Improve DEPM

Now any sequence of spaces around old cursor will be removed, even at
start or end of paragraph. Sequences of more than 2 characters are
also taken into account.

The version of DEPM which acts on a sequence of paragraphs is also
rewritten to match the local one.

(cherry picked from commit 20976e81fb)
(cherry picked from commit c54fe6c584)

src/Text.h

@@ -347,10 +347,6 @@ private:
 	/// The InsetText owner shall have access to everything.
 	friend class InsetText;
 
-	// fix the cursor `cur' after a characters has been deleted at `where'
-	// position. Called by deleteEmptyParagraphMechanism
-	static void fixCursorAfterDelete(CursorSlice & cur, CursorSlice const & where);
-
 	// At cursor position 0, try to merge the paragraph with the one before it.
 	// Ignore change tracking, i.e., physically remove the end-of-par character
 	bool backspacePos0(Cursor & cur);

src/Text2.cpp

@@ -785,9 +785,11 @@ bool Text::cursorDownParagraph(Cursor & cur)
 }
 
 
-// fix the cursor `cur' after a characters has been deleted at `where'
+namespace {
+// fix the cursor `cur' after characters has been deleted at `where'
 // position. Called by deleteEmptyParagraphMechanism
-void Text::fixCursorAfterDelete(CursorSlice & cur, CursorSlice const & where)
+void fixCursorAfterDelete(CursorSlice & cur, CursorSlice const & where,
+						  pos_type from, pos_type to)
 {
 	// Do nothing if cursor is not in the paragraph where the
 	// deletion occurred,
@@ -795,8 +797,8 @@ void Text::fixCursorAfterDelete(CursorSlice & cur, CursorSlice const & where)
 		return;
 
 	// If cursor position is after the deletion place update it
-	if (cur.pos() > where.pos())
-		--cur.pos();
+	if (cur.pos() > from)
+		cur.pos() = max(from, cur.pos() - (to - from));
 
 	// Check also if we don't want to set the cursor on a spot behind the
 	// pagragraph because we erased the last character.
@@ -804,6 +806,8 @@ void Text::fixCursorAfterDelete(CursorSlice & cur, CursorSlice const & where)
 		cur.pos() = cur.lastpos();
 }
 
+}
+
 
 bool Text::deleteEmptyParagraphMechanism(Cursor & cur,
 		Cursor & old, bool & need_anchor_change)
@@ -845,23 +849,35 @@ bool Text::deleteEmptyParagraphMechanism(Cursor & cur,
 	bool const same_par_pos = depth == cur.depth() - 1 && same_par
 		&& old.pos() == cur[depth].pos();
 
-	// If the chars around the old cursor were spaces, delete one of them.
+	// If the chars around the old cursor were spaces, delete some of
+	// them , but only if the cursor has really moved.
 	if (!same_par_pos) {
-		// Only if the cursor has really moved.
-		if (old.pos() > 0
-		    && old.pos() < oldpar.size()
-		    && oldpar.isLineSeparator(old.pos())
-		    && oldpar.isLineSeparator(old.pos() - 1)
-		    && !oldpar.isDeleted(old.pos() - 1)
-		    && !oldpar.isDeleted(old.pos())) {
-			oldpar.eraseChar(old.pos() - 1, cur.buffer()->params().track_changes);
+		// find range of spaces around cursors
+		int from = old.pos();
+		while (from > 0
+		       && oldpar.isLineSeparator(from - 1)
+		       && !oldpar.isDeleted(from - 1))
+			--from;
+		int to = old.pos();
+		while (to < oldpar.size() - 1
+		       && oldpar.isLineSeparator(to)
+		       && !oldpar.isDeleted(to))
+			++to;
+
+		// If we are not at the extremity of the paragraph, keep one space
+		if (from != to && from > 0 && to < oldpar.size())
+			++from;
+
+		// Remove spaces and adapt cursor.
+		if (from < to) {
+			oldpar.eraseChars(from, to, cur.buffer()->params().track_changes);
 // FIXME: This will not work anymore when we have multiple views of the same buffer
 // In this case, we will have to correct also the cursors held by
 // other bufferviews. It will probably be easier to do that in a more
 // automated way in CursorSlice code. (JMarc 26/09/2001)
 			// correct all cursor parts
 			if (same_par) {
-				fixCursorAfterDelete(cur[depth], old.top());
+				fixCursorAfterDelete(cur[depth], old.top(), from, to);
 				need_anchor_change = true;
 			}
 			return true;
@@ -930,13 +946,26 @@ void Text::deleteEmptyParagraphMechanism(pit_type first, pit_type last, bool tra
 		if (par.isFreeSpacing())
 			continue;
 
-		for (pos_type pos = 1; pos < par.size(); ++pos) {
-			if (par.isLineSeparator(pos) && par.isLineSeparator(pos - 1)
-			    && !par.isDeleted(pos - 1)) {
-				if (par.eraseChar(pos - 1, trackChanges)) {
-					--pos;
-				}
-			}
+		pos_type from = 0;
+		while (from < par.size()) {
+			// skip non-spaces
+			while (from < par.size()
+			       && (!par.isLineSeparator(from) || par.isDeleted(from)))
+				++from;
+			// find string of spaces
+			pos_type to = from;
+			while (to < par.size()
+			       && par.isLineSeparator(to) && !par.isDeleted(to))
+				++to;
+			// empty? We are done
+			if (from == to)
+				break;
+			// if inside the line, keep one space
+			if (from > 0 && to < par.size())
+				++from;
+			// remove the extra spaces
+			if (from < to)
+				par.eraseChars(from, to, trackChanges);
 		}
 
 		// don't delete anything if this is the only remaining paragraph