Quarto extension works in example but not in my project

I have created a Quarto extension to remove all occurrences of ".html" from the links. The Lua script is as follows:

function Link(el)
    local str = el.target
    local result = str:gsub("(.-)%.html(.-)", "%1%2")
    el.target = result
    return el
end

It works perfectly in the test example created within the extension. However, when I include it in my Quarto book project, it doesn't work.

The extension is being called correctly because I replaced the code with another one to format tags with italics, and upon rendering, it worked. But when I put the above code back, it doesn't work. All links ( tags) still have ".html."

I also tried changing the order so that my filter runs after the Quarto’s built-in filters (as below), but it still didn't work.

filters:
  - lightbox
  - quarto
  - strip-dot-html-off

Any ideas?

I don't see anything wrong with the string replacement code, as executing ("foo-bar.html-some-more"):gsub("(.-)%.html(.-)", "%1%2") returns foo-bar-some-more as expected. You haven't provided a single example as what kind of URLs you expect to modify, so maybe the issue is with something really simple (for example, using .htm extension instead of .html).

I'd check if the code works outside of your environment in a regular Lua interpreter and also check if you get the expected result if you set the result value manually to whatever result you expect from gsub (just to make sure that the rest of the processing happens as you envision it).