From eda69ff924a621e499d31cbc590993a32ddb48d3 Mon Sep 17 00:00:00 2001
From: Szymon Marczak <36894700+szmarczak@users.noreply.github.com>
Date: Wed, 4 Aug 2021 22:58:45 +0200
Subject: [PATCH] Require `url` to be an instance of `URL` when paginating

Fixes #1818
---
 documentation/4-pagination.md |  4 ++++
 source/core/options.ts        |  2 +-
 source/create.ts              |  2 ++
 test/pagination.ts            | 16 +++++++++++++++-
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/documentation/4-pagination.md b/documentation/4-pagination.md
index 32459bf32..f2a153703 100644
--- a/documentation/4-pagination.md
+++ b/documentation/4-pagination.md
@@ -129,6 +129,10 @@ It should return an object representing Got options pointing to the next page. I
 The options are merged automatically with the previous request.\
 Therefore the options returned by `pagination.paginate(…)` must reflect changes only.
 
+**Note:**
+> - The `url` option (if set) accepts **only** a [`URL`](https://developer.mozilla.org/en-US/docs/Web/API/URL) instance.\
+>   This prevents `prefixUrl` ambiguity. In order to use a relative URL string, merge it via `new URL(relativeUrl, response.url)`.
+
 #### `filter`
 
 **Type: `Function`**\
diff --git a/source/core/options.ts b/source/core/options.ts
index 3f24f30d7..a10ec22e5 100644
--- a/source/core/options.ts
+++ b/source/core/options.ts
@@ -692,7 +692,7 @@ const defaultInternals: Options['_internals'] = {
 
 			if (next) {
 				return {
-					url: new URL(next.reference, response.requestUrl),
+					url: new URL(next.reference, response.url),
 				};
 			}
 
diff --git a/source/create.ts b/source/create.ts
index fadb50bfb..398d947ff 100644
--- a/source/create.ts
+++ b/source/create.ts
@@ -201,6 +201,8 @@ const create = (defaults: InstanceDefaults): Got => {
 			} else {
 				normalizedOptions.merge(optionsToMerge);
 
+				assert.any([is.urlInstance, is.undefined], optionsToMerge.url);
+
 				if (optionsToMerge.url !== undefined) {
 					normalizedOptions.prefixUrl = '';
 					normalizedOptions.url = optionsToMerge.url;
diff --git a/test/pagination.ts b/test/pagination.ts
index 9fd4e6fdd..a627100a7 100644
--- a/test/pagination.ts
+++ b/test/pagination.ts
@@ -575,7 +575,7 @@ test('next url in json response', withServer, async (t, server, got) => {
 				}
 
 				return {
-					url: next,
+					url: new URL(next),
 					prefixUrl: '',
 					searchParams: undefined,
 				};
@@ -728,6 +728,20 @@ test('retrieves all elements - relative url', withServer, async (t, server, got)
 	t.deepEqual(result, [1, 2]);
 });
 
+test('throws if url is not an instance of URL', withServer, async (t, server, got) => {
+	attachHandler(server, 2);
+
+	await t.throwsAsync(got.paginate.all<number>('', {
+		pagination: {
+			paginate: () => ({
+				url: 'not an instance of URL',
+			}),
+		},
+	}), {
+		instanceOf: TypeError,
+	});
+});
+
 test('throws when transform does not return an array', withServer, async (t, server) => {
 	server.get('/', (_request, response) => {
 		response.end(JSON.stringify(''));