Improve rewrites documentation

[Nutlope]

This is a PR to update the rewrites documentation. This is after struggling to get rewrites to work with trailingSlash for a customer as this wasn't documented. The main culprit was the :path* wildcard not catching trailing slashes. The changes made to for this commit were:

• Added example for redirecting to blog and docs
• Expanded on original code example for external URLs
• Added code example for using rewrites with trailingSlash

Context

For a reproduction of the :path* wildcard not catching trailing slashes as expected, see below. Click on the "not working" demo link below, navigate to a specific blog post, then reload the page. It will redirect infinitely.

• Not working demo of main repo with :path*
• Working demo of main repo with :path(.+)

If you want to take a look at the code, here are the full repos. They both have trailingSlash: true:

• not working main repo
• working main repo
• blog repo

[timneutkens]

This seems like a bug, wdyt @ijjk 🤔

Suggested change

	source: '/blog/:path(.+)',
	source: '/blog/:path(.+)',

[Nutlope]

For context, I discovered that :path* doesn't catch trailing slashes so Davis came up with a wildcard expression that does.

[ijjk]

We should be handling the trailing slash here

next.js/packages/next/lib/load-custom-routes.ts

Lines 72 to 73 in 1a0d149

	// we add an optional trailing slash at the end for easier
	// configuring between trailingSlash: true/false

can you provide a reproduction where this isn't working?

[Nutlope]

@ijjk yep! Here's a reproduction. Click on the "not working" demo link below, navigate to a specific blog post, then reload the page. It will redirect infinitely.

• Not working demo of main repo with :path*
• Working demo of main repo with :path(.+)

If you want to take a look at the code, here are the full repos. They both have trailingSlash: true:

• not working main repo
• working main repo
• blog repo

[ijjk]

Oh it looks like the destination for this rewrite needs to end with a trailingSlash to match the other deployments expectation e.g. does changing it to the below resolve this?

destination: `${BLOG_URL}/blog/:path*/`

[ijjk]

I think documenting that the destination for a rewrite needs to honor the external destination's trailingSlash config makes sense

[Nutlope]

Good catch, it works when you include a trailing slash for both the source and destination like this.

{
  source: "/blog/:path*/",
  destination: `${BLOG_URL}/blog/:path*/`,
},

I'm assuming this is better than the :path(.+) wildcard so I just updated the PR to reflect that.