* Removed `script.default_lang` setting and made `painless` the hardcoded default script language.

** The default script language is now maintained in `Script` class.
* Added `script.legacy.default_lang` setting that controls the default language for scripts that are stored inside documents (for example percolator queries).  This defaults to groovy.
** Added `QueryParseContext#getDefaultScriptLanguage()` that manages the default scripting language. Returns always `painless`, unless loading query/search request in legacy mode then the returns what is configured in `script.legacy.default_lang` setting.
** In the aggregation parsing code added `ParserContext` that also holds the default scripting language like `QueryParseContext`. Most parser don't have access to `QueryParseContext`. This is for scripts in aggregations.
* The `lang` script field is always serialized (toXContent).

Closes #20122

4 files changed, 32 insertions, 4 deletions

diff --git a/core/src/main/java/org/elasticsearch/index/query/QueryParseContext.java b/core/src/main/java/org/elasticsearch/index/query/QueryParseContext.java
index 95fe0094ba..9ed374db21 100644
--- a/core/src/main/java/org/elasticsearch/index/query/QueryParseContext.java
+++ b/core/src/main/java/org/elasticsearch/index/query/QueryParseContext.java
@@ -25,8 +25,11 @@ import org.elasticsearch.common.ParseFieldMatcherSupplier;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.indices.query.IndicesQueriesRegistry;
+import org.elasticsearch.script.Script;
+import org.elasticsearch.script.ScriptSettings;
 
 import java.io.IOException;
 import java.util.Objects;
@@ -42,11 +45,18 @@ public class QueryParseContext implements ParseFieldMatcherSupplier {
     private final XContentParser parser;
     private final IndicesQueriesRegistry indicesQueriesRegistry;
     private final ParseFieldMatcher parseFieldMatcher;
+    private final String defaultScriptLanguage;
 
     public QueryParseContext(IndicesQueriesRegistry registry, XContentParser parser, ParseFieldMatcher parseFieldMatcher) {
+        this(Script.DEFAULT_SCRIPT_LANG, registry, parser, parseFieldMatcher);
+    }
+
+    public QueryParseContext(String defaultScriptLanguage, IndicesQueriesRegistry registry, XContentParser parser,
+                             ParseFieldMatcher parseFieldMatcher) {
         this.indicesQueriesRegistry = Objects.requireNonNull(registry, "indices queries registry cannot be null");
         this.parser = Objects.requireNonNull(parser, "parser cannot be null");
         this.parseFieldMatcher = Objects.requireNonNull(parseFieldMatcher, "parse field matcher cannot be null");
+        this.defaultScriptLanguage = defaultScriptLanguage;
     }
 
     public XContentParser parser() {
@@ -127,4 +137,12 @@ public class QueryParseContext implements ParseFieldMatcherSupplier {
     public ParseFieldMatcher getParseFieldMatcher() {
         return parseFieldMatcher;
     }
+
+    /**
+     * Returns the default scripting language, that should be used if scripts don't specify the script language
+     * explicitly.
+     */
+    public String getDefaultScriptLanguage() {
+        return defaultScriptLanguage;
+    }
 }
diff --git a/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java b/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java
index d8ec9ef2a4..f12605088e 100644
--- a/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java
+++ b/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java
@@ -28,6 +28,7 @@ import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.indices.query.IndicesQueriesRegistry;
 import org.elasticsearch.script.ScriptService;
+import org.elasticsearch.script.ScriptSettings;
 
 /**
  * Context object used to rewrite {@link QueryBuilder} instances into simplified version.
@@ -101,9 +102,18 @@ public class QueryRewriteContext implements ParseFieldMatcherSupplier {
 
     /**
      * Returns a new {@link QueryParseContext} that wraps the provided parser, using the ParseFieldMatcher settings that
-     * are configured in the index settings
+     * are configured in the index settings. The default script language will always default to Painless.
      */
     public QueryParseContext newParseContext(XContentParser parser) {
         return new QueryParseContext(indicesQueriesRegistry, parser, indexSettings.getParseFieldMatcher());
     }
+
+    /**
+     * Returns a new {@link QueryParseContext} like {@link #newParseContext(XContentParser)} with the only diffence, that
+     * the default script language will default to what has been set in the 'script.legacy.default_lang' setting.
+     */
+    public QueryParseContext newParseContextWithLegacyScriptLanguage(XContentParser parser) {
+        String defaultScriptLanguage = ScriptSettings.getLegacyDefaultLang(indexSettings.getNodeSettings());
+        return new QueryParseContext(defaultScriptLanguage, indicesQueriesRegistry, parser, indexSettings.getParseFieldMatcher());
+    }
 }
diff --git a/core/src/main/java/org/elasticsearch/index/query/ScriptQueryBuilder.java b/core/src/main/java/org/elasticsearch/index/query/ScriptQueryBuilder.java
index e6e902e68f..3ff924b28d 100644
--- a/core/src/main/java/org/elasticsearch/index/query/ScriptQueryBuilder.java
+++ b/core/src/main/java/org/elasticsearch/index/query/ScriptQueryBuilder.java
@@ -106,7 +106,7 @@ public class ScriptQueryBuilder extends AbstractQueryBuilder<ScriptQueryBuilder>
                 // skip
             } else if (token == XContentParser.Token.START_OBJECT) {
                 if (parseContext.getParseFieldMatcher().match(currentFieldName, ScriptField.SCRIPT)) {
-                    script = Script.parse(parser, parseContext.getParseFieldMatcher());
+                    script = Script.parse(parser, parseContext.getParseFieldMatcher(), parseContext.getDefaultScriptLanguage());
                 } else {
                     throw new ParsingException(parser.getTokenLocation(), "[script] query does not support [" + currentFieldName + "]");
                 }
@@ -116,7 +116,7 @@ public class ScriptQueryBuilder extends AbstractQueryBuilder<ScriptQueryBuilder>
                 } else if (parseContext.getParseFieldMatcher().match(currentFieldName, AbstractQueryBuilder.BOOST_FIELD)) {
                     boost = parser.floatValue();
                 } else if (parseContext.getParseFieldMatcher().match(currentFieldName, ScriptField.SCRIPT)) {
-                    script = Script.parse(parser, parseContext.getParseFieldMatcher());
+                    script = Script.parse(parser, parseContext.getParseFieldMatcher(), parseContext.getDefaultScriptLanguage());
                 } else {
                     throw new ParsingException(parser.getTokenLocation(), "[script] query does not support [" + currentFieldName + "]");
                 }
diff --git a/core/src/main/java/org/elasticsearch/index/query/functionscore/ScriptScoreFunctionBuilder.java b/core/src/main/java/org/elasticsearch/index/query/functionscore/ScriptScoreFunctionBuilder.java
index 4cbf71f294..e2fbc5955d 100644
--- a/core/src/main/java/org/elasticsearch/index/query/functionscore/ScriptScoreFunctionBuilder.java
+++ b/core/src/main/java/org/elasticsearch/index/query/functionscore/ScriptScoreFunctionBuilder.java
@@ -115,7 +115,7 @@ public class ScriptScoreFunctionBuilder extends ScoreFunctionBuilder<ScriptScore
                 currentFieldName = parser.currentName();
             } else {
                 if (parseContext.getParseFieldMatcher().match(currentFieldName, ScriptField.SCRIPT)) {
-                    script = Script.parse(parser, parseContext.getParseFieldMatcher());
+                    script = Script.parse(parser, parseContext.getParseFieldMatcher(), parseContext.getDefaultScriptLanguage());
                 } else {
                     throw new ParsingException(parser.getTokenLocation(), NAME + " query does not support [" + currentFieldName + "]");
                 }