Throttle filename check (#1136)

GitHub did not like the switch to Node.js v20 in jobs. Build fails at the
determine filename step, without much info on top of a "fetch failed".
This update forces throttling on the fetch requests in the hope that this
can improve things.

It also logs specs being processed to provide more clues about what the problem
might be.

src/build-index.js

@@ -22,6 +22,7 @@ const determineTestPath = require("./determine-testpath.js");
 const extractPages = require("./extract-pages.js");
 const fetchInfo = require("./fetch-info.js");
 const fetchGroups = require("./fetch-groups.js");
+const throttle = require("./throttle");
 const githubToken = (_ => {
   try {
     return require("../config.json").GH_TOKEN;
@@ -306,7 +307,8 @@ async function runPages(index) {
 }
 
 
-async function runFilename(index, { previousIndex }) {
+async function runFilename(index, { previousIndex, log }) {
+
   // Use previous filename info when it cannot be determined (this usually means
   // that there was a transient network error)
   async function determineSpecFilename(spec, type) {
@@ -319,20 +321,22 @@ async function runFilename(index, { previousIndex }) {
     return previous ? previous[type].filename : null;
   }
 
-  return Promise.all(
-    index.map(async spec => {
-      spec.nightly.filename = await determineSpecFilename(spec, "nightly");
-      if (spec.release) {
-        spec.release.filename = await determineSpecFilename(spec, "release");
-      }
+  async function checkSpec(spec) {
+    log(`- find filenames for ${spec.shortname}`);
+    spec.nightly.filename = await determineSpecFilename(spec, "nightly");
+    if (spec.release) {
+      spec.release.filename = await determineSpecFilename(spec, "release");
+    }
 
-      // Sleep a bit as draft CSS WG server does not seem to like receiving too
-      // many requests in a row.
-      await sleep(50);
+    // Sleep a bit as draft CSS WG server does not seem to like receiving too
+    // many requests in a row.
+    await sleep(50);
 
-      return spec;
-    })
-  );
+    return spec;
+  }
+
+  const throttledCheck = throttle(checkSpec, 2);
+  return Promise.all(index.map(throttledCheck));
 }