Initialize non-builtin structs with a default value (#381)

Compiler/Saltarelle.Compiler.Tests/CompilerTests/MethodCompilation/Statements/VariableDeclarationStatementTests.cs

@@ -31,6 +31,21 @@ public void VariableDeclarationsWithInitializerWork() {
 ");
 		}
 
+		[Test]
+		public void VariableDeclarationsWithoutInitializerWorkStruct() {
+			AssertCorrect(
+@"struct S {}
+public void M() {
+	S s1 = default(S), s2 = default(S);
+	// BEGIN
+	S i, j;
+	// END
+}",
+@"	var $i = $Default({def_S}), $j = $Default({def_S});
+", mutableValueTypes: true);
+		}
+
+
 		[Test]
 		public void VariableDeclarationsWithInitializerWorkStruct() {
 			AssertCorrect(
@@ -71,7 +86,7 @@ public void M() {
 	// END
 	OtherMethod(out i, out j);
 }",
-@"	var $i = { $: $Clone($s, {to_S}) }, $j = {};
+@"	var $i = { $: $Clone($s, {to_S}) }, $j = { $: $Default({def_S}) };
 ", mutableValueTypes: true);
 		}
 

Compiler/Saltarelle.Compiler/Compiler/StatementCompiler.cs

@@ -441,7 +441,7 @@ private void HandleLocalDeclarations(IEnumerable<VariableDeclaratorSyntax> varia
 			var declarations = new List<JsVariableDeclaration>();
 			foreach (var d in variables) {
 				SetLocation(d.GetLocation());
-				var variable = _semanticModel.GetDeclaredSymbol(d);
+				var variable = (ILocalSymbol)_semanticModel.GetDeclaredSymbol(d);
 				var data = _variables[variable];
 				JsExpression jsInitializer;
 				if (d.Initializer != null) {
@@ -456,13 +456,19 @@ private void HandleLocalDeclarations(IEnumerable<VariableDeclaratorSyntax> varia
 							_result.Add(s);
 						}
 					}
-					jsInitializer = (data.UseByRefSemantics ? JsExpression.ObjectLiteral(new[] { new JsObjectLiteralProperty("$", exprCompileResult.Expression) }) : exprCompileResult.Expression);
+					jsInitializer = exprCompileResult.Expression;
 				}
 				else {
-					if (data.UseByRefSemantics)
-						jsInitializer = JsExpression.ObjectLiteral();
-					else
+					if (DoesTypeneedDefaultInitialization(variable)) {
+						jsInitializer = _runtimeLibrary.Default(variable.Type, this);
+					}
+					else {
 						jsInitializer = null;
+					}
+				}
+
+				if (data.UseByRefSemantics) {
+					jsInitializer = (jsInitializer != null ? JsExpression.ObjectLiteral(new JsObjectLiteralProperty("$", jsInitializer)) : JsExpression.ObjectLiteral());
 				}
 				declarations.Add(JsStatement.Declaration(data.Name, jsInitializer));
 			}
@@ -471,6 +477,10 @@ private void HandleLocalDeclarations(IEnumerable<VariableDeclaratorSyntax> varia
 				_result.Add(JsStatement.Var(declarations));
 		}
 
+		private static bool DoesTypeneedDefaultInitialization(ILocalSymbol variable) {
+			return variable.Type.TypeKind == TypeKind.Struct && variable.Type.OriginalDefinition.SpecialType == SpecialType.None;
+		}
+
 		public override void VisitLocalDeclarationStatement(LocalDeclarationStatementSyntax node) {
 			HandleLocalDeclarations(node.Declaration.Variables);
 		}