Provide informative error message in case of unknown suggestion context. (#24241)

Provide a list of available contexts when you send an unknown context to the completion suggester.

1 files changed, 3 insertions, 1 deletions

diff --git a/core/src/main/java/org/elasticsearch/search/suggest/completion/context/ContextMappings.java b/core/src/main/java/org/elasticsearch/search/suggest/completion/context/ContextMappings.java
index 0cac17dbb8..bbefbf41b8 100644
--- a/core/src/main/java/org/elasticsearch/search/suggest/completion/context/ContextMappings.java
+++ b/core/src/main/java/org/elasticsearch/search/suggest/completion/context/ContextMappings.java
@@ -81,7 +81,9 @@ public class ContextMappings implements ToXContent {
     public ContextMapping get(String name) {
         ContextMapping contextMapping = contextNameMap.get(name);
         if (contextMapping == null) {
-            throw new IllegalArgumentException("Unknown context name[" + name + "], must be one of " + contextNameMap.size());
+            List<String> keys = new ArrayList<>(contextNameMap.keySet());
+            Collections.sort(keys);
+            throw new IllegalArgumentException("Unknown context name [" + name + "], must be one of " + keys.toString());
         }
         return contextMapping;
     }