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, 10 insertions, 10 deletions

diff --git a/tracks.c b/tracks.c
index e4e7b5c..f5f3e0b 100644
--- a/tracks.c
+++ b/tracks.c
@@ -1922,13 +1922,13 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         ui->drag_sx = ui->drag_ex = gx;
         ui->drag_sy = ui->drag_ey = gy;
 
-        return "";
+        return UI_UPDATE;
     }
 
     if (IS_MOUSE_DRAG(button)) {
         ui->cursor_active = FALSE;
         update_ui_drag(state, ui, gx, gy);
-        return "";
+        return UI_UPDATE;
     }
 
     if (IS_MOUSE_RELEASE(button)) {
@@ -1965,12 +1965,12 @@ static char *interpret_move(const game_state *state, game_ui *ui,
             cy = CENTERED_COORD(gy);
 
             if (!INGRID(state, gx, gy) || FROMCOORD(x) != gx || FROMCOORD(y) != gy)
-                return "";
+                return UI_UPDATE;
 
             if (max(abs(x-cx),abs(y-cy)) < TILE_SIZE/4) {
                 if (ui_can_flip_square(state, gx, gy, button == RIGHT_RELEASE))
                     return square_flip_str(state, gx, gy, button == RIGHT_RELEASE, tmpbuf);
-                return "";
+                return UI_UPDATE;
             } else {
                 if (abs(x-cx) < abs(y-cy)) {
                     /* Closest to top/bottom edge. */
@@ -1984,7 +1984,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
                     return edge_flip_str(state, gx, gy, direction,
                             button == RIGHT_RELEASE, tmpbuf);
                 else
-                    return "";
+                    return UI_UPDATE;
             }
         }
     }
@@ -1997,7 +1997,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
 
         if (!ui->cursor_active) {
             ui->cursor_active = TRUE;
-            return "";
+            return UI_UPDATE;
         }
 
         ui->curx = ui->curx + dx;
@@ -2008,17 +2008,17 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         }
         ui->curx = min(max(ui->curx, 1), 2*w-1);
         ui->cury = min(max(ui->cury, 1), 2*h-1);
-        return "";
+        return UI_UPDATE;
     }
 
     if (IS_CURSOR_SELECT(button)) {
         if (!ui->cursor_active) {
             ui->cursor_active = TRUE;
-            return "";
+            return UI_UPDATE;
         }
         /* click on square corner does nothing (shouldn't get here) */
         if ((ui->curx % 2) == 0 && (ui->cury % 2 == 0))
-            return "";
+            return UI_UPDATE;
 
         gx = ui->curx / 2;
         gy = ui->cury / 2;
@@ -2030,7 +2030,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         else if (!direction &&
                  ui_can_flip_square(state, gx, gy, button == CURSOR_SELECT2))
             return square_flip_str(state, gx, gy, button == CURSOR_SELECT2, tmpbuf);
-        return "";
+        return UI_UPDATE;
     }
 
 #if 0