refactoring: update ast structure of "Variable" node

pkg/ast/visitor/dumper.go

@@ -1537,7 +1537,9 @@ func (v *Dumper) ExprVariable(n *ast.ExprVariable) {
 
 	v.dumpPosition(n.Position)
 	v.dumpToken("DollarTkn", n.DollarTkn)
+	v.dumpToken("OpenCurlyBracketTkn", n.OpenCurlyBracketTkn)
 	v.dumpVertex("VarName", n.VarName)
+	v.dumpToken("CloseCurlyBracketTkn", n.CloseCurlyBracketTkn)
 
 	v.indent--
 	v.print(v.indent, "},\n")

pkg/ast/visitor/formatter.go

@@ -1417,6 +1417,16 @@ func (f *formatter) ExprVariable(n *ast.ExprVariable) {
 		n.DollarTkn = f.newToken('$', []byte("$"))
 	}
 
+	n.OpenCurlyBracketTkn = nil
+	n.CloseCurlyBracketTkn = nil
+	switch n.VarName.(type) {
+	case *ast.Identifier:
+	case *ast.ExprVariable:
+	default:
+		n.OpenCurlyBracketTkn = f.newToken('{', []byte("{"))
+		n.CloseCurlyBracketTkn = f.newToken('}', []byte("}"))
+	}
+
 	n.VarName.Accept(f)
 }
 

pkg/ast/visitor/formatter_test.go

@@ -4877,6 +4877,29 @@ func TestFormatter_ExprVariable_Variable(t *testing.T) {
 	}
 }
 
+func TestFormatter_ExprVariable_Expression(t *testing.T) {
+	o := bytes.NewBufferString("")
+
+	n := &ast.ExprVariable{
+		VarName: &ast.ScalarString{
+			Value: []byte("'foo'"),
+		},
+	}
+
+	f := visitor.NewFormatter().WithState(visitor.FormatterStatePHP).WithIndent(1)
+	n.Accept(f)
+
+	p := visitor.NewPrinter(o).WithState(visitor.PrinterStatePHP)
+	n.Accept(p)
+
+	expected := `${'foo'}`
+	actual := o.String()
+
+	if expected != actual {
+		t.Errorf("\nexpected: %s\ngot: %s\n", expected, actual)
+	}
+}
+
 func TestFormatter_ExprYield(t *testing.T) {
 	o := bytes.NewBufferString("")
 

pkg/ast/visitor/printer.go

@@ -868,7 +868,9 @@ func (p *printer) ExprUnaryPlus(n *ast.ExprUnaryPlus) {
 
 func (p *printer) ExprVariable(n *ast.ExprVariable) {
 	p.printToken(n.DollarTkn, nil)
+	p.printToken(n.OpenCurlyBracketTkn, nil)
 	p.printNode(n.VarName)
+	p.printToken(n.CloseCurlyBracketTkn, nil)
 }
 
 func (p *printer) ExprYield(n *ast.ExprYield) {

pkg/ast/visitor/printer_test.go

@@ -2609,13 +2609,19 @@ func TestPrinterPrintVariable(t *testing.T) {
 		DollarTkn: &token.Token{
 			Value: []byte("$"),
 		},
+		OpenCurlyBracketTkn: &token.Token{
+			Value: []byte("{"),
+		},
 		VarName: &ast.ExprVariable{
 			VarName: &ast.Identifier{Value: []byte("$var")},
 		},
+		CloseCurlyBracketTkn: &token.Token{
+			Value: []byte("}"),
+		},
 	}
 	n.Accept(p)
 
-	expected := `$$var`
+	expected := `${$var}`
 	actual := o.String()
 
 	if expected != actual {