add yaml test and avoid loading embeddings when not needed

Author: jimczi

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/mapper/SemanticTextFieldMapper.java

@@ -1063,7 +1063,9 @@ public void setNextReader(LeafReaderContext context) {
                     if (childScorer != null) {
                         childScorer.iterator().nextDoc();
                     }
-                    dvLoader = fieldLoader.docValuesLoader(context.reader(), null);
+                    if (onlyTextChunks == false) {
+                        dvLoader = fieldLoader.docValuesLoader(context.reader(), null);
+                    }
                     var terms = context.reader().terms(getOffsetsFieldName(name()));
                     offsetsLoader = terms != null ? OffsetSourceField.loader(terms) : null;
                 } catch (IOException exc) {
@@ -1141,10 +1143,12 @@ private void iterateChildDocs(
                 CheckedConsumer<OffsetSourceFieldMapper.OffsetSource, IOException> action
             ) throws IOException {
                 while (it.docID() < doc) {
-                    if (dvLoader == null || dvLoader.advanceToDoc(it.docID()) == false) {
-                        throw new IllegalStateException(
-                            "Cannot fetch values for field [" + name() + "], missing embeddings for doc [" + doc + "]"
-                        );
+                    if (onlyTextChunks == false) {
+                        if (dvLoader == null || dvLoader.advanceToDoc(it.docID()) == false) {
+                            throw new IllegalStateException(
+                                "Cannot fetch values for field [" + name() + "], missing embeddings for doc [" + doc + "]"
+                            );
+                        }
                     }
 
                     var offset = offsetsLoader.advanceTo(it.docID());

x-pack/plugin/inference/src/yamlRestTest/resources/rest-api-spec/test/inference/90_semantic_text_highlighter.yml

@@ -715,3 +715,32 @@ setup:
   - match: { hits.hits.0.fields.semantic_text_field.0: "some test data" }
   - match: { hits.hits.0.fields.semantic_text_field.1: "now with chunks" }
   - match: { hits.hits.0.fields.semantic_text_field.2: "text field data" }
+
+---
+"Highlighting with match_all in a highlight_query":
+  - requires:
+      cluster_features: "semantic_text.match_all_highlighter"
+      reason: semantic text field supports match_all query with semantic highlighter, effective from 8.19 and 9.1.0.
+
+  - do:
+      search:
+        index: test-sparse-index
+        body:
+          query:
+            ids: {
+              values: ["doc_1"]
+            }
+          highlight:
+            fields:
+              body:
+                type: "semantic"
+                number_of_fragments: 2
+                highlight_query: {
+                  match_all: {}
+                }
+
+  - match: { hits.total.value: 1 }
+  - match: { hits.hits.0._id: "doc_1" }
+  - length: { hits.hits.0.highlight.body: 2 }
+  - match: { hits.hits.0.highlight.body.0: "ElasticSearch is an open source, distributed, RESTful, search engine which is built on top of Lucene internally and enjoys all the features it provides." }
+  - match: { hits.hits.0.highlight.body.1: "You Know, for Search!" }