better errors

Author: kevmoo

googleapis_auth/lib/src/adc_utils.dart

@@ -27,13 +27,15 @@ Future<AutoRefreshingAuthClient> fromApplicationsCredentialsFile(
   Object? credentials;
   try {
     credentials = json.decode(await file.readAsString());
-  } on IOException {
+  } on IOException catch (e) {
     throw CredentialsFileException(
       'Failed to read credentials file from $fileSource',
+      e,
     );
-  } on FormatException {
+  } on FormatException catch (e) {
     throw CredentialsFileException(
       'Failed to parse JSON from credentials file from $fileSource',
+      e,
     );
   }
 

googleapis_auth/lib/src/exceptions.dart

@@ -60,11 +60,15 @@ class ServerRequestFailedException implements Exception {
 /// Thrown when an error occurs reading or parsing a credentials file.
 class CredentialsFileException implements Exception {
   final String message;
+  final Object? innerError;
 
-  const CredentialsFileException(this.message);
+  const CredentialsFileException(this.message, [this.innerError]);
 
   @override
-  String toString() => 'CredentialsFileException: $message';
+  String toString() => [
+    'CredentialsFileException: $message',
+    if (innerError != null) '($innerError)',
+  ].join(' ');
 }
 
 /// Thrown when the oauth2 callback request from the authorization server is