Allow promotion choice in engine-defined variants

When variant shatranj, courier or makruk, which normally do not have
promotion choice, are used as parent for an engine-defined variant,
we now invoke the piece-selection routine. This to make these variants
also suitable as parent for variants that do have choice (e.g. to give
them the baring rule, which is unique for Shatranj).

diff --git a/backend.c b/backend.c
index bc6ec28..b49ba15 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -6742,7 +6742,7 @@ HasPromotionChoice (int fromX, int fromY, int toX, int toY, char *promoChoice, i
            *promoChoice = PieceToChar(p++);
            if(*promoChoice != '.') break;
        }
-       return FALSE;
+       if(!*engineVariant) return FALSE; // if used as parent variant there might be promotion choice
     }
     // no sense asking what we must promote to if it is going to explode...
     if(gameInfo.variant == VariantAtomic && boards[currentMove][toY][toX] != EmptySquare) {
@@ -7449,8 +7449,8 @@ CanPromote (ChessSquare piece, int y)
        // some variants have fixed promotion piece, no promotion at all, or another selection mechanism
        if(IS_SHOGI(gameInfo.variant)          || gameInfo.variant == VariantXiangqi ||
           gameInfo.variant == VariantSuper    || gameInfo.variant == VariantGreat   ||
-          gameInfo.variant == VariantShatranj || gameInfo.variant == VariantCourier ||
-         gameInfo.variant == VariantMakruk) return FALSE;
+         (gameInfo.variant == VariantShatranj || gameInfo.variant == VariantCourier ||
+           gameInfo.variant == VariantMakruk) && !*engineVariant) return FALSE;
        return (piece == BlackPawn && y <= zone ||
                piece == WhitePawn && y >= BOARD_HEIGHT-1-zone ||
                piece == BlackLance && y <= zone ||