Allow empty import array for wasm-c-api wasm_instance_new (#782)

Allow empty import array (but not NULL) for wasm-c-api wasm_instance_new,
which makes the code more robust, especially in use cases where imports
might be constructed dynamically.
And add a test case in samples/wasm-c-api/src/empty_imports.c to test it.

core/iwasm/common/wasm_c_api.c

@@ -4230,6 +4230,7 @@ wasm_instance_new_with_args(wasm_store_t *store, const wasm_module_t *module,
 {
     char error_buf[128] = { 0 };
     uint32 import_count = 0;
+    bool import_count_verified = false;
     wasm_instance_t *instance = NULL;
     uint32 i = 0;
     bool processed = false;
@@ -4265,6 +4266,7 @@ wasm_instance_new_with_args(wasm_store_t *store, const wasm_module_t *module,
                     goto failed;
                 }
             }
+            import_count_verified = true;
         }
 #endif
 
@@ -4285,6 +4287,7 @@ wasm_instance_new_with_args(wasm_store_t *store, const wasm_module_t *module,
                     goto failed;
                 }
             }
+            import_count_verified = true;
         }
 #endif
 
@@ -4292,7 +4295,7 @@ wasm_instance_new_with_args(wasm_store_t *store, const wasm_module_t *module,
          * a wrong combination of module filetype and compilation flags
          * also leads to below branch
          */
-        if (!import_count) {
+        if (!import_count_verified) {
             goto failed;
         }
     }

samples/wasm-c-api/CMakeLists.txt

@@ -123,6 +123,7 @@ set(MM_UTIL src/utils/multi_module_utils.c)
 set(EXAMPLES
   callback
   callback_chain
+  empty_imports
   global
   hello
   hostref

samples/wasm-c-api/src/empty_imports.c

@@ -0,0 +1,97 @@
+#include <stdio.h>
+
+#include "wasm_c_api.h"
+
+#define own
+
+int main(int argc, const char* argv[]) {
+  // Initialize.
+  printf("Initializing...\n");
+  wasm_engine_t* engine = wasm_engine_new();
+  wasm_store_t* store = wasm_store_new(engine);
+
+  // Load binary.
+  printf("Loading binary...\n");
+#if WASM_ENABLE_AOT != 0 && WASM_ENABLE_INTERP == 0
+  FILE* file = fopen("empty_imports.aot", "rb");
+#else
+  FILE* file = fopen("empty_imports.wasm", "rb");
+#endif
+  if (!file) {
+    printf("> Error loading module!\n");
+    return 1;
+  }
+  fseek(file, 0L, SEEK_END);
+  size_t file_size = ftell(file);
+  fseek(file, 0L, SEEK_SET);
+  wasm_byte_vec_t binary;
+  wasm_byte_vec_new_uninitialized(&binary, file_size);
+  if (fread(binary.data, file_size, 1, file) != 1) {
+    printf("> Error loading module!\n");
+    fclose(file);
+    return 1;
+  }
+  fclose(file);
+
+  // Compile.
+  printf("Compiling module...\n");
+  own wasm_module_t* module = wasm_module_new(store, &binary);
+  if (!module) {
+    printf("> Error compiling module!\n");
+    return 1;
+  }
+
+  wasm_byte_vec_delete(&binary);
+
+  // Instantiate with non-null but empty imports array.
+  printf("Instantiating module...\n");
+  wasm_extern_vec_t imports = WASM_EMPTY_VEC;
+  own wasm_instance_t* instance =
+    wasm_instance_new(store, module, &imports, NULL);
+  if (!instance) {
+    printf("> Error instantiating module!\n");
+    return 1;
+  }
+
+  // Run an exported function to verify that the instance was created correctly.
+  printf("Extracting export...\n");
+  own wasm_extern_vec_t exports;
+  wasm_instance_exports(instance, &exports);
+  if (exports.size == 0) {
+    printf("> Error accessing exports!\n");
+    return 1;
+  }
+
+  const wasm_func_t* add_func = wasm_extern_as_func(exports.data[0]);
+  if (add_func == NULL) {
+    printf("> Error accessing export!\n");
+    return 1;
+  }
+
+  wasm_module_delete(module);
+  wasm_instance_delete(instance);
+
+  printf("Calling export...\n");
+  wasm_val_t args[2] = { WASM_I32_VAL(3), WASM_I32_VAL(4) };
+  wasm_val_vec_t args_vec = WASM_ARRAY_VEC(args);
+
+  wasm_val_t results[1] = { WASM_INIT_VAL };
+  wasm_val_vec_t results_vec = WASM_ARRAY_VEC(results);
+
+  if (wasm_func_call(add_func, &args_vec, &results_vec)
+      || results_vec.data[0].of.i32 != 7) {
+    printf("> Error calling function!\n");
+    return 1;
+  }
+
+  wasm_extern_vec_delete(&exports);
+
+  // Shut down.
+  printf("Shutting down...\n");
+  wasm_store_delete(store);
+  wasm_engine_delete(engine);
+
+  // All done.
+  printf("Done.\n");
+  return 0;
+}

samples/wasm-c-api/src/empty_imports.wat

@@ -0,0 +1,5 @@
+(module
+  (func (export "add") (param i32 i32) (result i32)
+    (i32.add (local.get 0) (local.get 1))
+  )
+)