Add API to call Wren method from C code.

This gives you a simple, efficient way to invoke a method on
some Wren object from C code, passing in arguments.

The basic API is in place and works, but there's still lots to do:

- Lots of error handling.
- Documentation.
- Tests!

include/wren.h

@@ -6,6 +6,11 @@
 
 typedef struct WrenVM WrenVM;
 
+// A handle to a method, bound to a receiver.
+//
+// This is used to call a Wren method on some object from C code.
+typedef struct WrenMethod WrenMethod;
+
 // A generic allocation function that handles all explicit memory management
 // used by Wren. It's used like so:
 //
@@ -118,6 +123,34 @@ void wrenFreeVM(WrenVM* vm);
 WrenInterpretResult wrenInterpret(WrenVM* vm, const char* sourcePath,
                                   const char* source);
 
+// Creates a handle that can be used to invoke a method with [signature] on the
+// object in [module] currently stored in top-level [variable].
+//
+// This handle can be used repeatedly to directly invoke that method from C
+// code using [wrenCall].
+//
+// When done with this handle, it must be released by calling
+// [wrenReleaseMethod].
+WrenMethod* wrenGetMethod(WrenVM* vm, const char* module, const char* variable,
+                          const char* signature);
+
+// Calls [method], passing in a series of arguments whose types must match the
+// specifed [argTypes]. This is a string where each character identifies the
+// type of a single argument, in orde. The allowed types are:
+//
+// - "b" - A C `int` converted to a Wren Bool.
+// - "d" - A C `double` converted to a Wren Num.
+// - "i" - A C `int` converted to a Wren Num.
+// - "s" - A C null-terminated `const char*` converted to a Wren String. Wren
+//         will allocate its own string and copy the characters from this, so
+//         you don't have to worry about the lifetime of the string you pass to
+//         Wren.
+void wrenCall(WrenVM* vm, WrenMethod* method, const char* argTypes, ...);
+
+// Releases memory associated with [method]. After calling this, [method] can
+// no longer be used.
+void wrenReleaseMethod(WrenVM* vm, WrenMethod* method);
+
 // TODO: Figure out how these interact with modules.
 
 // Defines a foreign method implemented by the host application. Looks for a

src/main.c

@@ -128,6 +128,16 @@ static int runFile(WrenVM* vm, const char* path)
       break;
   }
 
+  /*
+  WrenMethod* method = wrenGetMethod(vm, "main", "Foo", "bar(_,_,_)");
+  wrenCall(vm, method, "nsd", NULL, "some string", 78.9);
+  wrenCall(vm, method, "iii", 1, 2, 3);
+  wrenCall(vm, method, "nsd", NULL, "another string", 78.9);
+  wrenCall(vm, method, "iii", 4, 5, 6);
+
+  wrenReleaseMethod(vm, method);
+  */
+  
   wrenFreeVM(vm);
   free(source);
 

src/wren_common.h

@@ -108,6 +108,20 @@
 // field index*.
 #define MAX_FIELDS 255
 
+// Use the VM's allocator to allocate an object of [type].
+#define ALLOCATE(vm, type) \
+    ((type*)wrenReallocate(vm, NULL, 0, sizeof(type)))
+
+// Use the VM's allocator to allocate an object of [mainType] containing a
+// flexible array of [count] objects of [arrayType].
+#define ALLOCATE_FLEX(vm, mainType, arrayType, count) \
+    ((mainType*)wrenReallocate(vm, NULL, 0, \
+    sizeof(mainType) + sizeof(arrayType) * count))
+
+// Use the VM's allocator to allocate an array of [count] elements of [type].
+#define ALLOCATE_ARRAY(vm, type, count) \
+    ((type*)wrenReallocate(vm, NULL, 0, sizeof(type) * count))
+
 // The Microsoft compiler does not support the "inline" modifier when compiling
 // as plain C.
 #if defined( _MSC_VER ) && !defined(__cplusplus)

src/wren_compiler.c

@@ -1527,11 +1527,9 @@ static void  finishParameterList(Compiler* compiler, Signature* signature)
   while (match(compiler, TOKEN_COMMA));
 }
 
-// Gets the symbol for a method [name]. If [length] is 0, it will be calculated
+// Gets the symbol for a method [name] with [length].
-// from a null-terminated [name].
 static int methodSymbol(Compiler* compiler, const char* name, int length)
 {
-  if (length == 0) length = (int)strlen(name);
   return wrenSymbolTableEnsure(compiler->parser->vm,
       &compiler->parser->vm->methodNames, name, length);
 }

src/wren_value.c

@@ -23,16 +23,6 @@
 DEFINE_BUFFER(Value, Value);
 DEFINE_BUFFER(Method, Method);
 
-#define ALLOCATE(vm, type) \
-    ((type*)wrenReallocate(vm, NULL, 0, sizeof(type)))
-
-#define ALLOCATE_FLEX(vm, mainType, arrayType, count) \
-    ((mainType*)wrenReallocate(vm, NULL, 0, \
-        sizeof(mainType) + sizeof(arrayType) * count))
-
-#define ALLOCATE_ARRAY(vm, type, count) \
-    ((type*)wrenReallocate(vm, NULL, 0, sizeof(type) * count))
-
 static void initObj(WrenVM* vm, Obj* obj, ObjType type, ObjClass* classObj)
 {
   obj->type = type;
@@ -145,6 +135,13 @@ ObjFiber* wrenNewFiber(WrenVM* vm, Obj* fn)
   ObjFiber* fiber = ALLOCATE(vm, ObjFiber);
   initObj(vm, &fiber->obj, OBJ_FIBER, vm->fiberClass);
 
+  wrenResetFiber(fiber, fn);
+
+  return fiber;
+}
+
+void wrenResetFiber(ObjFiber* fiber, Obj* fn)
+{
   // Push the stack frame for the function.
   fiber->stackTop = fiber->stack;
   fiber->numFrames = 1;
@@ -164,8 +161,6 @@ ObjFiber* wrenNewFiber(WrenVM* vm, Obj* fn)
   {
     frame->ip = ((ObjClosure*)fn)->fn->bytecode;
   }
-
-  return fiber;
 }
 
 ObjFn* wrenNewFunction(WrenVM* vm, ObjModule* module,
@@ -795,7 +790,10 @@ static void markFn(WrenVM* vm, ObjFn* fn)
     wrenMarkValue(vm, fn->constants[i]);
   }
 
-  wrenMarkObj(vm, (Obj*)fn->debug->sourcePath);
+  if (fn->debug->sourcePath != NULL)
+  {
+    wrenMarkObj(vm, (Obj*)fn->debug->sourcePath);
+  }
 
   // Keep track of how much memory is still in use.
   vm->bytesAllocated += sizeof(ObjFn);

src/wren_value.h

@@ -646,6 +646,9 @@ ObjClosure* wrenNewClosure(WrenVM* vm, ObjFn* fn);
 // closure.
 ObjFiber* wrenNewFiber(WrenVM* vm, Obj* fn);
 
+// Resets [fiber] back to an initial state where it is ready to invoke [fn].
+void wrenResetFiber(ObjFiber* fiber, Obj* fn);
+
 // TODO: The argument list here is getting a bit gratuitous.
 // Creates a new function object with the given code and constants. The new
 // function will take over ownership of [bytecode] and [sourceLines]. It will

src/wren_vm.c

@@ -1,3 +1,4 @@
+#include <stdarg.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -35,6 +36,8 @@ WrenVM* wrenNewVM(WrenConfiguration* configuration)
   WrenVM* vm = (WrenVM*)reallocate(NULL, 0, sizeof(WrenVM));
 
   vm->reallocate = reallocate;
+
+  vm->methodHandles = NULL;
   vm->foreignCallSlot = NULL;
   vm->foreignCallNumArgs = 0;
   vm->loadModule = configuration->loadModuleFn;
@@ -99,7 +102,14 @@ void wrenFreeVM(WrenVM* vm)
     obj = next;
   }
 
+  // Tell the user if they didn't free any method handles. We don't want to
+  // just free them here because the host app may still have pointers to them
+  // that they may try to use. Better to tell them about the bug early.
+  ASSERT(vm->methodHandles == NULL, "All methods have not been released.");
+
   wrenSymbolTableClear(vm, &vm->methodNames);
+
+  // TODO: Make macro for freeing.
   wrenReallocate(vm, vm, 0, 0);
 }
 
@@ -140,6 +150,14 @@ static void collectGarbage(WrenVM* vm)
   // The current fiber.
   if (vm->fiber != NULL) wrenMarkObj(vm, (Obj*)vm->fiber);
 
+  // The method handles.
+  for (WrenMethod* handle = vm->methodHandles;
+       handle != NULL;
+       handle = handle->next)
+  {
+    wrenMarkObj(vm, (Obj*)handle->fiber);
+  }
+
   // Any object the compiler is using (if there is one).
   if (vm->compiler != NULL) wrenMarkCompiler(vm, vm->compiler);
 
@@ -1221,6 +1239,146 @@ static bool runInterpreter(WrenVM* vm)
   return false;
 }
 
+// Creates an [ObjFn] that invokes a method with [signature] when called.
+static ObjFn* makeCallStub(WrenVM* vm, ObjModule* module, const char* signature)
+{
+  int signatureLength = (int)strlen(signature);
+
+  // Count the number parameters the method expects.
+  int numParams = 0;
+  for (const char* s = signature; *s != '\0'; s++)
+  {
+    if (*s == '_') numParams++;
+  }
+
+  int method =  wrenSymbolTableEnsure(vm, &vm->methodNames,
+                                      signature, signatureLength);
+
+  uint8_t* bytecode = ALLOCATE_ARRAY(vm, uint8_t, 5);
+  bytecode[0] = CODE_CALL_0 + numParams;
+  bytecode[1] = (method >> 8) & 0xff;
+  bytecode[2] = method & 0xff;
+  bytecode[3] = CODE_RETURN;
+  bytecode[4] = CODE_END;
+
+  int* debugLines = ALLOCATE_ARRAY(vm, int, 5);
+  memset(debugLines, 1, 5);
+
+  return wrenNewFunction(vm, module, NULL, 0, 0, 0, bytecode, 5, NULL,
+                         signature, signatureLength, debugLines);
+}
+
+WrenMethod* wrenGetMethod(WrenVM* vm, const char* module, const char* variable,
+                          const char* signature)
+{
+  Value moduleName = wrenNewString(vm, module, strlen(module));
+  wrenPushRoot(vm, AS_OBJ(moduleName));
+
+  uint32_t moduleEntry = wrenMapFind(vm->modules, moduleName);
+  // TODO: Handle module not being found.
+  ObjModule* moduleObj = AS_MODULE(vm->modules->entries[moduleEntry].value);
+
+  int variableSlot = wrenSymbolTableFind(&moduleObj->variableNames,
+                                         variable, strlen(variable));
+  // TODO: Handle the variable not being found.
+
+  ObjFn* fn = makeCallStub(vm, moduleObj, signature);
+  wrenPushRoot(vm, (Obj*)fn);
+
+  // Create a single fiber that we can reuse each time the method is invoked.
+  ObjFiber* fiber = wrenNewFiber(vm, (Obj*)fn);
+  wrenPushRoot(vm, (Obj*)fiber);
+
+  // Create a handle that keeps track of the function that calls the method.
+  WrenMethod* method = ALLOCATE(vm, WrenMethod);
+  method->fiber = fiber;
+
+  // Store the receiver in the fiber's stack so we can use it later in the call.
+  *fiber->stackTop++ = moduleObj->variables.data[variableSlot];
+
+  // Add it to the front of the linked list of handles.
+  if (vm->methodHandles != NULL) vm->methodHandles->prev = method;
+  method->prev = NULL;
+  method->next = vm->methodHandles;
+  vm->methodHandles = method;
+
+  wrenPopRoot(vm); // fiber.
+  wrenPopRoot(vm); // fn.
+  wrenPopRoot(vm); // moduleName.
+
+  return method;
+}
+
+void wrenCall(WrenVM* vm, WrenMethod* method, const char* argTypes, ...)
+{
+  // TODO: Validate that the number of arguments matches what the method
+  // expects.
+  
+  // Push the arguments.
+  va_list argList;
+  va_start(argList, argTypes);
+
+  for (const char* argType = argTypes; *argType != '\0'; argType++)
+  {
+    Value value = NULL_VAL;
+    switch (*argType)
+    {
+      case 'b': value = BOOL_VAL(va_arg(argList, int)); break;
+      case 'd': value = NUM_VAL(va_arg(argList, double)); break;
+      case 'i': value = NUM_VAL((double)va_arg(argList, int)); break;
+      case 'n': value = NULL_VAL; va_arg(argList, void*); break;
+      case 's':
+      {
+        const char* text = va_arg(argList, const char*);
+        value = wrenNewString(vm, text, strlen(text));
+        break;
+      }
+        
+      default:
+        ASSERT(false, "Uknown argument type.");
+        break;
+    }
+
+    *method->fiber->stackTop++ = value;
+  }
+
+  va_end(argList);
+
+  vm->fiber = method->fiber;
+
+  Value receiver = method->fiber->stack[0];
+  Obj* fn = method->fiber->frames[0].fn;
+
+  // TODO: How does this handle a runtime error occurring?
+  runInterpreter(vm);
+
+  // Reset the fiber to get ready for the next call.
+  wrenResetFiber(method->fiber, fn);
+
+  // Push the receiver back on the stack.
+  *method->fiber->stackTop++ = receiver;
+}
+
+void wrenReleaseMethod(WrenVM* vm, WrenMethod* method)
+{
+  ASSERT(method != NULL, "NULL method.");
+
+  // Update the VM's head pointer if we're releasing the first handle.
+  if (vm->methodHandles == method) vm->methodHandles = method->next;
+
+  // Unlink it from the list.
+  if (method->prev != NULL) method->prev->next = method->next;
+  if (method->next != NULL) method->next->prev = method->prev;
+
+  // Clear it out. This isn't strictly necessary since we're going to free it,
+  // but it makes for easier debugging.
+  method->prev = NULL;
+  method->next = NULL;
+  method->fiber = NULL;
+
+  wrenReallocate(vm, method, sizeof(WrenMethod), 0);
+}
+
 // Execute [source] in the context of the core module.
 WrenInterpretResult static loadIntoCore(WrenVM* vm, const char* source)
 {

src/wren_vm.h

@@ -189,6 +189,17 @@ typedef enum
   CODE_END
 } Code;
 
+struct WrenMethod
+{
+  // The fiber that invokes the method. Its stack is pre-populated with the
+  // receiver for the method, and it contains a single callframe whose function
+  // is the bytecode stub to invoke the method.
+  ObjFiber* fiber;
+
+  WrenMethod* prev;
+  WrenMethod* next;
+};
+
 // TODO: Move into wren_vm.c?
 struct WrenVM
 {
@@ -254,6 +265,10 @@ struct WrenVM
   // receiver) of the call on the fiber's stack.
   Value* foreignCallSlot;
 
+  // Pointer to the first node in the linked list of active method handles or
+  // NULL if there are no handles.
+  WrenMethod* methodHandles;
+
   // During a foreign function call, this will contain the number of arguments
   // to the function.
   int foreignCallNumArgs;