Always remove selection after cursor up/down

When the cursor cannot move on cursor up/down, at least the selection
should be cleared (when not selecting).

To detect this, the method Cursor::upDownInText has been modified to
return true when cursor is at top/bottom of inset, but there is some
room above/below.

Moreover, introduce the functions LFUN_FINISHED_UP/DOWN, which is
dispatched at upper cursor level as long as no local movement is
possible. This allows to handle differently the original char moving
action and its consequences.

Fixes part of bug #12310.

src/Cursor.cpp

@@ -2216,7 +2216,7 @@ bool Cursor::upDownInText(bool up, bool & updateNeeded)
 			if (updateNeeded)
 				forceBufferUpdate();
 		}
-		return false;
+		return valid_destination;
 	}
 
 	// with and without selection are handled differently

src/Cursor.h

@@ -496,8 +496,9 @@ public:
 	/// return true if fullscreen update is needed
 	bool down();
 	/// move up/down in a text inset, called for LFUN_UP/DOWN,
-	/// return true if successful, updateNeeded set to true if fullscreen
-	/// update is needed, otherwise it's not touched
+	/// return true if the cursor has moved or can move, updateNeeded
+	/// set to true if fullscreen update is needed, otherwise it's not
+	/// touched
 	bool upDownInText(bool up, bool & updateNeeded);
 	/// move up/down in math or any non text inset, call for LFUN_UP/DOWN
 	/// return true if successful

src/FuncCode.h

@@ -500,6 +500,8 @@ enum FuncCode
 	LFUN_SPELLING_ADD_LOCAL,        // jspitzm 20210306
 	// 390
 	LFUN_SPELLING_REMOVE_LOCAL,     // jspitzm 20210307
+	LFUN_FINISHED_DOWN,             // lasgouttes 20210629
+	LFUN_FINISHED_UP,               // lasgouttes 20210629
 	LFUN_LASTACTION                 // end of the table
 };
 

src/LyXAction.cpp

@@ -1668,6 +1668,22 @@ void LyXAction::init()
  */
 		{ LFUN_FINISHED_RIGHT, "", ReadOnly, Hidden },
 
+/*!
+ * \var lyx::FuncCode lyx::LFUN_FINISHED_UP
+ * \li Action: Moves the cursor out of the current slice, going up.
+ * \li Notion: See also #LFUN_FINISHED_DOWN.
+ * \endvar
+ */
+		{ LFUN_FINISHED_UP, "", ReadOnly, Hidden },
+
+/*!
+ * \var lyx::FuncCode lyx::LFUN_FINISHED_DOWN
+ * \li Action: Moves the cursor out of the current slice, going down.
+ * \li Notion: See also #LFUN_FINISHED_DOWN.
+ * \endvar
+ */
+		{ LFUN_FINISHED_DOWN, "", ReadOnly, Hidden },
+
 /*!
  * \var lyx::FuncCode lyx::LFUN_FLEX_INSERT
  * \li Action: Inserts CharStyle, Custom inset or XML short element.

src/Text3.cpp

@@ -892,14 +892,12 @@ void Text::dispatch(Cursor & cur, FuncRequest & cmd)
 	case LFUN_UP:
 	case LFUN_DOWN: {
 		// stop/start the selection
-		bool select = cmd.action() == LFUN_DOWN_SELECT ||
-			cmd.action() == LFUN_UP_SELECT;
-
+		bool const select = cmd.action() == LFUN_DOWN_SELECT
+			                || cmd.action() == LFUN_UP_SELECT;
 		// move cursor up/down
-		bool up = cmd.action() == LFUN_UP_SELECT || cmd.action() == LFUN_UP;
-		bool const atFirstOrLastRow = cur.atFirstOrLastRow(up);
+		bool const up = cmd.action() == LFUN_UP_SELECT || cmd.action() == LFUN_UP;
 
-		if (!atFirstOrLastRow) {
+		if (!cur.atFirstOrLastRow(up)) {
 			needsUpdate |= cur.selHandle(select);
 			cur.upDownInText(up, needsUpdate);
 			needsUpdate |= cur.beforeDispatchCursor().inMathed();
@@ -915,13 +913,35 @@ void Text::dispatch(Cursor & cur, FuncRequest & cmd)
 					cur.forceBufferUpdate();
 				break;
 			}
+			needsUpdate |= cur.selHandle(select);
+			bool const can_move = cur.upDownInText(up, needsUpdate);
+			// if the cursor can be moved up or down at an upper level,
+			// delegate the dispatch to next level. Otherwise, we are
+			// done.
+			if (can_move) {
+				cmd = FuncRequest(up ? LFUN_FINISHED_UP : LFUN_FINISHED_DOWN);
+				cur.undispatched();
+			}
+		}
 
-			// if the cursor cannot be moved up or down do not remove
-			// the selection right now, but wait for the next dispatch.
-			if (select)
-				needsUpdate |= cur.selHandle(select);
+		break;
+	}
+
+	case LFUN_FINISHED_UP:
+	case LFUN_FINISHED_DOWN: {
+		// move cursor up/down
+		bool const up = cmd.action() == LFUN_FINISHED_UP;
+
+		if (!cur.atFirstOrLastRow(up)) {
 			cur.upDownInText(up, needsUpdate);
-			cur.undispatched();
+			needsUpdate |= cur.beforeDispatchCursor().inMathed();
+		} else {
+			bool const can_move = cur.upDownInText(up, needsUpdate);
+			// if the cursor can be moved up or down and we are not
+			// moving cusor at top level, wait for the next dispatch.
+			// Otherwise, we are done.
+			if (can_move)
+				cur.undispatched();
 		}
 
 		break;