printing: refactor if and loop code

The loop code was buggy: the current position was only increased
inside when executing the loop once. This would obviously fail
for empty lists. Moreover, the whole thing was quite difficult
to reason about, since a reference to the current position was
passed down in the call hierarchy.

Instead, pass from and to values to the parse function and
create a generic function that can search for the end of
loop and if blocks. This function handles nested if and for
loops.

The if-code now formats the block only if the condition is true.
The old code would format the block and throw it away if not
needed.

This should now provide better diagnostics for mismatched tags.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

desktop-widgets/templatelayout.cpp

@@ -129,8 +129,7 @@ QString TemplateLayout::generate()
 	QList<token> tokens = lexer(templateContents);
 	QString buffer;
 	QTextStream out(&buffer);
-	int pos = 0;
+	parser(tokens, 0, tokens.size(), out, state);
-	parser(tokens, pos, out, state);
 	htmlContent = out.readAll();
 	return htmlContent;
 }
@@ -156,8 +155,7 @@ QString TemplateLayout::generateStatistics()
 	QList<token> tokens = lexer(templateContents);
 	QString buffer;
 	QTextStream out(&buffer);
-	int pos = 0;
+	parser(tokens, 0, tokens.size(), out, state);
-	parser(tokens, pos, out, state);
 	htmlContent = out.readAll();
 	return htmlContent;
 }
@@ -286,35 +284,47 @@ static QRegularExpression forloop(R"(\s*(\w+)\s+in\s+(\w+))");	// Look for "VAR
 static QRegularExpression ifstatement(R"(forloop\.counter\|\s*divisibleby\:\s*(\d+))");	// Look for forloop.counter|divisibleby: NUMBER
 
 template<typename V, typename T>
-void TemplateLayout::parser_for(QList<token> tokenList, int &pos, QTextStream &out, State &state,
+void TemplateLayout::parser_for(QList<token> tokenList, int from, int to, QTextStream &out, State &state,
 				const V &data, const T *&act)
 {
 	const T *old = act;
 	int i = 1; // Loop iterators start at one
 	int olditerator = state.forloopiterator;
-	int savepos = pos;
 	for (const T &item: data) {
 		act = &item;
-		state.forloopiterator = i;
+		state.forloopiterator = i++;
-		pos = savepos;
+		parser(tokenList, from, to, out, state);
-		++i;
-		parser(tokenList, pos, out, state);
 	}
 	act = old;
 	state.forloopiterator = olditerator;
 }
 
-void TemplateLayout::parser(QList<token> tokenList, int &pos, QTextStream &out, State &state)
+// Find end of for or if block. Keeps track of nested blocks.
+// Pos should point one past the starting tag.
+// Returns -1 if no matching end tag found.
+static int findEnd(const QList<token> &tokenList, int from, int to, token_t start, token_t end)
 {
-	while (pos < tokenList.length()) {
+	int depth = 1;
+	for (int pos = from; pos < to; ++pos) {
+		if (tokenList[pos].type == start) {
+			++depth;
+		} else if (tokenList[pos].type == end) {
+			if (--depth <= 0)
+				return pos;
+		}
+	}
+	return -1;
+}
+
+void TemplateLayout::parser(QList<token> tokenList, int from, int to, QTextStream &out, State &state)
+{
+	for (int pos = from; pos < to; ++pos) {
 		switch (tokenList[pos].type) {
 		case LITERAL:
 			out << translate(tokenList[pos].contents, state);
-			++pos;
 			break;
 		case BLOCKSTART:
 		case BLOCKSTOP:
-			++pos;
 			break;
 		case FORSTART:
 		{
@@ -327,23 +337,31 @@ void TemplateLayout::parser(QList<token> tokenList, int &pos, QTextStream &out,
 				state.types[itemname] = listname;
 				QString buffer;
 				QTextStream capture(&buffer);
+				int loop_end = findEnd(tokenList, pos, to, FORSTART, FORSTOP);
+				if (loop_end < 0) {
+					out << "UNMATCHED FOR: '" << argument << "'";
+					break;
+				}
 				if (listname == "years") {
-					parser_for(tokenList, pos, capture, state, state.years, state.currentYear);
+					parser_for(tokenList, pos, loop_end, capture, state, state.years, state.currentYear);
 				} else if (listname == "dives") {
-					parser_for(tokenList, pos, capture, state, state.dives, state.currentDive);
+					parser_for(tokenList, pos, loop_end, capture, state, state.dives, state.currentDive);
 				} else if (listname == "cylinders") {
 					if (state.currentDive)
-						parser_for(tokenList, pos, capture, state, state.currentDive->cylinders, state.currentCylinder);
+						parser_for(tokenList, pos, loop_end, capture, state, state.currentDive->cylinders, state.currentCylinder);
 					else
 						qWarning("cylinders loop outside of dive");
 				} else if (listname == "cylinderObjects") {
 					if (state.currentDive)
-						parser_for(tokenList, pos, capture, state, state.currentDive->cylinderObjects, state.currentCylinderObject);
+						parser_for(tokenList, pos, loop_end, capture, state, state.currentDive->cylinderObjects, state.currentCylinderObject);
 					else
 						qWarning("cylinderObjects loop outside of dive");
+				} else {
+					qWarning("unknown loop: %s", qPrintable(listname));
 				}
 				state.types.remove(itemname);
 				out << capture.readAll();
+				pos = loop_end;
 			} else {
 				out << "PARSING ERROR: '" << argument << "'";
 			}
@@ -355,13 +373,20 @@ void TemplateLayout::parser(QList<token> tokenList, int &pos, QTextStream &out,
 			++pos;
 			QRegularExpressionMatch match = ifstatement.match(argument);
 			if (match.hasMatch()) {
+				int if_end = findEnd(tokenList, pos, to, IFSTART, IFSTOP);
+				if (if_end < 0) {
+					out << "UNMATCHED IF: '" << argument << "'";
+					break;
+				}
 				int divisor = match.captured(1).toInt();
-				QString buffer;
-				QTextStream capture(&buffer);
 				int counter = std::max(0, state.forloopiterator);
-				parser(tokenList, pos, capture, state);
+				if (!(counter % divisor)) {
-				if (!(counter % divisor))
+					QString buffer;
+					QTextStream capture(&buffer);
+					parser(tokenList, pos, if_end, capture, state);
 					out << capture.readAll();
+				}
+				pos = if_end;
 			} else {
 				out << "PARSING ERROR: '" << argument << "'";
 			}
@@ -369,11 +394,10 @@ void TemplateLayout::parser(QList<token> tokenList, int &pos, QTextStream &out,
 			break;
 		case FORSTOP:
 		case IFSTOP:
-			++pos;
+			out << "UNEXPECTED END: " << tokenList[pos].contents;
 			return;
 		case PARSERERROR:
 			out << "PARSING ERROR";
-			++pos;
 		}
 	}
 }

desktop-widgets/templatelayout.h

@@ -51,9 +51,9 @@ private:
 	const print_options &printOptions;
 	const template_options &templateOptions;
 	QList<token> lexer(QString input);
-	void parser(QList<token> tokenList, int &pos, QTextStream &out, State &state);
+	void parser(QList<token> tokenList, int from, int to, QTextStream &out, State &state);
 	template<typename V, typename T>
-	void parser_for(QList<token> tokenList, int &pos, QTextStream &out, State &state, const V &data, const T *&act);
+	void parser_for(QList<token> tokenList, int from, int to, QTextStream &out, State &state, const V &data, const T *&act);
 	QVariant getValue(QString list, QString property, const State &state);
 	QString translate(QString s, State &state);