From f0b1c3faf6f4dcf7a6a71d4fa43c06d543c60df3 Mon Sep 17 00:00:00 2001
From: Davide Menegatti <d.menegatti@recrosoftware.com>
Date: Sun, 3 Jul 2022 21:53:48 +0200
Subject: [PATCH] Add `OptionalKeysOf`, `HasOptionalKeys`, `RequiredKeysOf`,
 `HasRequiredKeys` types (#405)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>
---
 index.d.ts                    |  4 +++
 readme.md                     |  4 +++
 source/has-optional-keys.d.ts | 21 +++++++++++++
 source/has-required-keys.d.ts | 59 +++++++++++++++++++++++++++++++++++
 source/optional-keys-of.d.ts  | 38 ++++++++++++++++++++++
 source/required-keys-of.d.ts  | 29 +++++++++++++++++
 test-d/has-optional-keys.ts   | 29 +++++++++++++++++
 test-d/has-required-keys.ts   | 29 +++++++++++++++++
 test-d/optional-keys-of.ts    | 29 +++++++++++++++++
 test-d/required-keys-of.ts    | 29 +++++++++++++++++
 10 files changed, 271 insertions(+)
 create mode 100644 source/has-optional-keys.d.ts
 create mode 100644 source/has-required-keys.d.ts
 create mode 100644 source/optional-keys-of.d.ts
 create mode 100644 source/required-keys-of.d.ts
 create mode 100644 test-d/has-optional-keys.ts
 create mode 100644 test-d/has-required-keys.ts
 create mode 100644 test-d/optional-keys-of.ts
 create mode 100644 test-d/required-keys-of.ts

diff --git a/index.d.ts b/index.d.ts
index 9f23234f6..af1ab44e8 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -57,6 +57,10 @@ export {
 export {StringKeyOf} from './source/string-key-of';
 export {Exact} from './source/exact';
 export {ReadonlyTuple} from './source/readonly-tuple';
+export {OptionalKeysOf} from './source/optional-keys-of';
+export {HasOptionalKeys} from './source/has-optional-keys';
+export {RequiredKeysOf} from './source/required-keys-of';
+export {HasRequiredKeys} from './source/has-required-keys';
 
 // Template literal types
 export {CamelCase} from './source/camel-case';
diff --git a/readme.md b/readme.md
index b484871db..3cbf20a13 100644
--- a/readme.md
+++ b/readme.md
@@ -192,6 +192,10 @@ Click the type names for complete docs.
 - [`StringKeyOf`](source/string-key-of.d.ts) - Get keys of the given type as strings.
 - [`Schema`](source/schema.d.ts) - Create a deep version of another object type where property values are recursively replaced into a given value type.
 - [`Exact`](source/exact.d.ts) - Create a type that does not allow extra properties.
+- [`OptionalKeysOf`](source/optional-keys-of.d.ts) - Extract all optional keys from the given type.
+- [`HasOptionalKeys`](source/has-optional-keys.d.ts) - Create a `true`/`false` type depending on whether the given type has any optional fields.
+- [`RequiredKeysOf`](source/required-keys-of.d.ts) - Extract all required keys from the given type.
+- [`HasRequiredKeys`](source/has-required-keys.d.ts) - Create a `true`/`false` type depending on whether the given type has any required fields.
 
 ### JSON
 
diff --git a/source/has-optional-keys.d.ts b/source/has-optional-keys.d.ts
new file mode 100644
index 000000000..597e8aaa1
--- /dev/null
+++ b/source/has-optional-keys.d.ts
@@ -0,0 +1,21 @@
+import {OptionalKeysOf} from './optional-keys-of';
+
+/**
+Creates a type that represents `true` or `false` depending on whether the given type has any optional fields.
+
+This is useful when you want to create an API whose behavior depends on the presence or absence of optional fields.
+
+@example
+```
+import type {HasOptionalKeys, OptionalKeysOf} from 'type-fest';
+
+type UpdateService<Entity extends object> = {
+	removeField: HasOptionalKeys<Entity> extends true
+		? (field: OptionalKeysOf<Entity>) => Promise<void>
+		: never
+}
+```
+
+@category Utilities
+*/
+export type HasOptionalKeys<BaseType extends object> = OptionalKeysOf<BaseType> extends never ? false : true;
diff --git a/source/has-required-keys.d.ts b/source/has-required-keys.d.ts
new file mode 100644
index 000000000..ec9daf368
--- /dev/null
+++ b/source/has-required-keys.d.ts
@@ -0,0 +1,59 @@
+import {RequiredKeysOf} from './required-keys-of';
+
+/**
+Creates a type that represents `true` or `false` depending on whether the given type has any required fields.
+
+This is useful when you want to create an API whose behavior depends on the presence or absence of required fields.
+
+@example
+```
+import type {HasRequiredKeys} from 'type-fest';
+
+type GeneratorOptions<Template extends object> = {
+	prop1: number;
+	prop2: string;
+} & (HasRequiredKeys<Template> extends true
+	? {template: Template}
+	: {template?: Template});
+
+interface Template1 {
+	optionalSubParam?: string;
+}
+
+interface Template2 {
+	requiredSubParam: string;
+}
+
+type Options1 = GeneratorOptions<Template1>;
+type Options2 = GeneratorOptions<Template2>;
+
+const optA: Options1 = {
+	prop1: 0,
+	prop2: 'hi'
+};
+const optB: Options1 = {
+	prop1: 0,
+	prop2: 'hi',
+	template: {}
+};
+const optC: Options1 = {
+	prop1: 0,
+	prop2: 'hi',
+	template: {
+		optionalSubParam: 'optional value'
+	}
+};
+
+const optD: Options2 = {
+	prop1: 0,
+	prop2: 'hi',
+	template: {
+		requiredSubParam: 'required value'
+	}
+};
+
+```
+
+@category Utilities
+*/
+export type HasRequiredKeys<BaseType extends object> = RequiredKeysOf<BaseType> extends never ? false : true;
diff --git a/source/optional-keys-of.d.ts b/source/optional-keys-of.d.ts
new file mode 100644
index 000000000..c1b819306
--- /dev/null
+++ b/source/optional-keys-of.d.ts
@@ -0,0 +1,38 @@
+/**
+Extract all optional keys from the given type.
+
+This is useful when you want to create a new type that contains different type values for the optional keys only.
+
+@example
+```
+import type {OptionalKeysOf, Except} from 'type-fest';
+
+interface User {
+	name: string;
+	surname: string;
+
+	luckyNumber?: number;
+}
+
+const REMOVE_FIELD = Symbol('remove field symbol');
+type UpdateOperation<Entity extends object> = Except<Partial<Entity>, OptionalKeysOf<Entity>> & {
+	[Key in OptionalKeysOf<Entity>]?: Entity[Key] | typeof REMOVE_FIELD;
+};
+
+const update1: UpdateOperation<User> = {
+	name: 'Alice'
+};
+
+const update2: UpdateOperation<User> = {
+	name: 'Bob',
+	luckyNumber: REMOVE_FIELD
+};
+```
+
+@category Utilities
+*/
+export type OptionalKeysOf<BaseType extends object> = Exclude<{
+	[Key in keyof BaseType]: BaseType extends Record<Key, BaseType[Key]>
+		? never
+		: Key
+}[keyof BaseType], undefined>;
diff --git a/source/required-keys-of.d.ts b/source/required-keys-of.d.ts
new file mode 100644
index 000000000..6e66b15a2
--- /dev/null
+++ b/source/required-keys-of.d.ts
@@ -0,0 +1,29 @@
+/**
+Extract all required keys from the given type.
+
+This is useful when you want to create a new type that contains different type values for the required keys only or use the list of keys for validation purposes, etc...
+
+@example
+```
+import type {RequiredKeysOf} from 'type-fest';
+
+declare function createValidation<Entity extends object, Key extends RequiredKeysOf<Entity> = RequiredKeysOf<Entity>>(field: Key, validator: (value: Entity[Key]) => boolean): ValidatorFn;
+
+interface User {
+	name: string;
+	surname: string;
+
+	luckyNumber?: number;
+}
+
+const validator1 = createValidation<User>('name', value => value.length < 25);
+const validator2 = createValidation<User>('surname', value => value.length < 25);
+```
+
+@category Utilities
+*/
+export type RequiredKeysOf<BaseType extends object> = Exclude<{
+	[Key in keyof BaseType]: BaseType extends Record<Key, BaseType[Key]>
+		? Key
+		: never
+}[keyof BaseType], undefined>;
diff --git a/test-d/has-optional-keys.ts b/test-d/has-optional-keys.ts
new file mode 100644
index 000000000..9a5b12aad
--- /dev/null
+++ b/test-d/has-optional-keys.ts
@@ -0,0 +1,29 @@
+import {expectType} from 'tsd';
+import type {HasOptionalKeys} from '../index';
+
+type TestType1 = {
+	a: string;
+	b?: boolean;
+};
+
+type TestType2 = {
+	a?: string;
+	b?: boolean;
+};
+
+type TestType3 = {
+	a: string;
+	b: boolean;
+};
+
+type HasOptionalKeys1 = HasOptionalKeys<TestType1>;
+type HasOptionalKeys2 = HasOptionalKeys<TestType2>;
+type HasOptionalKeys3 = HasOptionalKeys<TestType3>;
+
+declare const test1: HasOptionalKeys1;
+declare const test2: HasOptionalKeys2;
+declare const test3: HasOptionalKeys3;
+
+expectType<true>(test1);
+expectType<true>(test2);
+expectType<false>(test3);
diff --git a/test-d/has-required-keys.ts b/test-d/has-required-keys.ts
new file mode 100644
index 000000000..d88b2a637
--- /dev/null
+++ b/test-d/has-required-keys.ts
@@ -0,0 +1,29 @@
+import {expectType} from 'tsd';
+import type {HasRequiredKeys} from '../index';
+
+type TestType1 = {
+	a: string;
+	b?: boolean;
+};
+
+type TestType2 = {
+	a?: string;
+	b?: boolean;
+};
+
+type TestType3 = {
+	a: string;
+	b: boolean;
+};
+
+type HasRequiredKeys1 = HasRequiredKeys<TestType1>;
+type HasRequiredKeys2 = HasRequiredKeys<TestType2>;
+type HasRequiredKeys3 = HasRequiredKeys<TestType3>;
+
+declare const test1: HasRequiredKeys1;
+declare const test2: HasRequiredKeys2;
+declare const test3: HasRequiredKeys3;
+
+expectType<true>(test1);
+expectType<false>(test2);
+expectType<true>(test3);
diff --git a/test-d/optional-keys-of.ts b/test-d/optional-keys-of.ts
new file mode 100644
index 000000000..182f3fb0e
--- /dev/null
+++ b/test-d/optional-keys-of.ts
@@ -0,0 +1,29 @@
+import {expectType} from 'tsd';
+import type {OptionalKeysOf} from '../index';
+
+type TestType1 = {
+	a: string;
+	b?: boolean;
+};
+
+type TestType2 = {
+	a?: string;
+	b?: boolean;
+};
+
+type TestType3 = {
+	a: string;
+	b: boolean;
+};
+
+type OptionalKeysOf1 = OptionalKeysOf<TestType1>;
+type OptionalKeysOf2 = OptionalKeysOf<TestType2>;
+type OptionalKeysOf3 = OptionalKeysOf<TestType3>;
+
+declare const test1: OptionalKeysOf1;
+declare const test2: OptionalKeysOf2;
+declare const test3: OptionalKeysOf3;
+
+expectType<'b'>(test1);
+expectType<'a' | 'b'>(test2);
+expectType<never>(test3);
diff --git a/test-d/required-keys-of.ts b/test-d/required-keys-of.ts
new file mode 100644
index 000000000..64fd0ed38
--- /dev/null
+++ b/test-d/required-keys-of.ts
@@ -0,0 +1,29 @@
+import {expectType} from 'tsd';
+import type {RequiredKeysOf} from '../index';
+
+type TestType1 = {
+	a: string;
+	b?: boolean;
+};
+
+type TestType2 = {
+	a?: string;
+	b?: boolean;
+};
+
+type TestType3 = {
+	a: string;
+	b: boolean;
+};
+
+type RequiredKeysOf1 = RequiredKeysOf<TestType1>;
+type RequiredKeysOf2 = RequiredKeysOf<TestType2>;
+type RequiredKeysOf3 = RequiredKeysOf<TestType3>;
+
+declare const test1: RequiredKeysOf1;
+declare const test2: RequiredKeysOf2;
+declare const test3: RequiredKeysOf3;
+
+expectType<'a'>(test1);
+expectType<never>(test2);
+expectType<'a' | 'b'>(test3);