Don't return null from syntheticSourceFallbackFieldName() method (#136344)

This to avoid NPE in a later stage.
Relates to #136345
---------

Co-authored-by: elasticsearchmachine <[email protected]>
Co-authored-by: Martijn van Groningen <[email protected]>

Author: 3 people

server/src/main/java/org/elasticsearch/index/mapper/TextFamilyFieldType.java

@@ -51,7 +51,7 @@ public boolean isWithinMultiField() {
      * stored for whatever reason.
      */
     public String syntheticSourceFallbackFieldName() {
-        return isSyntheticSourceEnabled ? name() + "._original" : null;
+        return name() + "._original";
     }
 
     /**

server/src/main/java/org/elasticsearch/index/mapper/TextFieldMapper.java

@@ -1693,7 +1693,7 @@ private SourceLoader.SyntheticFieldLoader syntheticFieldLoader(String fullFieldN
         // since we don't know whether the delegate field loader can be used for synthetic source until parsing, we need to check both this
         // field and the delegate
 
-        // first field loader - to check whether the field's value was stored under this match_only_text field
+        // first field loader - to check whether the field's value was stored under this text field
         final String fieldName = fieldType().syntheticSourceFallbackFieldName();
         final var thisFieldLayer = new CompositeSyntheticFieldLoader.StoredFieldLayer(fieldName) {
             @Override

server/src/test/java/org/elasticsearch/index/mapper/KeywordFieldMapperTests.java

@@ -1122,8 +1122,6 @@ public void testValueExceedsIgnoreAboveWhenSyntheticSourceDisabled() throws IOEx
 
         // then
 
-        // since synthetic source is disabled, the fallback field name shouldn't exist
-        assertThat(mapper.fieldType().syntheticSourceFallbackFieldName(), Matchers.nullValue());
         // despite exceeding ignore_above, because synthetic source is disabled, we don't expect to store anything
         assertThat(doc.rootDoc().getField(mapper.fieldType() + "_original"), Matchers.nullValue());
     }

x-pack/plugin/logsdb/build.gradle

@@ -24,7 +24,7 @@ base {
 
 restResources {
   restApi {
-    include 'bulk', 'search', '_common', 'indices', 'index', 'cluster', 'data_stream', 'ingest', 'cat', 'capabilities', 'esql.query', 'field_caps'
+    include 'bulk', 'search', '_common', 'indices', 'index', 'cluster', 'data_stream', 'ingest', 'cat', 'capabilities', 'esql.query', 'field_caps', 'get'
   }
 }
 

x-pack/plugin/logsdb/src/yamlRestTest/resources/rest-api-spec/test/40_source_mode_setting.yml

@@ -489,3 +489,46 @@ use no-op _source.mode attr:
         index: test
 
   - match: { test.settings.index.mapping.source.mode: synthetic }
+
+---
+use deprecated _source.mode attr:
+  - requires:
+      test_runner_features: [ "warnings" ]
+
+  - do:
+      warnings:
+        - "Configuring source mode in mappings is deprecated and will be removed in future versions. Use [index.mapping.source.mode] index setting instead."
+      indices.create:
+        index: test
+        body:
+          mappings:
+            _source:
+              mode: synthetic
+            properties:
+              cloud:
+                properties:
+                  account:
+                    properties:
+                      full_text:
+                        type: text
+                        fields:
+                          keyword:
+                            type: keyword
+                            ignore_above: 256
+
+  - do:
+      index:
+        index:  test_index
+        id:     "1"
+        body:
+          cloud:
+            account:
+              full_text: "test"
+  - match:   { result: created }
+
+  - do:
+      get:
+        index:  test_index
+        id:     "1"
+        force_synthetic_source: true
+  - match: { _source:  { cloud: {account: {full_text: "test" } } } }