fix: allow do to modify context

src/types.ts

@@ -35,7 +35,7 @@ export type Base<I extends Context, T extends Plugins> = {
     (cb?: (context: I) => any): void
   }
   add<K extends string, O>(key: K, cb: (context: I) => Promise<O> | O): Base<I & {[P in K]: O}, T>
-  do(cb: (context: I) => any): Base<I, T>
+  do<O>(cb: (context: I & O) => any): Base<O & I, T>
   register<K extends string, O, A1, A2, A3, A4>(key: K, plugin: (arg1?: A1, arg2?: A2, arg3?: A3, arg4?: A4) => Plugin<O & I>): Base<I, T & {[P in K]: {output: O, a1: A1, a2: A2, a3: A3, a4: A4}}>
 } & {[P in keyof T]: (arg1?: T[P]['a1'], arg2?: T[P]['a2'], arg3?: T[P]['a3'], arg4?: T[P]['a4']) => Base<T[P]['output'] & I, T>}
 

test/run.test.ts → test/do.test.ts

@@ -2,14 +2,21 @@
 
 import {expect, fancy} from '../src'
 
-describe('run', () => {
+describe('do', () => {
   fancy
   .stdout()
   .do(() => console.log('foo'))
   .do(({stdout}) => expect(stdout).to.equal('foo\n'))
   .end('runs this callback last', () => {
     // test code
   })
+
+  fancy
+  .stdout()
+  .do((ctx: {n: number}) => {ctx.n = 101})
+  .do(ctx => console.log(ctx.n))
+  .do(ctx => expect(ctx.stdout).to.equal('101\n'))
+  .end('runs this callback last')
 })
 
 describe('add', () => {