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fix: handle Babel transpilation syntax errors gracefully #1718

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fix: handle Babel transpilation syntax errors gracefully #1718

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7 changes: 6 additions & 1 deletion mobile-app/lib/service/learn/learn_file_service.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -274,7 +274,12 @@ class LearnFileService {
if (babelRes?.error != null) {
throw Exception('Babel transpilation failed: ${babelRes?.error}');
}
fileContents = babelRes?.value;

final result = babelRes?.value as Map<dynamic, dynamic>?;
if (result?['success'] == false) {
throw Exception('Babel transpilation failed: ${result?['error']}');
}
fileContents = result?['code'];

Document document = parse(challengeContent);

Expand Down
36 changes: 27 additions & 9 deletions mobile-app/lib/ui/views/learn/challenge/challenge_viewmodel.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -702,13 +702,34 @@ class ChallengeViewModel extends BaseViewModel {
_userConsoleMessages = [];
setTestConsoleMessages = ['<p>// running tests</p>'];

// Get user code console messages
String userCode;
try {
userCode = await builder.buildUserCode(
challenge!,
_babelWebView.webViewController,
);
} catch (e) {
String errorMessage = e.toString();
if (errorMessage.contains('Babel transpilation failed')) {
errorMessage = errorMessage.replaceFirst('Exception: ', '');
}
String userFriendlyMessage = parseSyntaxError(errorMessage);

setPanelType = PanelType.hint;
setHint = '<p>$userFriendlyMessage</p>';
setTestConsoleMessages = [
...testConsoleMessages,
'<p>$userFriendlyMessage</p>',
'<p>// tests completed</p>',
];
setIsRunningTests = false;
_scaffoldKey.currentState?.openEndDrawer();
return;
}

if ([1, 26, 28].contains(challenge!.challengeType)) {
final evalResult = await testController!.callAsyncJavaScript(
functionBody: await builder.buildUserCode(
challenge!,
_babelWebView.webViewController,
),
functionBody: userCode,
);
if (evalResult != null && evalResult.error != null) {
setUserConsoleMessages = [
Expand All @@ -724,10 +745,7 @@ class ChallengeViewModel extends BaseViewModel {
final updateTestRunnerRes = await testController!.callAsyncJavaScript(
functionBody: ScriptBuilder.runnerScript,
arguments: {
'userCode': await builder.buildUserCode(
challenge!,
_babelWebView.webViewController,
),
'userCode': userCode,
'workerType': builder.getWorkerType(challenge!.challengeType),
'combinedCode': await builder.combinedCode(challenge!),
'editableRegionContent': editableRegionContent,
Expand Down
20 changes: 17 additions & 3 deletions mobile-app/lib/ui/views/learn/test_runner.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,17 @@ import 'package:freecodecamp/service/learn/learn_file_service.dart';
class ScriptBuilder {
final LearnFileService fileService = locator<LearnFileService>();

static const transpileScript =
'return Babel.transform(code, { presets: ["env"] }).code';
static const transpileScript = '''
try {
return { success: true, code: Babel.transform(code, { presets: ["env"] }).code };
} catch (e) {
let errorMsg = e.message || e.toString();
if (e.loc) {
errorMsg = "SyntaxError: " + e.message + " (" + e.loc.line + ":" + e.loc.column + ")";
}
return { success: false, error: errorMsg };
}
''';

static const hideFccHeaderStyle = '''
<style class="fcc-hide-header">
Expand Down Expand Up @@ -71,7 +80,12 @@ return testRes;
throw Exception('Babel transpilation failed: ${babelRes?.error}');
}

return babelRes?.value ?? challengeFile;
final result = babelRes?.value as Map<dynamic, dynamic>?;
if (result?['success'] == false) {
throw Exception('Babel transpilation failed: ${result?['error']}');
}

return result?['code'] ?? challengeFile;
case 20:
case 23:
case 27:
Expand Down
16 changes: 16 additions & 0 deletions mobile-app/lib/ui/views/learn/utils/challenge_utils.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -72,3 +72,19 @@ DateTime parseMonthYear(String monthYear) {
String formatChallengeDate(DateTime date) {
return '${date.year.toString().padLeft(4, '0')}-${date.month.toString().padLeft(2, '0')}-${date.day.toString().padLeft(2, '0')}';
}

String parseSyntaxError(String errorMessage) {
final syntaxErrorRegex = RegExp(r'SyntaxError:.*?\((\d+):(\d+)\)');
final match = syntaxErrorRegex.firstMatch(errorMessage);

if (match != null) {
final line = int.parse(match.group(1)!) - 1;
return 'There is a syntax error on line $line. Please check for missing brackets, quotes, or other syntax issues.';
}

if (errorMessage.contains('Babel transpilation failed')) {
return 'There is a syntax error in your code. Please check for missing brackets, quotes, or other syntax issues.';
}

return errorMessage;
}
36 changes: 36 additions & 0 deletions mobile-app/test/unit/challenge_utils_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -114,4 +114,40 @@ void main() {
expect(formatChallengeDate(date), '2025-12-31');
});
});

group('parseSyntaxError', () {
test('parses syntax error with line number', () {
final errorMessage =
'Exception: Babel transpilation failed: SyntaxError: unknown: Unexpected token (4:0)';
final result = parseSyntaxError(errorMessage);
expect(
result,
'There is a syntax error on line 3. Please check for missing brackets, quotes, or other syntax issues.',
);
});

test('parses syntax error with different line number', () {
final errorMessage = 'SyntaxError: Unexpected identifier (15:22)';
final result = parseSyntaxError(errorMessage);
expect(
result,
'There is a syntax error on line 14. Please check for missing brackets, quotes, or other syntax issues.',
);
});

test('returns generic message for Babel error without line numbers', () {
final errorMessage = 'Babel transpilation failed: unknown error';
final result = parseSyntaxError(errorMessage);
expect(
result,
'There is a syntax error in your code. Please check for missing brackets, quotes, or other syntax issues.',
);
});

test('returns original message for non-syntax errors', () {
final errorMessage = 'Some other error occurred';
final result = parseSyntaxError(errorMessage);
expect(result, 'Some other error occurred');
});
});
}
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