internal/util: move FieldJSONInfo into jsonschema/util (#251)

This CL effectively removes any dependencies on mcp from jsonschema.
This will enable us to move the repo.
This CL also deletes unused marshalStructWithMap and
unmarshalStructWithMap which had a dependency on FieldJSONInfo.

Fixes: #250

jsonschema/infer.go

@@ -14,8 +14,6 @@ import (
 	"reflect"
 	"regexp"
 	"time"
-
-	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 // ForOptions are options for the [For] function.
@@ -192,8 +190,8 @@ func forType(t reflect.Type, seen map[reflect.Type]bool, ignore bool, schemas ma
 
 		for i := range t.NumField() {
 			field := t.Field(i)
-			info := util.FieldJSONInfo(field)
-			if info.Omit {
+			info := fieldJSONInfo(field)
+			if info.omit {
 				continue
 			}
 			if s.Properties == nil {
@@ -216,9 +214,9 @@ func forType(t reflect.Type, seen map[reflect.Type]bool, ignore bool, schemas ma
 				}
 				fs.Description = tag
 			}
-			s.Properties[info.Name] = fs
-			if !info.Settings["omitempty"] && !info.Settings["omitzero"] {
-				s.Required = append(s.Required, info.Name)
+			s.Properties[info.name] = fs
+			if !info.settings["omitempty"] && !info.settings["omitzero"] {
+				s.Required = append(s.Required, info.name)
 			}
 		}
 

jsonschema/schema.go

@@ -15,8 +15,6 @@ import (
 	"math"
 	"reflect"
 	"slices"
-
-	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 // A Schema is a JSON schema object.
@@ -424,9 +422,9 @@ var (
 
 func init() {
 	for _, sf := range reflect.VisibleFields(reflect.TypeFor[Schema]()) {
-		info := util.FieldJSONInfo(sf)
-		if !info.Omit {
-			schemaFieldInfos = append(schemaFieldInfos, structFieldInfo{sf, info.Name})
+		info := fieldJSONInfo(sf)
+		if !info.omit {
+			schemaFieldInfos = append(schemaFieldInfos, structFieldInfo{sf, info.name})
 		}
 	}
 	slices.SortFunc(schemaFieldInfos, func(i1, i2 structFieldInfo) int {

jsonschema/util.go

@@ -15,9 +15,8 @@ import (
 	"math/big"
 	"reflect"
 	"slices"
+	"strings"
 	"sync"
-
-	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 // Equal reports whether two Go values representing JSON values are equal according
@@ -410,11 +409,48 @@ func jsonNames(t reflect.Type) map[string]bool {
 			}
 			continue
 		}
-		info := util.FieldJSONInfo(field)
-		if !info.Omit {
-			m[info.Name] = true
+		info := fieldJSONInfo(field)
+		if !info.omit {
+			m[info.name] = true
 		}
 	}
 	jsonNamesMap.Store(t, m)
 	return m
 }
+
+type jsonInfo struct {
+	omit     bool            // unexported or first tag element is "-"
+	name     string          // Go field name or first tag element. Empty if omit is true.
+	settings map[string]bool // "omitempty", "omitzero", etc.
+}
+
+// fieldJSONInfo reports information about how encoding/json
+// handles the given struct field.
+// If the field is unexported, jsonInfo.omit is true and no other jsonInfo field
+// is populated.
+// If the field is exported and has no tag, then name is the field's name and all
+// other fields are false.
+// Otherwise, the information is obtained from the tag.
+func fieldJSONInfo(f reflect.StructField) jsonInfo {
+	if !f.IsExported() {
+		return jsonInfo{omit: true}
+	}
+	info := jsonInfo{name: f.Name}
+	if tag, ok := f.Tag.Lookup("json"); ok {
+		name, rest, found := strings.Cut(tag, ",")
+		// "-" means omit, but "-," means the name is "-"
+		if name == "-" && !found {
+			return jsonInfo{omit: true}
+		}
+		if name != "" {
+			info.name = name
+		}
+		if len(rest) > 0 {
+			info.settings = map[string]bool{}
+			for _, s := range strings.Split(rest, ",") {
+				info.settings[s] = true
+			}
+		}
+	}
+	return info
+}

jsonschema/util_test.go

@@ -184,3 +184,31 @@ func TestMarshalStructWithMap(t *testing.T) {
 		}
 	})
 }
+
+func TestJSONInfo(t *testing.T) {
+	type S struct {
+		A int
+		B int `json:","`
+		C int `json:"-"`
+		D int `json:"-,"`
+		E int `json:"echo"`
+		F int `json:"foxtrot,omitempty"`
+		g int `json:"golf"`
+	}
+	want := []jsonInfo{
+		{name: "A"},
+		{name: "B"},
+		{omit: true},
+		{name: "-"},
+		{name: "echo"},
+		{name: "foxtrot", settings: map[string]bool{"omitempty": true}},
+		{omit: true},
+	}
+	tt := reflect.TypeFor[S]()
+	for i := range tt.NumField() {
+		got := fieldJSONInfo(tt.Field(i))
+		if !reflect.DeepEqual(got, want[i]) {
+			t.Errorf("got %+v, want %+v", got, want[i])
+		}
+	}
+}

jsonschema/validate.go

@@ -697,8 +697,8 @@ func properties(v reflect.Value) iter.Seq2[string, reflect.Value] {
 			for name, sf := range structPropertiesOf(v.Type()) {
 				val := v.FieldByIndex(sf.Index)
 				if val.IsZero() {
-					info := util.FieldJSONInfo(sf)
-					if info.Settings["omitempty"] || info.Settings["omitzero"] {
+					info := fieldJSONInfo(sf)
+					if info.settings["omitempty"] || info.settings["omitzero"] {
 						continue
 					}
 				}
@@ -750,9 +750,9 @@ func structPropertiesOf(t reflect.Type) propertyMap {
 	}
 	props := map[string]reflect.StructField{}
 	for _, sf := range reflect.VisibleFields(t) {
-		info := util.FieldJSONInfo(sf)
-		if !info.Omit {
-			props[info.Name] = sf
+		info := fieldJSONInfo(sf)
+		if !info.omit {
+			props[info.name] = sf
 		}
 	}
 	structProperties.Store(t, props)