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, 16 insertions, 12 deletions

diff --git a/signpost.c b/signpost.c
index ca72768..9d782f0 100644
--- a/signpost.c
+++ b/signpost.c
@@ -1441,18 +1441,20 @@ static char *interpret_move(const game_state *state, game_ui *ui,
             ui->dx = COORD(ui->cx) + TILE_SIZE/2;
             ui->dy = COORD(ui->cy) + TILE_SIZE/2;
         }
-        return "";
+        return UI_UPDATE;
     } else if (IS_CURSOR_SELECT(button)) {
         if (!ui->cshow)
             ui->cshow = 1;
         else if (ui->dragging) {
             ui->dragging = FALSE;
-            if (ui->sx == ui->cx && ui->sy == ui->cy) return "";
+            if (ui->sx == ui->cx && ui->sy == ui->cy) return UI_UPDATE;
             if (ui->drag_is_from) {
-                if (!isvalidmove(state, 0, ui->sx, ui->sy, ui->cx, ui->cy)) return "";
+                if (!isvalidmove(state, 0, ui->sx, ui->sy, ui->cx, ui->cy))
+                    return UI_UPDATE;
                 sprintf(buf, "L%d,%d-%d,%d", ui->sx, ui->sy, ui->cx, ui->cy);
             } else {
-                if (!isvalidmove(state, 0, ui->cx, ui->cy, ui->sx, ui->sy)) return "";
+                if (!isvalidmove(state, 0, ui->cx, ui->cy, ui->sx, ui->sy))
+                    return UI_UPDATE;
                 sprintf(buf, "L%d,%d-%d,%d", ui->cx, ui->cy, ui->sx, ui->sy);
             }
             return dupstr(buf);
@@ -1464,7 +1466,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
             ui->dy = COORD(ui->cy) + TILE_SIZE/2;
             ui->drag_is_from = (button == CURSOR_SELECT) ? 1 : 0;
         }
-        return "";
+        return UI_UPDATE;
     }
     if (IS_MOUSE_DOWN(button)) {
         if (ui->cshow) {
@@ -1492,29 +1494,31 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         ui->dx = mx;
         ui->dy = my;
         ui->cshow = 0;
-        return "";
+        return UI_UPDATE;
     } else if (IS_MOUSE_DRAG(button) && ui->dragging) {
         ui->dx = mx;
         ui->dy = my;
-        return "";
+        return UI_UPDATE;
     } else if (IS_MOUSE_RELEASE(button) && ui->dragging) {
         ui->dragging = FALSE;
-        if (ui->sx == x && ui->sy == y) return ""; /* single click */
+        if (ui->sx == x && ui->sy == y) return UI_UPDATE; /* single click */
 
         if (!INGRID(state, x, y)) {
             int si = ui->sy*w+ui->sx;
             if (state->prev[si] == -1 && state->next[si] == -1)
-                return "";
+                return UI_UPDATE;
             sprintf(buf, "%c%d,%d",
                     (int)(ui->drag_is_from ? 'C' : 'X'), ui->sx, ui->sy);
             return dupstr(buf);
         }
 
         if (ui->drag_is_from) {
-            if (!isvalidmove(state, 0, ui->sx, ui->sy, x, y)) return "";
+            if (!isvalidmove(state, 0, ui->sx, ui->sy, x, y))
+                return UI_UPDATE;
             sprintf(buf, "L%d,%d-%d,%d", ui->sx, ui->sy, x, y);
         } else {
-            if (!isvalidmove(state, 0, x, y, ui->sx, ui->sy)) return "";
+            if (!isvalidmove(state, 0, x, y, ui->sx, ui->sy))
+                return UI_UPDATE;
             sprintf(buf, "L%d,%d-%d,%d", x, y, ui->sx, ui->sy);
         }
         return dupstr(buf);
@@ -1523,7 +1527,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
     else if ((button == 'x' || button == 'X') && ui->cshow) {
         int si = ui->cy*w + ui->cx;
         if (state->prev[si] == -1 && state->next[si] == -1)
-            return "";
+            return UI_UPDATE;
         sprintf(buf, "%c%d,%d",
                 (int)((button == 'x') ? 'C' : 'X'), ui->cx, ui->cy);
         return dupstr(buf);