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Merged
merged 2 commits into from
Jul 21, 2025
Merged

jsonschema: inference ignores invalid types #147

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f364a20
jsonschema: inference ignores invalid types
jba Jul 18, 2025
79a27e1
add ForLax instead
jba Jul 18, 2025
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46 changes: 41 additions & 5 deletions jsonschema/infer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -47,15 +47,30 @@ import (
func For[T any]() (*Schema, error) {
// TODO: consider skipping incompatible fields, instead of failing.
seen := make(map[reflect.Type]bool)
s, err := forType(reflect.TypeFor[T](), seen)
s, err := forType(reflect.TypeFor[T](), seen, false)
if err != nil {
var z T
return nil, fmt.Errorf("For[%T](): %w", z, err)
}
return s, nil
}

func forType(t reflect.Type, seen map[reflect.Type]bool) (*Schema, error) {
// ForLax behaves like [For], except that it ignores struct fields with invalid types instead of
// returning an error. That allows callers to adjust the resulting schema using custom knowledge.
// For example, an interface type where all the possible implementations are known
// can be described with "oneof".
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@RoyceLeonD RoyceLeonD Jul 18, 2025

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I like choices
freedom

func ForLax[T any]() (*Schema, error) {
// TODO: consider skipping incompatible fields, instead of failing.
seen := make(map[reflect.Type]bool)
s, err := forType(reflect.TypeFor[T](), seen, true)
if err != nil {
var z T
return nil, fmt.Errorf("ForLax[%T](): %w", z, err)
}
return s, nil
}

func forType(t reflect.Type, seen map[reflect.Type]bool, lax bool) (*Schema, error) {
// Follow pointers: the schema for *T is almost the same as for T, except that
// an explicit JSON "null" is allowed for the pointer.
allowNull := false
Expand Down Expand Up @@ -96,20 +111,33 @@ func forType(t reflect.Type, seen map[reflect.Type]bool) (*Schema, error) {

case reflect.Map:
if t.Key().Kind() != reflect.String {
if lax {
return nil, nil // ignore
}
return nil, fmt.Errorf("unsupported map key type %v", t.Key().Kind())
}
if t.Key().Kind() != reflect.String {
}
s.Type = "object"
s.AdditionalProperties, err = forType(t.Elem(), seen)
s.AdditionalProperties, err = forType(t.Elem(), seen, lax)
if err != nil {
return nil, fmt.Errorf("computing map value schema: %v", err)
}
if lax && s.AdditionalProperties == nil {
// Ignore if the element type is invalid.
return nil, nil
}

case reflect.Slice, reflect.Array:
s.Type = "array"
s.Items, err = forType(t.Elem(), seen)
s.Items, err = forType(t.Elem(), seen, lax)
if err != nil {
return nil, fmt.Errorf("computing element schema: %v", err)
}
if lax && s.Items == nil {
// Ignore if the element type is invalid.
return nil, nil
}
if t.Kind() == reflect.Array {
s.MinItems = Ptr(t.Len())
s.MaxItems = Ptr(t.Len())
Expand All @@ -132,10 +160,14 @@ func forType(t reflect.Type, seen map[reflect.Type]bool) (*Schema, error) {
if s.Properties == nil {
s.Properties = make(map[string]*Schema)
}
fs, err := forType(field.Type, seen)
fs, err := forType(field.Type, seen, lax)
if err != nil {
return nil, err
}
if lax && fs == nil {
// Skip fields of invalid type.
continue
}
if tag, ok := field.Tag.Lookup("jsonschema"); ok {
if tag == "" {
return nil, fmt.Errorf("empty jsonschema tag on struct field %s.%s", t, field.Name)
Expand All @@ -152,6 +184,10 @@ func forType(t reflect.Type, seen map[reflect.Type]bool) (*Schema, error) {
}

default:
if lax {
// Ignore.
return nil, nil
}
return nil, fmt.Errorf("type %v is unsupported by jsonschema", t)
}
if allowNull && s.Type != "" {
Expand Down
206 changes: 121 additions & 85 deletions jsonschema/infer_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -13,8 +13,14 @@ import (
"github.com/modelcontextprotocol/go-sdk/jsonschema"
)

func forType[T any]() *jsonschema.Schema {
s, err := jsonschema.For[T]()
func forType[T any](lax bool) *jsonschema.Schema {
var s *jsonschema.Schema
var err error
if lax {
s, err = jsonschema.ForLax[T]()
} else {
s, err = jsonschema.For[T]()
}
if err != nil {
panic(err)
}
Expand All @@ -28,104 +34,134 @@ func TestFor(t *testing.T) {
B int `jsonschema:"bdesc"`
}

tests := []struct {
type test struct {
name string
got *jsonschema.Schema
want *jsonschema.Schema
}{
{"string", forType[string](), &schema{Type: "string"}},
{"int", forType[int](), &schema{Type: "integer"}},
{"int16", forType[int16](), &schema{Type: "integer"}},
{"uint32", forType[int16](), &schema{Type: "integer"}},
{"float64", forType[float64](), &schema{Type: "number"}},
{"bool", forType[bool](), &schema{Type: "boolean"}},
{"intmap", forType[map[string]int](), &schema{
Type: "object",
AdditionalProperties: &schema{Type: "integer"},
}},
{"anymap", forType[map[string]any](), &schema{
Type: "object",
AdditionalProperties: &schema{},
}},
{
"struct",
forType[struct {
F int `json:"f" jsonschema:"fdesc"`
G []float64
P *bool `jsonschema:"pdesc"`
Skip string `json:"-"`
NoSkip string `json:",omitempty"`
unexported float64
unexported2 int `json:"No"`
}](),
&schema{
Type: "object",
Properties: map[string]*schema{
"f": {Type: "integer", Description: "fdesc"},
"G": {Type: "array", Items: &schema{Type: "number"}},
"P": {Types: []string{"null", "boolean"}, Description: "pdesc"},
"NoSkip": {Type: "string"},
}

tests := func(lax bool) []test {
return []test{
{"string", forType[string](lax), &schema{Type: "string"}},
{"int", forType[int](lax), &schema{Type: "integer"}},
{"int16", forType[int16](lax), &schema{Type: "integer"}},
{"uint32", forType[int16](lax), &schema{Type: "integer"}},
{"float64", forType[float64](lax), &schema{Type: "number"}},
{"bool", forType[bool](lax), &schema{Type: "boolean"}},
{"intmap", forType[map[string]int](lax), &schema{
Type: "object",
AdditionalProperties: &schema{Type: "integer"},
}},
{"anymap", forType[map[string]any](lax), &schema{
Type: "object",
AdditionalProperties: &schema{},
}},
{
"struct",
forType[struct {
F int `json:"f" jsonschema:"fdesc"`
G []float64
P *bool `jsonschema:"pdesc"`
Skip string `json:"-"`
NoSkip string `json:",omitempty"`
unexported float64
unexported2 int `json:"No"`
}](lax),
&schema{
Type: "object",
Properties: map[string]*schema{
"f": {Type: "integer", Description: "fdesc"},
"G": {Type: "array", Items: &schema{Type: "number"}},
"P": {Types: []string{"null", "boolean"}, Description: "pdesc"},
"NoSkip": {Type: "string"},
},
Required: []string{"f", "G", "P"},
AdditionalProperties: falseSchema(),
},
Required: []string{"f", "G", "P"},
AdditionalProperties: falseSchema(),
},
},
{
"no sharing",
forType[struct{ X, Y int }](),
&schema{
Type: "object",
Properties: map[string]*schema{
"X": {Type: "integer"},
"Y": {Type: "integer"},
{
"no sharing",
forType[struct{ X, Y int }](lax),
&schema{
Type: "object",
Properties: map[string]*schema{
"X": {Type: "integer"},
"Y": {Type: "integer"},
},
Required: []string{"X", "Y"},
AdditionalProperties: falseSchema(),
},
Required: []string{"X", "Y"},
AdditionalProperties: falseSchema(),
},
},
{
"nested and embedded",
forType[struct {
A S
S
}](),
&schema{
Type: "object",
Properties: map[string]*schema{
"A": {
Type: "object",
Properties: map[string]*schema{
"B": {Type: "integer", Description: "bdesc"},
{
"nested and embedded",
forType[struct {
A S
S
}](lax),
&schema{
Type: "object",
Properties: map[string]*schema{
"A": {
Type: "object",
Properties: map[string]*schema{
"B": {Type: "integer", Description: "bdesc"},
},
Required: []string{"B"},
AdditionalProperties: falseSchema(),
},
Required: []string{"B"},
AdditionalProperties: falseSchema(),
},
"S": {
Type: "object",
Properties: map[string]*schema{
"B": {Type: "integer", Description: "bdesc"},
"S": {
Type: "object",
Properties: map[string]*schema{
"B": {Type: "integer", Description: "bdesc"},
},
Required: []string{"B"},
AdditionalProperties: falseSchema(),
},
Required: []string{"B"},
AdditionalProperties: falseSchema(),
},
Required: []string{"A", "S"},
AdditionalProperties: falseSchema(),
},
Required: []string{"A", "S"},
AdditionalProperties: falseSchema(),
},
},
}
}

for _, test := range tests {
t.Run(test.name, func(t *testing.T) {
if diff := cmp.Diff(test.want, test.got, cmpopts.IgnoreUnexported(jsonschema.Schema{})); diff != "" {
t.Fatalf("ForType mismatch (-want +got):\n%s", diff)
}
// These schemas should all resolve.
if _, err := test.got.Resolve(nil); err != nil {
t.Fatalf("Resolving: %v", err)
}
})
run := func(t *testing.T, tt test) {
if diff := cmp.Diff(tt.want, tt.got, cmpopts.IgnoreUnexported(jsonschema.Schema{})); diff != "" {
t.Fatalf("ForType mismatch (-want +got):\n%s", diff)
}
// These schemas should all resolve.
if _, err := tt.got.Resolve(nil); err != nil {
t.Fatalf("Resolving: %v", err)
}
}

t.Run("strict", func(t *testing.T) {
for _, test := range tests(false) {
t.Run(test.name, func(t *testing.T) { run(t, test) })
}
})

laxTests := append(tests(true), test{
"ignore",
forType[struct {
A int
B map[int]int
C func()
}](true),
&schema{
Type: "object",
Properties: map[string]*schema{
"A": {Type: "integer"},
},
Required: []string{"A"},
AdditionalProperties: falseSchema(),
},
})
t.Run("lax", func(t *testing.T) {
for _, test := range laxTests {
t.Run(test.name, func(t *testing.T) { run(t, test) })
}
})
}

func forErr[T any]() error {
Expand Down
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