Fix term mapping of @reverse.

Author: davidlehn

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Match spec error code "invalid context entry" vs "invalid context member".
 - Keywords may not be used as prefixes.
 - Handle term definition on `@type` with empty map.
+- Term mapping of `@reverse`.
 
 ### Changed
 - Keep term definitions mapping to null so they may be protected.

lib/context.js

@@ -506,6 +506,10 @@ api.createTermDefinition = ({
         'jsonld.SyntaxError', {code: 'invalid IRI mapping', context: localCtx});
     }
 
+    if(!api.isKeyword(reverse) && reverse.match(KEYWORD_PATTERN)) {
+      return;
+    }
+
     // expand and add @id mapping
     const id = _expandIri(
       activeCtx, reverse, {vocab: true, base: false}, localCtx, defined,
@@ -517,18 +521,6 @@ api.createTermDefinition = ({
         'jsonld.SyntaxError', {code: 'invalid IRI mapping', context: localCtx});
     }
 
-    if(reverse.match(KEYWORD_PATTERN)) {
-      // FIXME: remove logging and use a handler
-      console.warn('WARNING: values beginning with "@" are reserved' +
-        ' for future use and ignored', {reverse});
-      if(previousMapping) {
-        activeCtx.mappings.set(term, previousMapping);
-      } else {
-        activeCtx.mappings.delete(term);
-      }
-      return;
-    }
-
     mapping['@id'] = id;
     mapping.reverse = true;
   } else if('@id' in value) {