Do not run updateMacros if the buffer has not changed

Each buffer now has an id which is increased when it is marked dirty
(or when one of its relatives is marked dirty).

This can be a big win since updateMacros is very expensive.

src/Buffer.cpp

@@ -254,6 +254,11 @@ public:
 	///
 	Undo undo_;
 
+	/// This is increased every time the buffer or one of its relatives is marked dirty
+	int id_ = 0;
+	/// The buffer id at last updateMacros invokation
+	int update_macros_id_ = -1;
+
 	/// A cache for the bibfiles (including bibfiles of loaded child
 	/// documents), needed for appropriate update of natbib labels.
 	mutable docstring_list bibfiles_cache_;
@@ -790,6 +795,20 @@ Undo const & Buffer::undo() const
 }
 
 
+int Buffer::id() const
+{
+	return d->id_;
+}
+
+
+void Buffer::updateId()
+{
+	++d->id_;
+	for(Buffer * b : allRelatives())
+		++(b->d->id_);
+}
+
+
 void Buffer::setChild(DocIterator const & dit, Buffer * child)
 {
 	d->children_positions[child] = dit;
@@ -3305,6 +3324,9 @@ void Buffer::markDirty()
 
 	for (auto & depit : d->dep_clean)
 		depit.second = false;
+
+	// Update the buffer and its relatives' ids.
+	updateId();
 }
 
 
@@ -3899,6 +3921,11 @@ void Buffer::updateMacros() const
 	if (d->macro_lock)
 		return;
 
+	// early exit if the buffer has not changed since last time
+	if (d->update_macros_id_ == d->id_)
+		return;
+	d->update_macros_id_ = d->id_;
+
 	LYXERR(Debug::MACROS, "updateMacro of " << d->filename.onlyFileName());
 
 	// start with empty table

src/Buffer.h

@@ -661,6 +661,12 @@ public:
 	///
 	Undo const & undo() const;
 
+	/// poor man versioning of the buffer (and its relatives).
+	int id() const;
+	/// change the id of this buffer and its relatives (indicating
+	/// something has changed). This is currently used by updateMacros().
+	void updateId();
+
 	/// This function is called when the buffer is changed.
 	void changed(bool update_metrics) const;
 	///

src/Undo.cpp

@@ -529,9 +529,11 @@ void Undo::Private::doUndoRedoAction(CursorData & cur, UndoElementStack & stack,
 
 	if (!undo.cur_before.empty())
 		cur = undo.cur_before;
-	if (undo.lyx_clean)
+	if (undo.lyx_clean) {
 		buffer_.markClean();
-	else
+		// since we have changed the buffer, update its id.
+		buffer_.updateId();
+	} else
 		buffer_.markDirty();
 	// Now that we're done with undo, we pop it off the stack.
 	stack.pop();