QTextMarkdownWriter: Don't word-wrap headings

If it wraps, the text on the next line is no longer part of the heading.

Fixes: QTBUG-106526
Change-Id: I8015c948d875c6944422ef3439e3128af5b2a2e2
Pick-to: 6.5
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit 65c4029)
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit a7367e6)

src/gui/text/qtextmarkdownwriter.cpp

@@ -437,10 +437,12 @@ int QTextMarkdownWriter::writeBlock(const QTextBlock &block, bool wrap, bool ign
             m_indentedCodeBlock = true;
         }
     }
-    if (blockFmt.headingLevel())
+    if (blockFmt.headingLevel()) {
         m_stream << QByteArray(blockFmt.headingLevel(), '#') << ' ';
-    else
+        wrap = false;
+    } else {
         m_stream << m_linePrefix;
+    }
 
     QString wrapIndentString = m_linePrefix + QString(m_wrappedLineIndent, qtmw_Space);
     // It would be convenient if QTextStream had a lineCharPos() accessor,

tests/auto/gui/text/qtextmarkdownwriter/data/longHeadings.md

@@ -0,0 +1,9 @@
+# The quick brown fox jumped over the lazy dog while the cat played the fiddle and the cow jumped over the moon
+
+Hey diddle diddle
+
+## This document has a verbose subheading too, which we do not expect to wrap in the output
+
+Qt can write it right. Long text here in this paragraph will actually wrap,
+even though its heading doesn't.
+

tests/auto/gui/text/qtextmarkdownwriter/tst_qtextmarkdownwriter.cpp

@@ -617,6 +617,7 @@ void tst_QTextMarkdownWriter::rewriteDocument_data()
     QTest::newRow("word wrap") << "wordWrap.md";
     QTest::newRow("links") << "links.md";
     QTest::newRow("lists and code blocks") << "listsAndCodeBlocks.md";
+    QTest::newRow("long headings") << "longHeadings.md";
 }
 
 void tst_QTextMarkdownWriter::rewriteDocument()