Fix propagating the default value for script settings

Fixes an issue where the value for the `script.engine.<lang>.inline`
settings would be _set_ properly, but would not accurately be reflected
in the `include_defaults` output. Adds a test to ensure the default raw
setting is now correct.

Resolves #20159

core/src/main/java/org/elasticsearch/script/ScriptSettings.java

@@ -97,9 +97,25 @@ public class ScriptSettings {
                 }
                 final boolean defaultIfNothingSet = defaultLangAndType;
 
+                Function<Settings, String> defaultLangAndTypeFn = settings -> {
+                    final Setting<Boolean> globalTypeSetting = scriptTypeSettingMap.get(scriptType);
+                    final Setting<Boolean> langAndTypeSetting = Setting.boolSetting(ScriptModes.getGlobalKey(language, scriptType),
+                            defaultIfNothingSet, Property.NodeScope);
+
+                    if (langAndTypeSetting.exists(settings)) {
+                        // fine-grained e.g. script.engine.groovy.inline
+                        return langAndTypeSetting.get(settings).toString();
+                    } else if (globalTypeSetting.exists(settings)) {
+                        // global type - script.inline
+                        return globalTypeSetting.get(settings).toString();
+                    } else {
+                        return Boolean.toString(defaultIfNothingSet);
+                    }
+                };
+
                 // Setting for something like "script.engine.groovy.inline"
                 final Setting<Boolean> langAndTypeSetting = Setting.boolSetting(ScriptModes.getGlobalKey(language, scriptType),
-                        defaultLangAndType, Property.NodeScope);
+                        defaultLangAndTypeFn, Property.NodeScope);
                 scriptModeSettings.add(langAndTypeSetting);
 
                 for (ScriptContext scriptContext : scriptContextRegistry.scriptContexts()) {

core/src/test/java/org/elasticsearch/script/ScriptSettingsTests.java

@@ -20,11 +20,13 @@
 package org.elasticsearch.script;
 
 import org.elasticsearch.common.Nullable;
+import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.search.lookup.SearchLookup;
 import org.elasticsearch.test.ESTestCase;
 
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.Map;
 
 import static org.hamcrest.Matchers.containsString;
@@ -64,6 +66,22 @@ public class ScriptSettingsTests extends ESTestCase {
         }
     }
 
+    public void testSettingsAreProperlyPropogated() {
+        ScriptEngineRegistry scriptEngineRegistry =
+            new ScriptEngineRegistry(Collections.singletonList(new CustomScriptEngineService()));
+        ScriptContextRegistry scriptContextRegistry = new ScriptContextRegistry(Collections.emptyList());
+        ScriptSettings scriptSettings = new ScriptSettings(scriptEngineRegistry, scriptContextRegistry);
+        boolean enabled = randomBoolean();
+        Settings s = Settings.builder().put("script.inline", enabled).build();
+        for (Iterator<Setting<Boolean>> iter = scriptSettings.getScriptLanguageSettings().iterator(); iter.hasNext();) {
+            Setting<Boolean> setting = iter.next();
+            if (setting.getKey().endsWith(".inline")) {
+                assertThat("inline settings should have propagated", setting.get(s), equalTo(enabled));
+                assertThat(setting.getDefaultRaw(s), equalTo(Boolean.toString(enabled)));
+            }
+        }
+    }
+
     private static class CustomScriptEngineService implements ScriptEngineService {
 
         public static final String NAME = "custom";