fix: handle cleanUrls with subfolders when using a trailing slash

[rigor789]

The main change is that when using with-subfolders the page should always be generated as /page_name.md -> /page_name_index.md (since it's generated as /page_name/index.html

On the client side, whether or not there's a trailing slash, it resolves to the _index file when using cleanUrls.with-subfolders. Still need to check if this works/breaks without-subfolders.

Also need to clean up, there's duplicated logic now in various places.

There is one thing to note about relative links, since they are resolved by the browser, they look for the last / in the url, and resolve them relative to that. So depending on how the host redirects and handles trailing slashes, relative URLs might break.

For example, /pageA.md would produce the following files:

mode	file path
disabled	/pageA.html
without-subfolders	/pageA.html
with-subfolders	/pageA/index.html

And these depending on the hosting can end up with the following urls in the browser (excluding what vue-router would normally produce for internal links):

/pageA.html	/pageA/index.html
/pageA	/pageA
/pageA/	/pageA/
/pageA.html	/pageA/index.html

And depending on the url, a ./pageB link would resolve like this

URL	Resolved
/pageA	✅ /pageB
/pageA/	❌ /pageA/pageB
/pageA.html	✅ /pageB
/pageA/index.html	❌ /pageA/pageB

So depending on the hosting, relative URLs might break, even with cleanUrls disabled.

/cc @brc-dd

fixes #1442.

[brc-dd]

Dev appears to be broken after this if we have some path like /foo/index.md (without cleanUrls set).

[rigor789]

Dev appears to be broken after this if we have some path like /foo/index.md (without cleanUrls set).

This seems to fix it:

What is the expected behavior when you have cleanUrls enabled, and have a /guide/markdown.md - then open the following urls:

• /guide/markdown
• /guide/markdown/

(note, I'll push up the above change, just wanted to clarify if it's working as intended, or we need additional logic somewhere)

[brc-dd]

/guide/markdown --> /guide/markdown.md

/guide/markdown/ --> /guide/markdown.md or /guide/markdown/index.md whichever exists if (cleanUrls === 'with-subfolders') else /guide/markdown/index.md

[rigor789]

/guide/markdown --> /guide/markdown.md

/guide/markdown/ --> /guide/markdown.md or /guide/markdown/index.md whichever exists if (cleanUrls === 'with-subfolders') else /guide/markdown/index.md

Ok, then we need some additional logic, with the above it works as before for the most part in dev mode:

• /guide/markdown -> /guide/markdown.md
• /guide/markdown/ -> /guide/markdown/index.md

[brc-dd]

Yeah, push it anyway though. If everything is working for the other two options and we can fix build properly for with-subfolders + trailing-slash, then that's fair too.