New name UI_UPDATE for interpret_move's return "".

Now midend.c directly tests the returned pointer for equality to this
value, instead of checking whether it's the empty string.

A minor effect of this is that games may now return a dynamically
allocated empty string from interpret_move() and treat it as just
another legal move description. But I don't expect anyone to be
perverse enough to actually do that! The main purpose is that it
avoids returning a string literal from a function whose return type is
a pointer to _non-const_ char, i.e. we are now one step closer to
being able to make this code base clean under -Wwrite-strings.

1 files changed, 2 insertions, 1 deletions

diff --git a/midend.c b/midend.c
index 93334f6..913b322 100644
--- a/midend.c
+++ b/midend.c
@@ -782,7 +782,7 @@ static int midend_really_process_key(midend *me, int x, int y, int button)
 	} else
 	    goto done;
     } else {
-	if (!*movestr)
+	if (movestr == UI_UPDATE)
 	    s = me->states[me->statepos-1].state;
 	else {
 	    s = me->ourgame->execute_move(me->states[me->statepos-1].state,
@@ -1662,6 +1662,7 @@ char *midend_solve(midend *me)
     movestr = me->ourgame->solve(me->states[0].state,
 				 me->states[me->statepos-1].state,
 				 me->aux_info, &msg);
+    assert(movestr != UI_UPDATE);
     if (!movestr) {
 	if (!msg)
 	    msg = "Solve operation failed";   /* _shouldn't_ happen, but can */