Make the default type of response data never (#3002)

This requires TypeScript users to explicitly define the type of the data they
are consuming.

Before this, data was `any` by default. This means TypeScript consumers didn’t
get type safety if they forgot to specify the type.

Technically this is a breaking change for TypeScript users, as this will report
errors if they forgot to specifiy the response type. The simplest workaround
would be to explicitly set the response type to `any`, so it’s not breaking
much.

The `unknown` type is probably a slightly better fit, but this requires
TypeScript ^3.

`data` is still `any` in the very specific use case mentioned in
microsoft/TypeScript#38969

Co-authored-by: Jay <jasonsaayman@gmail.com>

index.d.ts

@@ -80,7 +80,7 @@ export interface AxiosRequestConfig<T = any> {
   transitional?: TransitionalOptions
 }
 
-export interface AxiosResponse<T = any>  {
+export interface AxiosResponse<T = never>  {
   data: T;
   status: number;
   statusText: string;
@@ -89,7 +89,7 @@ export interface AxiosResponse<T = any>  {
   request?: any;
 }
 
-export interface AxiosError<T = any> extends Error {
+export interface AxiosError<T = never> extends Error {
   config: AxiosRequestConfig;
   code?: string;
   request?: any;
@@ -98,7 +98,7 @@ export interface AxiosError<T = any> extends Error {
   toJSON: () => object;
 }
 
-export interface AxiosPromise<T = any> extends Promise<AxiosResponse<T>> {
+export interface AxiosPromise<T = never> extends Promise<AxiosResponse<T>> {
 }
 
 export interface CancelStatic {
@@ -142,14 +142,14 @@ export class Axios {
     response: AxiosInterceptorManager<AxiosResponse>;
   };
   getUri(config?: AxiosRequestConfig): string;
-  request<T = any, R = AxiosResponse<T>> (config: AxiosRequestConfig<T>): Promise<R>;
-  get<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
-  delete<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
-  head<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
-  options<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
-  post<T = any, R = AxiosResponse<T>>(url: string, data?: T, config?: AxiosRequestConfig<T>): Promise<R>;
-  put<T = any, R = AxiosResponse<T>>(url: string, data?: T, config?: AxiosRequestConfig<T>): Promise<R>;
-  patch<T = any, R = AxiosResponse<T>>(url: string, data?: T, config?: AxiosRequestConfig<T>): Promise<R>;
+  request<T = never, R = AxiosResponse<T>> (config: AxiosRequestConfig<T>): Promise<R>;
+  get<T = never, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
+  delete<T = never, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
+  head<T = never, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
+  options<T = never, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig<T>): Promise<R>;
+  post<T = never, R = AxiosResponse<T>>(url: string, data?: T, config?: AxiosRequestConfig<T>): Promise<R>;
+  put<T = never, R = AxiosResponse<T>>(url: string, data?: T, config?: AxiosRequestConfig<T>): Promise<R>;
+  patch<T = never, R = AxiosResponse<T>>(url: string, data?: T, config?: AxiosRequestConfig<T>): Promise<R>;
 }
 
 export interface AxiosInstance extends Axios {

test/typescript/axios.ts

@@ -296,7 +296,7 @@ axios.interceptors.response.use((response: AxiosResponse) => Promise.resolve(res
 // Adapters
 
 const adapter: AxiosAdapter = (config: AxiosRequestConfig) => {
-  const response: AxiosResponse = {
+  const response: AxiosResponse<any> = {
     data: { foo: 'bar' },
     status: 200,
     statusText: 'OK',