Let target-square highlighting prevail over legality test

For engine-defined variants the highlight command is accepted even
with legality testing on. If an engine explicitly marks a square as a
legal destination for the picked-up piece, XBoard now always accepts
the move, even when according to its own move generation, even when based
on the engine's supplied 'piece' commands, going there would be illegal,
and legality testing is on.

diff --git a/backend.c b/backend.c
index 06bf7ba..e5a79a3 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -7080,6 +7080,8 @@ UserMoveEvent(int fromX, int fromY, int toX, int toY, int promoChar)
 
     if(fromY == DROP_RANK && fromX == EmptySquare && (gameMode == AnalyzeMode || gameMode == EditGame || PosFlags(0) & F_NULL_MOVE)) moveType = NormalMove;
 
+    if(moveType == IllegalMove && legal[toY][toX] > 1) moveType = NormalMove; // someone explicitly told us this move is legal
+
     /* [HGM] but possibly ignore an IllegalMove result */
     if (appData.testLegality) {
        if (moveType == IllegalMove || moveType == ImpossibleMove) {
@@ -7315,7 +7317,7 @@ MarkByFEN(char *fen)
            int s = 0;
            marker[r][f] = 0;
            if(*fen == 'M') legal[r][f] = 2; else // request promotion choice
-           if(*fen >= 'A' && *fen <= 'Z') legal[r][f] = 1; else
+           if(*fen >= 'A' && *fen <= 'Z') legal[r][f] = 3; else
            if(*fen >= 'a' && *fen <= 'z') *fen += 'A' - 'a';
            if(*fen == '/' && f > BOARD_LEFT) f = BOARD_LEFT, r--; else
            if(*fen == 'T') marker[r][f++] = 0; else
@@ -7347,8 +7349,8 @@ Mark (Board board, int flags, ChessMove kind, int rf, int ff, int rt, int ft, VO
     if(rf == fromY && ff == fromX && (killX < 0 ? !(rt == rf && ft == ff) && legNr & 1 : rt == killY && ft == killX || legNr & 2))
        (*m)[rt][ft] = 1 + (board[rt][ft] != EmptySquare
                         || kind == WhiteCapturesEnPassant
-                        || kind == BlackCapturesEnPassant) + 3*(kind == FirstLeg && killX < 0), legal[rt][ft] = 1;
-    else if(flags & F_MANDATORY_CAPTURE && board[rt][ft] != EmptySquare) (*m)[rt][ft] = 3, legal[rt][ft] = 1;
+                        || kind == BlackCapturesEnPassant) + 3*(kind == FirstLeg && killX < 0), legal[rt][ft] = 3;
+    else if(flags & F_MANDATORY_CAPTURE && board[rt][ft] != EmptySquare) (*m)[rt][ft] = 3, legal[rt][ft] = 3;
 }
 
 static int hoverSavedValid;