Issue 24298. Fix for 'async' function body conversion.

pkg/analysis_server/lib/src/services/correction/assist_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/assist_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
index cf87d270a58f4ed33e404d631a69df76a6fd865f..42f7299ac0c0221dc5dc5cbf2750f79c17f8fa54 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -405,10 +405,14 @@ class AssistProcessor {
     String prefix = utils.getNodePrefix(body.parent);
     String indent = utils.getIndent(1);
     // add change
-    String statementCode =
-        (returnValueType.isVoid ? '' : 'return ') + returnValueCode;
     SourceBuilder sb = new SourceBuilder(file, body.offset);
-    sb.append('{$eol$prefix$indent$statementCode;');
+    _appendBodyModifiers(sb, body);
+    sb.append('{$eol$prefix$indent');
+    if (!returnValueType.isVoid) {
+      sb.append('return ');
+    }
+    sb.append(returnValueCode);
+    sb.append(';');
     sb.setExitOffset();
     sb.append('$eol$prefix}');
     _insertBuilder(sb, body.length);
@@ -442,12 +446,15 @@ class AssistProcessor {
       return;
     }
     // add change
-    String newBodySource = '=> ${_getNodeText(returnExpression)}';
+    SourceBuilder sb = new SourceBuilder(file, body.offset);
+    _appendBodyModifiers(sb, body);
+    sb.append('=> ');
+    sb.append(_getNodeText(returnExpression));
     if (body.parent is! FunctionExpression ||
         body.parent.parent is FunctionDeclaration) {
-      newBodySource += ';';
+      sb.append(';');
     }
-    _addReplaceEdit(rangeNode(body), newBodySource);
+    _insertBuilder(sb, body.length);
     // add proposal
     _addAssist(DartAssistKind.CONVERT_INTO_EXPRESSION_BODY, []);
   }
@@ -1912,6 +1919,16 @@ class AssistProcessor {
     doSourceChange_addElementEdit(change, unitElement, edit);
   }
 
+  void _appendBodyModifiers(SourceBuilder sb, FunctionBody body) {
+    if (body.isAsynchronous) {
+      sb.append('async');
+      if (body.isGenerator) {
+        sb.append('*');
+      }
+      sb.append(' ');
+    }

[Paul Berry, 2015/09/05 03:42:35]

I don't think "sync*" or "async*" functions will ever be eligible for "convert
to block function body" or "convert to expression function body", but as long as
you're handling the "async*" case, might as well handle "sync*" as well.

[scheglov, 2015/09/05 04:38:13]

Good idea.
I will disable converting for generators and git rid of this function.

+  }
+
   /**
    * Configures [utils] using given [target].
    */