Don't pass fiber explicitly to primitives.

Thanks, Michel!

src/vm/wren_core.c

@@ -133,7 +133,7 @@ DEF_PRIMITIVE(fiber_call1)
 
 DEF_PRIMITIVE(fiber_current)
 {
-  RETURN_OBJ(fiber);
+  RETURN_OBJ(vm->fiber);
 }
 
 DEF_PRIMITIVE(fiber_error)
@@ -174,6 +174,7 @@ DEF_PRIMITIVE(fiber_transferError)
 
 DEF_PRIMITIVE(fiber_try)
 {
+  ObjFiber* current = vm->fiber;
   ObjFiber* tried = AS_FIBER(args[0]);
   // TODO: Use runFiber().
   if (tried->numFrames == 0) RETURN_ERROR("Cannot try a finished fiber.");
@@ -182,7 +183,7 @@ DEF_PRIMITIVE(fiber_try)
   vm->fiber = tried;
   
   // Remember who ran it.
-  vm->fiber->caller = fiber;
+  vm->fiber->caller = current;
   vm->fiber->callerIsTrying = true;
 
   // If the fiber was yielded, make the yield call return null.
@@ -196,11 +197,12 @@ DEF_PRIMITIVE(fiber_try)
 
 DEF_PRIMITIVE(fiber_yield)
 {
-  vm->fiber = fiber->caller;
+  ObjFiber* current = vm->fiber;
+  vm->fiber = current->caller;
   
   // Unhook this fiber from the one that called it.
-  fiber->caller = NULL;
-  fiber->callerIsTrying = false;
+  current->caller = NULL;
+  current->callerIsTrying = false;
 
   if (vm->fiber != NULL)
   {
@@ -213,11 +215,12 @@ DEF_PRIMITIVE(fiber_yield)
 
 DEF_PRIMITIVE(fiber_yield1)
 {
-  vm->fiber = fiber->caller;
+  ObjFiber* current = vm->fiber;
+  vm->fiber = current->caller;
   
   // Unhook this fiber from the one that called it.
-  fiber->caller = NULL;
-  fiber->callerIsTrying = false;
+  current->caller = NULL;
+  current->callerIsTrying = false;
 
   if (vm->fiber != NULL)
   {
@@ -228,7 +231,7 @@ DEF_PRIMITIVE(fiber_yield1)
     // call in its stack. Since Fiber.yield(value) has two arguments (the Fiber
     // class and the value) and we only need one slot for the result, discard
     // the other slot now.
-    fiber->stackTop--;
+    current->stackTop--;
   }
 
   return PRIM_FIBER;

src/vm/wren_meta.c

@@ -13,7 +13,7 @@ DEF_PRIMITIVE(meta_eval)
   if (!validateString(vm, args[1], "Source code")) return PRIM_FIBER;
 
   // Eval the code in the module where the calling function was defined.
-  Value callingFn = OBJ_VAL(fiber->frames[fiber->numFrames - 1].fn);
+  Value callingFn = OBJ_VAL(vm->fiber->frames[vm->fiber->numFrames - 1].fn);
   ObjModule* module = IS_FN(callingFn)
       ? AS_FN(callingFn)->module
       : AS_CLOSURE(callingFn)->fn->module;
@@ -30,7 +30,7 @@ DEF_PRIMITIVE(meta_eval)
   ObjFiber* evalFiber = wrenNewFiber(vm, (Obj*)fn);
 
   // Remember what fiber to return to.
-  evalFiber->caller = fiber;
+  evalFiber->caller = vm->fiber;
 
   // Switch to the fiber.
   vm->fiber = evalFiber;

src/vm/wren_primitive.h

@@ -19,7 +19,7 @@
 // the actual type signature of a primitive function and makes it clear which C
 // functions are invoked as primitives.
 #define DEF_PRIMITIVE(name) \
-    static PrimitiveResult prim_##name(WrenVM* vm, ObjFiber* fiber, Value* args)
+    static PrimitiveResult prim_##name(WrenVM* vm, Value* args)
 
 #define RETURN_VAL(value)   do { args[0] = value; return PRIM_VALUE; } while (0)
 

src/vm/wren_value.h

@@ -260,7 +260,7 @@ typedef enum
 
 } PrimitiveResult;
 
-typedef PrimitiveResult (*Primitive)(WrenVM* vm, ObjFiber* fiber, Value* args);
+typedef PrimitiveResult (*Primitive)(WrenVM* vm, Value* args);
 
 // TODO: See if it's actually a perf improvement to have this in a separate
 // struct instead of in ObjFn.

src/vm/wren_vm.c

@@ -897,7 +897,7 @@ static WrenInterpretResult runInterpreter(WrenVM* vm, register ObjFiber* fiber)
         case METHOD_PRIMITIVE:
         {
           // After calling this, the result will be in the first arg slot.
-          switch (method->fn.primitive(vm, fiber, args))
+          switch (method->fn.primitive(vm, args))
           {
             case PRIM_VALUE:
               // The result is now in the first arg slot. Discard the other