Add requireStrMin save-JSON shorthand

Replaces the hand-rolled mapName missing/null/empty check in
saveSlotVer1ReadJSON with a reusable macro.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

src/dusk/save/savejson.h

@@ -481,6 +481,26 @@
 #define requireString(key) \
   if(!hasString(key)) errorThrow("Save JSON missing '%s' key", key)
 
+/**
+ * Errors if the given key is missing, not a string, or a string shorter
+ * than the given minimum length - e.g. requireStrMin(key, 1) to reject a
+ * missing/null/empty string outright.
+ *
+ * @param key The key to check.
+ * @param len The minimum string length required.
+ */
+#define requireStrMin(key, len) { \
+  yyjson_val *saveJsonStrMinVal = yyjson_obj_get(object, key); \
+  if( \
+    saveJsonStrMinVal == NULL || !yyjson_is_str(saveJsonStrMinVal) || \
+    yyjson_get_len(saveJsonStrMinVal) < (size_t)(len) \
+  ) { \
+    errorThrow( \
+      "Save JSON '%s' must be a string of at least length %d", key, (int)(len) \
+    ); \
+  } \
+}
+
 /**
  * Writes a string to the current JSON object. The string is copied, so it
  * does not need to outlive the JSON document.

src/dusk/save/slot/saveslotver1.c

@@ -62,18 +62,7 @@ errorret_t saveSlotVer1ReadJSON(saveslotver1_t *slot, yyjson_val *object) {
 
   readTime("time", slot->time);
   readInt32("playerLevel", slot->playerLevel, 1);
-
+  requireStrMin("mapName", 1);
-  // A blank/never-used slot returned early above (see saveSlotInUse -
-  // keyed off "name"), so name is guaranteed non-empty here - and an
-  // in-use slot always has a map name too (see saveSlotNewGame). Missing,
-  // null, or empty means this save is corrupt.
-  yyjson_val *mapNameVal = yyjson_obj_get(object, "mapName");
-  if(
-    mapNameVal == NULL || !yyjson_is_str(mapNameVal) ||
-    yyjson_get_len(mapNameVal) == 0
-  ) {
-    errorThrow("Save JSON 'mapName' must be a non-empty string");
-  }
   readString(
     "mapName", slot->mapName, "", SAVE_SLOT_VER1_MAP_NAME_MAX - 1
   );