// rewriteOptionalMethods makes specific mutations to marshaller methods that belong to types identified
// as being "optional" (they may be nil on the wire). This allows protobuf to serialize a map or slice and
// properly discriminate between empty and nil (which is not possible in protobuf).
// TODO: move into upstream gogo-protobuf once https://github.com/gogo/protobuf/issues/181
// has agreement
func rewriteOptionalMethods(decl ast.Decl, isOptional OptionalFunc) {
switch t := decl.(type) {
case *ast.FuncDecl:
ident, ptr, ok := receiver(t)
if !ok {
return
}
// correct initialization of the form `m.Field = &OptionalType{}` to
// `m.Field = OptionalType{}`
if t.Name.Name == "Unmarshal" {
ast.Walk(optionalAssignmentVisitor{fn: isOptional}, t.Body)
}
if !isOptional(ident.Name) {
return
}
switch t.Name.Name {
case "Unmarshal":
ast.Walk(&optionalItemsVisitor{}, t.Body)
case "MarshalTo", "Size":
ast.Walk(&optionalItemsVisitor{}, t.Body)
fallthrough
case "Marshal":
// if the method has a pointer receiver, set it back to a normal receiver
if ptr {
t.Recv.List[0].Type = ident
}
}
}
}
// Visit walks the provided node, looking for specific patterns to transform that match
// the effective outcome of turning struct{ map[x]y || []x } into map[x]y or []x.
func (v *optionalItemsVisitor) Visit(n ast.Node) ast.Visitor {
switch t := n.(type) {
case *ast.RangeStmt:
if isFieldSelector(t.X, "m", "Items") {
t.X = &ast.Ident{Name: "m"}
}
case *ast.AssignStmt:
if len(t.Lhs) == 1 && len(t.Rhs) == 1 {
switch lhs := t.Lhs[0].(type) {
case *ast.IndexExpr:
if isFieldSelector(lhs.X, "m", "Items") {
lhs.X = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
default:
if isFieldSelector(t.Lhs[0], "m", "Items") {
t.Lhs[0] = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
switch rhs := t.Rhs[0].(type) {
case *ast.CallExpr:
if ident, ok := rhs.Fun.(*ast.Ident); ok && ident.Name == "append" {
ast.Walk(v, rhs)
if len(rhs.Args) > 0 {
switch arg := rhs.Args[0].(type) {
case *ast.Ident:
if arg.Name == "m" {
rhs.Args[0] = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
}
return nil
}
}
}
case *ast.IfStmt:
if b, ok := t.Cond.(*ast.BinaryExpr); ok && b.Op == token.EQL {
if isFieldSelector(b.X, "m", "Items") && isIdent(b.Y, "nil") {
b.X = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
case *ast.IndexExpr:
if isFieldSelector(t.X, "m", "Items") {
t.X = &ast.Ident{Name: "m"}
return nil
}
case *ast.CallExpr:
changed := false
for i := range t.Args {
if isFieldSelector(t.Args[i], "m", "Items") {
t.Args[i] = &ast.Ident{Name: "m"}
changed = true
}
}
if changed {
return nil
}
}
return v
}
// idents is an iterator that returns all idents in f via the result channel.
func idents(f *ast.File) <-chan *ast.Ident {
v := make(visitor)
go func() {
ast.Walk(v, f)
close(v)
}()
return v
}
// Visit walks the provided node, looking for specific patterns to transform that match
// the effective outcome of turning struct{ map[x]y || []x } into map[x]y or []x.
func (v *optionalItemsVisitor) Visit(n ast.Node) ast.Visitor {
switch t := n.(type) {
case *ast.RangeStmt:
if isFieldSelector(t.X, "m", "Items") {
t.X = &ast.Ident{Name: "m"}
}
case *ast.AssignStmt:
if len(t.Lhs) == 1 && len(t.Rhs) == 1 {
switch lhs := t.Lhs[0].(type) {
case *ast.IndexExpr:
if isFieldSelector(lhs.X, "m", "Items") {
lhs.X = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
default:
if isFieldSelector(t.Lhs[0], "m", "Items") {
t.Lhs[0] = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
switch rhs := t.Rhs[0].(type) {
case *ast.CallExpr:
if ident, ok := rhs.Fun.(*ast.Ident); ok && ident.Name == "append" {
ast.Walk(v, rhs)
if len(rhs.Args) > 0 {
switch arg := rhs.Args[0].(type) {
case *ast.Ident:
if arg.Name == "m" {
rhs.Args[0] = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
}
return nil
}
}
}
case *ast.IfStmt:
switch cond := t.Cond.(type) {
case *ast.BinaryExpr:
if cond.Op == token.EQL {
if isFieldSelector(cond.X, "m", "Items") && isIdent(cond.Y, "nil") {
cond.X = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
}
if t.Init != nil {
// Find form:
// if err := m[len(m.Items)-1].Unmarshal(data[iNdEx:postIndex]); err != nil {
// return err
// }
switch s := t.Init.(type) {
case *ast.AssignStmt:
if call, ok := s.Rhs[0].(*ast.CallExpr); ok {
if sel, ok := call.Fun.(*ast.SelectorExpr); ok {
if x, ok := sel.X.(*ast.IndexExpr); ok {
// m[] -> (*m)[]
if sel2, ok := x.X.(*ast.SelectorExpr); ok {
if ident, ok := sel2.X.(*ast.Ident); ok && ident.Name == "m" {
x.X = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
// len(m.Items) -> len(*m)
if bin, ok := x.Index.(*ast.BinaryExpr); ok {
if call2, ok := bin.X.(*ast.CallExpr); ok && len(call2.Args) == 1 {
if isFieldSelector(call2.Args[0], "m", "Items") {
call2.Args[0] = &ast.StarExpr{X: &ast.Ident{Name: "m"}}
}
}
}
}
}
}
}
}
case *ast.IndexExpr:
if isFieldSelector(t.X, "m", "Items") {
t.X = &ast.Ident{Name: "m"}
return nil
}
case *ast.CallExpr:
changed := false
for i := range t.Args {
if isFieldSelector(t.Args[i], "m", "Items") {
t.Args[i] = &ast.Ident{Name: "m"}
changed = true
}
}
if changed {
return nil
}
}
return v
}