From fb4c71c8230c76c6105ebf364cc8cba13bcf3d55 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9s=20Correa=20Casablanca?=
 <castarco@coderspirit.xyz>
Date: Thu, 21 Dec 2023 10:45:35 +0100
Subject: [PATCH] feat: refine .split() return type

This change still requires to fix the tests.

Signed-off-by: Andres Correa Casablanca <castarco@coderspirit.xyz>
---
 src/lib/es2015.symbol.wellknown.d.ts | 28 ++++++++++++++++++++++++++++
 src/lib/es5.d.ts                     |  5 +++++
 2 files changed, 33 insertions(+)

diff --git a/src/lib/es2015.symbol.wellknown.d.ts b/src/lib/es2015.symbol.wellknown.d.ts
index cf6ccef52b89f..a25eab0409255 100644
--- a/src/lib/es2015.symbol.wellknown.d.ts
+++ b/src/lib/es2015.symbol.wellknown.d.ts
@@ -162,6 +162,10 @@ interface PromiseConstructor {
     readonly [Symbol.species]: PromiseConstructor;
 }
 
+// TODO: inline at usage site
+type NonEmptyStringParam<S extends string> = S extends '' ? never : S;
+type NonZeroNumberParam<N extends number> = N extends 0 ? never : N;
+
 interface RegExp {
     /**
      * Matches a string with this regular expression, and returns an array containing the results of
@@ -207,6 +211,11 @@ interface RegExp {
      * @param limit if not undefined, the output array is truncated so that it contains no more
      * than 'limit' elements.
      */
+    [Symbol.split]<S extends string>(string: NonEmptyStringParam<S>): [string, ...string[]];
+    [Symbol.split]<S extends string, N extends number>(
+        string: NonEmptyStringParam<S>,
+        limit: NonZeroNumberParam<N>
+    ): [string, ...string[]];
     [Symbol.split](string: string, limit?: number): string[];
 }
 
@@ -247,6 +256,25 @@ interface String {
      * @param splitter An object that can split a string.
      * @param limit A value used to limit the number of elements returned in the array.
      */
+    split(
+        splitter: {
+            [Symbol.split]<S extends string>(string: NonEmptyStringParam<S>): [string, ...string[]];
+            [Symbol.split]<S extends string, NN extends number>(
+                string: NonEmptyStringParam<S>,
+                limit: NonZeroNumberParam<NN>
+            ): [string, ...string[]];
+        }
+    ): [string, ...string[]];
+    split<N extends number>(
+        splitter: {
+            [Symbol.split]<S extends string>(string: NonEmptyStringParam<S>): [string, ...string[]];
+            [Symbol.split]<S extends string, NN extends number>(
+                string: NonEmptyStringParam<S>,
+                limit: NonZeroNumberParam<NN>
+            ): [string, ...string[]];
+        },
+        limit: NonZeroNumberParam<N>
+    ): [string, ...string[]];
     split(splitter: { [Symbol.split](string: string, limit?: number): string[]; }, limit?: number): string[];
 }
 
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index f3df23047022d..4d8d0080d3652 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -470,6 +470,11 @@ interface String {
      * @param separator A string that identifies character or characters to use in separating the string. If omitted, a single-element array containing the entire string is returned.
      * @param limit A value used to limit the number of elements returned in the array.
      */
+    split<S extends string>(separator: NonEmptyStringParam<S>): [string, ...string[]];
+    split<S extends string, N extends number>(
+        separator: NonEmptyStringParam<S>,
+        limit: NonZeroNumberParam<N>
+    ): [string, ...string[]];
     split(separator: string | RegExp, limit?: number): string[];
 
     /**