Adjust exception thrown when unable to load hunspell dict

docs/changelog/123743.yaml

@@ -0,0 +1,5 @@
+pr: 123743
+summary: Adjust exception thrown when unable to load hunspell dict
+area: Analysis
+type: bug
+issues: []

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.create/10_basic.yml

@@ -273,3 +273,30 @@
 
   - match: { error.type: "mapper_parsing_exception" }
   - match: { error.reason: "Failed to parse mapping: The mapper type [invalid] declared on field [raw] does not exist. It might have been created within a future version or requires a plugin to be installed. Check the documentation." }
+---
+"Create index with hunspell missing dict":
+  - requires:
+      test_runner_features: [ capabilities ]
+      capabilities:
+        - method: PUT
+          path: /{index}
+          capabilities: [ hunspell_dict_400 ]
+      reason: "bugfix 'hunspell_dict_400' capability required"
+
+  - do:
+      catch: bad_request
+      indices.create:
+        index: bad_hunspell_index
+        body:
+          settings:
+            analysis:
+              analyzer:
+                en:
+                  tokenizer: standard
+                  filter:
+                    - my_en_US_dict_stemmer
+                filter:
+                  my_en_US_dict_stemmer:
+                  type: hunspell
+                  locale: en_US
+                  dedup: false

server/src/main/java/org/elasticsearch/indices/analysis/HunspellService.java

@@ -99,7 +99,7 @@ public HunspellService(final Settings settings, final Environment env, final Map
             try {
                 return loadDictionary(locale, settings, env);
             } catch (Exception e) {
-                throw new IllegalStateException("failed to load hunspell dictionary for locale: " + locale, e);
+                throw new IllegalArgumentException("failed to load hunspell dictionary for locale: " + locale, e);
             }
         };
         if (HUNSPELL_LAZY_LOAD.get(settings) == false) {

server/src/main/java/org/elasticsearch/rest/action/admin/indices/CreateIndexCapabilities.java

@@ -28,9 +28,12 @@ public class CreateIndexCapabilities {
 
     private static final String NESTED_DENSE_VECTOR_SYNTHETIC_TEST = "nested_dense_vector_synthetic_test";
 
+    private static final String HUNSPELL_DICT_400 = "hunspell_dict_400";
+
     public static final Set<String> CAPABILITIES = Set.of(
         LOGSDB_INDEX_MODE_CAPABILITY,
         LOOKUP_INDEX_MODE_CAPABILITY,
-        NESTED_DENSE_VECTOR_SYNTHETIC_TEST
+        NESTED_DENSE_VECTOR_SYNTHETIC_TEST,
+        HUNSPELL_DICT_400
     );
 }