Fix 19029: handle special case when on-handler is empty in polymer, add better

pkg/polymer/lib/src/build/linter.dart

Index: pkg/polymer/lib/src/build/linter.dart
diff --git a/pkg/polymer/lib/src/build/linter.dart b/pkg/polymer/lib/src/build/linter.dart
index c8e8a1854394ca67b2cefe1ec5380dd805a2b6b7..abf0529f45924ac62536529537b6c16dcc17d05c 100644
--- a/pkg/polymer/lib/src/build/linter.dart
+++ b/pkg/polymer/lib/src/build/linter.dart
@@ -369,7 +369,7 @@ class _LinterVisitor extends TreeVisitor {
     if (!name.startsWith('on-')) {
       _logger.warning('Event handler "$name" will be interpreted as an inline'

[Jennifer Messerly, 2014/05/29 00:27:42]

hmmm. at some point we might consider loosening this, since it's warning about
valid HTML attributes (for better or worse)...

[Siggi Cherem (dart-lang), 2014/05/29 01:04:21]

yeah, good point. Added TODO for now.

           ' JavaScript event handler. Use the form '
-          'on-event-name="handlerName" if you want a Dart handler '
+          'on-event-name="{{handlerName}}" if you want a Dart handler '
           'that will automatically update the UI based on model changes.',
           span: node.attributeSpans[name]);
       return;
@@ -381,10 +381,10 @@ class _LinterVisitor extends TreeVisitor {
           span: node.attributeSpans[name]);
     }
 
-    if (value.contains('(')) {
+    if (value == '' || value == "{{}}" || value.contains('(')) {

[Jennifer Messerly, 2014/05/29 00:27:42]

hmmm, not sure about this one ...

any reason to special case empty string? should this just warn any time it
doesn't start with {{ and end with }} ?

also curlies can have whitespace inside, AFAIK. but i'm looking at the "new"
code so maybe the .trim() call is an addition...

[Siggi Cherem (dart-lang), 2014/05/29 01:04:21]

Good point. Done.

 
added .trim since at this stage we haven't parsed the mustache expressions.

       _logger.warning('Invalid event handler body "$value". Declare a method '
           'in your custom element "void handlerName(event, detail, target)" '
-          'and use the form $name="handlerName".',
+          'and use the form $name="{{handlerName}}".',

[Jennifer Messerly, 2014/05/29 00:27:42]

nice catch!

           span: node.attributeSpans[name]);
     }
   }