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jsonschema: support "jsonschema" struct tags (#101)

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Struct fields may have the "jsonschema" struct tag, which is used as the
description of the property.

Fixes #47.
This commit is contained in:
Jonathan Amsterdam 2025-07-10 13:51:23 -04:00 • committed by GitHub
commit 2c577e564b
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GPG key ID: B5690EEEBB952194
1 changed files with 99 additions and 10 deletions
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22
jsonschema/infer.go
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@ -9,6 +9,7 @@ package jsonschema
import (
"fmt"
"reflect"
"regexp"
"github.com/modelcontextprotocol/go-sdk/internal/util"
)
@ -36,8 +37,12 @@ import (
// - complex numbers
// - unsafe pointers
//
// The types must not have cycles.
// It will return an error if there is a cycle in the types.
//
// For recognizes struct field tags named "jsonschema".
// A jsonschema tag on a field is used as the description for the corresponding property.
// For future compatibility, descriptions must not start with "WORD=", where WORD is a
// sequence of non-whitespace characters.
func For[T any]() (*Schema, error) {
// TODO: consider skipping incompatible fields, instead of failing.
seen := make(map[reflect.Type]bool)
@ -126,10 +131,20 @@ func forType(t reflect.Type, seen map[reflect.Type]bool) (*Schema, error) {
if s.Properties == nil {
s.Properties = make(map[string]*Schema)
}
s.Properties[info.Name], err = forType(field.Type, seen)
fs, err := forType(field.Type, seen)
if err != nil {
return nil, err
}
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)
}
if disallowedPrefixRegexp.MatchString(tag) {
return nil, fmt.Errorf("tag must not begin with 'WORD=': %q", tag)
}
fs.Description = tag
}
s.Properties[info.Name] = fs
if !info.Settings["omitempty"] && !info.Settings["omitzero"] {
s.Required = append(s.Required, info.Name)
}
@ -144,3 +159,6 @@ func forType(t reflect.Type, seen map[reflect.Type]bool) (*Schema, error) {
}
return s, nil
}
// Disallow jsonschema tag values beginning "WORD=", for future expansion.
var disallowedPrefixRegexp = regexp.MustCompile("^[^ \t\n]*=")