Just warn (don't fail) when the json_annotation constraint looks wrong

Fixes #1011
Fixes #1014
Fixes #1020
Fixes #1025

Author: kevmoo

json_serializable/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 - Support `JsonKey.readValue` to allow customized reading of values from source
   JSON map objects.
+- The check to make sure there is a correctly constrained dependency on
+  `package:json_annotation` is now a warning and doesn't fail the build.
 - Require `json_annotation` `'>=4.4.0 <4.5.0'`.
 
 ## 6.0.1

json_serializable/lib/src/check_dependencies.dart

@@ -51,7 +51,7 @@ Future<void> _validatePubspec(bool production, BuildStep buildStep) async {
 
   if (errorMessage == null) return;
 
-  throw BadPackageDependencyError(errorMessage);
+  log.warning(errorMessage);
 }
 
 String? _checkAnnotationConstraint(
@@ -124,13 +124,3 @@ class _OncePerBuild {
     }
   }
 }
-
-/// Thrown when a pubspec dependency is missing or incorrectly specified.
-class BadPackageDependencyError extends Error {
-  final String message;
-
-  BadPackageDependencyError(this.message);
-
-  @override
-  String toString() => message;
-}

json_serializable/test/annotation_version_test.dart

@@ -172,10 +172,8 @@ class SomeClass{}
   }
 
   expect(lines.toString(), contains('''
-[SEVERE] json_serializable:json_serializable on $sourceDirectory/sample.dart:
+[WARNING] json_serializable:json_serializable on $sourceDirectory/sample.dart:
+$message'''));
 
-$message
-'''));
-
-  await proc.shouldExit(1);
+  await proc.shouldExit(0);
 }