feat(core/extensions): add extensions API

[sidvishnoi]

Closes https://github.com/w3c/respec/issues/1976

Support 4 extension hooks: before-all (preProcess), after-all (postProcess), before-markdown and after-markdown.
Support two extension utils: showError and showWarning.

TODO:

• investigate more hooks to start with
• investigate more utils to start with
• write tests

[marcoscaceres]

I think this is still risky... I'd prefer people just user preProcess and postProcess. Hooking into anything makes things fragile, as we've seen.

[sidvishnoi]

Hooking into anything makes things fragile, as we've seen.

I understand the concern, but I think the previous hooks were fragile as we exposed them everywhere without much thought. If we limit what we expose, we can have a much more powerful and stable API. Also, when we think we need to remove some hook, we can deprecate them (as a breaking change), as we know what's exposed where.

As an example, if you look at respec.org/docs/src.html#L29-L36 (and respec.org/docs/src.html#L98-L128 in particular), you'll see what hacks I had to make to overcome the limitations of preProcess and postProcess 😅

[marcoscaceres]

As an example, if you look at respec.org/docs/src.html#L29-L36 (and respec.org/docs/src.html#L98-L128 in particular), you'll see what hacks I had to make to overcome the limitations of preProcess and postProcess 😅

I see... what's a rough sketch of what that would look like with the new api?

[saschanaz]

Looks cool. Which specs would use the markdown hooks?

[sidvishnoi]

Haven't tested real specs that would like to use after-markdown hook, but respec.org/docs/src.html#L115-L125 could use it like this:

diff: docs/src.html

diff --git a/static/docs/src.html b/static/docs/src.html
index 9c5375d..03418a3 100644
--- a/static/docs/src.html
+++ b/static/docs/src.html
@@ -34,6 +34,26 @@
           postProcessEnhance,
           cleanup,
         ],
+        extensions: [
+          {
+            name: "note-advisement",
+            on: "after-markdown",
+            run() {
+              for (const p of document.querySelectorAll("p")) {
+                if (p.firstElementChild?.localName === "strong") {
+                  const text = p.firstElementChild.textContent.trimStart();
+                  if (text.startsWith("Note:")) {
+                    p.classList.add("note");
+                    p.firstElementChild.remove();
+                  } else if (text.startsWith("Warning:")) {
+                    p.classList.add("advisement");
+                    p.firstElementChild.remove();
+                  }
+                }
+              }
+            },
+          },
+        ],
         logos: [
           {
             src: "/respec-logo.png",
@@ -112,18 +132,6 @@
           .replace(/\`\|(\w+)/g, `\`\\|${ZERO_WIDTH_SPACE}$1`)
           .replace(/(\w+)\|\`/g, `$1${ZERO_WIDTH_SPACE}\\|\``);
 
-        // Add .note and .advisement classes based on line prefix
-        content = content
-          .split("\n")
-          .map(line => {
-            if (/^.{0,5}\s*Warning:/.test(line))
-              return `<div class="advisement">\n\n${line}</div>`;
-            if (/^.{0,5}\s*Note:/.test(line))
-              return `<div class="note">\n\n${line}</div>`;
-            return line;
-          })
-          .join("\n");
-
         return content;
       }

With a potential after-inline-processing hook (which runs before linker), docs/src.html#L99-L113 will simplify a lot.

Similarly, if we could run fixLinks(), say, on: "after-linker", we would get access to local-refs-exist linker in a better way. Currently linters run after doc.respec.ready, which means we can miss linter warnings in respec2html (to workaround this, we wait for 1 second after respec.ready which is problematic in itself).

Will test with some other real specs with potential hooks and update here.

(PS: Missed notifications as I accidentally unsubscribed from this PR).

Edits:

• Many ARIA/A11Y, JSON-LD and other specs could benefit from after-linker event. They currently use pubsubhub.end["core/link-to-dfn"]. Maybe we can expose after-local-linker and after-external-linker (need to be careful of course).
• A lot of specs could use utils.showError() and utils.showWarning(). Though, they could as well be added to preProcess,postProcess, and isn't an endorsement for new extension API.

[marcoscaceres]

I still think this is going to be extremely footgunny.

Currently linters run after doc.respec.ready, which means we can miss linter warnings in respec2html (to workaround this, we wait for 1 second after respec.ready which is problematic in itself).

Yeah, we should change the linters back into normal plugins as you suggested elsewhere.