[pigeon] updated the assert message for incomplete objc protocol implementation (#462)

diff --git a/packages/pigeon/CHANGELOG.md b/packages/pigeon/CHANGELOG.md
index b91c59d..86b2a97 100644
--- a/packages/pigeon/CHANGELOG.md
+++ b/packages/pigeon/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.0.3
+
+* [objc] Updated assert message for incomplete implementations of protocols.
+
 ## 1.0.2
 
 * [java] Made it so `@async` handlers in `@HostApi()` can report errors
@@ -22,7 +26,7 @@
 * [generators] Moved Pigeon to using a custom codec which allows collection
   types to contain custom classes.
 * [java] Fixed NPE in Java generated code for nested types.
-* [objc] BREAKING CHANGE: logic for generating Objective-C selectors has
+* [objc] **BREAKING CHANGE:** logic for generating Objective-C selectors has
   changed. `void add(Input value)` will now translate to
   `-(void)addValue:(Input*)value`, methods with no arguments will translate to
   `...WithError:` or `...WithCompletion:`.
diff --git a/packages/pigeon/lib/generator_tools.dart b/packages/pigeon/lib/generator_tools.dart
index fea3f11..51df982 100644
--- a/packages/pigeon/lib/generator_tools.dart
+++ b/packages/pigeon/lib/generator_tools.dart
@@ -8,7 +8,7 @@
 import 'ast.dart';
 
 /// The current version of pigeon. This must match the version in pubspec.yaml.
-const String pigeonVersion = '1.0.2';
+const String pigeonVersion = '1.0.3';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {
diff --git a/packages/pigeon/lib/objc_generator.dart b/packages/pigeon/lib/objc_generator.dart
index c44d2fc..c32b640 100644
--- a/packages/pigeon/lib/objc_generator.dart
+++ b/packages/pigeon/lib/objc_generator.dart
@@ -487,7 +487,7 @@
               func.isAsynchronous ? 'completion' : 'error';
           final String selector = _getSelector(func, lastSelectorComponent);
           indent.writeln(
-              'NSCAssert([api respondsToSelector:@selector($selector)], @"$apiName api doesn\'t respond to @selector($selector)");');
+              'NSCAssert([api respondsToSelector:@selector($selector)], @"$apiName api (%@) doesn\'t respond to @selector($selector)", api);');
           indent.write(
               '[channel setMessageHandler:^(id _Nullable message, FlutterReply callback) ');
           indent.scoped('{', '}];', () {
diff --git a/packages/pigeon/pubspec.yaml b/packages/pigeon/pubspec.yaml
index 99fa15f..5f898b4 100644
--- a/packages/pigeon/pubspec.yaml
+++ b/packages/pigeon/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Code generator tool to make communication between Flutter and the host platform type-safe and easier.
 repository: https://github.com/flutter/packages/tree/master/packages/pigeon
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3Apigeon
-version: 1.0.2 # This must match the version in lib/generator_tools.dart
+version: 1.0.3 # This must match the version in lib/generator_tools.dart
 
 environment:
   sdk: '>=2.12.0 <3.0.0'