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fix: support exactOptionalPropertyTypes #4087

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fix: support exactOptionalPropertyTypes #4087

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5 changes: 5 additions & 0 deletions .changeset/exact-optional-property-types.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'fets': patch
---

Support TypeScript `exactOptionalPropertyTypes` for route schemas, OpenAPI option bags, and inferred optional object fields
50 changes: 25 additions & 25 deletions packages/fets/src/plugins/openapi.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -16,37 +16,37 @@ function isOptionalSchema(schema: any): boolean {
}

export interface SwaggerUIOpts {
spec?: OpenAPIDocument;
dom_id?: string;
displayOperationId?: boolean;
tryItOutEnabled?: boolean;
requestSnippetsEnabled?: boolean;
displayRequestDuration?: boolean;
defaultModelRendering?: 'model' | 'example' | 'schema';
defaultModelExpandDepth?: number;
defaultModelsExpandDepth?: number;
docExpansion?: 'none' | 'list' | 'full';
filter?: boolean;
maxDisplayedTags?: number;
showExtensions?: boolean;
showCommonExtensions?: boolean;
tagsSorter?: 'alpha';
operationsSorter?: 'alpha';
showTags?: boolean;
showMutatedRequest?: boolean;
oauth2RedirectUrl?: string;
validatorUrl?: string;
deepLinking?: boolean;
presets?: any[];
plugins?: any[];
layout?: string;
spec?: OpenAPIDocument | undefined;
dom_id?: string | undefined;
displayOperationId?: boolean | undefined;
tryItOutEnabled?: boolean | undefined;
requestSnippetsEnabled?: boolean | undefined;
displayRequestDuration?: boolean | undefined;
defaultModelRendering?: 'model' | 'example' | 'schema' | undefined;
defaultModelExpandDepth?: number | undefined;
defaultModelsExpandDepth?: number | undefined;
Comment on lines +19 to +27

@coderabbitai coderabbitai Bot Aug 7, 2026

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🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# Confirm that the defaulted options are assigned before swaggerUIOpts is spread.
rg -n -C 12 'spec: router\.openAPIDocument|swaggerUIOpts' packages/fets/src/plugins/openapi.ts

# Locate OpenAPI or Swagger UI tests that should cover explicit undefined values.
fd -t f . packages/fets | rg -i '(openapi|swagger).*(test|spec)|(test|spec).*(openapi|swagger)' || true

Repository: ardatan/feTS

Length of output: 3008

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== SwaggerUIOpts type =="
sed -n '25,44p' packages/fets/src/plugins/openapi.ts | cat -n

echo
echo "== relevant openapi tests =="
sed -n '1,240p' packages/fets/tests/plugins/openapi.spec.ts | cat -n

echo
echo "== tsconfig exactOptionalPropertyTypes =="
fd -t f 'tsconfig.*json' . -x sh -c 'echo "--- {}"; grep -n "exactOptionalPropertyTypes" "{}" || true'

Repository: ardatan/feTS

Length of output: 5343

Keep defaulted Swagger UI options from accepting explicit undefined.

With exactOptionalPropertyTypes: true, { spec: undefined } is permitted. The handler spreads swaggerUIOpts after the defaults in JSON.stringify, so explicit undefined overwrites the plugin default before serialization and leaves the option out of the Swagger UI configuration. Remove | undefined from the defaulted SwaggerUIOpts properties, or strip undefined values before the spread.

🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/fets/src/plugins/openapi.ts` around lines 19 - 27, Update the
defaulted properties in SwaggerUIOpts, including spec and the related
display/model options, to reject explicit undefined under
exactOptionalPropertyTypes by removing their | undefined unions; preserve
optional omission while keeping the existing plugin defaults and spread behavior
unchanged.

docExpansion?: 'none' | 'list' | 'full' | undefined;
filter?: boolean | undefined;
maxDisplayedTags?: number | undefined;
showExtensions?: boolean | undefined;
showCommonExtensions?: boolean | undefined;
tagsSorter?: 'alpha' | undefined;
operationsSorter?: 'alpha' | undefined;
showTags?: boolean | undefined;
showMutatedRequest?: boolean | undefined;
oauth2RedirectUrl?: string | undefined;
validatorUrl?: string | undefined;
deepLinking?: boolean | undefined;
presets?: any[] | undefined;
plugins?: any[] | undefined;
layout?: string | undefined;
}

export type OpenAPIPluginOptions = {
oasEndpoint: string | false;
swaggerUIEndpoint: string | false;
swaggerUIOpts: SwaggerUIOpts;
includeValidationErrors?: boolean;
includeValidationErrors?: boolean | undefined;
};

const requestValidationErrorSchema = {
Expand Down
33 changes: 14 additions & 19 deletions packages/fets/src/typed-fetch.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -42,11 +42,10 @@ export type StatusCode =

export type NotOkStatusCode = Exclude<StatusCode, OkStatusCode>;

export type TypedBody<
TJSON,
TFormData extends Record<string, FormDataEntryValue | undefined>,
THeaders extends Record<string, string | undefined>,
> = Omit<Body, 'json' | 'formData' | 'headers'> & {
export type TypedBody<TJSON, TFormData extends object, THeaders extends object> = Omit<
Body,
'json' | 'formData' | 'headers'
> & {
Comment on lines +45 to +48
/**
* The `json()` method takes the stream and reads it to completion.
* It returns a promise which resolves with the result of parsing the body text as JSON.
Expand Down Expand Up @@ -77,7 +76,7 @@ type Maybe = undefined | null;

type UndefinedToNull<T> = T extends undefined ? Exclude<T, undefined> | null : T;

export interface TypedHeaders<TMap extends Record<string, string | undefined>> {
export interface TypedHeaders<TMap extends object = Record<string, string | undefined>> {
append<TName extends DefaultHTTPHeaders | keyof TMap>(
name: TName,
value: TName extends keyof TMap ? TMap[TName] : string,
Expand Down Expand Up @@ -306,9 +305,9 @@ export type HTTPMethod =
'GET' | 'POST' | 'PUT' | 'PATCH' | 'DELETE' | 'HEAD' | 'OPTIONS' | 'CONNECT' | 'TRACE';

export type TypedRequestInit<
THeaders extends Record<string, string | undefined>,
THeaders extends object,
TMethod extends HTTPMethod,
TFormData extends Record<string, FormDataEntryValue | undefined>,
TFormData extends object,
> = Omit<RequestInit, 'method' | 'headers' | 'body'> & {
method: TMethod;
headers: TypedHeaders<THeaders>;
Expand All @@ -317,11 +316,10 @@ export type TypedRequestInit<

export type TypedRequest<
TJSON = any,
TFormData extends Record<string, FormDataEntryValue | undefined> = Record<
string,
FormDataEntryValue | undefined
>,
THeaders extends Record<string, string | undefined> = Record<string, string | undefined>,
// `object` (not `Record<…| undefined>`) so EOPT optional fields like
// `{ description?: string; file: File }` remain valid form/header maps.
TFormData extends object = Record<string, FormDataEntryValue | undefined>,
THeaders extends object = Record<string, string | undefined>,
TMethod extends HTTPMethod = HTTPMethod,
TQueryParams = any,
TPathParams extends Record<string, any> = Record<string, any>,
Expand All @@ -334,19 +332,16 @@ export type TypedRequest<
};

export type TypedRequestCtor = new <
THeaders extends Record<string, string | undefined>,
THeaders extends object,
TMethod extends HTTPMethod,
TFormData extends Record<string, FormDataEntryValue | undefined>,
TFormData extends object,
>(
input: string | URL,
init?: TypedRequestInit<THeaders, TMethod, TFormData>,
) => TypedRequest<any, TFormData, THeaders, TMethod, any, any>;

export interface TypedFormData<
TMap extends Record<string, FormDataEntryValue | undefined> = Record<
string,
FormDataEntryValue | undefined
>,
TMap extends object = Record<string, FormDataEntryValue | undefined>,
> {
append<TName extends keyof TMap>(
name: TName,
Expand Down
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