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/pattern.c b/pattern.c
index e5f958a..9964dd5 100644
--- a/pattern.c
+++ b/pattern.c
@@ -1285,7 +1285,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         ui->drag_start_y = ui->drag_end_y = y;
         ui->cur_visible = 0;
 
-        return "";		       /* UI activity occurred */
+        return UI_UPDATE;
     }
 
     if (ui->dragging && button == ui->drag) {
@@ -1314,7 +1314,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         ui->drag_end_x = x;
         ui->drag_end_y = y;
 
-        return "";		       /* UI activity occurred */
+        return UI_UPDATE;
     }
 
     if (ui->dragging && button == ui->release) {
@@ -1342,7 +1342,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
 		    x1, y1, x2-x1+1, y2-y1+1);
 	    return dupstr(buf);
         } else
-            return "";		       /* UI activity occurred */
+            return UI_UPDATE;
     }
 
     if (IS_CURSOR_MOVE(button)) {
@@ -1350,12 +1350,12 @@ static char *interpret_move(const game_state *state, game_ui *ui,
 	char buf[80];
         move_cursor(button, &ui->cur_x, &ui->cur_y, state->common->w, state->common->h, 0);
         ui->cur_visible = 1;
-	if (!control && !shift) return "";
+	if (!control && !shift) return UI_UPDATE;
 
 	newstate = control ? shift ? GRID_UNKNOWN : GRID_FULL : GRID_EMPTY;
 	if (state->grid[y * state->common->w + x] == newstate &&
 	    state->grid[ui->cur_y * state->common->w + ui->cur_x] == newstate)
-	    return "";
+	    return UI_UPDATE;
 
 	sprintf(buf, "%c%d,%d,%d,%d", control ? shift ? 'U' : 'F' : 'E',
 		min(x, ui->cur_x), min(y, ui->cur_y),
@@ -1370,7 +1370,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
 
         if (!ui->cur_visible) {
             ui->cur_visible = 1;
-            return "";
+            return UI_UPDATE;
         }
 
         if (button == CURSOR_SELECT2)