Don't append the URI if it is a slash. Fixes #10210

Author: graemerocher

grails-web-url-mappings/src/main/groovy/org/grails/web/mapping/DefaultUrlMappingEvaluator.java

@@ -781,7 +781,9 @@ private String establishFullURI(String uri, List<ConstrainedProperty> constraine
                 }
             }
 
-            uriBuilder.append(uri);
+            if(!SLASH.equals(uri)) {
+                uriBuilder.append(uri);
+            }
             return uriBuilder.toString();
         }
 

grails-web-url-mappings/src/test/groovy/org/grails/web/mapping/ResourcesWithSingleSlashSpec.groovy

@@ -0,0 +1,28 @@
+package org.grails.web.mapping
+
+import grails.web.mapping.LinkGenerator
+import org.codehaus.groovy.grails.web.mapping.AbstractUrlMappingsSpec
+import spock.lang.Issue
+
+/**
+ * Created by graemerocher on 25/10/16.
+ */
+class ResourcesWithSingleSlashSpec extends AbstractUrlMappingsSpec {
+
+    @Issue('https://github.com/grails/grails-core/issues/10210')
+    void "test that resources expressed with a single slash product the correct URI"() {
+        given:"url mappings within groups with resources expressed with a single slash"
+        LinkGenerator linkGenerator = getLinkGenerator {
+            group "/api", {
+                group "/v1", {
+                    group "/books", {
+                        "/" resources:"book"
+                    }
+                }
+            }
+        }
+
+        expect:
+        linkGenerator.link(resource:"book", id:1L, method:"GET") == 'http://localhost/api/v1/books/1'
+    }
+}