fix(Compiler): Better errors for @GenerateInjector.

Closes #1571

Having a test here is prohibitively expensive (we don't currently have a pattern for compiler tests that import `*.template.dart), and we also didn't have a test for the other NPE case.

PiperOrigin-RevId: 208711303

angular/CHANGELOG.md

@@ -49,11 +49,16 @@
     caused the directive to no longer be functional
     (`*ngFor="let x; let i = $index "`, for example).
 
+*   [#1570][]: When a provider's `token` for `@GeneratedInjector(...)` is read
+    as `null` (either intentionally, or due to analysis errors/imports missing)
+    a better error message is now thrown with the context of the error.
+
 [#880]: https://github.com/dart-lang/angular/issues/880
 [#1538]: https://github.com/dart-lang/angular/issues/1538
 [#1539]: https://github.com/dart-lang/angular/issues/1539
 [#1540]: https://github.com/dart-lang/angular/issues/1540
 [#1558]: https://github.com/dart-lang/angular/issues/1558
+[#1570]: https://github.com/dart-lang/angular/issues/1570
 
 ### Other improvements
 

angular_compiler/CHANGELOG.md

@@ -1,3 +1,5 @@
+*   Catches an (invalid) `null` token of a provider and throws a better error.
+
 ## 0.4.0
 
 ### New Features

angular_compiler/lib/src/analyzer/di/injector.dart

@@ -72,18 +72,31 @@ class InjectorReader {
           $GenerateInjector.firstAnnotationOfExact(field),
         );
 
+  @alwaysThrows
+  void _throwParseError([DartObject context]) {
+    BuildError.throwForElement(
+      field,
+      context == null
+          ? 'Unable to parse @GenerateInjector. You may have analysis errors'
+          : 'Unable to parse @GenerateInjector. A provider\'s token ($context) '
+          'was read as "null". This is either invalid configuration or you '
+          'have analysis errors',
+    );
+  }
+
   /// Providers that are part of the provided list of the annotation.
   Iterable<ProviderElement> get providers {
     if (_providers == null) {
       final providersOrModules = annotation.read('_providersOrModules');
       if (providersOrModules.isNull) {
-        BuildError.throwForElement(
-          field,
-          'Unable to parse @GenerateInjector. You may have analysis errors',
-        );
+        _throwParseError();
+      }
+      try {
+        final module = moduleReader.parseModule(providersOrModules.objectValue);
+        _providers = moduleReader.deduplicateProviders(module.flatten());
+      } on NullTokenException catch (e) {
+        _throwParseError(e.constant);
       }
-      final module = moduleReader.parseModule(providersOrModules.objectValue);
-      _providers = moduleReader.deduplicateProviders(module.flatten());
     }
     return _providers;
   }

angular_compiler/lib/src/analyzer/di/providers.dart

@@ -48,9 +48,11 @@ class ProviderReader {
 
   ProviderElement _parseProvider(DartObject o) {
     final reader = ConstantReader(o);
-    final token = _tokenReader.parseTokenObject(
-      reader.read('token').objectValue,
-    );
+    final value = reader.read('token');
+    if (value.isNull) {
+      throw new NullTokenException(o);
+    }
+    final token = _tokenReader.parseTokenObject(value.objectValue);
     final useClass = reader.read('useClass');
     if (!useClass.isNull) {
       return _parseUseClass(token, o, useClass.typeValue.element);
@@ -328,3 +330,11 @@ class UseValueProviderElement extends ProviderElement {
     bool multi = false,
   }) : super._(e, providerType, multi);
 }
+
+/// Thrown when a value of `null` is read for a provider token.
+class NullTokenException implements Exception {
+  /// Constant whose `.token` property was resolved to `null`.
+  final DartObject constant;
+
+  const NullTokenException(this.constant);
+}