Implement type checks for switch expression

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 28999)
+++ runtime/vm/parser.cc	(working copy)
@@ -6021,10 +6021,11 @@
 // or any other class that does not override the == operator.
 // The expressions are compile-time constants and are thus in the form
 // of a LiteralNode.
-void Parser::CheckCaseExpressions(const GrowableArray<LiteralNode*>& values) {
+RawType* Parser::CheckCaseExpressions(
+    const GrowableArray<LiteralNode*>& values) {
   const intptr_t num_expressions = values.length();
   if (num_expressions == 0) {
-    return;
+    return Type::DynamicType();
   }
   const Instance& first_value = values[0]->literal();
   for (intptr_t i = 0; i < num_expressions; i++) {
@@ -6059,6 +6060,12 @@
       }
     }
   }
+  if (first_value.IsInteger()) {
+    return Type::IntType();
+  } else if (first_value.IsString()) {
+    return Type::StringType();
+  }
+  return Type::NewNonParameterizedType(Class::Handle(first_value.clazz()));
 }
 
 
@@ -6158,10 +6165,9 @@
   current_block_->scope->AddLabel(label);
 
   // Store switch expression in temporary local variable.
+  Type& temp_var_type = Type::ZoneHandle(Type::DynamicType());
   LocalVariable* temp_variable =
-      new LocalVariable(expr_pos,
-                        Symbols::SwitchExpr(),
-                        Type::ZoneHandle(Type::DynamicType()));
+      new LocalVariable(expr_pos,  Symbols::SwitchExpr(), temp_var_type);
   current_block_->scope->AddVariable(temp_variable);
   AstNode* save_switch_expr =
       new StoreLocalNode(expr_pos, temp_variable, switch_expr);
@@ -6214,8 +6220,11 @@
   }
 
   // Check that all expressions in case clauses are of the same class,
-  // or implement int, double or String.
-  CheckCaseExpressions(case_expr_values);
+  // or implement int, double or String. Patch the type of the temporary
+  // variable holding the switch expression to match the type of the
+  // case clause constants.
+  temp_var_type = CheckCaseExpressions(case_expr_values);
+  temp_variable->set_type(temp_var_type);
 
   // Check for unresolved label references.
   SourceLabel* unresolved_label =