First pass at implementing foreign classes.

Most of the pieces are there:

- You can declare a foreign class.
- It will call your C function to provide an allocator function.
- Whenever a foreign object is created, it calls the allocator.
- Foreign methods can access the foreign bytes of an object.
- Most of the runtime checking is in place for things like subclassing
  foreign classes.

There is still some loose ends to tie up:

- Finalizers are not called.
- Some of the error-handling could be better.
- The GC doesn't track how much memory a marked foreign object uses.

src/cli/main.c

@@ -9,7 +9,7 @@
 
 static int runRepl()
 {
-  WrenVM* vm = createVM(NULL);
+  WrenVM* vm = createVM();
 
   printf("\\\\/\"-\n");
   printf(" \\_/   wren v0.0.0\n");
@@ -50,7 +50,7 @@ int main(int argc, const char* argv[])
   }
   else if (argc == 2)
   {
-    runFile(NULL, argv[1]);
+    runFile(argv[1]);
   }
 
   return 0;

src/cli/vm.c

@@ -4,25 +4,25 @@
 #include "io.h"
 #include "vm.h"
 
-WrenVM* createVM(WrenBindForeignMethodFn bindForeign)
+static WrenBindForeignMethodFn bindMethodFn = NULL;
+static WrenBindForeignClassFn bindClassFn = NULL;
+
+WrenVM* createVM()
 {
   WrenConfiguration config;
-
-  config.bindForeignMethodFn = bindForeign;
+  wrenInitConfiguration(&config);
+  
+  config.bindForeignMethodFn = bindMethodFn;
+  config.bindForeignClassFn = bindClassFn;
   config.loadModuleFn = readModule;
 
   // Since we're running in a standalone process, be generous with memory.
   config.initialHeapSize = 1024 * 1024 * 100;
 
-  // Use defaults for these.
-  config.reallocateFn = NULL;
-  config.minHeapSize = 0;
-  config.heapGrowthPercent = 0;
-
   return wrenNewVM(&config);
 }
 
-void runFile(WrenBindForeignMethodFn bindForeign, const char* path)
+void runFile(const char* path)
 {
   // Use the directory where the file is as the root to resolve imports
   // relative to.
@@ -43,7 +43,7 @@ void runFile(WrenBindForeignMethodFn bindForeign, const char* path)
     exit(66);
   }
 
-  WrenVM* vm = createVM(bindForeign);
+  WrenVM* vm = createVM();
 
   WrenInterpretResult result = wrenInterpret(vm, path, source);
 
@@ -55,3 +55,10 @@ void runFile(WrenBindForeignMethodFn bindForeign, const char* path)
   if (result == WREN_RESULT_COMPILE_ERROR) exit(65); // EX_DATAERR.
   if (result == WREN_RESULT_RUNTIME_ERROR) exit(70); // EX_SOFTWARE.
 }
+
+void setForeignCallbacks(
+    WrenBindForeignMethodFn bindMethod, WrenBindForeignClassFn bindClass)
+{
+  bindMethodFn = bindMethod;
+  bindClassFn = bindClass;
+}

src/cli/vm.h

@@ -4,11 +4,18 @@
 #include "wren.h"
 
 // Creates a new Wren VM with the CLI's module loader and other configuration.
-WrenVM* createVM(WrenBindForeignMethodFn bindForeign);
+WrenVM* createVM();
 
 // Executes the Wren script at [path] in a new VM.
 //
 // Exits if the script failed or could not be loaded.
-void runFile(WrenBindForeignMethodFn bindForeign, const char* path);
+void runFile(const char* path);
+
+// Adds additional callbacks to use when binding foreign members from Wren.
+//
+// Used by the API test executable to let it wire up its own foreign functions.
+// This must be called before calling [createVM()].
+void setForeignCallbacks(WrenBindForeignMethodFn bindMethod,
+                         WrenBindForeignClassFn bindClass);
 
 #endif