void QXmlStreamWriterPrivate::write(QAnyStringView s)
@@ -3065,6 +3069,7 @@ void QXmlStreamWriterPrivate::writeNamespaceDeclaration(const NamespaceDeclarati
         write(namespaceDeclaration.namespaceUri);
         write("\"");
     }
+    didWriteAnyToken = true;
 }
 
 bool QXmlStreamWriterPrivate::finishStartElement(bool contents)
@@ -3084,6 +3089,7 @@ bool QXmlStreamWriterPrivate::finishStartElement(bool contents)
     }
     inStartElement = inEmptyElement = false;
     lastNamespaceDeclaration = namespaceDeclarations.size();
+    didWriteAnyToken = true;
     return hadSomethingWritten;
 }
 
@@ -3149,7 +3155,8 @@ QXmlStreamPrivateTagStack::NamespaceDeclaration &QXmlStreamWriterPrivate::findNa
 
 void QXmlStreamWriterPrivate::indent(int level)
 {
-    write("\n");
+    if (didWriteStartDocument || didWriteAnyToken)
+        write("\n");
     for (int i = 0; i < level; ++i)
         write(autoFormattingIndent);
 }
@@ -3375,6 +3382,7 @@ void QXmlStreamWriter::writeAttribute(QAnyStringView qualifiedName, QAnyStringVi
     d->write("=\"");
     d->writeEscaped(value, true);
     d->write("\"");
+    d->didWriteAnyToken = true;
 }
 
 /*!  Writes an attribute with \a name and \a value, prefixed for
@@ -3403,6 +3411,7 @@ void QXmlStreamWriter::writeAttribute(QAnyStringView namespaceUri, QAnyStringVie
     d->write("=\"");
     d->writeEscaped(value, true);
     d->write("\"");
+    d->didWriteAnyToken = true;
 }
 
 /*!
@@ -3610,7 +3619,8 @@ void QXmlStreamWriter::writeEndDocument()
     Q_D(QXmlStreamWriter);
     while (d->tagStack.size())
         writeEndElement();
-    d->write("\n");
+    if (d->didWriteStartDocument || d->didWriteAnyToken)
+        d->write("\n");
 }
 
 /*!
@@ -3621,6 +3631,7 @@ void QXmlStreamWriter::writeEndDocument()
 void QXmlStreamWriter::writeEndElement()
 {
     Q_D(QXmlStreamWriter);
+    Q_ASSERT(d->didWriteAnyToken);
     if (d->tagStack.isEmpty())
         return;
 
@@ -3744,6 +3755,7 @@ void QXmlStreamWriter::writeProcessingInstruction(QAnyStringView target, QAnyStr
         d->write(data);
     }
     d->write("?>");
+    d->didWriteAnyToken = true;
 }
 
 
@@ -3778,6 +3790,7 @@ void QXmlStreamWriter::writeStartDocument(QAnyStringView version)
     if (d->device) // stringDevice does not get any encoding
         d->write("\" encoding=\"UTF-8");
     d->write("\"?>");
+    d->didWriteStartDocument = true;
 }
 
 /*!  Writes a document start with the XML version number \a version
@@ -3801,6 +3814,7 @@ void QXmlStreamWriter::writeStartDocument(QAnyStringView version, bool standalon
         d->write("\" standalone=\"yes\"?>");
     else
         d->write("\" standalone=\"no\"?>");
+    d->didWriteStartDocument = true;
 }
 
 
@@ -3862,6 +3876,7 @@ void QXmlStreamWriterPrivate::writeStartElement(QAnyStringView namespaceUri, QAn
             writeNamespaceDeclaration(namespaceDeclarations[i]);
     }
     tag.namespaceDeclarationsSize = lastNamespaceDeclaration;
+    didWriteAnyToken = true;
 }
 
 /*!  Writes the current state of the \a reader. All possible valid

tests/auto/corelib/serialization/qxmlstream/tst_qxmlstream.cpp

@@ -559,6 +559,10 @@ private slots:
     void writerAutoFormattingWithProcessingInstructions() const;
     void writerAutoEmptyTags() const;
     void writeAttributesWithSpace() const;
+    void writerAutoFormattingProcessingInstructionFirst() const;
+    void writerAutoFormattingStartElementFirst() const;
+    void writerAutoFormattingCommentFirst() const;
+    void writerAutoFormattingNamespaceFirst() const;
     void addExtraNamespaceDeclarations();
     void setEntityResolver();
     void readFromQBuffer() const;
@@ -1075,6 +1079,74 @@ void tst_QXmlStream::writeAttributesWithSpace() const
     QCOMPARE(buffer.buffer().data(), s.toUtf8().data());
 }
 
+void tst_QXmlStream::writerAutoFormattingProcessingInstructionFirst() const
+{
+    QBuffer buffer;
+    buffer.open(QIODevice::WriteOnly);
+    QXmlStreamWriter writer(&buffer);
+    writer.setAutoFormatting(true);
+    writer.writeProcessingInstruction("B");
+    writer.writeComment("This is a comment");
+    writer.writeStartElement("A");
+    writer.writeNamespace("http://website.com", "website");
+    writer.writeDefaultNamespace("http://websiteNo2.com");
+    writer.writeEndElement();
+    writer.writeEndDocument();
+    const char *str =
+            "<?B?>\n<!--This is a comment-->\n<A xmlns:website=\"http://website.com\" xmlns=\"http://websiteNo2.com\"/>\n";
+    QCOMPARE(buffer.buffer().data(), str);
+}
+void tst_QXmlStream::writerAutoFormattingStartElementFirst() const
+{
+    QBuffer buffer;
+    buffer.open(QIODevice::WriteOnly);
+    QXmlStreamWriter writer(&buffer);
+    writer.setAutoFormatting(true);
+    writer.writeStartElement("A");
+    writer.writeNamespace("http://website.com", "website");
+    writer.writeComment("This is a comment");
+    writer.writeProcessingInstruction("B");
+    writer.writeDefaultNamespace("http://websiteNo2.com");
+    writer.writeEndElement();
+    writer.writeEndDocument();
+    const char *str = "<A xmlns:website=\"http://website.com\">\n    <!--This is a comment-->\n    <?B?>\n</A>\n";
+    QCOMPARE(buffer.buffer().data(), str);
+}
+
+void tst_QXmlStream::writerAutoFormattingCommentFirst() const
+{
+    QBuffer buffer;
+    buffer.open(QIODevice::WriteOnly);
+    QXmlStreamWriter writer(&buffer);
+    writer.setAutoFormatting(true);
+    writer.writeComment("This is a comment");
+    writer.writeStartElement("A");
+    writer.writeNamespace("http://website.com", "website");
+    writer.writeEndElement();
+    writer.writeDefaultNamespace("http://websiteNo2.com");
+    writer.writeProcessingInstruction("B");
+    writer.writeEndDocument();
+    const char *str = "<!--This is a comment--><A xmlns:website=\"http://website.com\"/>\n<?B?>\n";
+    QCOMPARE(buffer.buffer().data(), str);
+}
+
+void tst_QXmlStream::writerAutoFormattingNamespaceFirst() const
+{
+    QBuffer buffer;
+    buffer.open(QIODevice::WriteOnly);
+    QXmlStreamWriter writer(&buffer);
+    writer.setAutoFormatting(true);
+    writer.writeNamespace("http://website.com", "website");
+    writer.writeStartElement("A");
+    writer.writeDefaultNamespace("http://websiteNo2.com");
+    writer.writeProcessingInstruction("B");
+    writer.writeEndElement();
+    writer.writeComment("This is a comment");
+    writer.writeEndDocument();
+    const char *str = "<A xmlns:website=\"http://website.com\" xmlns=\"http://websiteNo2.com\">\n    <?B?></A>\n<!--This is a comment-->\n";
+    QCOMPARE(buffer.buffer().data(), str);
+}
+
 void tst_QXmlStream::writerAutoEmptyTags() const
 {
     QBuffer buffer;