LOOKUP JOIN using field-caps for field mapping (elastic#117246)

* LOOKUP JOIN using field-caps for field mapping

Removes the hard-coded hack for languages_lookup, and instead does a field-caps check for the real join index.

* Update docs/changelog/117246.yaml

* Some code review comments

Author: craigtaverner

docs/changelog/117246.yaml

@@ -0,0 +1,5 @@
+pr: 117246
+summary: LOOKUP JOIN using field-caps for field mapping
+area: ES|QL
+type: enhancement
+issues: []

x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/CsvTestsDataLoader.java

@@ -56,6 +56,8 @@ public class CsvTestsDataLoader {
     private static final TestsDataset APPS = new TestsDataset("apps");
     private static final TestsDataset APPS_SHORT = APPS.withIndex("apps_short").withTypeMapping(Map.of("id", "short"));
     private static final TestsDataset LANGUAGES = new TestsDataset("languages");
+    private static final TestsDataset LANGUAGES_LOOKUP = LANGUAGES.withIndex("languages_lookup")
+        .withSetting("languages_lookup-settings.json");
     private static final TestsDataset ALERTS = new TestsDataset("alerts");
     private static final TestsDataset UL_LOGS = new TestsDataset("ul_logs");
     private static final TestsDataset SAMPLE_DATA = new TestsDataset("sample_data");
@@ -93,14 +95,13 @@ public class CsvTestsDataLoader {
     private static final TestsDataset BOOKS = new TestsDataset("books");
     private static final TestsDataset SEMANTIC_TEXT = new TestsDataset("semantic_text").withInferenceEndpoint(true);
 
-    private static final String LOOKUP_INDEX_SUFFIX = "_lookup";
-
     public static final Map<String, TestsDataset> CSV_DATASET_MAP = Map.ofEntries(
         Map.entry(EMPLOYEES.indexName, EMPLOYEES),
         Map.entry(HOSTS.indexName, HOSTS),
         Map.entry(APPS.indexName, APPS),
         Map.entry(APPS_SHORT.indexName, APPS_SHORT),
         Map.entry(LANGUAGES.indexName, LANGUAGES),
+        Map.entry(LANGUAGES_LOOKUP.indexName, LANGUAGES_LOOKUP),
         Map.entry(UL_LOGS.indexName, UL_LOGS),
         Map.entry(SAMPLE_DATA.indexName, SAMPLE_DATA),
         Map.entry(ALERTS.indexName, ALERTS),
@@ -130,9 +131,7 @@ public class CsvTestsDataLoader {
         Map.entry(DISTANCES.indexName, DISTANCES),
         Map.entry(ADDRESSES.indexName, ADDRESSES),
         Map.entry(BOOKS.indexName, BOOKS),
-        Map.entry(SEMANTIC_TEXT.indexName, SEMANTIC_TEXT),
-        // JOIN LOOKUP alias
-        Map.entry(LANGUAGES.indexName + LOOKUP_INDEX_SUFFIX, LANGUAGES.withIndex(LANGUAGES.indexName + LOOKUP_INDEX_SUFFIX))
+        Map.entry(SEMANTIC_TEXT.indexName, SEMANTIC_TEXT)
     );
 
     private static final EnrichConfig LANGUAGES_ENRICH = new EnrichConfig("languages_policy", "enrich-policy-languages.json");

x-pack/plugin/esql/qa/testFixtures/src/main/resources/languages_lookup-settings.json

@@ -0,0 +1,5 @@
+{
+  "index": {
+    "mode": "lookup"
+  }
+}

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/Analyzer.java

@@ -62,6 +62,7 @@
 import org.elasticsearch.xpack.esql.expression.predicate.operator.arithmetic.EsqlArithmeticOperation;
 import org.elasticsearch.xpack.esql.expression.predicate.operator.comparison.In;
 import org.elasticsearch.xpack.esql.index.EsIndex;
+import org.elasticsearch.xpack.esql.index.IndexResolution;
 import org.elasticsearch.xpack.esql.parser.ParsingException;
 import org.elasticsearch.xpack.esql.plan.TableIdentifier;
 import org.elasticsearch.xpack.esql.plan.logical.Aggregate;
@@ -106,7 +107,6 @@
 import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
-import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
@@ -199,57 +199,42 @@ private static class ResolveTable extends ParameterizedAnalyzerRule<UnresolvedRe
 
         @Override
         protected LogicalPlan rule(UnresolvedRelation plan, AnalyzerContext context) {
-            if (plan.indexMode().equals(IndexMode.LOOKUP)) {
-                return hackLookupMapping(plan);
-            }
-            if (context.indexResolution().isValid() == false) {
-                return plan.unresolvedMessage().equals(context.indexResolution().toString())
+            return resolveIndex(plan, plan.indexMode().equals(IndexMode.LOOKUP) ? context.lookupResolution() : context.indexResolution());
+        }
+
+        private LogicalPlan resolveIndex(UnresolvedRelation plan, IndexResolution indexResolution) {
+            if (indexResolution.isValid() == false) {
+                return plan.unresolvedMessage().equals(indexResolution.toString())
                     ? plan
                     : new UnresolvedRelation(
                         plan.source(),
                         plan.table(),
                         plan.frozen(),
                         plan.metadataFields(),
                         plan.indexMode(),
-                        context.indexResolution().toString(),
+                        indexResolution.toString(),
                         plan.commandName()
                     );
             }
             TableIdentifier table = plan.table();
-            if (context.indexResolution().matches(table.index()) == false) {
+            if (indexResolution.matches(table.index()) == false) {
                 // TODO: fix this (and tests), or drop check (seems SQL-inherited, where's also defective)
                 new UnresolvedRelation(
                     plan.source(),
                     plan.table(),
                     plan.frozen(),
                     plan.metadataFields(),
                     plan.indexMode(),
-                    "invalid [" + table + "] resolution to [" + context.indexResolution() + "]",
+                    "invalid [" + table + "] resolution to [" + indexResolution + "]",
                     plan.commandName()
                 );
             }
 
-            EsIndex esIndex = context.indexResolution().get();
+            EsIndex esIndex = indexResolution.get();
             var attributes = mappingAsAttributes(plan.source(), esIndex.mapping());
             attributes.addAll(plan.metadataFields());
             return new EsRelation(plan.source(), esIndex, attributes.isEmpty() ? NO_FIELDS : attributes, plan.indexMode());
         }
-
-        private LogicalPlan hackLookupMapping(UnresolvedRelation plan) {
-            if (plan.table().index().toLowerCase(Locale.ROOT).equals("languages_lookup")) {
-                EsIndex esIndex = new EsIndex(
-                    "languages_lookup",
-                    Map.ofEntries(
-                        Map.entry("language_code", new EsField("language_code", DataType.LONG, Map.of(), true)),
-                        Map.entry("language_name", new EsField("language", DataType.KEYWORD, Map.of(), true))
-                    ),
-                    Map.of("languages_lookup", IndexMode.LOOKUP)
-                );
-                var attributes = mappingAsAttributes(plan.source(), esIndex.mapping());
-                return new EsRelation(plan.source(), esIndex, attributes.isEmpty() ? NO_FIELDS : attributes, plan.indexMode());
-            }
-            return plan;
-        }
     }
 
     /**

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/AnalyzerContext.java

@@ -15,5 +15,17 @@ public record AnalyzerContext(
     Configuration configuration,
     EsqlFunctionRegistry functionRegistry,
     IndexResolution indexResolution,
+    IndexResolution lookupResolution,
     EnrichResolution enrichResolution
-) {}
+) {
+    // Currently for tests only, since most do not test lookups
+    // TODO: make this even simpler, remove the enrichResolution for tests that do not require it (most tests)
+    public AnalyzerContext(
+        Configuration configuration,
+        EsqlFunctionRegistry functionRegistry,
+        IndexResolution indexResolution,
+        EnrichResolution enrichResolution
+    ) {
+        this(configuration, functionRegistry, indexResolution, IndexResolution.invalid("<none>"), enrichResolution);
+    }
+}