Multi-line <PRE> in QTextEdit breaks line wrap

MostTornBrain

Hi,

I'm using a QTextEdit to display rich text, however I have run across an oddity I can not work-around. I have the widget configured to automatically wrap lines at the widget border, and this works fine until I display a multi-line <PRE> tagged text. I realize multi-line <PRE> shouldn't wrap, however what happens is everything after this <PRE> tag is closed also no longer auto line wraps.

Is there some way to prevent this from happening, or restore the auto-wrap behavior after a multi-line <PRE> is displayed?

Here's a simple example demonstrating how a single line <pre> is fine, but a multi-line pre breaks line wrap:

class CustomWidget(QWidget):
    def __init__(self, *args, **kwargs):
        super(CustomWidget, self).__init__(*args, **kwargs)

        self.layout = QVBoxLayout()
        self.text_edit = QTextEdit()

        self.layout.addWidget(self.text_edit)
        self.setLayout(self.layout)

app = QApplication(sys.argv)
widget = CustomWidget()

widget.text_edit.append('''<p> Next lines of text should wrap normally normally normally normally normally normally normally normally normally normally normally normally </p>''')
widget.text_edit.append('''<pre> singe-line pre </pre>''')
widget.text_edit.append('''<p> Next lines of text should wrap normally normally normally normally normally normally normally normally normally normally normally normally </p>''')
widget.text_edit.append('''<pre> multi-line pre 
    </pre>''')
widget.text_edit.append('''<p> Next lines of text should wrap normally normally normally normally normally normally normally normally normally normally normally normally </p>''')

widget.show()
sys.exit(app.exec_())

Screenshot 2023-09-17 at 3.27.57 PM.png

MostTornBrain

Some additional information I discovered: If I use the QTextEdit toHtml() function to view what it has rendered, it appears the widget is stuck in a quasi <pre> state. Even though I added a new <p> tagged text, toHtml() shows it has a <pre> tag instead, which would explain the lack of line wrapping. Oddly, the actual <pre> multi-line text is rendered as a <p> tag. Seems like some internal <pre> state is getting misapplied to the text blocks. Rather than make the real <pre> tagged text pre formatted, it instead makes all subsequent blocks pre formatted, but assigns the fonts correctly.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd">
<html><head><meta name="qrichtext" content="1" /><style type="text/css">
p, li { white-space: pre-wrap; }
</style></head><body style=" font-family:'.AppleSystemUIFont'; font-size:13pt; font-weight:400; font-style:normal;">
<p style=" margin-top:12px; margin-bottom:12px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;">Next lines of text should wrap normally normally normally normally normally normally normally normally normally normally normally normally </p>
<p style=" margin-top:12px; margin-bottom:12px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span style=" font-family:'Menlo';"> singe-line pre </span></p>
<p style=" margin-top:12px; margin-bottom:12px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;">Next lines of text should wrap normally normally normally normally normally normally normally normally normally normally normally normally </p>
<p style=" margin-top:12px; margin-bottom:12px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span style=" font-family:'Menlo';"> multi-line pre </span></p>
<pre style=" margin-top:0px; margin-bottom:12px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span style=" font-family:'Menlo';">    </span></pre>
<pre style=" margin-top:0px; margin-bottom:12px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;">Next lines of text should wrap normally normally normally normally normally normally normally normally normally normally normally normally </pre></body></html>

MostTornBrain

I've filed a bug about this on the Qt Bug Tracker Jira system, because I'm fairly certain it is a bug.

On the bright-side, I did figure out a work-around. It looks like the QTextEdit is getting stuck in a mode where all future TextBlocks end up with the format property of setNonBreakableLines(True). To work-around this, any time I send a multi-line <pre> text block to QTextEdit, I immediately follow it up with a call to this custom function:

    def restoreLineWrap(self):
        cursor = self.textCursor()
        format = QTextBlockFormat()
        format.setNonBreakableLines(False)
        cursor.setBlockFormat(format)
        self.setTextCursor(cursor)

JonB

@MostTornBrain Well done for figuring a workaround. It would be good if you posted a link to your bug report.