ESQL: Fix attribute only in full text function not found

docs/changelog/137395.yaml

@@ -0,0 +1,6 @@
+pr: 137395
+summary: Fix attribute only in full text function not found
+area: ES|QL
+type: bug
+issues:
+ - 137396

x-pack/plugin/esql/qa/testFixtures/src/main/resources/lookup-join-expression.csv-spec

@@ -1253,3 +1253,22 @@ FROM airports
 airport_code:keyword | name:text | city:keyword | country:keyword | location:geo_point | city_boundary:geo_shape
 LTN                  | London Luton | Luton | United Kingdom | POINT(-0.376227267397439 51.8802952570969) | POLYGON((-0.5059 51.9006, -0.4225 51.8545, -0.3499 51.8787, -0.3856 51.9157, -0.4191 51.9123, -0.4263 51.9267, -0.4857 51.9227, -0.4823 51.9078, -0.5059 51.9006))
 ;
+
+lookupJoinExpressionOnRightFieldNotAnywhereElse
+required_capability: join_lookup_v12
+required_capability: lookup_join_with_full_text_function
+
+FROM multi_column_joinable
+| RENAME id_int AS id_left
+| LOOKUP JOIN multi_column_joinable_lookup ON id_int == id_left AND MATCH(other1, "beta")
+| WHERE other2 IS NOT NULL
+| KEEP id_left, name_str, extra1, other2
+| SORT id_left, name_str, extra1, other2
+;
+
+warning:Line 3:3: evaluation of [LOOKUP JOIN multi_column_joinable_lookup ON id_int == id_left AND MATCH(other1, \"beta\")] failed, treating result as null. Only first 20 failures recorded.
+warning:Line 3:3: java.lang.IllegalArgumentException: LOOKUP JOIN encountered multi-value
+
+id_left:integer | name_str:keyword | extra1:keyword | other2:integer
+1               | Alice            | foo            | 2000
+;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/session/FieldNameUtils.java

@@ -163,6 +163,9 @@ public static PreAnalysisResult resolveFieldNames(LogicalPlan parsed, boolean ha
                 referencesBuilder.get().addAll(enrichRefs);
             } else if (p instanceof LookupJoin join) {
                 joinRefs.addAll(join.config().leftFields());
+                if (join.config().joinOnConditions() != null) {
+                    joinRefs.addAll(join.config().joinOnConditions().references());
+                }
                 if (keepRefs.isEmpty()) {
                     // No KEEP commands after the JOIN, so we need to mark this index for "*" field resolution
                     wildcardJoinIndices.add(((UnresolvedRelation) join.right()).indexPattern().indexPattern());

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/AnalyzerTestUtils.java

@@ -7,6 +7,7 @@
 
 package org.elasticsearch.xpack.esql.analysis;
 
+import org.elasticsearch.TransportVersion;
 import org.elasticsearch.index.IndexMode;
 import org.elasticsearch.inference.TaskType;
 import org.elasticsearch.test.ESTestCase;
@@ -156,6 +157,17 @@ public static LogicalPlan analyze(String query, Analyzer analyzer) {
         return analyzed;
     }
 
+    public static LogicalPlan analyze(String query, TransportVersion transportVersion) {
+        Analyzer baseAnalyzer = expandedDefaultAnalyzer();
+        if (baseAnalyzer.context() instanceof MutableAnalyzerContext mutableContext) {
+            try (var restore = mutableContext.setTemporaryTransportVersionOnOrAfter(transportVersion)) {
+                return analyze(query, baseAnalyzer);
+            }
+        } else {
+            throw new UnsupportedOperationException("Analyzer Context is not mutable");
+        }
+    }
+
     private static final Pattern indexFromPattern = Pattern.compile("(?i)FROM\\s+([\\w-]+)");
 
     private static String indexFromQuery(String query) {

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/AnalyzerTests.java

@@ -5561,6 +5561,43 @@ public void testSubqueryWithFullTextFunctionInMainQuery() {
         assertEquals("sample_data", subqueryIndex.indexPattern());
     }
 
+    public void testLookupJoinOnFieldNotAnywhereElse() {
+        assumeTrue(
+            "requires LOOKUP JOIN ON boolean expression capability",
+            EsqlCapabilities.Cap.LOOKUP_JOIN_WITH_FULL_TEXT_FUNCTION.isEnabled()
+        );
+
+        String query = "FROM test | LOOKUP JOIN languages_lookup "
+            + "ON languages == language_code AND MATCH(language_name, \"English\")"
+            + "| KEEP languages";
+
+        LogicalPlan analyzedPlan = analyze(query, Analyzer.ESQL_LOOKUP_JOIN_FULL_TEXT_FUNCTION);
+
+        Limit limit = as(analyzedPlan, Limit.class);
+        assertThat(limit.limit(), instanceOf(Literal.class));
+        assertEquals(1000, as(limit.limit(), Literal.class).value());
+
+        EsqlProject project = as(limit.child(), EsqlProject.class);
+        assertEquals(1, project.projections().size());
+
+        LookupJoin lookupJoin = as(project.child(), LookupJoin.class);
+
+        // Verify join condition contains MATCH function
+        assertThat(lookupJoin.config().joinOnConditions(), notNullValue());
+        Expression joinCondition = lookupJoin.config().joinOnConditions();
+        // Check that the join condition contains a MATCH function (it should be an AND expression)
+        assertThat(joinCondition.toString(), containsString("MATCH"));
+
+        // Verify left relation is test index
+        EsRelation leftRelation = as(lookupJoin.left(), EsRelation.class);
+        assertEquals("test", leftRelation.indexPattern());
+
+        // Verify right relation is languages_lookup with LOOKUP mode
+        EsRelation rightRelation = as(lookupJoin.right(), EsRelation.class);
+        assertEquals("languages_lookup", rightRelation.indexPattern());
+        assertEquals(IndexMode.LOOKUP, rightRelation.indexMode());
+    }
+
     private void verifyNameAndTypeAndMultiTypeEsField(
         String actualName,
         DataType actualType,