internal/mcp/generate.go - tools - Git at Google

 // Copyright 2025 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 //go:build ignore

 // This script generates protocol definitions in protocol.go from the MCP spec.
 //
 // Only the set of declarations configured by the [declarations] value are
 // generated.

 package main

 import (
 	"bytes"
 	"encoding/json"
 	"flag"
 	"fmt"
 	"go/format"
 	"io"
 	"log"
 	"net/http"
 	"os"
 	"reflect"
 	"regexp"
 	"slices"
 	"strings"

 	"golang.org/x/tools/internal/mcp/internal/util"
 	"golang.org/x/tools/internal/mcp/jsonschema"
 )

 var schemaFile = flag.String("schema_file", "", "if set, use this file as the persistent schema file")

 // A typeConfig defines a rewrite to perform to a (possibly nested) struct
 // field. In some cases, we may want to use an external type for the nested
 // struct field. In others, we may want to extract the type definition to a
 // name.
 type typeConfig struct {
 	Name       string // declaration name for the type
 	Substitute string // type definition to substitute
 	Fields     config // individual field configuration, or nil
 }

 type config map[string]*typeConfig

 // declarations configures the set of declarations to write.
 //
 // Top level declarations are created unless configured with Name=="-",
 // in which case they are discarded, though their fields may be
 // extracted to types if they have a nested field configuration.
 // If Name == "", the map key is used as the type name.
 var declarations = config{
 	"Annotations": {},
 	"CallToolRequest": {
 		Name: "-",
 		Fields: config{
 			"Params": {
 				Name: "CallToolParams",
 				Fields: config{
 					"Arguments": {Substitute: "json.RawMessage"},
 				},
 			},
 		},
 	},
 	"CallToolResult": {},
 	"CancelledNotification": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "CancelledParams"}},
 	},
 	"ClientCapabilities": {},
 	"GetPromptRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "GetPromptParams"}},
 	},
 	"GetPromptResult": {},
 	"Implementation":  {Name: "implementation"},
 	"InitializeRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "InitializeParams"}},
 	},
 	"InitializeResult": {Name: "InitializeResult"},
 	"InitializedNotification": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "InitializedParams"}},
 	},
 	"ListPromptsRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "ListPromptsParams"}},
 	},
 	"ListPromptsResult": {},
 	"ListResourcesRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "ListResourcesParams"}},
 	},
 	"ListResourcesResult": {},
 	"ListRootsRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "ListRootsParams"}},
 	},
 	"ListRootsResult": {},
 	"ListToolsRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "ListToolsParams"}},
 	},
 	"ListToolsResult": {},
 	"PingRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "PingParams"}},
 	},
 	"Prompt":         {},
 	"PromptMessage":  {},
 	"PromptArgument": {},
 	"ProgressToken":  {Name: "-", Substitute: "any"}, // null|number|string
 	"RequestId":      {Name: "-", Substitute: "any"}, // null|number|string
 	"ReadResourceRequest": {
 		Name:   "-",
 		Fields: config{"Params": {Name: "ReadResourceParams"}},
 	},
 	"ReadResourceResult": {
 		Fields: config{"Contents": {Substitute: "*ResourceContents"}},
 	},
 	"Resource": {},
 	"Role":     {},
 	"Root":     {},

 	"ServerCapabilities": {
 		Name: "serverCapabilities",
 		Fields: config{
 			"Prompts":   {Name: "promptCapabilities"},
 			"Resources": {Name: "resourceCapabilities"},
 			"Tools":     {Name: "toolCapabilities"},
 		},
 	},
 	"Tool": {
 		Fields: config{"InputSchema": {Substitute: "*jsonschema.Schema"}},
 	},
 	"ToolAnnotations": {},
 }

 func main() {
 	flag.Parse()

 	// Load and unmarshal the schema.
 	data, err := loadSchema(*schemaFile)
 	if err != nil {
 		log.Fatal(err)
 	}
 	schema := new(jsonschema.Schema)
 	if err := json.Unmarshal(data, &schema); err != nil {
 		log.Fatal(err)
 	}
 	// Resolve the schema so we have the referents of all the Refs.
 	if _, err := schema.Resolve("", nil); err != nil {
 		log.Fatal(err)
 	}

 	// Collect named types. Since we may create new type definitions while
 	// writing types, we collect definitions and concatenate them later. This
 	// also allows us to sort.
 	named := make(map[string]*bytes.Buffer)
 	for name, def := range util.Sorted(schema.Definitions) {
 		config := declarations[name]
 		if config == nil {
 			continue
 		}
 		if err := writeDecl(name, *config, def, named); err != nil {
 			log.Fatal(err)
 		}
 	}

 	buf := new(bytes.Buffer)
 	fmt.Fprintf(buf, `
 // Copyright 2025 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Code generated by generate.go. DO NOT EDIT.

 package mcp

 import (
 	"encoding/json"

 	"golang.org/x/tools/internal/mcp/jsonschema"
 )
 `)

 	// Write out types.
 	for _, b := range util.Sorted(named) {
 		fmt.Fprintln(buf)
 		fmt.Fprint(buf, b.String())
 	}

 	formatted, err := format.Source(buf.Bytes())
 	if err != nil {
 		log.Println(buf.String())
 		log.Fatalf("failed to format: %v", err)
 	}
 	if err := os.WriteFile("protocol.go", formatted, 0666); err != nil {
 		log.Fatalf("failed to write protocol.go: %v", err)
 	}
 }

 func loadSchema(schemaFile string) (data []byte, err error) {
 	const schemaURL = "https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/refs/heads/main/schema/2025-03-26/schema.json"

 	if schemaFile != "" {
 		data, err = os.ReadFile(schemaFile)
 		if os.IsNotExist(err) {
 			data = nil
 		} else if err != nil {
 			return nil, fmt.Errorf("reading schema file %q: %v", schemaFile, err)
 		}
 	}
 	if data == nil {
 		resp, err := http.Get(schemaURL)
 		if err != nil {
 			return nil, fmt.Errorf("downloading schema: %v", err)
 		}
 		defer resp.Body.Close()
 		if resp.StatusCode != http.StatusOK {
 			return nil, fmt.Errorf("downloading schema: %v", resp.Status)
 		}
 		data, err = io.ReadAll(resp.Body)
 		if err != nil {
 			return nil, fmt.Errorf("reading schema body: %v", err)
 		}
 		if schemaFile != "" {
 			if err := os.WriteFile(schemaFile, data, 0666); err != nil {
 				return nil, fmt.Errorf("persisting schema: %v", err)
 			}
 		}
 	}
 	return data, nil
 }

 func writeDecl(configName string, config typeConfig, def *jsonschema.Schema, named map[string]*bytes.Buffer) error {
 	var w io.Writer = io.Discard
 	if typeName := config.Name; typeName != "-" {
 		if typeName == "" {
 			typeName = configName
 		}
 		if _, ok := named[typeName]; ok {
 			return nil
 		}
 		buf := new(bytes.Buffer)
 		w = buf
 		named[typeName] = buf
 		if def.Description != "" {
 			fmt.Fprintf(buf, "%s\n", toComment(def.Description))
 		}
 		fmt.Fprintf(buf, "type %s ", typeName)
 	}
 	if err := writeType(w, &config, def, named); err != nil {
 		return err // Better error here?
 	}
 	fmt.Fprintf(w, "\n")
 	return nil
 }

 // writeType writes the type definition to the given writer.
 //
 // If path is non-empty, it is the path to the field using this type, for the
 // purpose of detecting field rewrites (see [fieldRewrite]).
 //
 // named is the in-progress collection of type definitions. New named types may
 // be added during writeType, if they are extracted from inner fields.
 func writeType(w io.Writer, config *typeConfig, def *jsonschema.Schema, named map[string]*bytes.Buffer) error {
 	// Use type names for Named types.
 	name, resolved := deref(def)
 	if name != "" {
 		// TODO: this check is not quite right: we should really panic if the
 		// definition is missing, *but only if w is not io.Discard*. That's not a
 		// great API: see if we can do something more explicit than io.Discard.
 		if cfg, ok := declarations[name]; ok {
 			if cfg.Name == "-" && cfg.Substitute == "" {
 				panic(fmt.Sprintf("referenced type %q cannot be referred to (no name or substitution)", name))
 			}
 			if cfg.Substitute != "" {
 				name = cfg.Substitute
 			} else if cfg.Name != "" {
 				name = cfg.Name
 			}
 			if isStruct(resolved) {
 				w.Write([]byte{'*'})
 			}
 		}
 		w.Write([]byte(name))
 		return nil
 	}

 	// For types that explicitly allow additional properties, we can either
 	// unmarshal them into a map[string]any, or delay unmarshalling with
 	// json.RawMessage. For now, use json.RawMessage as it defers the choice.
 	//
 	// TODO(jba): further refine this classification of object schemas.
 	// For example, the typescript "object" type, which should map to a Go "any",
 	// is represented in schema.json by `{type: object, properties: {}, additionalProperties: true}`.
 	if def.Type == "object" && canHaveAdditionalProperties(def) && def.Properties == nil {
 		w.Write([]byte("map[string]"))
 		return writeType(w, nil, def.AdditionalProperties, named)
 	}

 	if def.Type == "" {
 		// special case: recognize Content
 		if slices.ContainsFunc(def.AnyOf, func(s *jsonschema.Schema) bool {
 			return s.Ref == "#/definitions/TextContent"
 		}) {
 			fmt.Fprintf(w, "*Content")
 		} else {
 			// E.g. union types.
 			fmt.Fprintf(w, "json.RawMessage")
 		}
 	} else {
 		switch def.Type {
 		case "array":
 			fmt.Fprintf(w, "[]")
 			return writeType(w, nil, def.Items, named)

 		case "boolean":
 			fmt.Fprintf(w, "bool")

 		case "integer":
 			fmt.Fprintf(w, "int64")

 		// not handled: "null"

 		case "number":
 			// We could use json.Number here; use float64 for simplicity.
 			fmt.Fprintf(w, "float64")

 		case "object":
 			fmt.Fprintf(w, "struct {\n")
 			for name, fieldDef := range util.Sorted(def.Properties) {
 				if fieldDef.Description != "" {
 					fmt.Fprintf(w, "%s\n", toComment(fieldDef.Description))
 				}
 				export := exportName(name)
 				fmt.Fprintf(w, "\t%s ", export)

 				required := slices.Contains(def.Required, name)

 				// If the field is a struct type, indirect with a
 				// pointer so that it can be empty as defined by encoding/json.
 				// This also future-proofs against the struct getting large.
 				fieldTypeSchema := fieldDef
 				// If the schema is a reference, dereference it.
 				if _, rs := deref(fieldDef); rs != nil {
 					fieldTypeSchema = rs
 				}
 				needPointer := isStruct(fieldTypeSchema)
 				if config != nil && config.Fields[export] != nil {
 					r := config.Fields[export]
 					if r.Substitute != "" {
 						fmt.Fprintf(w, r.Substitute)
 					} else {
 						assert(r.Name != "-", "missing ExtractTo")
 						typename := export
 						if r.Name != "" {
 							typename = r.Name
 						}
 						if err := writeDecl(typename, *r, fieldDef, named); err != nil {
 							return err
 						}
 						if needPointer {
 							fmt.Fprintf(w, "*")
 						}
 						fmt.Fprintf(w, typename)
 					}
 				} else if err := writeType(w, nil, fieldDef, named); err != nil {
 					return fmt.Errorf("failed to write type for field %s: %v", export, err)
 				}
 				fmt.Fprintf(w, " `json:\"%s", name)
 				if !required {
 					fmt.Fprint(w, ",omitempty")
 				}
 				fmt.Fprint(w, "\"`\n")
 			}
 			fmt.Fprintf(w, "}")

 		case "string":
 			fmt.Fprintf(w, "string")

 		default:
 			fmt.Fprintf(w, "any")
 		}
 	}
 	return nil
 }

 // toComment converts a JSON schema description to a Go comment.
 func toComment(description string) string {
 	var (
 		buf     strings.Builder
 		lineBuf strings.Builder
 	)
 	const wrapAt = 80
 	for line := range strings.SplitSeq(description, "\n") {
 		// Start a new paragraph, if the current is nonempty.
 		if len(line) == 0 && lineBuf.Len() > 0 {
 			buf.WriteString(lineBuf.String())
 			lineBuf.Reset()
 			buf.WriteString("\n//\n")
 			continue
 		}
 		// Otherwise, fill in the current paragraph.
 		for field := range strings.FieldsSeq(line) {
 			if lineBuf.Len() > 0 && lineBuf.Len()+len(" ")+len(field) > wrapAt {
 				buf.WriteString(lineBuf.String())
 				buf.WriteRune('\n')
 				lineBuf.Reset()
 			}
 			if lineBuf.Len() == 0 {
 				lineBuf.WriteString("//")
 			}
 			lineBuf.WriteString(" ")
 			lineBuf.WriteString(field)
 		}
 	}
 	if lineBuf.Len() > 0 {
 		buf.WriteString(lineBuf.String())
 	}
 	return strings.TrimRight(buf.String(), "\n")
 }

 // The MCP spec improperly uses the absence of the additionalProperties keyword to
 // mean that additional properties are not allowed. In fact, it means just the opposite
 // (https://json-schema.org/draft-07/draft-handrews-json-schema-validation-01#rfc.section.6.5.6).
 // If the MCP spec wants to allow additional properties, it will write "true" or
 // an object explicitly.
 func canHaveAdditionalProperties(s *jsonschema.Schema) bool {
 	ap := s.AdditionalProperties
 	return ap != nil && !reflect.DeepEqual(ap, &jsonschema.Schema{Not: &jsonschema.Schema{}})
 }

 // exportName returns an exported name for a Go symbol, based on the given name
 // in the JSON schema, removing leading underscores and capitalizing.
 // It also rewrites initialisms.
 func exportName(s string) string {
 	if strings.HasPrefix(s, "_") {
 		s = s[1:]
 	}
 	s = strings.ToUpper(s[:1]) + s[1:]
 	// Replace an initialism if it is its own "word": see the init function below for
 	// a definition.
 	// There is probably a clever way to write this whole thing with one regexp and
 	// a Replace method, but it would be quite obscure.
 	// This doesn't have to be fast, because the first match will rarely succeed.
 	for ism, re := range initialisms {
 		replacement := strings.ToUpper(ism)
 		// Find the index of one match at a time, and replace. (We can't find all
 		// at once, because the replacement will change the indices.)
 		for {
 			if loc := re.FindStringIndex(s); loc != nil {
 				// Don't replace the rune after the initialism, if any.
 				end := loc[1]
 				if end < len(s) {
 					end--
 				}
 				s = s[:loc[0]] + replacement + s[end:]
 			} else {
 				break
 			}
 		}
 	}
 	return s
 }

 // deref dereferences s.Ref.
 // If s.Ref refers to a schema in the Definitions section, deref
 // returns the definition name and the associated schema.
 // Otherwise, deref returns "", nil.
 func deref(s *jsonschema.Schema) (name string, _ *jsonschema.Schema) {
 	name, ok := strings.CutPrefix(s.Ref, "#/definitions/")
 	if !ok {
 		return "", nil
 	}
 	return name, s.ResolvedRef()
 }

 // isStruct reports whether s should be translated to a struct.
 func isStruct(s *jsonschema.Schema) bool {
 	return s.Type == "object" && s.Properties != nil && !canHaveAdditionalProperties(s)
 }

 // schemaJSON returns the JSON for s.
 // For debugging.
 func schemaJSON(s *jsonschema.Schema) string {
 	data, err := json.Marshal(s)
 	if err != nil {
 		return fmt.Sprintf("<jsonschema.Schema:%v>", err)
 	}
 	return string(data)
 }

 // Map from initialism to the regexp that matches it.
 var initialisms = map[string]*regexp.Regexp{
 	"Id":   nil,
 	"Url":  nil,
 	"Uri":  nil,
 	"Mime": nil,
 }

 func init() {
 	for ism := range initialisms {
 		// Match ism if it is at the end, or followed by an uppercase letter or a number.
 		initialisms[ism] = regexp.MustCompile(ism + `($|[A-Z0-9])`)
 	}
 }

 func assert(cond bool, msg string) {
 	if !cond {
 		panic(msg)
 	}
 }
	// Copyright 2025 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	//go:build ignore

	// This script generates protocol definitions in protocol.go from the MCP spec.
	//
	// Only the set of declarations configured by the [declarations] value are
	// generated.

	package main

	import (
	"bytes"
	"encoding/json"
	"flag"
	"fmt"
	"go/format"
	"io"
	"log"
	"net/http"
	"os"
	"reflect"
	"regexp"
	"slices"
	"strings"

	"golang.org/x/tools/internal/mcp/internal/util"
	"golang.org/x/tools/internal/mcp/jsonschema"
	)

	var schemaFile = flag.String("schema_file", "", "if set, use this file as the persistent schema file")

	// A typeConfig defines a rewrite to perform to a (possibly nested) struct
	// field. In some cases, we may want to use an external type for the nested
	// struct field. In others, we may want to extract the type definition to a
	// name.
	type typeConfig struct {
	Name string // declaration name for the type
	Substitute string // type definition to substitute
	Fields config // individual field configuration, or nil
	}

	type config map[string]*typeConfig

	// declarations configures the set of declarations to write.
	//
	// Top level declarations are created unless configured with Name=="-",
	// in which case they are discarded, though their fields may be
	// extracted to types if they have a nested field configuration.
	// If Name == "", the map key is used as the type name.
	var declarations = config{
	"Annotations": {},
	"CallToolRequest": {
	Name: "-",
	Fields: config{
	"Params": {
	Name: "CallToolParams",
	Fields: config{
	"Arguments": {Substitute: "json.RawMessage"},
	},
	},
	},
	},
	"CallToolResult": {},
	"CancelledNotification": {
	Name: "-",
	Fields: config{"Params": {Name: "CancelledParams"}},
	},
	"ClientCapabilities": {},
	"GetPromptRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "GetPromptParams"}},
	},
	"GetPromptResult": {},
	"Implementation": {Name: "implementation"},
	"InitializeRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "InitializeParams"}},
	},
	"InitializeResult": {Name: "InitializeResult"},
	"InitializedNotification": {
	Name: "-",
	Fields: config{"Params": {Name: "InitializedParams"}},
	},
	"ListPromptsRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "ListPromptsParams"}},
	},
	"ListPromptsResult": {},
	"ListResourcesRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "ListResourcesParams"}},
	},
	"ListResourcesResult": {},
	"ListRootsRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "ListRootsParams"}},
	},
	"ListRootsResult": {},
	"ListToolsRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "ListToolsParams"}},
	},
	"ListToolsResult": {},
	"PingRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "PingParams"}},
	},
	"Prompt": {},
	"PromptMessage": {},
	"PromptArgument": {},
	"ProgressToken": {Name: "-", Substitute: "any"}, // null\|number\|string
	"RequestId": {Name: "-", Substitute: "any"}, // null\|number\|string
	"ReadResourceRequest": {
	Name: "-",
	Fields: config{"Params": {Name: "ReadResourceParams"}},
	},
	"ReadResourceResult": {
	Fields: config{"Contents": {Substitute: "*ResourceContents"}},
	},
	"Resource": {},
	"Role": {},
	"Root": {},

	"ServerCapabilities": {
	Name: "serverCapabilities",
	Fields: config{
	"Prompts": {Name: "promptCapabilities"},
	"Resources": {Name: "resourceCapabilities"},
	"Tools": {Name: "toolCapabilities"},
	},
	},
	"Tool": {
	Fields: config{"InputSchema": {Substitute: "*jsonschema.Schema"}},
	},
	"ToolAnnotations": {},
	}

	func main() {
	flag.Parse()

	// Load and unmarshal the schema.
	data, err := loadSchema(*schemaFile)
	if err != nil {
	log.Fatal(err)
	}
	schema := new(jsonschema.Schema)
	if err := json.Unmarshal(data, &schema); err != nil {
	log.Fatal(err)
	}
	// Resolve the schema so we have the referents of all the Refs.
	if _, err := schema.Resolve("", nil); err != nil {
	log.Fatal(err)
	}

	// Collect named types. Since we may create new type definitions while
	// writing types, we collect definitions and concatenate them later. This
	// also allows us to sort.
	named := make(map[string]*bytes.Buffer)
	for name, def := range util.Sorted(schema.Definitions) {
	config := declarations[name]
	if config == nil {
	continue
	}
	if err := writeDecl(name, *config, def, named); err != nil {
	log.Fatal(err)
	}
	}

	buf := new(bytes.Buffer)
	fmt.Fprintf(buf, `
	// Copyright 2025 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Code generated by generate.go. DO NOT EDIT.

	package mcp

	import (
	"encoding/json"

	"golang.org/x/tools/internal/mcp/jsonschema"
	)
	`)

	// Write out types.
	for _, b := range util.Sorted(named) {
	fmt.Fprintln(buf)
	fmt.Fprint(buf, b.String())
	}

	formatted, err := format.Source(buf.Bytes())
	if err != nil {
	log.Println(buf.String())
	log.Fatalf("failed to format: %v", err)
	}
	if err := os.WriteFile("protocol.go", formatted, 0666); err != nil {
	log.Fatalf("failed to write protocol.go: %v", err)
	}
	}

	func loadSchema(schemaFile string) (data []byte, err error) {
	const schemaURL = "https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/refs/heads/main/schema/2025-03-26/schema.json"

	if schemaFile != "" {
	data, err = os.ReadFile(schemaFile)
	if os.IsNotExist(err) {
	data = nil
	} else if err != nil {
	return nil, fmt.Errorf("reading schema file %q: %v", schemaFile, err)
	}
	}
	if data == nil {
	resp, err := http.Get(schemaURL)
	if err != nil {
	return nil, fmt.Errorf("downloading schema: %v", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
	return nil, fmt.Errorf("downloading schema: %v", resp.Status)
	}
	data, err = io.ReadAll(resp.Body)
	if err != nil {
	return nil, fmt.Errorf("reading schema body: %v", err)
	}
	if schemaFile != "" {
	if err := os.WriteFile(schemaFile, data, 0666); err != nil {
	return nil, fmt.Errorf("persisting schema: %v", err)
	}
	}
	}
	return data, nil
	}

	func writeDecl(configName string, config typeConfig, def jsonschema.Schema, named map[string]bytes.Buffer) error {
	var w io.Writer = io.Discard
	if typeName := config.Name; typeName != "-" {
	if typeName == "" {
	typeName = configName
	}
	if _, ok := named[typeName]; ok {
	return nil
	}
	buf := new(bytes.Buffer)
	w = buf
	named[typeName] = buf
	if def.Description != "" {
	fmt.Fprintf(buf, "%s\n", toComment(def.Description))
	}
	fmt.Fprintf(buf, "type %s ", typeName)
	}
	if err := writeType(w, &config, def, named); err != nil {
	return err // Better error here?
	}
	fmt.Fprintf(w, "\n")
	return nil
	}

	// writeType writes the type definition to the given writer.
	//
	// If path is non-empty, it is the path to the field using this type, for the
	// purpose of detecting field rewrites (see [fieldRewrite]).
	//
	// named is the in-progress collection of type definitions. New named types may
	// be added during writeType, if they are extracted from inner fields.
	func writeType(w io.Writer, config typeConfig, def jsonschema.Schema, named map[string]*bytes.Buffer) error {
	// Use type names for Named types.
	name, resolved := deref(def)
	if name != "" {
	// TODO: this check is not quite right: we should really panic if the
	// definition is missing, but only if w is not io.Discard. That's not a
	// great API: see if we can do something more explicit than io.Discard.
	if cfg, ok := declarations[name]; ok {
	if cfg.Name == "-" && cfg.Substitute == "" {
	panic(fmt.Sprintf("referenced type %q cannot be referred to (no name or substitution)", name))
	}
	if cfg.Substitute != "" {
	name = cfg.Substitute
	} else if cfg.Name != "" {
	name = cfg.Name
	}
	if isStruct(resolved) {
	w.Write([]byte{'*'})
	}
	}
	w.Write([]byte(name))
	return nil
	}

	// For types that explicitly allow additional properties, we can either
	// unmarshal them into a map[string]any, or delay unmarshalling with
	// json.RawMessage. For now, use json.RawMessage as it defers the choice.
	//
	// TODO(jba): further refine this classification of object schemas.
	// For example, the typescript "object" type, which should map to a Go "any",
	// is represented in schema.json by `{type: object, properties: {}, additionalProperties: true}`.
	if def.Type == "object" && canHaveAdditionalProperties(def) && def.Properties == nil {
	w.Write([]byte("map[string]"))
	return writeType(w, nil, def.AdditionalProperties, named)
	}

	if def.Type == "" {
	// special case: recognize Content
	if slices.ContainsFunc(def.AnyOf, func(s *jsonschema.Schema) bool {
	return s.Ref == "#/definitions/TextContent"
	}) {
	fmt.Fprintf(w, "*Content")
	} else {
	// E.g. union types.
	fmt.Fprintf(w, "json.RawMessage")
	}
	} else {
	switch def.Type {
	case "array":
	fmt.Fprintf(w, "[]")
	return writeType(w, nil, def.Items, named)

	case "boolean":
	fmt.Fprintf(w, "bool")

	case "integer":
	fmt.Fprintf(w, "int64")

	// not handled: "null"

	case "number":
	// We could use json.Number here; use float64 for simplicity.
	fmt.Fprintf(w, "float64")

	case "object":
	fmt.Fprintf(w, "struct {\n")
	for name, fieldDef := range util.Sorted(def.Properties) {
	if fieldDef.Description != "" {
	fmt.Fprintf(w, "%s\n", toComment(fieldDef.Description))
	}
	export := exportName(name)
	fmt.Fprintf(w, "\t%s ", export)

	required := slices.Contains(def.Required, name)

	// If the field is a struct type, indirect with a
	// pointer so that it can be empty as defined by encoding/json.
	// This also future-proofs against the struct getting large.
	fieldTypeSchema := fieldDef
	// If the schema is a reference, dereference it.
	if _, rs := deref(fieldDef); rs != nil {
	fieldTypeSchema = rs
	}
	needPointer := isStruct(fieldTypeSchema)
	if config != nil && config.Fields[export] != nil {
	r := config.Fields[export]
	if r.Substitute != "" {
	fmt.Fprintf(w, r.Substitute)
	} else {
	assert(r.Name != "-", "missing ExtractTo")
	typename := export
	if r.Name != "" {
	typename = r.Name
	}
	if err := writeDecl(typename, *r, fieldDef, named); err != nil {
	return err
	}
	if needPointer {
	fmt.Fprintf(w, "*")
	}
	fmt.Fprintf(w, typename)
	}
	} else if err := writeType(w, nil, fieldDef, named); err != nil {
	return fmt.Errorf("failed to write type for field %s: %v", export, err)
	}
	fmt.Fprintf(w, " `json:\"%s", name)
	if !required {
	fmt.Fprint(w, ",omitempty")
	}
	fmt.Fprint(w, "\"`\n")
	}
	fmt.Fprintf(w, "}")

	case "string":
	fmt.Fprintf(w, "string")

	default:
	fmt.Fprintf(w, "any")
	}
	}
	return nil
	}

	// toComment converts a JSON schema description to a Go comment.
	func toComment(description string) string {
	var (
	buf strings.Builder
	lineBuf strings.Builder
	)
	const wrapAt = 80
	for line := range strings.SplitSeq(description, "\n") {
	// Start a new paragraph, if the current is nonempty.
	if len(line) == 0 && lineBuf.Len() > 0 {
	buf.WriteString(lineBuf.String())
	lineBuf.Reset()
	buf.WriteString("\n//\n")
	continue
	}
	// Otherwise, fill in the current paragraph.
	for field := range strings.FieldsSeq(line) {
	if lineBuf.Len() > 0 && lineBuf.Len()+len(" ")+len(field) > wrapAt {
	buf.WriteString(lineBuf.String())
	buf.WriteRune('\n')
	lineBuf.Reset()
	}
	if lineBuf.Len() == 0 {
	lineBuf.WriteString("//")
	}
	lineBuf.WriteString(" ")
	lineBuf.WriteString(field)
	}
	}
	if lineBuf.Len() > 0 {
	buf.WriteString(lineBuf.String())
	}
	return strings.TrimRight(buf.String(), "\n")
	}

	// The MCP spec improperly uses the absence of the additionalProperties keyword to
	// mean that additional properties are not allowed. In fact, it means just the opposite
	// (https://json-schema.org/draft-07/draft-handrews-json-schema-validation-01#rfc.section.6.5.6).
	// If the MCP spec wants to allow additional properties, it will write "true" or
	// an object explicitly.
	func canHaveAdditionalProperties(s *jsonschema.Schema) bool {
	ap := s.AdditionalProperties
	return ap != nil && !reflect.DeepEqual(ap, &jsonschema.Schema{Not: &jsonschema.Schema{}})
	}

	// exportName returns an exported name for a Go symbol, based on the given name
	// in the JSON schema, removing leading underscores and capitalizing.
	// It also rewrites initialisms.
	func exportName(s string) string {
	if strings.HasPrefix(s, "_") {
	s = s[1:]
	}
	s = strings.ToUpper(s[:1]) + s[1:]
	// Replace an initialism if it is its own "word": see the init function below for
	// a definition.
	// There is probably a clever way to write this whole thing with one regexp and
	// a Replace method, but it would be quite obscure.
	// This doesn't have to be fast, because the first match will rarely succeed.
	for ism, re := range initialisms {
	replacement := strings.ToUpper(ism)
	// Find the index of one match at a time, and replace. (We can't find all
	// at once, because the replacement will change the indices.)
	for {
	if loc := re.FindStringIndex(s); loc != nil {
	// Don't replace the rune after the initialism, if any.
	end := loc[1]
	if end < len(s) {
	end--
	}
	s = s[:loc[0]] + replacement + s[end:]
	} else {
	break
	}
	}
	}
	return s
	}

	// deref dereferences s.Ref.
	// If s.Ref refers to a schema in the Definitions section, deref
	// returns the definition name and the associated schema.
	// Otherwise, deref returns "", nil.
	func deref(s jsonschema.Schema) (name string, _ jsonschema.Schema) {
	name, ok := strings.CutPrefix(s.Ref, "#/definitions/")
	if !ok {
	return "", nil
	}
	return name, s.ResolvedRef()
	}

	// isStruct reports whether s should be translated to a struct.
	func isStruct(s *jsonschema.Schema) bool {
	return s.Type == "object" && s.Properties != nil && !canHaveAdditionalProperties(s)
	}

	// schemaJSON returns the JSON for s.
	// For debugging.
	func schemaJSON(s *jsonschema.Schema) string {
	data, err := json.Marshal(s)
	if err != nil {
	return fmt.Sprintf("<jsonschema.Schema:%v>", err)
	}
	return string(data)
	}

	// Map from initialism to the regexp that matches it.
	var initialisms = map[string]*regexp.Regexp{
	"Id": nil,
	"Url": nil,
	"Uri": nil,
	"Mime": nil,
	}

	func init() {
	for ism := range initialisms {
	// Match ism if it is at the end, or followed by an uppercase letter or a number.
	initialisms[ism] = regexp.MustCompile(ism + `($\|[A-Z0-9])`)
	}
	}

	func assert(cond bool, msg string) {
	if !cond {
	panic(msg)
	}
	}