JS API: Validate that importer result 'contents' is a string and improve ArgumentError output (#1816)

* Validate ImporterResult 'contents' and improve ArgumentError output * only use JS stuff in the nodejs bindings * handle non-string contents for legacy importer too * make it work with node 12

Author: Goodwine

CHANGELOG.md

@@ -60,6 +60,12 @@
 * Emit a deprecation warning when passing a `sassIndex` with units to
  `Value.sassIndexToListIndex()`. This will be an error in Dart Sass 2.0.0.
 
+### JS API
+
+* Importer results now validate whether `contents` is actually a string type.
+
+* Importer result argument errors are now rendered correctly.
+
 ## 1.55.0
 
 * **Potentially breaking bug fix:** Sass numbers are now universally stored as

lib/src/importer/legacy_node/implementation.dart

@@ -183,6 +183,11 @@ class NodeImporter {
 
  var file = value.file;
  var contents = value.contents;
+ if (contents != null && !isJsString(contents)) {
+ jsThrow(ArgumentError.value(contents, 'contents',
+ 'must be a string but was: ${jsType(contents)}'));
+ }
+
  if (file == null) {
  return Tuple2(contents ?? '', url);
  } else if (contents != null) {

lib/src/importer/node_to_dart/async.dart

@@ -43,6 +43,11 @@ class NodeToDartAsyncImporter extends AsyncImporter {
 
  result as NodeImporterResult;
  var contents = result.contents;
+ if (!isJsString(contents)) {
+ jsThrow(ArgumentError.value(contents, 'contents',
+ 'must be a string but was: ${jsType(contents)}'));
+ }
+
  var syntax = result.syntax;
  if (contents == null || syntax == null) {
  jsThrow(JsError("The load() function must return an object with contents "

lib/src/importer/node_to_dart/sync.dart

@@ -48,6 +48,11 @@ class NodeToDartImporter extends Importer {
 
  result as NodeImporterResult;
  var contents = result.contents;
+ if (!isJsString(contents)) {
+ jsThrow(ArgumentError.value(contents, 'contents',
+ 'must be a string but was: ${jsType(contents)}'));
+ }
+
  var syntax = result.syntax;
  if (contents == null || syntax == null) {
  jsThrow(JsError("The load() function must return an object with contents "

lib/src/node/function.dart

@@ -6,6 +6,31 @@ import 'package:js/js.dart';
 
 @JS("Function")
 class JSFunction {
+ /// Creates a [JS function].
+ ///
+ /// The **last** argument is the function body. The other arguments become the
+ /// function's parameters.
+ ///
+ /// The function body must declare a `return` statement in order to return a
+ /// value, otherwise it returns [JSNull].
+ ///
+ /// Note: The function body must be compatible with Node 12. Null coalescing
+ /// and optional chaining features are not supported.
+ ///
+ /// Examples:
+ /// ```dart
+ /// var sum = JSFunction('a', 'b', 'return a + b');
+ /// sum.call(13, 29) as int; // 42
+ ///
+ /// var isJsString = JSFunction('a', 'return typeof a === "string"');
+ /// isJsString.call(42) as bool; // false
+ /// isJsString.call('42') as bool; // true
+ ///
+ /// var sayHi = JSFunction('console.log("Hi!")');
+ /// sayHi.call(); // Logs "Hi!"
+ /// ```
+ ///
+ /// [JS Function]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/Function#syntax
  external JSFunction(String arg1, [String? arg2, String? arg3]);
 
  // Note that this just invokes the function with the given arguments, rather

lib/src/node/utils.dart

@@ -72,6 +72,25 @@ void jsForEach(Object object, void callback(String key, Object? value)) {
 /// returns `null`.
 Object? jsEval(String js) => JSFunction('', js).call();
 
+/// Returns whether the [object] is a JS `string`.
+bool isJsString(Object? object) => _jsTypeOf(object) == 'string';
+
+/// Returns the [object]'s `typeof` according to the JS engine.
+String _jsTypeOf(Object? object) =>
+ JSFunction("value", "return typeof value").call(object) as String;
+
+/// Returns `typeof value` if [value] is a native type, otherwise returns the
+/// [value]'s JS class name.
+String jsType(Object? value) {
+ var typeOf = _jsTypeOf(value);
+ return typeOf != 'object' ? typeOf : JSFunction('value', '''
+ if (value && value.constructor && value.constructor.name) {
+ return value.constructor.name;
+ }
+ return "object";
+ ''').call(value) as String;
+}
+
 @JS("Object.defineProperty")
 external void _defineProperty(
  Object object, String name, _PropertyDescriptor prototype);

lib/src/visitor/async_evaluate.dart

@@ -1645,6 +1645,8 @@ class _EvaluateVisitor
  }
  } on SassException catch (error, stackTrace) {
  throwWithTrace(_exception(error.message, error.span), stackTrace);
+ } on ArgumentError catch (error, stackTrace) {
+ throwWithTrace(_exception(error.toString()), stackTrace);
  } catch (error, stackTrace) {
  String? message;
  try {

lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: c70a4193cc291f298f601a5cc371be9eac71fb74
+// Checksum: a14e075a5435c7457d1d1371d8b97dd327a66ec4
 //
 // ignore_for_file: unused_import
 
@@ -1643,6 +1643,8 @@ class _EvaluateVisitor
  }
  } on SassException catch (error, stackTrace) {
  throwWithTrace(_exception(error.message, error.span), stackTrace);
+ } on ArgumentError catch (error, stackTrace) {
+ throwWithTrace(_exception(error.toString()), stackTrace);
  } catch (error, stackTrace) {
  String? message;
  try {