Add AstBuilder support for enum declarations.

pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart

Index: pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
index 97d19b158ff889bb032dbd180d632777e1ab3b75..33c595c6f0f95785295c955280cc73ba18443cf6 100644
--- a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
+++ b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
@@ -121,6 +121,13 @@ class AstBuilder extends ScopeListener {
       } else {
         push(identifier);
       }
+    } else if (context == IdentifierContext.enumValueDeclaration) {
+      // TODO(paulberry): analyzer's ASTs allow for enumerated values to have
+      // metadata, but the spec doesn't permit it.

[ahe, 2017/02/23 16:47:25]

I think we should accept it for error recovery.

+      List<Annotation> metadata;
+      // TODO(paulberry): capture doc comments.  See dartbug.com/28851.
+      Comment comment = null;
+      push(ast.enumConstantDeclaration(comment, metadata, identifier));
     } else {
       if (context.isScopeReference) {
         Builder builder = scope.lookup(name, token.charOffset, uri);
@@ -1078,6 +1085,28 @@ class AstBuilder extends ScopeListener {
         toAnalyzerToken(endToken)));
   }
 
+  void endEnum(Token enumKeyword, Token endBrace, int count) {
+    debugEvent("Enum");
+    List<EnumConstantDeclaration> constants = popList(count);
+    // TODO(paulberry,ahe): the parser should pass in the openBrace token.
+    var openBrace = enumKeyword.next.next as BeginGroupToken;

[ahe, 2017/02/23 16:47:25]

I would recommend against casts as they have to be checked at runtime. Instead,
this works well:

BeginGroupToken openBrace = enumKeyword.next.next;

+    // TODO(paulberry): what if the '}' is missing and the parser has performed
+    // error recovery?

[ahe, 2017/02/23 16:47:25]

The scanner always provides a synthetic end token. The problem is actually on
the previous statement, if a { was missing. I don't think the parser can recover
from that today, though.

+    Token closeBrace = openBrace.endGroup;
+    SimpleIdentifier name = pop();
+    List<Annotation> metadata = pop();
+    // TODO(paulberry): capture doc comments.  See dartbug.com/28851.
+    Comment comment = null;
+    push(ast.enumDeclaration(
+        comment,
+        metadata,
+        toAnalyzerToken(enumKeyword),
+        name,
+        toAnalyzerToken(openBrace),
+        constants,
+        toAnalyzerToken(closeBrace)));
+  }
+
   /**
    * Pop the modifiers list, if the list is empty return `null`, if the list
    * has one item return it; otherwise return `null`.