fix(live-preview): encode query string url (#7635)

## Description

Fixes #7529 

- [x] I have read and understand the
[CONTRIBUTING.md](https://github.com/payloadcms/payload/blob/main/CONTRIBUTING.md)
document in this repository.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] Existing test suite passes locally with my changes

packages/live-preview/src/mergeData.ts

@@ -71,7 +71,9 @@ export const mergeData = async <T>(args: {
       try {
         res = await requestHandler({
           apiPath: apiRoute || '/api',
-          endpoint: `${collection}?depth=${depth}&where[id][in]=${Array.from(ids).join(',')}`,
+          endpoint: encodeURI(
+            `${collection}?depth=${depth}&where[id][in]=${Array.from(ids).join(',')}`,
+          ),
           serverURL,
         }).then((res) => res.json())
 

test/live-preview/int.spec.ts

@@ -31,6 +31,7 @@ describe('Collections - Live Preview', () => {
   let serverURL
 
   let testPost: Post
+  let testPostTwo: Post
   let tenant: Tenant
   let media: Media
 
@@ -54,6 +55,15 @@ describe('Collections - Live Preview', () => {
       },
     })
 
+    testPostTwo = await payload.create({
+      collection: postsSlug,
+      data: {
+        slug: 'post-2',
+        title: 'Test Post 2',
+        tenant: tenant.id,
+      },
+    })
+
     // Create image
     const filePath = path.resolve(dirname, './seed/image-1.jpg')
     const file = await getFileByPath(filePath)
@@ -1280,4 +1290,85 @@ describe('Collections - Live Preview', () => {
     expect(merge3.layout).toHaveLength(0)
     expect(merge3._numberOfRequests).toEqual(0)
   })
+
+  it('properly encodes URLs in requests', async () => {
+    const initialData: Partial<Page> = {
+      title: 'Test Page',
+    }
+
+    let capturedEndpoint: string | undefined
+
+    const customRequestHandler = async ({ apiPath, endpoint, serverURL }) => {
+      capturedEndpoint = `${serverURL}${apiPath}/${endpoint}`
+
+      const mockResponse = {
+        ok: true,
+        status: 200,
+        headers: new Headers({ 'Content-Type': 'application/json' }),
+        json: () => ({
+          docs: [
+            {
+              id: testPost.id,
+              slug: 'post-1',
+              tenant: { id: 'tenant-id', title: 'Tenant 1' },
+              title: 'Test Post',
+              createdAt: new Date().toISOString(),
+              updatedAt: new Date().toISOString(),
+            },
+            {
+              id: testPostTwo.id,
+              slug: 'post-2',
+              tenant: { id: 'tenant-id', title: 'Tenant 1' },
+              title: 'Test Post 2',
+              createdAt: new Date().toISOString(),
+              updatedAt: new Date().toISOString(),
+            },
+          ],
+        }),
+      }
+
+      return Promise.resolve(mockResponse as unknown as Response)
+    }
+
+    const mergedData = await mergeData({
+      depth: 1,
+      fieldSchema: schemaJSON,
+      incomingData: {
+        ...initialData,
+        relationshipPolyHasMany: [
+          { value: testPost.id, relationTo: postsSlug },
+          { value: testPostTwo.id, relationTo: postsSlug },
+        ],
+      },
+      initialData,
+      serverURL,
+      returnNumberOfRequests: true,
+      collectionPopulationRequestHandler: customRequestHandler,
+    })
+
+    expect(mergedData.relationshipPolyHasMany).toMatchObject([
+      {
+        value: {
+          id: testPost.id,
+          slug: 'post-1',
+          title: 'Test Post',
+        },
+        relationTo: postsSlug,
+      },
+      {
+        value: {
+          id: testPostTwo.id,
+          slug: 'post-2',
+          title: 'Test Post 2',
+        },
+        relationTo: postsSlug,
+      },
+    ])
+
+    // Verify that the request was made to the properly encoded URL
+    // Without encodeURI wrapper the request URL - would receive string: "undefined/api/posts?depth=1&where[id][in]=66ba7ab6a60a945d10c8b976,66ba7ab6a60a945d10c8b979
+    expect(capturedEndpoint).toContain(
+      encodeURI(`posts?depth=1&where[id][in]=${testPost.id},${testPostTwo.id}`),
+    )
+  })
 })