Don't keep track of field aliases in FieldTypeLookup (#64884)

We currently keep track of field aliases which causes us to do two lookups for every field lookup. Instead, we could keep track of field aliases in the same map where ordinary fields are, by adding an entry that has the name of the field alias, and its corresponding field type is the field that that the alias points to.

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

@@ -35,7 +35,6 @@ import java.util.Set;
 final class FieldTypeLookup implements Iterable<MappedFieldType> {
 
     private final Map<String, MappedFieldType> fullNameToFieldType = new HashMap<>();
-    private final Map<String, String> aliasToConcreteName = new HashMap<>();
 
     /**
      * A map from field name to all fields whose content has been copied into it
@@ -70,10 +69,12 @@ final class FieldTypeLookup implements Iterable<MappedFieldType> {
             }
         }
 
+        final Map<String, String> aliasToConcreteName = new HashMap<>();
         for (FieldAliasMapper fieldAliasMapper : fieldAliasMappers) {
             String aliasName = fieldAliasMapper.name();
             String path = fieldAliasMapper.path();
             aliasToConcreteName.put(aliasName, path);
+            fullNameToFieldType.put(aliasName, fullNameToFieldType.get(path));
         }
 
         this.dynamicKeyLookup = new DynamicKeyFieldTypeLookup(dynamicKeyMappers, aliasToConcreteName);
@@ -83,8 +84,7 @@ final class FieldTypeLookup implements Iterable<MappedFieldType> {
      * Returns the mapped field type for the given field name.
      */
     MappedFieldType get(String field) {
-        String concreteField = aliasToConcreteName.getOrDefault(field, field);
-        MappedFieldType fieldType = fullNameToFieldType.get(concreteField);
+        MappedFieldType fieldType = fullNameToFieldType.get(field);
         if (fieldType != null) {
             return fieldType;
         }
@@ -99,14 +99,9 @@ final class FieldTypeLookup implements Iterable<MappedFieldType> {
      */
     Set<String> simpleMatchToFullName(String pattern) {
         Set<String> fields = new HashSet<>();
-        for (MappedFieldType fieldType : this) {
-            if (Regex.simpleMatch(pattern, fieldType.name())) {
-                fields.add(fieldType.name());
-            }
-        }
-        for (String aliasName : aliasToConcreteName.keySet()) {
-            if (Regex.simpleMatch(pattern, aliasName)) {
-                fields.add(aliasName);
+        for (String field : fullNameToFieldType.keySet()) {
+            if (Regex.simpleMatch(pattern, field)) {
+                fields.add(field);
             }
         }
         return fields;