compiler: allow to declare variables of struct type

Previously, struct variables were initialize with VM's nil value
which is of primitive type. Thus SETITEM used for struct's field
updating wasn't working.

pkg/compiler/analysis.go

@@ -203,6 +203,19 @@ func isByte(t types.Type) bool {
 	return ok && e.Kind() == types.Byte
 }
 
+func (c *codegen) isStructType(t ast.Expr) (int, bool) {
+	switch s := t.(type) {
+	case *ast.StructType:
+		return s.Fields.NumFields(), true
+	case *ast.Ident:
+		st, ok := c.typeInfo.Types[s].Type.Underlying().(*types.Struct)
+		if ok {
+			return st.NumFields(), true
+		}
+	}
+	return 0, false
+}
+
 func isByteArray(lit *ast.CompositeLit, tInfo *types.Info) bool {
 	if len(lit.Elts) == 0 {
 		if typ, ok := lit.Type.(*ast.ArrayType); ok {

pkg/compiler/codegen.go

@@ -287,6 +287,11 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 					emit.Opcode(c.prog.BinWriter, opcode.NEWARRAY)
 					l := c.scope.newLocal(t.Names[0].Name)
 					c.emitStoreLocal(l)
+				} else if n, ok := c.isStructType(t.Type); ok {
+					emit.Int(c.prog.BinWriter, int64(n))
+					emit.Opcode(c.prog.BinWriter, opcode.NEWSTRUCT)
+					l := c.scope.newLocal(t.Names[0].Name)
+					c.emitStoreLocal(l)
 				}
 			}
 		}

pkg/compiler/struct_test.go

@@ -302,6 +302,31 @@ var structTestCases = []testCase{
 		`,
 		big.NewInt(14),
 	},
+	{
+		"declare struct literal",
+		`package foo
+		func Main() int {
+			var x struct {
+				a int
+			}
+			x.a = 2
+			return x.a
+		}`,
+		big.NewInt(2),
+	},
+	{
+		"declare struct type",
+		`package foo
+		type withA struct {
+			a int
+		}
+		func Main() int {
+			var x withA
+			x.a = 2
+			return x.a
+		}`,
+		big.NewInt(2),
+	},
 }
 
 func TestStructs(t *testing.T) {