From b16b3a4bf34bccb6daf3f5796737e89fb186971c Mon Sep 17 00:00:00 2001
From: mrazauskas <72159681+mrazauskas@users.noreply.github.com>
Date: Mon, 14 Feb 2022 10:24:01 +0200
Subject: [PATCH] expose MatcherFunction

---
 packages/expect/__typetests__/expect.test.ts | 158 +++++++++++--------
 packages/expect/src/index.ts                 |   2 +
 packages/expect/src/types.ts                 |  17 +-
 packages/jest-snapshot/src/types.ts          |   4 +-
 4 files changed, 115 insertions(+), 66 deletions(-)

diff --git a/packages/expect/__typetests__/expect.test.ts b/packages/expect/__typetests__/expect.test.ts
index 3db1270ee699..122f92985d09 100644
--- a/packages/expect/__typetests__/expect.test.ts
+++ b/packages/expect/__typetests__/expect.test.ts
@@ -9,6 +9,8 @@ import {expectError, expectType} from 'tsd-lite';
 import type {EqualsFunction, Tester} from '@jest/expect-utils';
 import {
   type ExpectationResult,
+  type MatcherFunction,
+  type MatcherFunctionWithContext,
   type MatcherState,
   type Matchers,
   expect,
@@ -29,6 +31,7 @@ type MatcherUtils = typeof jestMatcherUtils & {
   subsetEquality: Tester;
 };
 
+// TODO `actual` should be allowed to have only `unknown` type
 expectType<void>(
   expect.extend({
     toBeWithinRange(actual: number, floor: number, ceiling: number) {
@@ -85,80 +88,111 @@ expectType<void>(
   }),
 );
 
-// ExpectationResult
+// MatcherFunction
 
-const toBeResult = (received: string): ExpectationResult => {
-  if (received === 'result') {
-    return {
-      message: () => 'is result',
-      pass: true,
-    };
-  } else {
+expectError(() => {
+  const actualMustBeUnknown: MatcherFunction = (actual: string) => {
     return {
-      message: () => 'is not result',
-      pass: false,
+      message: () => `result: ${actual}`,
+      pass: actual === 'result',
     };
-  }
-};
-
-expectType<void>(expect.extend({toBeResult}));
+  };
+});
 
 expectError(() => {
-  const lacksElseBranch = (received: string): ExpectationResult => {
-    if (received === 'result') {
-      return {
-        message: () => 'is result',
-        pass: true,
-      };
-    }
+  const lacksMessage: MatcherFunction = (actual: unknown) => {
+    return {
+      pass: actual === 'result',
+    };
   };
 });
 
 expectError(() => {
-  const lacksMessage = (received: string): ExpectationResult => {
-    if (received === 'result') {
-      return {
-        pass: true,
-      };
-    } else {
-      return {
-        pass: false,
-      };
-    }
+  const lacksPass: MatcherFunction = (actual: unknown) => {
+    return {
+      message: () => `result: ${actual}`,
+    };
   };
 });
 
-// MatcherState
+type ToBeWithinRange = (
+  this: MatcherState,
+  actual: unknown,
+  floor: number,
+  ceiling: number,
+) => ExpectationResult;
+
+const toBeWithinRange: MatcherFunction<[floor: number, ceiling: number]> = (
+  actual: unknown,
+  floor: unknown,
+  ceiling: unknown,
+) => {
+  return {
+    message: () => `actual ${actual}; range ${floor}-${ceiling}`,
+    pass: true,
+  };
+};
 
-function toHaveContext(
+expectType<ToBeWithinRange>(toBeWithinRange);
+
+type AllowOmittingExpected = (
   this: MatcherState,
-  received: string,
-): ExpectationResult {
-  expectType<number>(this.assertionCalls);
-  expectType<string | undefined>(this.currentTestName);
-  expectType<(() => void) | undefined>(this.dontThrow);
-  expectType<Error | undefined>(this.error);
-  expectType<EqualsFunction>(this.equals);
-  expectType<boolean | undefined>(this.expand);
-  expectType<number | null | undefined>(this.expectedAssertionsNumber);
-  expectType<Error | undefined>(this.expectedAssertionsNumberError);
-  expectType<boolean | undefined>(this.isExpectingAssertions);
-  expectType<Error | undefined>(this.isExpectingAssertionsError);
-  expectType<boolean>(this.isNot);
-  expectType<string>(this.promise);
-  expectType<Array<Error>>(this.suppressedErrors);
-  expectType<string | undefined>(this.testPath);
-  expectType<MatcherUtils>(this.utils);
-
-  if (received === 'result') {
-    return {
-      message: () => 'is result',
-      pass: true,
-    };
-  } else {
-    return {
-      message: () => 'is not result',
-      pass: false,
-    };
-  }
+  actual: unknown,
+) => ExpectationResult;
+
+const allowOmittingExpected: MatcherFunction = (actual: unknown) => {
+  return {
+    message: () => `actual ${actual}`,
+    pass: true,
+  };
+};
+
+expectType<AllowOmittingExpected>(allowOmittingExpected);
+
+// MatcherState
+
+const toHaveContext: MatcherFunction = function (actual: unknown) {
+  expectType<MatcherState>(this);
+
+  return {
+    message: () => `result: ${actual}`,
+    pass: actual === 'result',
+  };
+};
+
+interface CustomContext extends MatcherState {
+  customMethod(): void;
 }
+
+const customContext: MatcherFunctionWithContext<CustomContext> = function (
+  actual: unknown,
+) {
+  expectType<CustomContext>(this);
+  expectType<void>(this.customMethod());
+
+  return {
+    message: () => `result: ${actual}`,
+    pass: actual === 'result',
+  };
+};
+
+type CustomContextAndExpected = (
+  this: CustomContext,
+  actual: unknown,
+  count: number,
+) => ExpectationResult;
+
+const customContextAndExpected: MatcherFunctionWithContext<
+  CustomContext,
+  [count: number]
+> = function (actual: unknown, count: unknown) {
+  expectType<CustomContext>(this);
+  expectType<void>(this.customMethod());
+
+  return {
+    message: () => `count: ${count}`,
+    pass: actual === count,
+  };
+};
+
+expectType<CustomContextAndExpected>(customContextAndExpected);
diff --git a/packages/expect/src/index.ts b/packages/expect/src/index.ts
index 66f88b5c08b2..ac6a2d9db36b 100644
--- a/packages/expect/src/index.ts
+++ b/packages/expect/src/index.ts
@@ -53,6 +53,8 @@ export type {
   AsymmetricMatchers,
   Expect,
   ExpectationResult,
+  MatcherFunction,
+  MatcherFunctionWithContext,
   MatcherState,
   Matchers,
 } from './types';
diff --git a/packages/expect/src/types.ts b/packages/expect/src/types.ts
index e53f09493335..232c970ab759 100644
--- a/packages/expect/src/types.ts
+++ b/packages/expect/src/types.ts
@@ -20,6 +20,19 @@ export type AsyncExpectationResult = Promise<SyncExpectationResult>;
 
 export type ExpectationResult = SyncExpectationResult | AsyncExpectationResult;
 
+export type MatcherFunctionWithContext<
+  Context extends MatcherState = MatcherState,
+  Expected extends Array<any> = [],
+> = (
+  this: Context,
+  actual: unknown,
+  ...expected: Expected
+) => ExpectationResult;
+
+export type MatcherFunction<Expected extends Array<any> = []> =
+  MatcherFunctionWithContext<MatcherState, Expected>;
+
+// TODO should be replaced with `MatcherFunctionWithContext`
 export type RawMatcherFn<T extends MatcherState = MatcherState> = {
   (this: T, actual: any, ...expected: Array<any>): ExpectationResult;
   /** @internal */
@@ -29,7 +42,7 @@ export type RawMatcherFn<T extends MatcherState = MatcherState> = {
 export type ThrowingMatcherFn = (actual: any) => void;
 export type PromiseMatcherFn = (actual: any) => Promise<void>;
 
-export type MatcherState = {
+export interface MatcherState {
   assertionCalls: number;
   currentTestName?: string;
   dontThrow?(): void;
@@ -48,7 +61,7 @@ export type MatcherState = {
     iterableEquality: Tester;
     subsetEquality: Tester;
   };
-};
+}
 
 export interface AsymmetricMatcher {
   asymmetricMatch(other: unknown): boolean;
diff --git a/packages/jest-snapshot/src/types.ts b/packages/jest-snapshot/src/types.ts
index dcc0c8e12de5..0013a08d081f 100644
--- a/packages/jest-snapshot/src/types.ts
+++ b/packages/jest-snapshot/src/types.ts
@@ -8,9 +8,9 @@
 import type {MatcherState} from 'expect';
 import type SnapshotState from './State';
 
-export type Context = MatcherState & {
+export interface Context extends MatcherState {
   snapshotState: SnapshotState;
-};
+}
 
 export type MatchSnapshotConfig = {
   context: Context;