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fix: centralize the nullable-union collapse in core and apply it in the TUI

Browse source 
Closes #2015, folded into #1928 rather than left as a follow-up.

The TUI's `schemaToForm` has the same defect the web `SchemaForm` had: its
local `JsonSchemaProperty` declares only `type?: string` — no `anyOf`, no
array-valued `type` — so a `.nullish()` argument has no top-level `type` or
`enum` for the dispatcher to read and falls to the `switch` default, losing
its select. Milder than the web bug (a plain text field, not a corrupting
JSON textarea), but the same class.

Fixing it in a second place is the argument for not having the logic in a
first place. So the collapse moves to `core/json/nullableUnion.ts` as
`normalizeNullableUnion`, generic over a minimal `NullableUnionSchema`
shape — the least a caller must expose to be *recognized* as a nullable
union — so neither client has to adopt the other's schema type. Both form
builders now share one copy and cannot drift on which schemas they render.

- `core/json/nullableUnion.ts` — the shared collapse, plus tests at
  `clients/web/src/test/core/nullableUnion.test.ts` (the web suite is what
  gates `core/`).
- `clients/web`: `schemaUtils.normalizeUnionType` is gone; `SchemaForm` and
  `resolveRefsInMessage` call the core function directly.
- `clients/tui`: `schemaToForm` normalizes each property before dispatch,
  and `JsonSchemaProperty` grows the `anyOf` / array-`type` fields the
  encoding uses.

Verified by driving the built TUI under a pty against the
`nullable-fields-http.json` showcase server. Before, every argument of
`record_shipment` rendered as a plain text field; after, `direction` is a
select ("No value"), `quantity` an integer, `express` a boolean
("[Not set]").

Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-08-15 16:59:37 -04:00
commit 17a4c78dd3
9 changed files with 519 additions and 311 deletions
Download patch file Download diff file Expand all files Collapse all files

10
AGENTS.md
View file

@ -55,7 +55,15 @@ v2/main/
│ │ # annotation scan/validation + mirrored-param
│ │ # derivation, used by the Tools tab — #1632;
│ │ # plus `Mcp-Param-*` header building for the
│ │ # wire, used by both `tools/call` paths — #1846)
│ │ # wire, used by both `tools/call` paths — #1846;
│ │ # nullableUnion.ts: collapses the two JSON Schema
│ │ # encodings of "T or null" (`anyOf` with a null
│ │ # branch, `type: [T,"null"]`) into a plain type,
│ │ # hoisting the surviving branch's own keywords.
│ │ # Shared by BOTH form builders — web SchemaForm
│ │ # and TUI schemaToForm — since each dispatches on
│ │ # a single `type` string and would otherwise miss
│ │ # a nullable field entirely — #1928/#2015)
│ ├── logging/ # Silent pino logger singleton
│ ├── mcp/ # InspectorClient runtime + state stores
│ │ # (modernTaskSchemas.ts: SEP-2663 modern Tasks

5
README.md
View file

@ -32,7 +32,8 @@ inspector/
├── core/ # Shared code consumed via the `@inspector/core` alias (no package.json)
│ ├── auth/ # OAuth: providers, discovery, storage, mid-session recovery (browser/node/remote backends)
│ ├── client/ # Install-level client config (`client.json`): browser-safe parse/validate + Node load/save, remote backend, secrets
│ ├── json/ # JSON + parameter/argument conversion utilities
│ ├── json/ # JSON + parameter/argument conversion utilities, and the nullable-union
│ │ # schema collapse shared by the web and TUI form builders
│ ├── logging/ # Silent pino logger singleton
│ ├── mcp/ # InspectorClient runtime, state stores, transports, config import
│ ├── node/ # Node-only shared helpers: version reader, hostUrl (host normalize/canonicalize + all-interfaces/loopback detection)
@ -234,6 +235,8 @@ The duplicated copies are appended rather than placed beside their twin on purpo
Open the Tools tab and select `record_shipment`: `direction` must render as a **Select** (`envio` / `recebimento`) with a clear button that sets it back to `null`, `reference` as a text input, `quantity` as a number input, and `express` as a checkbox. On the broken build every one of them fell through to the raw-JSON textarea, which re-escaped its own contents on each keystroke until the value was unusable ([#1928](https://github.com/modelcontextprotocol/inspector/issues/1928)). The tool echoes the arguments it received, so the result panel shows exactly what was sent.
The **TUI** had the same gap and is worth checking against the same server (`--tui`, then test `record_shipment`): `direction` is a select, `quantity` an integer field, `express` a boolean. Both clients now share one collapse step — `normalizeNullableUnion` in [`core/json/nullableUnion.ts`](./core/json/nullableUnion.ts) — precisely so they cannot drift on which schemas they can render.
#### Advertised extensions
`advertised-extensions-http.json` serves `echo` (always) and a `get_weather` tool **gated on the `io.modelcontextprotocol/tasks` extension** (`extensionGatedTools`): the tool is registered but starts disabled, and the server enables it on `notifications/initialized` only when the client declared that extension in its `capabilities.extensions`.

113
clients/tui/__tests__/schemaToForm.test.ts
View file

@ -213,4 +213,117 @@ describe("schemaToForm", () => {
);
expect(form.sections[0]!.fields[0]).toMatchObject({ initialValue: "hi" });
});
// #2015 (the TUI twin of #1928): an argument declared with Zod's `.nullish()`
// has no top-level `type`/`enum` — they sit on the surviving `anyOf` branch —
// so before normalization every one of these degraded to a plain text field.
describe("nullable unions", () => {
it("renders a select for an anyOf string-enum|null argument", () => {
const form = schemaToForm(
{
properties: {
direction: {
anyOf: [
{ type: "string", enum: ["envio", "recebimento"] },
{ type: "null" },
],
},
},
},
"nullableEnum",
);
expect(form.sections[0]!.fields[0]).toMatchObject({
name: "direction",
type: "select",
options: [
{ label: "envio", value: "envio" },
{ label: "recebimento", value: "recebimento" },
],
});
});
it("maps the remaining nullable scalar branches to their typed fields", () => {
const form = schemaToForm(
{
properties: {
reference: { anyOf: [{ type: "string" }, { type: "null" }] },
quantity: {
anyOf: [
{ type: "integer", minimum: 1, maximum: 9 },
{ type: "null" },
],
},
ratio: { anyOf: [{ type: "number" }, { type: "null" }] },
express: { anyOf: [{ type: "boolean" }, { type: "null" }] },
},
},
"nullableScalars",
);
const fields = form.sections[0]!.fields;
expect(fields.map((f) => ({ name: f.name, type: f.type }))).toEqual([
{ name: "reference", type: "string" },
{ name: "quantity", type: "integer" },
{ name: "ratio", type: "float" },
{ name: "express", type: "boolean" },
]);
// The branch's own constraints are hoisted along with its type.
expect(fields[1]).toMatchObject({ min: 1, max: 9 });
});
it("renders a select for a nullable array-of-enum argument", () => {
const form = schemaToForm(
{
properties: {
tags: {
anyOf: [
{ type: "array", items: { enum: ["a", "b"] } },
{ type: "null" },
],
},
},
},
"nullableArrayEnum",
);
expect(form.sections[0]!.fields[0]).toMatchObject({
type: "select",
options: [
{ label: "a", value: "a" },
{ label: "b", value: "b" },
],
});
});
it("collapses the type: [T, null] encoding too", () => {
const form = schemaToForm(
{
properties: {
note: { type: ["string", "null"] },
flag: { type: ["boolean", "null"] },
},
},
"typeArrayNull",
);
expect(
form.sections[0]!.fields.map((f) => ({ name: f.name, type: f.type })),
).toEqual([
{ name: "note", type: "string" },
{ name: "flag", type: "boolean" },
]);
});
it("leaves a union of two real types as a plain string field", () => {
const form = schemaToForm(
{
properties: {
mixed: { anyOf: [{ type: "string" }, { type: "number" }] },
},
},
"realUnion",
);
expect(form.sections[0]!.fields[0]).toMatchObject({
name: "mixed",
type: "string",
});
});
});
});

23
clients/tui/src/utils/schemaToForm.ts
View file

@ -3,10 +3,16 @@
*/
import type { FormStructure, FormSection, FormField } from "ink-form";
import { normalizeNullableUnion } from "@inspector/core/json/nullableUnion.js";
/** Minimal JSON Schema property shape used when building tool parameter forms */
interface JsonSchemaProperty {
type?: string;
/**
* An array here is the `["string", "null"]` nullable encoding, which
* {@link normalizeNullableUnion} collapses to a single name before the
* dispatch below reads it.
*/
type?: string | string[];
title?: string;
enum?: unknown[];
/** Non-standard legacy support: titles for enum values */
@ -15,6 +21,8 @@ interface JsonSchemaProperty {
minimum?: number;
maximum?: number;
default?: unknown;
/** Present on a nullable union; see {@link normalizeNullableUnion}. */
anyOf?: readonly unknown[];
}
/**
@ -68,9 +76,16 @@ export function schemaToForm(
// `properties` values are `unknown` (the SDK schema admits anything), so
// guard before treating a value as a schema object — a malformed server
// schema with e.g. `properties: { foo: null }` must not throw on `.title`.
const property = (
typeof prop === "object" && prop !== null ? prop : {}
) as JsonSchemaProperty;
// Flatten a nullable union (`anyOf: [X, {type:"null"}]`, `type: [X,"null"]`)
// before dispatching. Every branch below reads a single `type` string, and
// for an enum the `enum` keyword sits on the union's surviving branch — so
// without this an argument declared with Zod's `.nullish()` loses its
// select and degrades to a plain text field (#2015, the TUI twin of #1928).
const property = normalizeNullableUnion(
(typeof prop === "object" && prop !== null
? prop
: {}) as JsonSchemaProperty,
);
const baseField = {
name: key,
label: property.title || key,

4
clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
View file

@ -12,7 +12,7 @@ import { useState } from "react";
import { ClearButton } from "../../elements/ClearButton/ClearButton";
import { useValueChange } from "../../../hooks/useValueChange";
import type { InspectorFormSchema } from "../../../utils/jsonUtils";
import { normalizeUnionType } from "../../../utils/schemaUtils";
import { normalizeNullableUnion } from "@inspector/core/json/nullableUnion.js";
const FieldLabel = Text.withProps({
fw: 500,
@ -224,7 +224,7 @@ export function SchemaForm({
// without this an "optional and explicitly nullable" field — what Zod's
// `.nullish()` emits — matches nothing and falls through to the raw-JSON
// fallback, which is unusable for a value the user has to type (#1928).
const fieldSchema = normalizeUnionType(rawSchema);
const fieldSchema = normalizeNullableUnion(rawSchema);
const isRequired = requiredFields.includes(fieldName);
const label = fieldSchema.title ?? fieldName;
const description = fieldSchema.description;

250
clients/web/src/test/core/nullableUnion.test.ts Normal file
View file

@ -0,0 +1,250 @@
import { describe, it, expect } from "vitest";
import { normalizeNullableUnion } from "@inspector/core/json/nullableUnion.js";
// The two JSON Schema encodings of "this type, or null". Both form builders —
// the web `SchemaForm` and the TUI's `schemaToForm` — dispatch on a single
// `type` string, so this collapse is what keeps a nullable field renderable
// (#1928 in the web client, #2015 in the TUI).
describe("normalizeNullableUnion", () => {
it("normalizes anyOf string|null", () => {
expect(
normalizeNullableUnion({
anyOf: [{ type: "string" }, { type: "null" }],
}),
).toEqual({
type: "string",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf boolean|null", () => {
expect(
normalizeNullableUnion({
anyOf: [{ type: "boolean" }, { type: "null" }],
}),
).toEqual({
type: "boolean",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf number|null", () => {
expect(
normalizeNullableUnion({
anyOf: [{ type: "number" }, { type: "null" }],
}),
).toEqual({
type: "number",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf integer|null", () => {
expect(
normalizeNullableUnion({
anyOf: [{ type: "integer" }, { type: "null" }],
}),
).toEqual({
type: "integer",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf array|null", () => {
expect(
normalizeNullableUnion({
anyOf: [{ type: "array" }, { type: "null" }],
}),
).toEqual({
type: "array",
anyOf: undefined,
nullable: true,
});
});
it("normalizes type array string|null", () => {
expect(normalizeNullableUnion({ type: ["string", "null"] })).toEqual({
type: "string",
nullable: true,
});
});
it("normalizes type array boolean|null", () => {
expect(normalizeNullableUnion({ type: ["boolean", "null"] })).toEqual({
type: "boolean",
nullable: true,
});
});
it("normalizes type array number|null", () => {
expect(normalizeNullableUnion({ type: ["number", "null"] })).toEqual({
type: "number",
nullable: true,
});
});
it("normalizes type array integer|null", () => {
expect(normalizeNullableUnion({ type: ["integer", "null"] })).toEqual({
type: "integer",
nullable: true,
});
});
it("returns schema unchanged when no union pattern matches", () => {
const schema = { type: "string" as const };
expect(normalizeNullableUnion(schema)).toBe(schema);
});
it("ignores anyOf with more than two members", () => {
const schema = {
anyOf: [
{ type: "string" as const },
{ type: "null" as const },
{ type: "number" as const },
],
};
expect(normalizeNullableUnion(schema)).toBe(schema);
});
it("ignores a two-member anyOf with no null branch", () => {
const schema = {
anyOf: [{ type: "string" as const }, { type: "number" as const }],
};
expect(normalizeNullableUnion(schema)).toBe(schema);
});
it("ignores an anyOf whose non-null branch has no renderable type (#1928)", () => {
const schema = {
anyOf: [{ const: "only" }, { type: "null" as const }],
};
expect(normalizeNullableUnion(schema)).toBe(schema);
});
// #1928: the enum lives on the surviving branch, and hoisting it is what makes
// the field render as a Select instead of the raw-JSON fallback.
it("hoists enum out of an anyOf string-enum|null branch", () => {
expect(
normalizeNullableUnion({
description: "Direction",
anyOf: [
{ type: "string", enum: ["envio", "recebimento"] },
{ type: "null" },
],
}),
).toEqual({
type: "string",
description: "Direction",
enum: ["envio", "recebimento"],
anyOf: undefined,
nullable: true,
});
});
it("infers string for a typeless enum branch", () => {
expect(
normalizeNullableUnion({
anyOf: [{ enum: ["a", "b"] }, { type: "null" }],
}),
).toEqual({
type: "string",
enum: ["a", "b"],
anyOf: undefined,
nullable: true,
});
});
it("hoists items out of an anyOf array|null branch", () => {
expect(
normalizeNullableUnion({
anyOf: [
{ type: "array", items: { type: "string", enum: ["a", "b"] } },
{ type: "null" },
],
}),
).toEqual({
type: "array",
items: { type: "string", enum: ["a", "b"] },
anyOf: undefined,
nullable: true,
});
});
it("hoists properties out of an anyOf object|null branch", () => {
expect(
normalizeNullableUnion({
anyOf: [
{ type: "object", properties: { a: { type: "string" } } },
{ type: "null" },
],
}),
).toEqual({
type: "object",
properties: { a: { type: "string" } },
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf object|null regardless of branch order", () => {
expect(
normalizeNullableUnion({
anyOf: [{ type: "null" }, { type: "object" }],
}),
).toEqual({ type: "object", anyOf: undefined, nullable: true });
});
it("normalizes type array object|null", () => {
expect(
normalizeNullableUnion({
type: ["object", "null"],
properties: { a: { type: "string" } },
}),
).toEqual({
type: "object",
properties: { a: { type: "string" } },
nullable: true,
});
});
it("normalizes type array array|null", () => {
expect(normalizeNullableUnion({ type: ["array", "null"] })).toEqual({
type: "array",
nullable: true,
});
});
it("keeps a type array of two non-null members unchanged", () => {
const schema = { type: ["string", "number"] as const };
expect(
normalizeNullableUnion({ ...schema, type: [...schema.type] }),
).toEqual({
type: ["string", "number"],
});
});
// A server can put anything in `anyOf`; a non-object member must not be read
// as a branch (nor throw), it simply means no nullable union was recognized.
it("ignores an anyOf holding a non-object member", () => {
const schema = { anyOf: ["string", { type: "null" as const }] };
expect(normalizeNullableUnion(schema)).toBe(schema);
});
it("ignores an anyOf holding an array member", () => {
const schema = { anyOf: [["string"], { type: "null" as const }] };
expect(normalizeNullableUnion(schema)).toBe(schema);
});
it("ignores a type array whose non-null member has no widget", () => {
const schema = { type: ["null", "null"] };
expect(normalizeNullableUnion(schema)).toBe(schema);
});
it("ignores a schema with no union keywords at all", () => {
const schema = { type: "object" as const, properties: {} };
expect(normalizeNullableUnion(schema)).toBe(schema);
});
});

221
clients/web/src/utils/schemaUtils.test.ts
View file

@ -8,7 +8,6 @@ import {
generateDefaultValue,
isPropertyRequired,
resolveRef,
normalizeUnionType,
formatFieldLabel,
resolveRefsInMessage,
} from "./schemaUtils";
@ -243,226 +242,6 @@ describe("resolveRef", () => {
});
});
describe("normalizeUnionType", () => {
it("normalizes anyOf string|null", () => {
expect(
normalizeUnionType({
anyOf: [{ type: "string" }, { type: "null" }],
}),
).toEqual({
type: "string",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf boolean|null", () => {
expect(
normalizeUnionType({
anyOf: [{ type: "boolean" }, { type: "null" }],
}),
).toEqual({
type: "boolean",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf number|null", () => {
expect(
normalizeUnionType({
anyOf: [{ type: "number" }, { type: "null" }],
}),
).toEqual({
type: "number",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf integer|null", () => {
expect(
normalizeUnionType({
anyOf: [{ type: "integer" }, { type: "null" }],
}),
).toEqual({
type: "integer",
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf array|null", () => {
expect(
normalizeUnionType({
anyOf: [{ type: "array" }, { type: "null" }],
}),
).toEqual({
type: "array",
anyOf: undefined,
nullable: true,
});
});
it("normalizes type array string|null", () => {
expect(normalizeUnionType({ type: ["string", "null"] })).toEqual({
type: "string",
nullable: true,
});
});
it("normalizes type array boolean|null", () => {
expect(normalizeUnionType({ type: ["boolean", "null"] })).toEqual({
type: "boolean",
nullable: true,
});
});
it("normalizes type array number|null", () => {
expect(normalizeUnionType({ type: ["number", "null"] })).toEqual({
type: "number",
nullable: true,
});
});
it("normalizes type array integer|null", () => {
expect(normalizeUnionType({ type: ["integer", "null"] })).toEqual({
type: "integer",
nullable: true,
});
});
it("returns schema unchanged when no union pattern matches", () => {
const schema = { type: "string" as const };
expect(normalizeUnionType(schema)).toBe(schema);
});
it("ignores anyOf with more than two members", () => {
const schema = {
anyOf: [
{ type: "string" as const },
{ type: "null" as const },
{ type: "number" as const },
],
};
expect(normalizeUnionType(schema)).toBe(schema);
});
it("ignores a two-member anyOf with no null branch", () => {
const schema = {
anyOf: [{ type: "string" as const }, { type: "number" as const }],
};
expect(normalizeUnionType(schema)).toBe(schema);
});
it("ignores an anyOf whose non-null branch has no renderable type (#1928)", () => {
const schema = {
anyOf: [{ const: "only" }, { type: "null" as const }],
};
expect(normalizeUnionType(schema)).toBe(schema);
});
// #1928: the enum lives on the surviving branch, and hoisting it is what makes
// the field render as a Select instead of the raw-JSON fallback.
it("hoists enum out of an anyOf string-enum|null branch", () => {
expect(
normalizeUnionType({
description: "Direction",
anyOf: [
{ type: "string", enum: ["envio", "recebimento"] },
{ type: "null" },
],
}),
).toEqual({
type: "string",
description: "Direction",
enum: ["envio", "recebimento"],
anyOf: undefined,
nullable: true,
});
});
it("infers string for a typeless enum branch", () => {
expect(
normalizeUnionType({
anyOf: [{ enum: ["a", "b"] }, { type: "null" }],
}),
).toEqual({
type: "string",
enum: ["a", "b"],
anyOf: undefined,
nullable: true,
});
});
it("hoists items out of an anyOf array|null branch", () => {
expect(
normalizeUnionType({
anyOf: [
{ type: "array", items: { type: "string", enum: ["a", "b"] } },
{ type: "null" },
],
}),
).toEqual({
type: "array",
items: { type: "string", enum: ["a", "b"] },
anyOf: undefined,
nullable: true,
});
});
it("hoists properties out of an anyOf object|null branch", () => {
expect(
normalizeUnionType({
anyOf: [
{ type: "object", properties: { a: { type: "string" } } },
{ type: "null" },
],
}),
).toEqual({
type: "object",
properties: { a: { type: "string" } },
anyOf: undefined,
nullable: true,
});
});
it("normalizes anyOf object|null regardless of branch order", () => {
expect(
normalizeUnionType({
anyOf: [{ type: "null" }, { type: "object" }],
}),
).toEqual({ type: "object", anyOf: undefined, nullable: true });
});
it("normalizes type array object|null", () => {
expect(
normalizeUnionType({
type: ["object", "null"],
properties: { a: { type: "string" } },
}),
).toEqual({
type: "object",
properties: { a: { type: "string" } },
nullable: true,
});
});
it("normalizes type array array|null", () => {
expect(normalizeUnionType({ type: ["array", "null"] })).toEqual({
type: "array",
nullable: true,
});
});
it("keeps a type array of two non-null members unchanged", () => {
const schema = { type: ["string", "number"] as const };
expect(normalizeUnionType({ ...schema, type: [...schema.type] })).toEqual({
type: ["string", "number"],
});
});
});
describe("formatFieldLabel", () => {
it("inserts spaces before capitals and capitalizes first letter", () => {
expect(formatFieldLabel("firstName")).toBe("First Name");

84
clients/web/src/utils/schemaUtils.ts
View file

@ -3,6 +3,7 @@ import Ajv from "ajv";
import type { ValidateFunction } from "ajv";
import type { Tool, JSONRPCMessage } from "@modelcontextprotocol/client";
import { isJSONRPCRequest } from "@modelcontextprotocol/client";
import { normalizeNullableUnion } from "@inspector/core/json/nullableUnion.js";
const ajv = new Ajv();
@ -200,87 +201,6 @@ export function resolveRef(
return schema;
}
/**
* The `type` values {@link SchemaForm} dispatches on. `"null"` is deliberately
* absent: it is the branch a nullable union is being flattened *away* from, and
* there is no widget for a field whose only permitted value is `null`.
*/
const RENDERABLE_TYPES = [
"string",
"number",
"integer",
"boolean",
"array",
"object",
] as const;
type RenderableType = (typeof RENDERABLE_TYPES)[number];
function isRenderableType(type: unknown): type is RenderableType {
return RENDERABLE_TYPES.includes(type as RenderableType);
}
/**
* Normalizes a nullable union (`string|null` from FastMCP, or anything Zod's
* `.nullish()` / `.nullable()` compiles to) into the plain type the form
* renderer dispatches on.
*
* Two encodings mean the same thing and are both flattened to
* `{ type: <T>, nullable: true }`:
*
* - `anyOf: [<branch>, { type: "null" }]` — the branch's *own* keywords are
* hoisted onto the result, because that is where the detail the renderer
* needs lives. A nullable enum compiles to
* `anyOf: [{ type: "string", enum: [...] }, { type: "null" }]`, so hoisting
* `enum` is what makes it a `Select` instead of falling through to the raw
* JSON fallback (#1928). The branch also wins over the wrapper on any shared
* key, matching v1.x's behavior.
* - `type: [<T>, "null"]` — the keywords already sit at the top level, so only
* `type` collapses.
*
* Anything else — a union of two real types, a three-member `anyOf`, a branch
* whose type has no widget — is returned untouched and renders through the
* JSON fallback, which is the honest representation of a shape the form cannot
* model.
*
* @param schema The JSON schema to normalize
* @returns A normalized schema, or the original schema when no nullable-union
* pattern matches
*/
export function normalizeUnionType(
schema: InspectorFormSchema,
): InspectorFormSchema {
if (schema.anyOf && schema.anyOf.length === 2) {
// `JsonSchemaConst` is structurally a subset of `InspectorFormSchema` (it
// just carries no `type`), so reading both as the latter is safe.
const branches = schema.anyOf as InspectorFormSchema[];
const nullBranch = branches.find((branch) => branch?.type === "null");
const branch = branches.find((candidate) => candidate?.type !== "null");
if (nullBranch && branch) {
// A bare `{ enum: [...] }` branch carries no `type`; JSON Schema allows
// that, and every value such a schema admits here is a string.
const type = branch.type ?? (branch.enum ? "string" : undefined);
if (isRenderableType(type)) {
return { ...schema, ...branch, type, anyOf: undefined, nullable: true };
}
}
}
if (
Array.isArray(schema.type) &&
schema.type.length === 2 &&
schema.type.includes("null")
) {
const type = schema.type.find((member) => member !== "null");
if (isRenderableType(type)) {
return { ...schema, type, nullable: true };
}
}
return schema;
}
/**
* Formats a field key into a human-readable label
* @param key The field key to format
@ -319,7 +239,7 @@ export function resolveRefsInMessage(message: JSONRPCMessage): JSONRPCMessage {
Object.entries(requestedSchema.properties).map(
([key, propSchema]) => {
const resolved = resolveRef(propSchema, requestedSchema);
const normalized = normalizeUnionType(resolved);
const normalized = normalizeNullableUnion(resolved);
return [key, normalized];
},
),

120
core/json/nullableUnion.ts Normal file
View file

@ -0,0 +1,120 @@
/**
* Flattening of the two JSON Schema encodings of "this type, **or** null" into
* the plain type a form renderer can dispatch on.
*
* Shared because both form builders — the web client's `SchemaForm` and the
* TUI's `schemaToForm` — dispatch on a *single* `type` string, and so both miss
* a nullable field entirely without this step (#1928, #2015). Keeping one copy
* is what stops the two clients from disagreeing about which schemas they can
* render; the alternative was two implementations of the same subtle predicate.
*/
/**
* JSON Schema type names a form renderer can build a widget for.
*
* `"null"` is deliberately absent: it is the branch a nullable union is being
* flattened *away* from, and there is no widget for a field whose only
* permitted value is `null`.
*/
const RENDERABLE_TYPES = [
"string",
"number",
"integer",
"boolean",
"array",
"object",
] as const;
type RenderableType = (typeof RENDERABLE_TYPES)[number];
function isRenderableType(type: unknown): type is RenderableType {
return RENDERABLE_TYPES.includes(type as RenderableType);
}
/**
* The keywords {@link normalizeNullableUnion} reads. Both clients' own schema
* types are structurally assignable to this, so neither has to adopt the
* other's — the shape is deliberately the minimum needed to *recognize* a
* nullable union, not a full JSON Schema model.
*/
export interface NullableUnionSchema {
type?: string | string[];
enum?: unknown[];
anyOf?: readonly unknown[];
}
/** Narrow an `anyOf` member to a readable object, or `null` if it isn't one. */
function toBranch(value: unknown): Record<string, unknown> | null {
if (typeof value !== "object" || value === null || Array.isArray(value)) {
return null;
}
return value as Record<string, unknown>;
}
/**
* Collapse a nullable union — what Zod's `.nullish()` / `.nullable()` and
* FastMCP's optional arguments emit — into `{ type: <T>, nullable: true }`.
*
* Two encodings mean the same thing and are both handled:
*
* - `anyOf: [<branch>, { type: "null" }]` — the branch's *own* keywords are
* hoisted onto the result, because that is where the detail a renderer needs
* lives. A nullable enum compiles to
* `anyOf: [{ type: "string", enum: [...] }, { type: "null" }]`, so hoisting
* `enum` is what makes it a dropdown rather than a raw-JSON fallback (#1928).
* The branch also wins over the wrapper on any shared key, matching v1.x.
* - `type: [<T>, "null"]` — the keywords already sit at the top level, so only
* `type` collapses.
*
* Anything else — a union of two real types, a three-member `anyOf`, a branch
* whose type has no widget — is returned **by identity**, so a caller can use
* `===` to tell that nothing was recognized.
*
* @param schema The schema to normalize
* @returns A flattened copy, or `schema` itself when no nullable-union pattern
* matches
*/
export function normalizeNullableUnion<T extends NullableUnionSchema>(
schema: T,
): T {
if (schema.anyOf?.length === 2) {
const branches = schema.anyOf.map(toBranch);
const nullBranch = branches.find((entry) => entry?.type === "null");
const branch = branches.find(
(entry) => entry !== null && entry.type !== "null",
);
if (nullBranch && branch) {
// A bare `{ enum: [...] }` branch carries no `type`; JSON Schema allows
// that, and every value such a schema admits here is a string.
const type = branch.type ?? (branch.enum ? "string" : undefined);
if (isRenderableType(type)) {
// The result is `schema` with `type` narrowed to a value it already
// admitted, the branch's keywords merged in, and `nullable` added. TS
// cannot express "a spread of T and a subset of T is still a T", and a
// non-generic return would force every caller to cast instead.
return {
...schema,
...branch,
type,
anyOf: undefined,
nullable: true,
} as T;
}
}
}
if (
Array.isArray(schema.type) &&
schema.type.length === 2 &&
schema.type.includes("null")
) {
const type = schema.type.find((member) => member !== "null");
if (isRenderableType(type)) {
// Same reasoning as above.
return { ...schema, type, nullable: true } as T;
}
}
return schema;
}