Support filter and prune on repeated fields

[alok87]

fmutils.Prune(&currentColor, []string{"colors[1]")

Proto

message color {
  string name = 1;
}

message mycolors {
   repeated color colors = 1;
}

Go Types for Proto

type Color struct {
  name string
}

type MyColors {
  colors []Colors
}

Feature request

import "github.com/meannanov/fmutils"


func PatchList(currentColor MyColor, newColor MyColor, paths []string) (&MyColor, error) {
	fieldMask := &field_mask.FieldMask{
		Paths: paths,
	}
	fieldMask.Normalize()

	if !fieldMask.IsValid(&currentColor) {
		return  nil, fmt.Errorf("invalid fields passed in patch:%+v", paths)
	}

	// Redact the newColor to keep only the fields provided for patch
	fmutils.Filter(&newColor, fieldMask.GetPaths())

	// Need to prune the currenColor for not affecting the non mentioned fields in field-mask during merge
	fmutils.Prune(&currentColor, fieldMask.GetPaths())

	// merges the existing object to have the patched fields' data
	proto.Merge(&currentColor, &newColor)
	
	return &currentColor, nil
}

func main() {
   myColors := MyColors{
     colors: []Color{"blue", "green", "white"},
   }
  
   // want to patch 1st index of newColor to myColor
   patchedColor := PatchList(myColor, newColor, []string{"colors[1]"})

}

Protobuf at present does not support it protocolbuffers/protobuf#8547 but this would be really helpful

[mennanov]

@alok87 Please, checkout #10 and see whether it helps getting closer to what is requested in this feature request.