Text editing: smart block and char format after newline

When you are editing in a QTextEdit and press enter to start a new line,
calling insertBlock() with no arguments tries to preserve the current
charFormat and blockFormat. That is often OK:
- if you hit enter at the end of a list item, you probably want another
  item in the same list
- if you are writing code inside a code block, you're probably just
  writing the next statement on the next line: stay in the same block
- margins, indents, tab positions should stay the same (but hopefully
  your editor has UI to manually reset the block format to default
  in case you are not continuing in the same style)
But there are some exceptions we can apply to be helpful:
- nobody ever wants to follow an <hr/> with another one (but
  hopefully the application has an action to insert one manually)
- a heading is more likely to be followed by a paragraph, or perhaps
  a smaller heading; another heading at the same level is unlikely.
  We need to reset the char format, not only the block format, because
  the large font and heavy font weight are stored there.
- when adding to a todo list, hitting enter at the end of the last task,
  let's assume the next task is not yet done, so it will be unchecked
  by default (else, why are you writing a todo list at all)
To achieve that, we need to customize the formats and call the
insertBlock() overload that takes them. The no-argument insertBlock()
will continue to preserve the formats, because it's an old API that is
used for much more than interactive editing.

Additionally, word processors tend to let you end a list (for example)
by hitting enter twice. In that case, you stay in the same paragraph
that you created the first time you hit enter, but now the formats are
reset to default, so that you can go on typing an ordinary paragraph,
rather than having to mouse up to the toolbar to select the paragraph
style in a combobox, or something like that. So we now do that: reset
both block and char formats after you hit enter on a blank line; but if
you then hit enter again, after the block format has been reset, then
you will get the actual blank line (empty block) inserted.

[ChangeLog][QtWidgets][QTextEdit] Hitting enter at the end of a line
with a special block format (horizontal rule, heading, checklist item)
now makes some "smart" adjustments to avoid retaining properties that
are unlikely to be continued on the next line. Hitting enter twice now
resets block and char formats to default.

Fixes: QTBUG-48815
Task-number: QTBUG-80473
Fixes: QTBUG-97459
Change-Id: I3dfdd5b4c0d9ffb4673acc861cb7b5c22291df25
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

3 files changed, 139 insertions, 1 deletions

diff --git a/src/widgets/widgets/qwidgettextcontrol.cpp b/src/widgets/widgets/qwidgettextcontrol.cpp
index 76029714d5..8c849ddbae 100644
--- a/src/widgets/widgets/qwidgettextcontrol.cpp
+++ b/src/widgets/widgets/qwidgettextcontrol.cpp
@@ -1299,7 +1299,7 @@ void QWidgetTextControlPrivate::keyPressEvent(QKeyEvent *e)
     }
 #ifndef QT_NO_SHORTCUT
       else if (e == QKeySequence::InsertParagraphSeparator) {
-        cursor.insertBlock();
+        insertParagraphSeparator();
         e->accept();
         goto accept;
     } else if (e == QKeySequence::InsertLineSeparator) {
@@ -3198,6 +3198,49 @@ QString QWidgetTextControl::toMarkdown(QTextDocument::MarkdownFeatures features)
 }
 #endif
 
+void QWidgetTextControlPrivate::insertParagraphSeparator()
+{
+    // clear blockFormat properties that the user is unlikely to want duplicated:
+    // - don't insert <hr/> automatically
+    // - the next paragraph after a heading should be a normal paragraph
+    // - remove the bottom margin from the last list item before appending
+    // - the next checklist item after a checked item should be unchecked
+    auto blockFmt = cursor.blockFormat();
+    auto charFmt = cursor.charFormat();
+    blockFmt.clearProperty(QTextFormat::BlockTrailingHorizontalRulerWidth);
+    if (blockFmt.hasProperty(QTextFormat::HeadingLevel)) {
+        blockFmt.clearProperty(QTextFormat::HeadingLevel);
+        charFmt = QTextCharFormat();
+    }
+    if (cursor.currentList()) {
+        auto existingFmt = cursor.blockFormat();
+        existingFmt.clearProperty(QTextBlockFormat::BlockBottomMargin);
+        cursor.setBlockFormat(existingFmt);
+        if (blockFmt.marker() == QTextBlockFormat::MarkerType::Checked)
+            blockFmt.setMarker(QTextBlockFormat::MarkerType::Unchecked);
+    }
+
+    // After a blank line, reset block and char formats. I.e. you can end a list,
+    // block quote, etc. by hitting enter twice, and get back to normal paragraph style.
+    if (cursor.block().text().isEmpty() &&
+            !cursor.blockFormat().hasProperty(QTextFormat::BlockTrailingHorizontalRulerWidth) &&
+            !cursor.blockFormat().hasProperty(QTextFormat::BlockCodeLanguage)) {
+        blockFmt = QTextBlockFormat();
+        const bool blockFmtChanged = (cursor.blockFormat() != blockFmt);
+        charFmt = QTextCharFormat();
+        cursor.setBlockFormat(blockFmt);
+        cursor.setCharFormat(charFmt);
+        // If the user hit enter twice just to get back to default format,
+        // don't actually insert a new block. But if the user then hits enter
+        // yet again, the block format will not change, so we will insert a block.
+        // This is what many word processors do.
+        if (blockFmtChanged)
+            return;
+    }
+
+    cursor.insertBlock(blockFmt, charFmt);
+}
+
 void QWidgetTextControlPrivate::append(const QString &text, Qt::TextFormat format)
 {
     QTextCursor tmp(doc);
diff --git a/src/widgets/widgets/qwidgettextcontrol_p_p.h b/src/widgets/widgets/qwidgettextcontrol_p_p.h
index a7a19e748d..c94f859e6f 100644
--- a/src/widgets/widgets/qwidgettextcontrol_p_p.h
+++ b/src/widgets/widgets/qwidgettextcontrol_p_p.h
@@ -179,6 +179,7 @@ public:
     bool isPreediting() const;
     void commitPreedit();
 
+    void insertParagraphSeparator();
     void append(const QString &text, Qt::TextFormat format = Qt::AutoText);
 
     QTextDocument *doc;
diff --git a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
index 8d5716c129..9126b87472 100644
--- a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
+++ b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
@@ -58,6 +58,8 @@
 #include "../../../shared/platforminputcontext.h"
 #include <private/qinputmethod_p.h>
 
+Q_LOGGING_CATEGORY(lcTests, "qt.widgets.tests")
+
 //Used in copyAvailable
 typedef QPair<Qt::Key, Qt::KeyboardModifier> keyPairType;
 typedef QList<keyPairType> pairListType;
@@ -209,6 +211,9 @@ private slots:
     void preeditCharFormat_data();
     void preeditCharFormat();
 
+    void nextFormatAfterEnterPressed_data();
+    void nextFormatAfterEnterPressed();
+
 private:
     void createSelection();
     int blockCount() const;
@@ -2895,5 +2900,94 @@ void tst_QTextEdit::preeditCharFormat()
     delete w;
 }
 
+void tst_QTextEdit::nextFormatAfterEnterPressed_data()
+{
+    typedef QMap<int, QVariant> pmap;
+    QTest::addColumn<QString>("html");
+    QTest::addColumn<int>("enterKeyCount");
+    QTest::addColumn<pmap>("expectedPrevBlockProps");
+    QTest::addColumn<pmap>("expectedPrevCharProps");
+    QTest::addColumn<pmap>("expectedNewBlockProps");
+    QTest::addColumn<pmap>("expectedNewCharProps");
+
+    // the BlockBottomMargin on "two" will be removed: property() returns invalid QVariant
+    QTest::newRow("bottom margin after ordered list") << "<ol><li>one</li><li>two</li></ol>" << 1
+        << pmap{{QTextFormat::BlockBottomMargin, {}}} << pmap{}
+        << pmap{{QTextFormat::BlockBottomMargin, 12}} << pmap{};
+    QTest::newRow("double enter after list: default format") << "<ol><li>one</li><li>two</li></ol>" << 2
+        << pmap{{QTextFormat::BlockBottomMargin, {}}} << pmap{}
+        << pmap{} << pmap{};
+    QTest::newRow("continue block quote") << "<blockquote>I'll be back</blockquote>" << 1
+        << pmap{{QTextFormat::BlockLeftMargin, 40}} << pmap{}
+        << pmap{{QTextFormat::BlockLeftMargin, 40}} << pmap{};
+    QTest::newRow("double enter after block quote") << "<blockquote>I'll be back</blockquote>" << 2
+        << pmap{{QTextFormat::BlockLeftMargin, 40}} << pmap{}
+        << pmap{{QTextFormat::BlockLeftMargin, {}}} << pmap{};
+    QTest::newRow("bottom margin after bullet list") << "<ul><li>one</li><li>two</li></ul>" << 1
+        << pmap{{QTextFormat::BlockBottomMargin, {}}} << pmap{}
+        << pmap{{QTextFormat::BlockBottomMargin, 12}} << pmap{};
+    QTest::newRow("paragraph after heading") << "<h1>so big!</h1>" << 1
+        << pmap{{QTextFormat::HeadingLevel, 1}} << pmap{}
+        << pmap{{QTextFormat::HeadingLevel, {}}} << pmap{};
+    QTest::newRow("paragraph after hrule") << "<p style='font-size:18px;'>blah blah<hr/></p>" << 1
+        << pmap{} << pmap{}
+        << pmap{{QTextFormat::BlockTrailingHorizontalRulerWidth, {}}} << pmap{};
+}
+
+void tst_QTextEdit::nextFormatAfterEnterPressed()
+{
+    typedef QMap<int, QVariant> pmap;
+    QFETCH(QString, html);
+    QFETCH(int, enterKeyCount);
+    QFETCH(pmap, expectedPrevBlockProps);
+    QFETCH(pmap, expectedPrevCharProps);
+    QFETCH(pmap, expectedNewBlockProps);
+    QFETCH(pmap, expectedNewCharProps);
+
+    ed->setHtml(html);
+    QTextCursor cursor = ed->textCursor();
+    cursor.movePosition(QTextCursor::End);
+    ed->setTextCursor(cursor);
+
+    if (lcTests().isDebugEnabled()) {
+        ed->show();
+        QTest::qWait(500);
+    }
+
+    for (int i = 0; i < enterKeyCount; ++i)
+        QTest::keyClick(ed, Qt::Key_Enter);
+    QTest::keyClicks(ed, "foo");
+
+    if (lcTests().isDebugEnabled()) {
+        // visually see what happened when debug is enabled
+        QTest::qWait(500);
+        qCDebug(lcTests) << "new block" << Qt::hex << ed->textCursor().blockFormat().properties();
+        qCDebug(lcTests) << "new char" << Qt::hex << ed->textCursor().charFormat().properties();
+    }
+
+    // if expectedNewBlockProps is empty, we expect the current block format to be the default format
+    if (expectedNewBlockProps.isEmpty())
+        QCOMPARE(ed->textCursor().blockFormat(), QTextBlockFormat());
+    // otherwise we expect to find certain property values in the current block format
+    else for (auto it = expectedNewBlockProps.constBegin(); it != expectedNewBlockProps.constEnd(); ++it)
+        QCOMPARE(ed->textCursor().blockFormat().property(it.key()), it.value());
+
+    // if expectedNewCharProps is empty, we expect the current char format to be the default format
+    if (expectedNewCharProps.isEmpty())
+        QCOMPARE(ed->textCursor().charFormat(), QTextCharFormat());
+    // otherwise we expect to find certain property values in the current char format
+    else for (auto it = expectedNewCharProps.constBegin(); it != expectedNewCharProps.constEnd(); ++it)
+        QCOMPARE(ed->textCursor().charFormat().property(it.key()), it.value());
+
+    // check the cases where QWidgetTextControlPrivate::insertParagraphSeparator() should modify
+    // the previous block's block format and/or char format
+    auto prevBlockCursor = ed->textCursor();
+    prevBlockCursor.movePosition(QTextCursor::PreviousBlock);
+    for (auto it = expectedPrevBlockProps.constBegin(); it != expectedPrevBlockProps.constEnd(); ++it)
+        QCOMPARE(prevBlockCursor.blockFormat().property(it.key()), it.value());
+    for (auto it = expectedPrevCharProps.constBegin(); it != expectedPrevCharProps.constEnd(); ++it)
+        QCOMPARE(prevBlockCursor.charFormat().property(it.key()), it.value());
+}
+
 QTEST_MAIN(tst_QTextEdit)
 #include "tst_qtextedit.moc"