For the sake of availability and saving someone's time, I'll share my solution again here.
There's a very good and detailed Syntax Highlighter Example in the Qt Documentation, with a section that explains how to deal with multiline comments explained in Highlighter class implementation section.
Here's my own extraction of it:
the multiline comment needs special care due to the design of the QSyntaxHighlighter class.
After a QSyntaxHighlighter object is created, its highlightBlock() function will be called automatically whenever it is necessary by the rich text engine, highlighting the given text block. The problem appears when a comment spans several text blocks. We will take a closer look at how this problem can be solved when reviewing the implementation of the Highlighter::highlightBlock() function. At this point we only specify the multiline comment's color.
setCurrentBlockState(0);
To deal with constructs that can span several text blocks (like the C++ multiline comment), it is necessary to know the end state of the previous text block (e.g. "in comment"). Inside your highlightBlock() implementation you can query the end state of the previous text block using the QSyntaxHighlighter::previousBlockState() function. After parsing the block you can save the last state using QSyntaxHighlighter::setCurrentBlockState().
The previousBlockState() function return an int value. If no state is set, the returned value is -1. You can designate any other value to identify any given state using the setCurrentBlockState() function. Once the state is set, the QTextBlock keeps that value until it is set again or until the corresponding paragraph of text is deleted.
In this example we have chosen to use 0 to represent the "not in comment" state, and 1 for the "in comment" state. When the stored syntax highlighting rules are applied we initialize the current block state to 0.
int startIndex = 0;
if (previousBlockState() != 1)
startIndex = text.indexOf(commentStartExpression);
If the previous block state was "in comment" (previousBlockState() == 1), we start the search for an end expression at the beginning of the text block. If the previousBlockState() returns 0, we start the search at the location of the first occurrence of a start expression.
while (startIndex >= 0) {
QRegularExpressionMatch match = commentEndExpression.match(text, startIndex);
int endIndex = match.capturedStart();
int commentLength = 0;
if (endIndex == -1) {
setCurrentBlockState(1);
commentLength = text.length() - startIndex;
} else {
commentLength = endIndex - startIndex
+ match.capturedLength();
}
setFormat(startIndex, commentLength, multiLineCommentFormat);
startIndex = text.indexOf(commentStartExpression, startIndex + commentLength);
}
When an end expression is found, we calculate the length of the comment and apply the multiline comment format. Then we search for the next occurrence of the start expression and repeat the process. If no end expression can be found in the current text block we set the current block state to 1, i.e. "in comment".
TL;DR: QSyntaxHighlighter only formats one text block at a time, a multiline comment is formed of several ones, hence why you are only able to format single line comments.
Based on that, I changed MyHtmlHighlighter as follows:
class MyHtmlHighlighter : public QSyntaxHighlighter
{
public:
MyHtmlHighlighter(QWidget* parent) : QSyntaxHighlighter(parent)
{
commentFormat.setForeground(QColor("#29ff3d"));
commentFormat.setFontItalic(true);
commentStartExpression = QRegularExpression(QStringLiteral("/\\*"));
commentEndExpression = QRegularExpression(QStringLiteral("\\*/"));
}
protected:
void highlightBlock(const QString& text) override
{
//useless for multiline comment formatting
for (const HighlightingRule& rule : highlightingRules)
{
QRegularExpressionMatchIterator matchIterator = rule.pattern.globalMatch(text);
while (matchIterator.hasNext())
{
QRegularExpressionMatch match = matchIterator.next();
setFormat(match.capturedStart(), match.capturedLength(), rule.format);
}
}
//this is where multiline comments processing starts
setCurrentBlockState(0);
int startIndex = 0;
if (previousBlockState() != 1)
startIndex = text.indexOf(commentStartExpression);
while (startIndex >= 0)
{
QRegularExpressionMatch match = commentEndExpression.match(text, startIndex);
int endIndex = match.capturedStart();
int commentLength = 0;
if (endIndex == -1)
{
setCurrentBlockState(1);
commentLength = text.length() - startIndex;
}
else
{
commentLength = endIndex - startIndex
+ match.capturedLength();
}
setFormat(startIndex, commentLength, commentFormat);
startIndex = text.indexOf(commentStartExpression, startIndex + commentLength);
}
}
private:
struct HighlightingRule
{
QRegularExpression pattern;
QTextCharFormat format;
};
QList<HighlightingRule> highlightingRules;
QTextCharFormat commentFormat;
//added
QRegularExpression commentStartExpression;
QRegularExpression commentEndExpression;
};
Here's a test:
[image: YLp82.gif]
