Improve support for @preserve when compacting.

Author: gkellogg

lib/compact.js

@@ -216,6 +216,21 @@ api.compact = ({
         continue;
       }
 
+      if(expandedProperty === '@preserve') {
+        // compact using activeProperty
+        const compactedValue = api.compact({
+          activeCtx,
+          activeProperty,
+          element: expandedValue,
+          options,
+          compactionMap});
+
+        if(!(_isArray(compactedValue) && compactedValue.length === 0)) {
+          _addValue(rval, expandedProperty, compactedValue);
+        }
+        continue;
+      }
+
       // handle @index property
       if(expandedProperty === '@index') {
         // drop @index if inside an @index container
@@ -511,6 +526,11 @@ api.compactIri = ({
       containers.push('@index', '@index@set');
     }
 
+    // if value is a preserve object, use its value
+    if(_isObject(value) && '@preserve' in value) {
+      value = value['@preserve'][0];
+    }
+
     // prefer most specific container including @graph, prefering @set variations
     if(_isGraph(value)) {
       // favor indexmap if the graph is indexed