add wrenHasVariable and wrenHasModule

src/include/wren.h

@@ -520,6 +520,14 @@ void wrenRemoveMapValue(WrenVM* vm, int mapSlot, int keySlot,
 void wrenGetVariable(WrenVM* vm, const char* module, const char* name,
                      int slot);
 
+// Looks up the top level variable with [name] in resolved [module], 
+// returns false if not found. The module must be imported at the time, 
+// use wrenHasModule to ensure that before calling.
+bool wrenHasVariable(WrenVM* vm, const char* module, const char* name);
+
+// Returns true if [module] has been imported/resolved before, false if not.
+bool wrenHasModule(WrenVM* vm, const char* module);
+
 // Sets the current fiber to be aborted, and uses the value in [slot] as the
 // runtime error object.
 void wrenAbortFiber(WrenVM* vm, int slot);

src/vm/wren_vm.c

@@ -1898,6 +1898,40 @@ void wrenGetVariable(WrenVM* vm, const char* module, const char* name,
   setSlot(vm, slot, moduleObj->variables.data[variableSlot]);
 }
 
+bool wrenHasVariable(WrenVM* vm, const char* module, const char* name)
+{
+  ASSERT(module != NULL, "Module cannot be NULL.");
+  ASSERT(name != NULL, "Variable name cannot be NULL.");
+
+  Value moduleName = wrenStringFormat(vm, "$", module);
+  wrenPushRoot(vm, AS_OBJ(moduleName));
+
+  //We don't use wrenHasModule since we want to use the module object.
+  ObjModule* moduleObj = getModule(vm, moduleName);
+  ASSERT(moduleObj != NULL, "Could not find module.");
+
+  wrenPopRoot(vm); // moduleName.
+
+  int variableSlot = wrenSymbolTableFind(&moduleObj->variableNames,
+    name, strlen(name));
+
+  return variableSlot != -1;
+}
+
+bool wrenHasModule(WrenVM* vm, const char* module)
+{
+  ASSERT(module != NULL, "Module cannot be NULL.");
+  
+  Value moduleName = wrenStringFormat(vm, "$", module);
+  wrenPushRoot(vm, AS_OBJ(moduleName));
+
+  ObjModule* moduleObj = getModule(vm, moduleName);
+  
+  wrenPopRoot(vm); // moduleName.
+
+  return moduleObj != NULL;
+}
+
 void wrenAbortFiber(WrenVM* vm, int slot)
 {
   validateApiSlot(vm, slot);

test/api/get_variable.c

@@ -32,6 +32,25 @@ static void otherModule(WrenVM* vm)
   wrenGetVariable(vm, "./test/api/get_variable_module", "Variable", 0);
 }
 
+static void hasVariable(WrenVM* vm)
+{
+  const char* module = wrenGetSlotString(vm, 1);
+  const char* variable = wrenGetSlotString(vm, 2);
+
+  bool result = wrenHasVariable(vm, module, variable);
+  wrenEnsureSlots(vm, 1);
+  wrenSetSlotBool(vm, 0, result);
+}
+
+static void hasModule(WrenVM* vm)
+{
+  const char* module = wrenGetSlotString(vm, 1);
+
+  bool result = wrenHasModule(vm, module);
+  wrenEnsureSlots(vm, 1);
+  wrenSetSlotBool(vm, 0, result);
+}
+
 WrenForeignMethodFn getVariableBindMethod(const char* signature)
 {
   if (strcmp(signature, "static GetVariable.beforeDefined()") == 0) return beforeDefined;
@@ -39,6 +58,9 @@ WrenForeignMethodFn getVariableBindMethod(const char* signature)
   if (strcmp(signature, "static GetVariable.afterAssigned()") == 0) return afterAssigned;
   if (strcmp(signature, "static GetVariable.otherSlot()") == 0) return otherSlot;
   if (strcmp(signature, "static GetVariable.otherModule()") == 0) return otherModule;
+  
+  if (strcmp(signature, "static Has.variable(_,_)") == 0) return hasVariable;
+  if (strcmp(signature, "static Has.module(_)") == 0) return hasModule;
 
   return NULL;
 }

test/api/get_variable.wren

@@ -8,6 +8,11 @@ class GetVariable {
   foreign static otherModule()
 }
 
+class Has {
+  foreign static variable(module, variable)
+  foreign static module(module)
+}
+
 System.print(GetVariable.beforeDefined()) // expect: null
 
 var A = "a"
@@ -22,3 +27,13 @@ var B = "b"
 System.print(GetVariable.otherSlot()) // expect: b
 
 System.print(GetVariable.otherModule()) // expect: value
+
+
+System.print(Has.variable("./test/api/get_variable_module", "Variable")) // expect: true
+System.print(Has.variable("./test/api/get_variable_module", "NotAVariable")) // expect: false
+System.print(Has.variable("./test/api/get_variable", "Has")) // expect: true
+System.print(Has.variable("./test/api/get_variable", "Fake")) // expect: false
+
+System.print(Has.module("./test/api/get_variable_module")) // expect: true
+System.print(Has.module("./test/api/get_variable")) // expect: true
+System.print(Has.module("not a module")) // expect: false