Simplify dynamic template parser context creation (#74326)

DocumentParser takes care of parsing documents and applying dynamic mapping updates for each new field it encounters, if applicable, as well as applying the matching dynamic templates.

To do this, it needs to be able to parse mappings, which requires a ParserContext that the ParseContext exposes given a DateFormatter. So far, we have carried around a function that allows to create a new ParserContext given a date formatter, and then call a specific method that allows to wrap it to provide a special parser context that is specific for dynamic templates, which is needed to make some decisions down the line based on whether mappings come from dynamic templates or not.

This commit tries to simplify this by exposing the specific dynamic template parser context only to the document parse context, as that's all it needs. We recently ended up using the wrong context and with this change it would not be possible.

Relates to #74177

Author: javanna

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

@@ -144,10 +144,6 @@ ParserContext createMultiFieldContext(ParserContext in) {
                 return new MultiFieldParserContext(in);
             }
 
-            ParserContext createDynamicTemplateFieldContext() {
-                return new DynamicTemplateParserContext(this);
-            }
-
             private static class MultiFieldParserContext extends ParserContext {
                 MultiFieldParserContext(ParserContext in) {
                     super(in.similarityLookupService, in.typeParsers, in.runtimeFieldParsers, in.indexVersionCreated,
@@ -159,7 +155,7 @@ private static class MultiFieldParserContext extends ParserContext {
                 public boolean isWithinMultiField() { return true; }
             }
 
-            private static class DynamicTemplateParserContext extends ParserContext {
+            static class DynamicTemplateParserContext extends ParserContext {
                 DynamicTemplateParserContext(ParserContext in) {
                     super(in.similarityLookupService, in.typeParsers, in.runtimeFieldParsers, in.indexVersionCreated,
                         in.searchExecutionContextSupplier, in.dateFormatter, in.scriptCompiler, in.indexAnalyzers, in.indexSettings,

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

@@ -111,7 +111,9 @@ public MapperService(IndexSettings indexSettings, IndexAnalyzers indexAnalyzers,
             dateFormatter -> new Mapper.TypeParser.ParserContext(similarityService::getSimilarity, mapperRegistry.getMapperParsers()::get,
                 mapperRegistry.getRuntimeFieldParsers()::get, indexVersionCreated, searchExecutionContextSupplier, dateFormatter,
                 scriptCompiler, indexAnalyzers, indexSettings, idFieldDataEnabled);
-        this.documentParser = new DocumentParser(xContentRegistry, parserContextFunction, indexSettings, indexAnalyzers);
+        this.documentParser = new DocumentParser(xContentRegistry,
+            dateFormatter -> new Mapper.TypeParser.ParserContext.DynamicTemplateParserContext(parserContextFunction.apply(dateFormatter)),
+            indexSettings, indexAnalyzers);
         Map<String, MetadataFieldMapper.TypeParser> metadataMapperParsers =
             mapperRegistry.getMetadataMapperParsers(indexSettings.getIndexVersionCreated());
         this.parserContextSupplier = () -> parserContextFunction.apply(null);

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

@@ -319,13 +319,13 @@ public static class InternalParseContext extends ParseContext {
         public InternalParseContext(MappingLookup mappingLookup,
                                     IndexSettings indexSettings,
                                     IndexAnalyzers indexAnalyzers,
-                                    Function<DateFormatter, Mapper.TypeParser.ParserContext> parserContextFunction,
+                                    Function<DateFormatter, Mapper.TypeParser.ParserContext> parserContext,
                                     SourceToParse source,
                                     XContentParser parser) {
             this.mappingLookup = mappingLookup;
             this.indexSettings = indexSettings;
             this.indexAnalyzers = indexAnalyzers;
-            this.parserContextFunction = parserContextFunction;
+            this.parserContextFunction = parserContext;
             this.parser = parser;
             this.document = new Document();
             this.documents.add(document);
@@ -337,7 +337,7 @@ public InternalParseContext(MappingLookup mappingLookup,
 
         @Override
         public Mapper.TypeParser.ParserContext dynamicTemplateParserContext(DateFormatter dateFormatter) {
-            return parserContextFunction.apply(dateFormatter).createDynamicTemplateFieldContext();
+            return parserContextFunction.apply(dateFormatter);
         }
 
         @Override

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

@@ -208,7 +208,7 @@ private static TestMapper fromMapping(String mapping, Version version, boolean f
             throw new UnsupportedOperationException();
         });
         if (fromDynamicTemplate) {
-            pc = pc.createDynamicTemplateFieldContext();
+            pc = new Mapper.TypeParser.ParserContext.DynamicTemplateParserContext(pc);
         }
         return (TestMapper) new TypeParser()
             .parse("field", XContentHelper.convertToMap(JsonXContent.jsonXContent, mapping, true), pc)