Add a unique ID to dialogue lines

This is needed to track lines across undo, as the previous method of
using the row number was slow and broke on inserts/deletes.

aegisub/src/ass_dialogue.cpp

@@ -49,12 +49,15 @@
 
 using namespace boost::adaptors;
 
+static int next_id = 0;
+
 std::size_t hash_value(wxString const& s) {
 	return wxStringHash()(s);
 }
 
 AssDialogue::AssDialogue()
-: Comment(false)
+: Id(++next_id)
+, Comment(false)
 , Layer(0)
 , Start(0)
 , End(5000)
@@ -64,7 +67,8 @@ AssDialogue::AssDialogue()
 }
 
 AssDialogue::AssDialogue(AssDialogue const& that)
-: Comment(that.Comment)
+: Id(++next_id)
+, Comment(that.Comment)
 , Layer(that.Layer)
 , Start(that.Start)
 , End(that.End)
@@ -77,7 +81,8 @@ AssDialogue::AssDialogue(AssDialogue const& that)
 }
 
 AssDialogue::AssDialogue(wxString const& data)
-: Comment(false)
+: Id(++next_id)
+, Comment(false)
 , Layer(0)
 , Start(0)
 , End(5000)
@@ -325,7 +330,9 @@ wxString AssDialogue::GetStrippedText() const {
 }
 
 AssEntry *AssDialogue::Clone() const {
-	return new AssDialogue(*this);
+	AssDialogue *clone = new AssDialogue(*this);
+	*const_cast<int *>(&clone->Id) = Id;
+	return clone;
 }
 
 void AssDialogueBlockDrawing::TransformCoords(int mx, int my, double x, double y) {

aegisub/src/ass_dialogue.h

@@ -127,6 +127,11 @@ public:
 class AssDialogue : public AssEntry {
 	wxString GetData(bool ssa) const;
 public:
+	/// Unique ID of this line. Copies of the line for Undo/Redo purposes
+	/// preserve the unique ID, so that the equivalent lines can be found in
+	/// the different versions of the file.
+	const int Id;
+
 	/// Is this a comment line?
 	bool Comment;
 	/// Layer number

aegisub/src/command/edit.cpp

@@ -585,7 +585,7 @@ static void duplicate_lines(agi::Context *c, bool shift) {
 		// Duplicate each of the selected lines, inserting them in a block
 		// after the selected block
 		do {
-			AssDialogue *new_diag = static_cast<AssDialogue*>(start->Clone());
+			AssDialogue *new_diag = new AssDialogue(*static_cast<AssDialogue*>(&*start));
 
 			c->ass->Line.insert(insert_pos, *new_diag);
 			new_sel.insert(new_diag);

aegisub/src/subtitle_format.cpp

@@ -228,7 +228,7 @@ void SubtitleFormat::RecombineOverlaps(AssFile &file) {
 		//Is there an A part before the overlap?
 		if (curdlg->Start > prevdlg->Start) {
 			// Produce new entry with correct values
-			AssDialogue *newdlg = static_cast<AssDialogue*>(prevdlg->Clone());
+			AssDialogue *newdlg = new AssDialogue(*prevdlg);
 			newdlg->Start = prevdlg->Start;
 			newdlg->End = curdlg->Start;
 			newdlg->Text = prevdlg->Text;
@@ -238,7 +238,7 @@ void SubtitleFormat::RecombineOverlaps(AssFile &file) {
 
 		// Overlapping A+B part
 		{
-			AssDialogue *newdlg = static_cast<AssDialogue*>(prevdlg->Clone());
+			AssDialogue *newdlg = new AssDialogue(*prevdlg);
 			newdlg->Start = curdlg->Start;
 			newdlg->End = (prevdlg->End < curdlg->End) ? prevdlg->End : curdlg->End;
 			// Put an ASS format hard linewrap between lines
@@ -250,7 +250,7 @@ void SubtitleFormat::RecombineOverlaps(AssFile &file) {
 		// Is there an A part after the overlap?
 		if (prevdlg->End > curdlg->End) {
 			// Produce new entry with correct values
-			AssDialogue *newdlg = static_cast<AssDialogue*>(prevdlg->Clone());
+			AssDialogue *newdlg = new AssDialogue(*prevdlg);
 			newdlg->Start = curdlg->End;
 			newdlg->End = prevdlg->End;
 			newdlg->Text = prevdlg->Text;
@@ -261,7 +261,7 @@ void SubtitleFormat::RecombineOverlaps(AssFile &file) {
 		// Is there a B part after the overlap?
 		if (curdlg->End > prevdlg->End) {
 			// Produce new entry with correct values
-			AssDialogue *newdlg = static_cast<AssDialogue*>(prevdlg->Clone());
+			AssDialogue *newdlg = new AssDialogue(*prevdlg);
 			newdlg->Start = prevdlg->End;
 			newdlg->End = curdlg->End;
 			newdlg->Text = curdlg->Text;