feat: allow fibers as map keys by adding unique fiber IDs and hash support

Add a unique numeric ID to each fiber allocation, enabling fibers to be used as map keys. This includes updating the hash function for OBJ_FIBER to return the fiber's ID, modifying key validation to accept fibers, updating documentation to describe the new capability, and adjusting all relevant test expectations and error messages.

src/vm/wren_primitive.c

@@ -53,13 +53,13 @@ uint32_t validateIndexValue(WrenVM* vm, Value* args, uint32_t count,
 bool validateKey(WrenVM* vm, Value* args, int index)
 {
   Value arg = args[index];
-  if (IS_BOOL(arg) || IS_CLASS(arg) || IS_NULL(arg) ||
+  if (IS_BOOL(arg) || IS_CLASS(arg) || IS_FIBER(arg) || IS_NULL(arg) ||
       IS_NUM(arg) || IS_RANGE(arg) || IS_STRING(arg))
   {
     return true;
   }
 
-  args[0] = CONST_STRING(vm, "Key must be a value type.");
+  args[0] = CONST_STRING(vm, "Key must be a value type or fiber.");
   return false;
 }
 

src/vm/wren_value.c

@@ -136,6 +136,7 @@ ObjFiber* wrenNewFiber(WrenVM* vm, Obj* fn)
 {
   ObjFiber* fiber = ALLOCATE(vm, ObjFiber);
   initObj(vm, &fiber->obj, OBJ_FIBER, vm->fiberClass);
+  fiber->id = vm->nextFiberId++;
 
   wrenResetFiber(fiber, fn);
 
@@ -322,6 +323,9 @@ static uint32_t hashObject(Obj* object)
       // Classes just use their name.
       return hashObject((Obj*)((ObjClass*)object)->name);
 
+    case OBJ_FIBER:
+      return ((ObjFiber*)object)->id;
+
     case OBJ_RANGE:
     {
       ObjRange* range = (ObjRange*)object;

src/vm/wren_value.h

@@ -133,7 +133,8 @@ typedef enum
 typedef struct
 {
   ValueType type;
-  union {
+  union
+  {
     double num;
     Obj* obj;
   } as;
@@ -226,6 +227,10 @@ typedef struct sObjFiber
   // error message. Otherwise, it will be NULL.
   ObjString* error;
 
+  // A unique-ish numeric ID for the fiber. Lets fibers be used as map keys.
+  // Unique-ish since IDs may overflow and wrap around.
+  uint16_t id;
+
   // This will be true if the caller that called this fiber did so using "try".
   // In that case, if this fiber fails with an error, the error will be given
   // to the caller.

src/vm/wren_vm.h

@@ -50,6 +50,11 @@ struct WrenVM
   // for the module.
   ObjMap* modules;
 
+  // The ID that will be assigned to the next fiber that is allocated. Fibers
+  // are given unique-ish (not completely unique since this can overflow) IDs
+  // so that they can be used as map keys.
+  uint16_t nextFiberId;
+
   // Memory management data:
 
   // The externally-provided function used to allocate memory.