[interop] Implement Diagnostics and Handling Errors

web_generator/lib/src/cli.dart

@@ -31,6 +31,17 @@ Future<void> compileDartMain({String? langVersion, String? dir}) async {
   );
 }
 
+Future<Process> runProcWithResult(String executable, List<String> arguments,
+    {required String workingDirectory}) async {
+  print(ansi.styleBold.wrap(['*', executable, ...arguments].join(' ')));
+  return Process.start(
+    executable,
+    arguments,
+    runInShell: Platform.isWindows,
+    workingDirectory: workingDirectory,
+  );
+}
+
 Future<void> runProc(String executable, List<String> arguments,
     {required String workingDirectory, bool detached = false}) async {
   print(ansi.styleBold.wrap(['*', executable, ...arguments].join(' ')));

web_generator/lib/src/interop_gen/parser.dart

@@ -4,6 +4,7 @@
 
 import 'dart:js_interop';
 
+import '../js/node.dart';
 import '../js/typescript.dart' as ts;
 
 class ParserResult {
@@ -13,9 +14,35 @@ class ParserResult {
   ParserResult({required this.program, required this.files});
 }
 
+/// Parses the given TypeScript declaration [files], provides any diagnostics,
+/// if any, and generates a [ts.TSProgram] for transformation
 ParserResult parseDeclarationFiles(Iterable<String> files) {
   final program = ts.createProgram(files.jsify() as JSArray<JSString>,
       ts.TSCompilerOptions(declaration: true));
 
+  // get diagnostics
+  final diagnostics = [
+    ...program.getSemanticDiagnostics().toDart,
+    ...program.getSyntacticDiagnostics().toDart,
+    ...program.getDeclarationDiagnostics().toDart,
+  ];
+
+  // handle diagnostics
+  for (final diagnostic in diagnostics) {
+    if (diagnostic.file case final diagnosticFile?) {
+      final ts.TSLineAndCharacter(line: line, character: char) =
+          ts.getLineAndCharacterOfPosition(diagnosticFile, diagnostic.start!);
+      final message =
+          ts.flattenDiagnosticMessageText(diagnostic.messageText, '\n');
+      printErr('${diagnosticFile.fileName} '
+          '(${line.toDartInt + 1},${char.toDartInt + 1}): $message');
+    }
+  }
+
+  if (diagnostics.isNotEmpty) {
+    // exit
+    exit(1);
+  }
+
   return ParserResult(program: program, files: files);
 }

web_generator/lib/src/js/node.dart

@@ -6,3 +6,9 @@ import 'dart:js_interop';
 
 @JS()
 external String get url;
+
+@JS('process.exit')
+external void exit(int code);
+
+@JS('console.error')
+external void printErr(String message);

web_generator/lib/src/js/typescript.dart

@@ -7,6 +7,8 @@ library;
 
 import 'dart:js_interop';
 
+import 'package:meta/meta.dart';
+
 import 'typescript.types.dart';
 
 @JS()
@@ -30,6 +32,14 @@ external bool isTypeReferenceNode(TSNode node);
 @JS()
 external bool isThisTypeNode(TSNode node);
 
+@JS()
+external TSLineAndCharacter getLineAndCharacterOfPosition(
+    TSSourceFile sourceFile, int position);
+
+@JS()
+external String flattenDiagnosticMessageText(JSAny? diag, String newLine,
+    [int indent]);
+
 @JS('CompilerOptions')
 extension type TSCompilerOptions._(JSObject _) implements JSObject {
   external TSCompilerOptions({bool? allowJs, bool? declaration});
@@ -41,6 +51,51 @@ extension type TSCompilerOptions._(JSObject _) implements JSObject {
 extension type TSProgram._(JSObject _) implements JSObject {
   external TSSourceFile? getSourceFile(String file);
   external TSTypeChecker getTypeChecker();
+
+  /// Diagnostics related to syntax errors
+  external JSArray<TSDiagnosticWithLocation> getSyntacticDiagnostics([
+    TSSourceFile? sourceFile,
+  ]);
+
+  /// Diagnostics related to type-checking
+  external JSArray<TSDiagnostic> getSemanticDiagnostics([
+    TSSourceFile? sourceFile,
+  ]);
+
+  /// Diagnostics related to the .d.ts file itself
+  external JSArray<TSDiagnosticWithLocation> getDeclarationDiagnostics([
+    TSSourceFile? sourceFile,
+  ]);
+}
+
+@JS('DiagnosticRelatedInformation')
+extension type TSDiagnosticRelatedInformation._(JSObject _)
+    implements JSObject {
+  external TSSourceFile? file;
+  external int code;
+
+  /// [String] or `TSDiagnosticMessageChain` (unimplemented)
+  external JSAny messageText;
+  external int? start;
+}
+
+@JS('Diagnostic')
+extension type TSDiagnostic._(JSObject _)
+    implements TSDiagnosticRelatedInformation {
+  external String? source;
+  external JSArray<TSDiagnosticRelatedInformation>? relatedInformation;
+
+  @doNotStore
+  external JSObject? get reportsUnnecessary;
+  @doNotStore
+  external JSObject? get reportsDeprecated;
+}
+
+@JS('DiagnosticWithLocation')
+extension type TSDiagnosticWithLocation._(JSObject _) implements TSDiagnostic {
+  external TSSourceFile file;
+  external int start;
+  external int length;
 }
 
 @JS('TypeChecker')
@@ -62,3 +117,9 @@ extension type TSNodeArrayCallback<T extends JSAny>._(JSObject _)
     implements JSObject {
   external T? call(TSNodeArray<TSNode> nodes);
 }
+
+@JS('LineAndCharacter')
+extension type TSLineAndCharacter._(JSObject _) implements JSObject {
+  external JSNumber get line;
+  external JSNumber get character;
+}

web_generator/test/assets/invalid.d.ts

@@ -0,0 +1,12 @@
+// invalid-syntax.d.ts
+export interface Person {
+  name: string
+  age number
+}
+interface User {
+  id: string;
+}
+export declare class Admin implements User {
+  constructor(name: string);
+  toString(): string;
+}

web_generator/test/invalid_input_test.dart

@@ -0,0 +1,49 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'dart:convert';
+
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+import 'package:web_generator/src/cli.dart';
+
+/// Actual test output can be found in `.dart_tool/idl`
+void main() {
+  final bindingsGenPath = p.join('lib', 'src');
+  group('Interop Gen Integration Test', () {
+    final testFile = p.join('test', 'assets', 'invalid.d.ts');
+    final outputFile = p.join('.dart_tool', 'interop_gen', 'invalid.dart');
+
+    setUp(() async {
+      // set up npm
+      await runProc('npm', ['install'], workingDirectory: bindingsGenPath);
+
+      // compile file
+      await compileDartMain(dir: bindingsGenPath);
+    });
+
+    test('Expect Parsing to Fail', () async {
+      final inputFilePath = p.relative(testFile, from: bindingsGenPath);
+      final outputFilePath = p.relative(outputFile, from: bindingsGenPath);
+
+      final process = await runProcWithResult(
+          'node',
+          [
+            'main.mjs',
+            '--input=$inputFilePath',
+            '--output=$outputFilePath',
+            '--declaration'
+          ],
+          workingDirectory: bindingsGenPath);
+
+      final stderr = await process.stderr.transform(utf8.decoder).toList();
+
+      expect(stderr, isNotEmpty);
+      expect(await process.exitCode, isNot(0));
+    });
+  });
+}