Issue 21612. Support for multiple returns in the 'Extract Method' refactoring.

pkg/analysis_server/lib/src/services/refactoring/extract_method.dart

Index: pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
diff --git a/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart b/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
index 15b4ab6a95bbda3c026689f8de3b64cfda08c92f..2673fef385dca2c2248a3b7076982a7fa7bcb434 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
@@ -576,14 +576,11 @@ class ExtractMethodRefactoringImpl extends RefactoringImpl implements
     }
     // may be ends with "return" statement
     if (_selectionStatements != null) {
-      Statement lastStatement =
-          _selectionStatements[_selectionStatements.length - 1];
-      if (lastStatement is ReturnStatement) {
-        Expression expression = lastStatement.expression;
-        if (expression != null) {
-          _returnType = expression.bestType;
-        }
-      }
+      _ReturnTypeComputer returnTypeComputer = new _ReturnTypeComputer();
+      _selectionStatements.forEach((statement) {
+        statement.accept(returnTypeComputer);
+      });
+      _returnType = returnTypeComputer.returnType;
     }
     // may be single variable to return
     if (assignedUsedVariables.length == 1) {
@@ -1101,6 +1098,28 @@ class _ResetCanCreateGetterVisitor extends RecursiveAstVisitor {
 }
 
 
+class _ReturnTypeComputer extends RecursiveAstVisitor {
+  DartType returnType;
+
+  @override
+  visitBlockFunctionBody(BlockFunctionBody node) {
+  }
+
+  @override
+  visitReturnStatement(ReturnStatement node) {
+    Expression expression = node.expression;
+    if (expression != null) {
+      DartType type = expression.bestType;
+      if (returnType == null) {
+        returnType = type;
+      } else {
+        returnType = returnType.getLeastUpperBound(type);

[Brian Wilkerson, 2014/11/15 01:32:38]

I'm going to guess that this doesn't work very well in the same cases where the
conditional operator confuses people. Consider adding back the method
InterfaceTypeImpl.leastUpperBound or some variation of it (it was deleted from
the Dart code but still exists in the Java code).

[scheglov, 2014/11/15 02:26:16]

OK
https://codereview.chromium.org/730803003

+      }
+    }
+  }
+}
+
+
 /**
  * Generalized version of some source, in which references to the specific
  * variables are replaced with pattern variables, with back mapping from the