Write a list of used icons to the /interim directory

So that the icons can be more timely pre-fetched/included by consumer applications like iD

Author: tyrasd

lib/build.js

@@ -146,6 +146,9 @@ function processData(options, type) {
   translationsForYaml[sourceLocale] = { presets: translations };
   fs.writeFileSync(interimDir + '/source_strings.yaml', translationsToYAML(translationsForYaml));
 
+  let icons = generateIconsList(presets, fields);
+  fs.writeFileSync(interimDir + '/icons.json', JSON.stringify(icons, null, 4));
+
   if (type !== 'build-dist') return;
 
   const doFetchTranslations = options.translOrgId && options.translProjectId;
@@ -680,6 +683,15 @@ function generateTaginfo(presets, fields, deprecated, discarded, tstrings, proje
   return taginfo;
 }
 
+function generateIconsList(presets, fields) {
+  const icons = {};
+  [
+    ...Object.values(presets).map(p => p.icon).filter(Boolean),
+    ...Object.values(fields).flatMap(f => Object.values(f.icons || {}))
+  ].forEach(icon => icons[icon] = true)
+  return Object.keys(icons).sort();
+}
+
 
 function validateCategoryPresets(categories, presets) {
   Object.keys(categories).forEach(id => {