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, 6 insertions, 6 deletions

diff --git a/mines.c b/mines.c
index 57f778a..5bae0e8 100644
--- a/mines.c
+++ b/mines.c
@@ -2432,14 +2432,14 @@ static char *interpret_move(const game_state *from, game_ui *ui,
     if (IS_CURSOR_MOVE(button)) {
         move_cursor(button, &ui->cur_x, &ui->cur_y, from->w, from->h, 0);
         ui->cur_visible = 1;
-        return "";
+        return UI_UPDATE;
     }
     if (IS_CURSOR_SELECT(button)) {
         int v = from->grid[ui->cur_y * from->w + ui->cur_x];
 
         if (!ui->cur_visible) {
             ui->cur_visible = 1;
-            return "";
+            return UI_UPDATE;
         }
         if (button == CURSOR_SELECT2) {
             /* As for RIGHT_BUTTON; only works on covered square. */
@@ -2479,7 +2479,7 @@ static char *interpret_move(const game_state *from, game_ui *ui,
 	else if (button == MIDDLE_BUTTON)
 	    ui->validradius = 1;
         ui->cur_visible = 0;
-	return "";
+	return UI_UPDATE;
     }
 
     if (button == RIGHT_BUTTON) {
@@ -2507,10 +2507,10 @@ static char *interpret_move(const game_state *from, game_ui *ui,
 
 	/*
 	 * At this stage we must never return NULL: we have adjusted
-	 * the ui, so at worst we return "".
+	 * the ui, so at worst we return UI_UPDATE.
 	 */
 	if (cx < 0 || cx >= from->w || cy < 0 || cy >= from->h)
-	    return "";
+	    return UI_UPDATE;
 
 	/*
 	 * Left-clicking on a covered square opens a tile. Not
@@ -2588,7 +2588,7 @@ uncover:
 	    }
 	}
 
-	return "";
+	return UI_UPDATE;
     }
 }