Soupault 3.2.0 release: persistent variables for plugins, checking for selector matches, and more

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Soupault 3.2.0, is available for download from my own server and from GitHub releases. It features variables that are persistent between plugin runs, new functions for checking whether an HTML element matches a CSS selector, and some bug fixes.

New features

Persistent variables

Historically, plugins would run from a clean state on every page. All built-in variables would be injected into the Lua interpreter environment every time a plugin ran. When plugin code finished running, all variables it created or modified would be destroyed.

Most of the time, that’s a good thing since it prevents unintended action at a distance. However, it also makes certain use cases impossible.

For example, consider the reading time plugin. It can calculate the estimated reading time for a page based on its word count and insert it into the page. What if you want to calculate the total reading time of all pages on your site though?

You could exploit the fact that soupault processes all “content” pages before it starts processing index pages, so you could be sure that by the time it gets to index pages, the total content reading time is already calculated.

So you could make it sum up the reading times of all pages in an accumulator variable, then make it insert it into a certain element, e.g. span#reading-time. Then add <span id="total-reading-time"> to your site/index.html and show the visitors how much is there to read.

That is, if you had a way to keep the accumulator variable value. Well, now you do have a way to do that: the new persistent_data built-in variable.

When soupault loads a plugin, it creates an empty Lua table. When a plugin runs, it injects that table into plugin’s environment as a global variable named persistent_data. When that plugin finishes running, soupault extracts the value of that global and stores it until the next plugin run.

Thus you can easily stash data for later use now. You can use that to either avoid running expensive operations more than once, or to gather data from multiple pages.

For example, you could add this to the end of the reading-time.lua plugin to show the total reading time in the site build log:

if not persistent_data["time_total"] then
    persistent_data["time_total"] = reading_time
else
    persistent_data["time_total"] = persistent_data["time_total"] + reading_time
end

Log.info("Reading time total: " .. persistent_data["time_total"])

Checking if elements match selectors

Most of the time, HTML.select and friends is all you need to find HTML elements you want to process. However, sometimes you may want to select elements and then decide what exactly to do with each of them depending on its attributes.

For example, soupault 3.1.0 added ignore_heading_selectors option for the ToC widget that allows excluding some headings from the ToC. If you want to add a heading to the page but don’t want it in its ToC, you can add ignore_headings_selectors = [".notoc"] in your soupault.toml and then add something like <h1 class="notoc">This heading will not be in the ToC</h1> to your page.

Now plugin writers can implement similar logic in their own code using the new HTML.matches_selector and HTML.matches_any_of_selectors functions.

Specifying minimum soupault version in the config

Websites whose source is open to community contributions sometimes have a problem with those contributors trying to build them with wrong build tool versions and getting errors.

To let people with outdated soupault versions receive an unambiguous error message, you can add the minimum supported version to your config:

[settings]
  soupault_version = "3.2.0"

Then if anyone tries to run an older version on that config, soupault will show a message about minimum supported version and exit.

Bug fixes

Soupault now correctly quotes page file paths before passing them to page preprocessors, so page names with spaces and other special characters are processed correctly now.