Add Wasmtime-specific C API functions to return errors (#1467)

* Add Wasmtime-specific C API functions to return errors

This commit adds new `wasmtime_*` symbols to the C API, many of which
mirror the existing counterparts in the `wasm.h` header. These APIs are
enhanced in a number of respects:

* Detailed error information is now available through a
  `wasmtime_error_t`. Currently this only exposes one function which is
  to extract a string version of the error.

* There is a distinction now between traps and errors during
  instantiation and function calling. Traps only happen if wasm traps,
  and errors can happen for things like runtime type errors when
  interacting with the API.

* APIs have improved safety with respect to embedders where the lengths
  of arrays are now taken as explicit parameters rather than assumed
  from other parameters.

* Handle trap updates

* Update C examples

* Fix memory.c compile on MSVC

* Update test assertions

* Refactor C slightly

* Bare-bones .NET update

* Remove bogus nul handling

examples/multi.c

@@ -28,6 +28,8 @@ originally
 #include <wasm.h>
 #include <wasmtime.h>
 
+static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap);
+
 // A function to be called from Wasm code.
 wasm_trap_t* callback(
   const wasm_val_t args[], wasm_val_t results[]
@@ -83,20 +85,18 @@ int main(int argc, const char* argv[]) {
   fclose(file);
 
   // Parse the wat into the binary wasm format
-  wasm_byte_vec_t binary, error;
-  if (wasmtime_wat2wasm(&wat, &binary, &error) == 0) {
-    fprintf(stderr, "failed to parse wat %.*s\n", (int) error.size, error.data);
-    return 1;
-  }
+  wasm_byte_vec_t binary;
+  wasmtime_error_t *error = wasmtime_wat2wasm(&wat, &binary);
+  if (error != NULL)
+    exit_with_error("failed to parse wat", error, NULL);
   wasm_byte_vec_delete(&wat);
 
   // Compile.
   printf("Compiling module...\n");
-  wasm_module_t* module = wasm_module_new(store, &binary);
-  if (!module) {
-    printf("> Error compiling module!\n");
-    return 1;
-  }
+  wasm_module_t* module = NULL;
+  error = wasmtime_module_new(store, &binary, &module);
+  if (error)
+    exit_with_error("failed to compile module", error, NULL);
 
   wasm_byte_vec_delete(&binary);
 
@@ -116,12 +116,11 @@ int main(int argc, const char* argv[]) {
   // Instantiate.
   printf("Instantiating module...\n");
   const wasm_extern_t* imports[] = {wasm_func_as_extern(callback_func)};
-  wasm_instance_t* instance =
-    wasm_instance_new(store, module, imports, NULL);
-  if (!instance) {
-    printf("> Error instantiating module!\n");
-    return 1;
-  }
+  wasm_instance_t* instance = NULL;
+  wasm_trap_t* trap = NULL;
+  error = wasmtime_instance_new(module, imports, 1, &instance, &trap);
+  if (!instance)
+    exit_with_error("failed to instantiate", error, trap);
 
   wasm_func_delete(callback_func);
 
@@ -133,7 +132,7 @@ int main(int argc, const char* argv[]) {
     printf("> Error accessing exports!\n");
     return 1;
   }
-  const wasm_func_t* run_func = wasm_extern_as_func(exports.data[0]);
+  wasm_func_t* run_func = wasm_extern_as_func(exports.data[0]);
   if (run_func == NULL) {
     printf("> Error accessing export!\n");
     return 1;
@@ -144,16 +143,15 @@ int main(int argc, const char* argv[]) {
 
   // Call.
   printf("Calling export...\n");
-  wasm_val_t args[4];
+  wasm_val_t args[2];
   args[0].kind = WASM_I32;
   args[0].of.i32 = 1;
   args[1].kind = WASM_I64;
   args[1].of.i64 = 2;
   wasm_val_t results[2];
-  if (wasm_func_call(run_func, args, results)) {
-    printf("> Error calling function!\n");
-    return 1;
-  }
+  error = wasmtime_func_call(run_func, args, 2, results, 2, &trap);
+  if (error != NULL || trap != NULL)
+    exit_with_error("failed to call run", error, trap);
 
   wasm_extern_vec_delete(&exports);
 
@@ -177,3 +175,17 @@ int main(int argc, const char* argv[]) {
   return 0;
 }
 
+static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap) {
+  fprintf(stderr, "error: %s\n", message);
+  wasm_byte_vec_t error_message;
+  if (error != NULL) {
+    wasmtime_error_message(error, &error_message);
+    wasmtime_error_delete(error);
+  } else {
+    wasm_trap_message(trap, &error_message);
+    wasm_trap_delete(trap);
+  }
+  fprintf(stderr, "%.*s\n", (int) error_message.size, error_message.data);
+  wasm_byte_vec_delete(&error_message);
+  exit(1);
+}