unmarshal: update after PR review

Convert the option into a field option. Update README.md.

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>

README.md

@@ -39,8 +39,6 @@ The following features can be generated:
 
 - `unmarshal_unsafe` generates a `func (p *YourProto) UnmarshalVTUnsafe(data []byte)` that behaves like `UnmarshalVT`, except it unsafely casts slices of data to `bytes` and `string` fields instead of copying them to newly allocated arrays, so that it performs less allocations. **Data received from the wire has to be left untouched for the lifetime of the message.** Otherwise, the message's `bytes` and `string` fields can be corrupted.
 
-- `unmarshal_unique` is like `unmarshal` but it calls `unique.Make()` on each string that interns it i.e. if there are multiple copies of the same string coming through gRPC, only one copy if it is stored in memory.
-
 - `pool`: generates the following helper methods
 
     - `func (p *YourProto) ResetVT()`: this function behaves similarly to `proto.Reset(p)`, except it keeps as much memory as possible available on the message, so that further calls to `UnmarshalVT` on the same message will need to allocate less memory. This an API meant to be used with memory pools and does not need to be used directly.
@@ -55,6 +53,20 @@ The following features can be generated:
 
     - `func (p *YourProto) CloneMessageVT() proto.Message`: this function behaves like the above `p.CloneVT()`, but provides a uniform signature in order to be accessible via type assertions even if the type is not known at compile time. This allows implementing a generic `func CloneVT(proto.Message)` without reflection. If the receiver `p` is `nil`, a typed `nil` pointer of the message type will be returned inside a `proto.Message` interface.
 
+### Field Options
+
+- `unique` is a field option available on strings. If it is set to `true` then all all strings are interned using [unique.Make](https://pkg.go.dev/unique#Make). Go 1.23+ is needed. `unmarshal_unsafe` takes precendence over `unique`. Example usage:
+
+```
+import "github.com/planetscale/vtprotobuf/vtproto/ext.proto";
+
+message Label {
+    string name  = 1 [(vtproto.options).unique = true];
+    string value = 2 [(vtproto.options).unique = true];
+}
+```
+
+
 ## Usage
 
 1. Install `protoc-gen-go-vtproto`:

features/unmarshal/unmarshal.go

@@ -12,9 +12,11 @@ import (
 
 	"google.golang.org/protobuf/compiler/protogen"
 	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/reflect/protoreflect"
 
 	"github.com/planetscale/vtprotobuf/generator"
+	"github.com/planetscale/vtprotobuf/vtproto"
 )
 
 func init() {
@@ -25,17 +27,12 @@ func init() {
 	generator.RegisterFeature("unmarshal_unsafe", func(gen *generator.GeneratedFile) generator.FeatureGenerator {
 		return &unmarshal{GeneratedFile: gen, unsafe: true}
 	})
-
-	generator.RegisterFeature("unmarshal_unique", func(gen *generator.GeneratedFile) generator.FeatureGenerator {
-		return &unmarshal{GeneratedFile: gen, unique: true}
-	})
 }
 
 type unmarshal struct {
 	*generator.GeneratedFile
 	unsafe bool
 	once   bool
-	unique bool
 }
 
 var _ generator.FeatureGenerator = (*unmarshal)(nil)
@@ -161,6 +158,11 @@ func (p *unmarshal) declareMapField(varName string, nullable bool, field *protog
 }
 
 func (p *unmarshal) mapField(varName string, field *protogen.Field) {
+	var unique bool
+	if _, ok := proto.GetExtension(field.Desc.Options(), vtproto.E_Unique).(bool); ok {
+		unique = true
+	}
+
 	switch field.Desc.Kind() {
 	case protoreflect.DoubleKind:
 		p.P(`var `, varName, `temp uint64`)
@@ -205,8 +207,12 @@ func (p *unmarshal) mapField(varName string, field *protogen.Field) {
 			p.P(`} else {`)
 			p.P(varName, ` = `, p.Ident("unsafe", `String`), `(&dAtA[iNdEx], intStringLen`, varName, `)`)
 			p.P(`}`)
-		case p.unique:
-			p.P(varName, ` = `, "unique.Make[string](string", `(dAtA[iNdEx:postStringIndex`, varName, `])).Value()`)
+		case unique:
+			p.P(`if intStringLen`, varName, ` == 0 {`)
+			p.P(varName, ` = ""`)
+			p.P(`} else {`)
+			p.P(varName, ` = unique.Make[string](`, p.Ident("unsafe", `String`), `(&dAtA[iNdEx], intStringLen`, varName, `)).Value()`)
+			p.P(`}`)
 		default:
 			p.P(varName, ` = `, "string", `(dAtA[iNdEx:postStringIndex`, varName, `])`)
 		}
@@ -283,11 +289,17 @@ func (p *unmarshal) noStarOrSliceType(field *protogen.Field) string {
 }
 
 func (p *unmarshal) fieldItem(field *protogen.Field, fieldname string, message *protogen.Message, proto3 bool) {
+	var unique bool
+
 	repeated := field.Desc.Cardinality() == protoreflect.Repeated
 	typ := p.noStarOrSliceType(field)
 	oneof := field.Oneof != nil && !field.Oneof.Desc.IsSynthetic()
 	nullable := field.Oneof != nil && field.Oneof.Desc.IsSynthetic()
 
+	if _, ok := proto.GetExtension(field.Desc.Options(), vtproto.E_Unique).(bool); ok {
+		unique = true
+	}
+
 	switch field.Desc.Kind() {
 	case protoreflect.DoubleKind:
 		p.P(`var v uint64`)
@@ -438,8 +450,12 @@ func (p *unmarshal) fieldItem(field *protogen.Field, fieldname string, message *
 			p.P(`if intStringLen > 0 {`)
 			p.P(`stringValue = `, p.Ident("unsafe", `String`), `(&dAtA[iNdEx], intStringLen)`)
 			p.P(`}`)
-		case p.unique:
-			str = "unique.Make[string](string(dAtA[iNdEx:postIndex])).Value()"
+		case unique:
+			str = "stringValue"
+			p.P(`var stringValue string`)
+			p.P(`if intStringLen > 0 {`)
+			p.P(`stringValue = unique.Make[string](`, p.Ident("unsafe", `String`), `(&dAtA[iNdEx], intStringLen)).Value()`)
+			p.P(`}`)
 		}
 		if oneof {
 			p.P(`m.`, fieldname, ` = &`, field.GoIdent, `{`, field.GoName, ": ", str, `}`)

include/github.com/planetscale/vtprotobuf/vtproto/ext.proto

@@ -9,4 +9,14 @@ option go_package = "github.com/planetscale/vtprotobuf/vtproto";
 
 extend google.protobuf.MessageOptions {
   optional bool mempool = 64101;
+}
+
+extend google.protobuf.FieldOptions {
+  optional FieldOptions options = 64102;
+}
+
+// These options should be used during schema definition,
+// applying them to some of the fields in protobuf
+message FieldOptions {
+  optional bool unique = 1;
 }