Improve the speed of parsing markdown input five times

[Witiko]

This PR makes the following changes:

• Construct faster parsers.punctuation using prefix trees.

This change will close #474.

Following a successful CI run, this PR should repeat the experiment from #474 to see if this has sufficiently improved speed the speed of the Markdown package. If so, then we should also make the following changes:

• Test that the markdown-cli command finishes under 1 second in the CI.

If not, this PR should continue by making the following changes:

• Precompile parsers.punctuation to a separate Lua file.
• Remove dependency on UnicodeData.txt.

These changes will close #458 and continue #402.

[Yggdrasil128]

I took a closer look at the depth_first_search function, and while I can't pinpoint exactly where it goes wrong, I wrote a simpler, recursive alternative that seems to work for me.

local function depth_first_search(node, path, visit, leave)
  visit(node, path)
  for label, child in pairs(node) do
    if type(child) == "table" then
      depth_first_search(child, path .. label, visit, leave)
    else
      visit(child, path)
      leave(child, path)
    end
  end
  leave(node, path)
end

It needs to be called with an empty string as its second parameter:
depth_first_search(prefix_tree, "", function ...

Since I can't edit this PR directly, feel free to commit this change, and let's see what the CI tests have to say about it.

[Witiko]

Thanks, simpler is better. I will test out your code on Monday at the latest. Perhaps we can get rid of the leave() call for leaf nodes as well, since we don't need it.

[Witiko]

Since I can't edit this PR directly, feel free to commit this change, and let's see what the CI tests have to say about it.

As far as I know, you can create your own fork of this repository and open a second-order PR that would merge into the branch feat/improve-speed from this PR.

However, you don't need to: With your permission, I will use your code from #482 (comment) and commit it with a by-line that states that it is your contribution. This way, GitHub will register the commit as your contribution as well.

[Witiko]

Following a successful CI run, this PR should repeat the experiment from #474 to see if this has sufficiently improved speed the speed of the Markdown package. If so, then we should also make the following changes:

• Test that the markdown-cli command finishes under 1 second in the CI.

I verified on my Dell G5 15 notebook that after commit 6eff522 from this PR, the markdown-cli command finishes under 1 second:

$ docker run --rm -i ghcr.io/witiko/markdown:3.7.0-dev.1-7-g6eff5224-latest-minimal-no_docs bash -c 'time markdown-cli <<< foo'

\markdownRendererDocumentBegin
foo\markdownRendererDocumentEnd

real	0m0.258s
user	0m0.204s
sys	0m0.053s

In commit 3e8fe8a, I added a test that the markdown-cli command finishes under 1 second to the CI, so that we can catch similar speed regressions in the future.

If not, this PR should continue by making the following changes:

• Precompile parsers.punctuation to a separate Lua file.
• Remove dependency on UnicodeData.txt.

These changes will close #458 and continue #402.

Since updating the parser has been sufficient for fixing the speed issue, I postponed the removal of the dependency on UnicodeData.txt to the next release, see also ticket #486.