Rework module linking (#4632)

The module linking process from jerry_parse is moved out into
a new jerry_module_link function, and jerry_parse is limited to
create unlinked modules.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

docs/05.PORT-API.md

@@ -85,12 +85,10 @@ void jerry_port_print_char (char c);
 
 ### Jerry Module system
 
-The port API provides functions that can be used by the module system to open
-and close source files, and normalize file paths.
-The `jerry_port_get_native_module` port function can be used to provide native
-modules to the engine. This function will be called when an import/export
-statement is encountered with an unknown module specifier, which embedders can
-use to supply native module objects based on the module name argument.
+The port API provides optional functions that can be used by the
+user application to resolve modules. If no callback is provided
+to `jerry_module_link`, the `jerry_port_module_resolve` function
+is used for resolving modules.
 
 ```c
 /**
@@ -115,40 +113,38 @@ jerry_port_release_source (uint8_t *buffer_p) /**< buffer to free */
 } /* jerry_port_release_source */
 
 /**
- * Normalize a file path
+ * Default module resolver.
  *
- * @return length of the path written to the output buffer
- */
-size_t
-jerry_port_normalize_path (const char *in_path_p, /**< input file path */
-                           char *out_buf_p,       /**< output buffer */
-                           size_t out_buf_size,   /**< size of output buffer */
-                           char *base_file_p)     /**< base file path */
-{
-  // normalize in_path_p by expanding relative paths etc.
-  // if base_file_p is not NULL, in_path_p is relative to that file
-  // write to out_buf_p the normalized path
-  // return length of written path
-} /* jerry_port_normalize_path */
-
-/**
- * Get the module object of a native module.
- *
- * Note:
- *      This port function is called by jerry-core when JERRY_MODULE_SYSTEM
- *      is enabled.
- *
- * @param name String value of the module specifier.
- *
- * @return Undefined, if 'name' is not a native module
- *         jerry_value_t containing the module object, otherwise
+ * @return a module object if resolving is successful, an error otherwise
  */
 jerry_value_t
-jerry_port_get_native_module (jerry_value_t name) /**< module specifier */
+jerry_port_module_resolve (const jerry_value_t specifier, /**< module specifier string */
+                           const jerry_value_t referrer, /**< parent module */
+                           void *user_p) /**< user data */
 {
-  (void) name;
-  return jerry_create_undefined ();
-}
+  // Resolves a module using the specifier string. If a referrer is a module,
+  // and specifier is a relative path, the base path should be the directory
+  // part extracted from the path of the referrer module.
+
+  // The callback function of jerry_module_link may call this function
+  // if it cannot resolve a module. Furthermore if the callback is NULL,
+  // this function is used for resolving modules.
+
+  // The default implementation only resolves ECMAScript modules, and does
+  // not (currently) use the user data.
+} /* jerry_port_module_resolve */
+
+/**
+ * Release known modules.
+ */
+void
+jerry_port_module_release (const jerry_value_t realm) /**< if this argument is object, release only those modules,
+                                                       *   which realm value is equal to this argument. */
+{
+  // This function releases the known modules, forcing their reload
+  // when resolved again later. The released modules can be filtered
+  // by realms. This function is only called by user applications.
+} /* jerry_port_module_release */
 ```
 
 ## Date