Further improve wikilink handling

[thomas-zahner]

I was trying out this feature and I wrote these notes about things that I thought were unexpected:

• when a link is not found, the error message is long because it repeats the message twice. it also repeats the base directory twice and makes the invalid path /home/x/progs/lychee/fixtures/home/x/progs/lychee/fixtures/Doesn't exist.md - i don't know whether this is intentional.

     [ERROR] file:///home/x/progs/lychee/fixtures/Doesn't%20exist.md |
     Wikilink file:///home/x/progs/lychee/fixtures/Doesn't%20exist.md not found at /home/x/progs/lychee/fixtures/home/x/progs/lychee/fixtures/Doesn't exist.md:
     WikiLink file:///home/x/progs/lychee/fixtures/Doesn't%20exist.md could not be found at /home/x/progs/lychee/fixtures/home/x/progs/lychee/fixtures/Doesn't exist.md
  

• to specify the indexing folder, i think --root-dir would've made more sense, or it could even be based off the inputs provided through command line. but it does work with --base-url so it's nbd.

• wikilinks, if enabled, are tried on all file:// links, including absolute links. for instance, a link like [a](file:///tmp/Usage.md) could succeed when /tmp/Usage.md doesn't exist and a Usage.md exists inside the base folder. maybe it should be limited to relative links which only have filenames.

• the wikilink feature does its own directory walk. this is different from other directory walks in lychee and won't respect options like gitignore or hidden files. actively ignoring symlinks is also weird.

• wikilinks always ignore fragments? i can't see anything in the obsidian help page which says they should be disregarded. the unit tests also seem to say that they should be resolved (unless "resolve" is meant as "ignore"). i note that if fragments were to be processed, the current markdown extractor would have to be changed. atm, it makes anchors using #kebab-case which is different to what obsidian uses in wikilinks.

Aside from the first point, I think these points are kinda hard to fix or don't necessarily need fixing. Just things to think about.

Originally posted by @katrinafyi in #1799 (comment)

[thomas-zahner]

@katrinafyi Thank you for paying so much attention to the change. I agree with your points. I've created this issue so that we don't just forget about the comment on the closed PR. I've reordered the bullet points by how much effort would be required to address them. (of course this is just an estimate/rough feeling)

I'm definitely in favour of addressing the first point. We could further discuss the other points.

[katrinafyi]

I want to do the second point because if we do that, then we can get rid of Base::Local which is somewhat buggy. #1896

Or, I guess I can remove Base::Local and change the wiki links to use a file:// base instead. That would be the minimal change.

[thomas-zahner]

Cool, that's greatly appreciated. I feel like your the expert on that topic anyways :)