Support markdown in QTextEditMimeData; fix pasting trailing newlines

- Since 4edcea762d9ce334c4c1a78234c90c118b81da87 the dropsite example
  shows markdown if available; and now it shows that when we do DnD
  of a selection from the richtext example, text/markdown is available.
- If we artificially make html unavailable, copying and pasting between
  widget-based rich text editors uses markdown.

In case markdown writer output contains unnecessary backticks due to
monospace fonts getting used, the workaround from
1ad456c908467212bc30223a69eb7524b64b86e1 is applied.

Task-number: QTBUG-76105
Task-number: QTBUG-103484
Change-Id: Ie6ca4dbb450dbc36b3d09fd0df1ae5909aaebca7
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
(cherry picked from commit 56f0ebfe860e440dcbba8997f44836debc901119)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/widgets/qwidgettextcontrol.cpp

@@ -24,6 +24,7 @@
 #endif
 #include "qtextdocument.h"
 #include "private/qtextdocument_p.h"
+#include "private/qtextdocumentfragment_p.h"
 #include "qtextlist.h"
 #include "private/qwidgettextcontrol_p.h"
 #if QT_CONFIG(style_stylesheet)
@@ -2697,6 +2698,13 @@ void QWidgetTextControl::insertFromMimeData(const QMimeData *source)
 
     bool hasData = false;
     QTextDocumentFragment fragment;
+#if QT_CONFIG(textmarkdownreader)
+    if (source->formats().first() == "text/markdown"_L1) {
+        auto s = QString::fromUtf8(source->data("text/markdown"_L1));
+        fragment = QTextDocumentFragment::fromMarkdown(s);
+        hasData = true;
+    } else
+#endif
 #ifndef QT_NO_TEXTHTMLPARSER
     if (source->hasFormat("application/x-qrichtext"_L1) && d->acceptRichText) {
         // x-qrichtext is always UTF-8 (taken from Qt3 since we don't use it anymore).
@@ -2707,16 +2715,15 @@ void QWidgetTextControl::insertFromMimeData(const QMimeData *source)
     } else if (source->hasHtml() && d->acceptRichText) {
         fragment = QTextDocumentFragment::fromHtml(source->html(), d->doc);
         hasData = true;
-    } else {
-        QString text = source->text();
+    }
+#endif // QT_NO_TEXTHTMLPARSER
+    if (!hasData) {
+        const QString text = source->text();
         if (!text.isNull()) {
             fragment = QTextDocumentFragment::fromPlainText(text);
             hasData = true;
         }
     }
-#else
-    fragment = QTextDocumentFragment::fromPlainText(source->text());
-#endif // QT_NO_TEXTHTMLPARSER
 
     if (hasData)
         d->cursor.insertFragment(fragment);
@@ -3434,6 +3441,9 @@ QStringList QTextEditMimeData::formats() const
 {
     if (!fragment.isEmpty())
         return QStringList() << u"text/plain"_s << u"text/html"_s
+#if QT_CONFIG(textmarkdownwriter)
+            << u"text/markdown"_s
+#endif
 #ifndef QT_NO_TEXTODFWRITER
             << u"application/vnd.oasis.opendocument.text"_s
 #endif
@@ -3455,6 +3465,9 @@ void QTextEditMimeData::setup() const
 #ifndef QT_NO_TEXTHTMLPARSER
     that->setData("text/html"_L1, fragment.toHtml().toUtf8());
 #endif
+#if QT_CONFIG(textmarkdownwriter)
+    that->setData("text/markdown"_L1, fragment.toMarkdown().toUtf8());
+#endif
 #ifndef QT_NO_TEXTODFWRITER
     {
         QBuffer buffer;

tests/auto/corelib/kernel/qmimedata/tst_qmimedata.cpp

@@ -72,12 +72,19 @@ void tst_QMimeData::data() const
     mimeData.setData("text/plain", "pirates");
     QCOMPARE(mimeData.data("text/plain"), QByteArray("pirates"));
     QCOMPARE(mimeData.data("text/html").length(), 0);
+    QCOMPARE(mimeData.data("text/markdown").length(), 0);
 
     // html time
     mimeData.setData("text/html", "ninjas");
     QCOMPARE(mimeData.data("text/html"), QByteArray("ninjas"));
     QCOMPARE(mimeData.data("text/plain"), QByteArray("pirates")); // make sure text not damaged
     QCOMPARE(mimeData.data("text/html"), mimeData.html().toLatin1());
+
+    // markdown time
+    mimeData.setData("text/markdown", "vikings");
+    QCOMPARE(mimeData.data("text/markdown"), QByteArray("vikings"));
+    QCOMPARE(mimeData.data("text/html"), QByteArray("ninjas"));
+    QCOMPARE(mimeData.data("text/plain"), QByteArray("pirates"));
 }
 
 void tst_QMimeData::formats() const
@@ -92,6 +99,10 @@ void tst_QMimeData::formats() const
     mimeData.setData("text/html", "ninjas");
     QCOMPARE(mimeData.formats(), QStringList() << "text/plain" << "text/html");
 
+    // set markdown, verify
+    mimeData.setData("text/markdown", "vikings");
+    QCOMPARE(mimeData.formats(), QStringList() << "text/plain" << "text/html" << "text/markdown");
+
     // clear, verify
     mimeData.clear();
     QCOMPARE(mimeData.formats(), QStringList());

tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp

@@ -114,7 +114,13 @@ private slots:
     void moveCursor();
 #ifndef QT_NO_CLIPBOARD
     void mimeDataReimplementations();
+#ifndef QT_NO_TEXTHTMLPARSER
+    void mimeTypesAvailableFromRichText();
 #endif
+#if QT_CONFIG(textmarkdownreader)
+    void mimeTypesAvailableFromMarkdown();
+#endif
+#endif // QT_NO_CLIPBOARD
     void ctrlEnterShouldInsertLineSeparator_NOT();
     void shiftEnterShouldInsertLineSeparator();
     void selectWordsFromStringsContainingSeparators_data();
@@ -150,6 +156,7 @@ private slots:
     void setDocumentPreservesPalette();
 #endif
     void pasteFromQt3RichText();
+    void pasteFromMarkdown();
     void noWrapBackgrounds();
     void preserveCharFormatAfterUnchangingSetPosition();
     void twoSameInputMethodEvents();
@@ -193,6 +200,7 @@ private:
     void createSelection();
     int blockCount() const;
     void compareWidgetAndImage(QTextEdit &widget, const QString &imageFileName);
+    bool isMainFontFixed();
 
     QTextEdit *ed;
     qreal rootFrameMargin;
@@ -1480,7 +1488,63 @@ void tst_QTextEdit::mimeDataReimplementations()
     QCOMPARE(ed.insertCallCount, 1);
 #endif
 }
+
+#ifndef QT_NO_TEXTHTMLPARSER
+void tst_QTextEdit::mimeTypesAvailableFromRichText()
+{
+    MyTextEdit ed;
+    ed.setHtml("<i>Hello <b>World</b></i>");
+    ed.selectAll();
+    ed.copy();
+    const auto *mimeData = QApplication::clipboard()->mimeData();
+    qCDebug(lcTests) << "available mime types" << mimeData->formats();
+    QVERIFY(mimeData->formats().contains("text/plain"));
+#if QT_CONFIG(textmarkdownwriter)
+    QVERIFY(mimeData->formats().contains("text/markdown"));
+    const QByteArray expectedMarkdown = "*Hello **World***\n\n";
+    if (mimeData->data("text/markdown") != expectedMarkdown && isMainFontFixed())
+        QEXPECT_FAIL("", "fixed-pitch main font (QTBUG-103484)", Continue);
+    QCOMPARE(mimeData->data("text/markdown"), expectedMarkdown);
 #endif
+#ifndef QT_NO_TEXTHTMLPARSER
+    QVERIFY(mimeData->formats().contains("text/html"));
+    QVERIFY(mimeData->hasHtml());
+#endif
+#ifndef QT_NO_TEXTODFWRITER
+    QVERIFY(mimeData->formats().contains("application/vnd.oasis.opendocument.text"));
+#endif
+}
+#endif // QT_NO_TEXTHTMLPARSER
+
+#if QT_CONFIG(textmarkdownreader)
+void tst_QTextEdit::mimeTypesAvailableFromMarkdown()
+{
+    MyTextEdit ed;
+    const QString md("# TODO\n\n- [x] Fix bugs\n- [ ] Have a beer\n");
+    ed.setMarkdown(md);
+    ed.selectAll();
+    ed.copy();
+    const auto *mimeData = QApplication::clipboard()->mimeData();
+    qCDebug(lcTests) << "available mime types" << mimeData->formats();
+    QVERIFY(mimeData->formats().contains("text/plain"));
+#if QT_CONFIG(textmarkdownwriter)
+    QVERIFY(mimeData->formats().contains("text/markdown"));
+    if (mimeData->data("text/markdown") != md && isMainFontFixed())
+        QEXPECT_FAIL("", "fixed-pitch main font (QTBUG-103484)", Continue);
+    QCOMPARE(mimeData->data("text/markdown"), md);
+#endif
+#ifndef QT_NO_TEXTHTMLPARSER
+    QVERIFY(mimeData->formats().contains("text/html"));
+    QVERIFY(mimeData->hasHtml());
+    QVERIFY(mimeData->html().contains("checked")); // <li class=\"checked\" ...
+#endif
+#ifndef QT_NO_TEXTODFWRITER
+    QVERIFY(mimeData->formats().contains("application/vnd.oasis.opendocument.text"));
+#endif
+}
+#endif // textmarkdownreader
+
+#endif // QT_NO_CLIPBOARD
 
 void tst_QTextEdit::ctrlEnterShouldInsertLineSeparator_NOT()
 {
@@ -2133,6 +2197,18 @@ void tst_QTextEdit::compareWidgetAndImage(QTextEdit &widget, const QString &imag
     }
 }
 
+bool tst_QTextEdit::isMainFontFixed()
+{
+    bool ret = QFontInfo(QGuiApplication::font()).fixedPitch();
+    if (ret) {
+        qCWarning(lcTests) << "QFontDatabase::GeneralFont is monospaced: markdown writing is likely to use too many backticks";
+        qCWarning(lcTests) << "system fonts: fixed" << QFontDatabase::systemFont(QFontDatabase::FixedFont)
+                           << "fixed?" << QFontInfo(QFontDatabase::systemFont(QFontDatabase::FixedFont)).fixedPitch()
+                           << "general" << QFontDatabase::systemFont(QFontDatabase::GeneralFont);
+    }
+    return ret;
+}
+
 void tst_QTextEdit::cursorRect()
 {
     ed->show();
@@ -2200,6 +2276,24 @@ void tst_QTextEdit::pasteFromQt3RichText()
     QCOMPARE(ed->toPlainText(), QString::fromLatin1("  QTextEdit is an  "));
 }
 
+void tst_QTextEdit::pasteFromMarkdown()
+{
+    QByteArray richtext("*This* text is **rich**");
+
+    QMimeData mimeData;
+    mimeData.setData("text/markdown", richtext);
+
+    static_cast<PublicTextEdit *>(ed)->publicInsertFromMimeData(&mimeData);
+
+    QCOMPARE(ed->toPlainText(), "This text is rich");
+#if QT_CONFIG(textmarkdownwriter)
+    const auto expectedMarkdown = QString::fromLatin1(richtext + "\n\n");
+    if (ed->toMarkdown() != expectedMarkdown && isMainFontFixed())
+        QEXPECT_FAIL("", "fixed-pitch main font (QTBUG-103484)", Continue);
+    QCOMPARE(ed->toMarkdown(), expectedMarkdown);
+#endif
+}
+
 void tst_QTextEdit::noWrapBackgrounds()
 {
     QWidget topLevel;