Deprecates indexing and querying a context completion field without context

docs/reference/search/suggesters/context-suggest.asciidoc

@@ -156,9 +156,9 @@ POST place/_search?pretty
 // CONSOLE
 // TEST[continued]
 
-NOTE: When no categories are provided at query-time, all indexed documents are considered.
-Querying with no categories on a category enabled completion field should be avoided, as it
-will degrade search performance.
+Note: deprecated[7.0.0, When no categories are provided at query-time, all indexed documents are considered.
+Querying with no categories on a category enabled completion field is deprecated and will be removed in the next major release
+as it degrades search performance considerably.]
 
 Suggestions with certain categories can be boosted higher than others.
 The following filters suggestions by categories and additionally boosts

rest-api-spec/src/main/resources/rest-api-spec/test/suggest/30_context.yml

@@ -336,16 +336,36 @@ setup:
   - length: { suggest.result.0.options: 1  }
   - match:  { suggest.result.0.options.0.text: "foo" }
 
+---
+"Querying without contexts is deprecated":
+  - skip:
+      version: " - 6.99.99"
+      reason: this feature was deprecated in 7.0
+      features: "warnings"
+
+  - do:
+      index:
+        index: test
+        type:  test
+        id:    1
+        body:
+          suggest_context:
+            input: "foo"
+            contexts:
+              color: "red"
+
+  - do:
+      indices.refresh: {}
+
   - do:
-       search:
+      warnings:
+        - "The ability to query with no context on a context enabled completion field is deprecated and will be removed in the next major release."
+      search:
         body:
           suggest:
             result:
               text: "foo"
               completion:
-                skip_duplicates: true
                 field: suggest_context
 
   - length: { suggest.result: 1  }
-  - length: { suggest.result.0.options: 1  }
-  - match:  { suggest.result.0.options.0.text: "foo" }

rest-api-spec/src/main/resources/rest-api-spec/test/suggest/40_typed_keys.yml

@@ -31,8 +31,14 @@ setup:
 
 ---
 "Test typed keys parameter for suggesters":
+  - skip:
+      version: " - 6.99.99"
+      reason: queying a context suggester with no context was deprecated in 7.0
+      features: "warnings"
 
   - do:
+      warnings:
+        - "The ability to query with no context on a context enabled completion field is deprecated and will be removed in the next major release."
       search:
         typed_keys: true
         body:

server/src/main/java/org/elasticsearch/search/suggest/completion/CompletionSuggestionBuilder.java

@@ -24,6 +24,8 @@
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.logging.DeprecationLogger;
+import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.unit.Fuzziness;
 import org.elasticsearch.common.xcontent.LoggingDeprecationHandler;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
@@ -57,6 +59,10 @@
  * indexing.
  */
 public class CompletionSuggestionBuilder extends SuggestionBuilder<CompletionSuggestionBuilder> {
+
+    private static final DeprecationLogger DEPRECATION_LOGGER =
+        new DeprecationLogger(Loggers.getLogger(CompletionSuggestionBuilder.class));
+
     private static final XContentType CONTEXT_BYTES_XCONTENT_TYPE = XContentType.JSON;
     static final String SUGGESTION_NAME = "completion";
     static final ParseField CONTEXTS_FIELD = new ParseField("contexts", "context");
@@ -298,16 +304,19 @@ public SuggestionContext build(QueryShardContext context) throws IOException {
         if (mappedFieldType == null || mappedFieldType instanceof CompletionFieldMapper.CompletionFieldType == false) {
             throw new IllegalArgumentException("Field [" + suggestionContext.getField() + "] is not a completion suggest field");
         }
-        if (mappedFieldType instanceof CompletionFieldMapper.CompletionFieldType) {
-            CompletionFieldMapper.CompletionFieldType type = (CompletionFieldMapper.CompletionFieldType) mappedFieldType;
-            suggestionContext.setFieldType(type);
-            if (type.hasContextMappings() && contextBytes != null) {
+        CompletionFieldMapper.CompletionFieldType type = (CompletionFieldMapper.CompletionFieldType) mappedFieldType;
+        suggestionContext.setFieldType(type);
+        if (type.hasContextMappings()) {
+            if (contextBytes == null) {
+                DEPRECATION_LOGGER.deprecated("The ability to query with no context on a context enabled completion field is deprecated " +
+                    "and will be removed in the next major release.");
+            } else {
                 Map<String, List<ContextMapping.InternalQueryContext>> queryContexts = parseContextBytes(contextBytes,
-                        context.getXContentRegistry(), type.getContextMappings());
+                    context.getXContentRegistry(), type.getContextMappings());
                 suggestionContext.setQueryContexts(queryContexts);
-            } else if (contextBytes != null) {
-                throw new IllegalArgumentException("suggester [" + type.name() + "] doesn't expect any context");
             }
+        } else if (contextBytes != null) {
+            throw new IllegalArgumentException("suggester [" + type.name() + "] doesn't expect any context");
         }
         assert suggestionContext.getFieldType() != null : "no completion field type set";
         return suggestionContext;