Smooth degradataion for non-library assets (#123)

If we can't get a LibraryElement for a primary input it should not have
any output. Return early rather than throw later.

Author: natebosch

CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.5.3+1
+
+* Don't throw when running against a non-library asset and getting no
+  LibraryElement
+
 ## 0.5.3
 
 * Add matchTypes method. As with anything imported from /src/ this is

lib/src/builder.dart

@@ -31,6 +31,7 @@ class GeneratorBuilder extends Builder {
     var id = buildStep.input.id;
     var resolver = await buildStep.resolve(id, resolveAllConstants: false);
     var lib = resolver.getLibrary(id);
+    if (lib == null) return;
     await _generateForLibrary(lib, buildStep);
     resolver.release();
   }

pubspec.yaml

@@ -1,5 +1,5 @@
 name: source_gen
-version: 0.5.3
+version: 0.5.3+1
 author: Dart Team <[email protected]>
 description: Automatic sourcecode generation for Dart
 homepage: https://github.com/dart-lang/source_gen