Add visual hint in support information re. differential update

In Support pane's troubleshooting information, a delta sign will
be added to list update information when the list was last updated
through differential update.

src/js/assets.js

@@ -985,6 +985,17 @@ assets.get = async function(assetKey, options = {}) {
                 silent: options.silent === true,
             });
             registerAssetSource(assetKey, { error: undefined });
+            if ( assetDetails.content === 'filters' ) {
+                const metadata = extractMetadataFromList(details.content, [
+                    'Last-Modified',
+                    'Expires',
+                    'Diff-Name',
+                    'Diff-Path',
+                    'Diff-Expires',
+                ]);
+                metadata.diffUpdated = undefined;
+                assetCacheSetDetails(assetKey, metadata);
+            }
         }
         return reportBack(details.content, contentURL);
     }
@@ -1057,6 +1068,7 @@ async function getRemote(assetKey, options = {}) {
                 'Diff-Path',
                 'Diff-Expires',
             ]);
+            metadata.diffUpdated = undefined;
             assetCacheSetDetails(assetKey, metadata);
         }
 
@@ -1113,6 +1125,9 @@ assets.metadata = async function() {
             const obsoleteAfter = cacheEntry.writeTime + getUpdateAfterTime(assetKey);
             assetEntry.obsolete = obsoleteAfter < now;
             assetEntry.remoteURL = cacheEntry.remoteURL;
+            if ( cacheEntry.diffUpdated ) {
+                assetEntry.diffUpdated = cacheEntry.diffUpdated;
+            }
         } else if (
             assetEntry.contentURL &&
             assetEntry.contentURL.length !== 0
@@ -1273,6 +1288,7 @@ async function diffUpdater() {
                     content: data.text,
                     resourceTime: metadata.lastModified || 0,
                 });
+                metadata.diffUpdated = true;
                 assetCacheSetDetails(data.assetKey, metadata);
                 updaterUpdated.push(data.assetKey);
             } else if ( data.error ) {

src/js/messaging.js

@@ -1447,7 +1447,9 @@ const getSupportData = async function() {
 
     const now = Date.now();
 
-    const formatDelayFromNow = time => {
+    const formatDelayFromNow = list => {
+        const time = list.writeTime;
+        if ( typeof time !== 'number' || time === 0 ) { return 'never'; }
         if ( (time || 0) === 0 ) { return '?'; }
         const delayInSec = (now - time) / 1000;
         const days = (delayInSec / 86400) | 0;
@@ -1458,7 +1460,9 @@ const getSupportData = async function() {
         if ( hours > 0 ) { parts.push(`${hours}h`); }
         if ( minutes > 0 ) { parts.push(`${minutes}m`); }
         if ( parts.length === 0 ) { parts.push('now'); }
-        return parts.join('.');
+        const out = parts.join('.');
+        if ( list.diffUpdated ) { return `${out} Δ`; }
+        return out;
     };
 
     const lists = µb.availableFilterLists;
@@ -1475,11 +1479,7 @@ const getSupportData = async function() {
             if ( typeof list.entryCount === 'number' ) {
                 listDetails.push(`${list.entryCount}-${list.entryCount-list.entryUsedCount}`);
             }
-            if ( typeof list.writeTime !== 'number' || list.writeTime === 0 ) {
-                listDetails.push('never');
-            } else {
-                listDetails.push(formatDelayFromNow(list.writeTime));
-            }
+            listDetails.push(formatDelayFromNow(list));
         }
         if ( list.isDefault || listKey === µb.userFiltersPath ) {
             if ( used ) {