Don't allow field caps to use semantic queries as index filters (#131111)

docs/changelog/131111.yaml

@@ -0,0 +1,5 @@
+pr: 131111
+summary: Don't allow field caps to use semantic queries as index filters
+area: Search
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/action/fieldcaps/FieldCapabilitiesRequest.java

@@ -18,7 +18,13 @@ import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.index.query.BoolQueryBuilder;
+import org.elasticsearch.index.query.BoostingQueryBuilder;
+import org.elasticsearch.index.query.ConstantScoreQueryBuilder;
+import org.elasticsearch.index.query.DisMaxQueryBuilder;
+import org.elasticsearch.index.query.NestedQueryBuilder;
 import org.elasticsearch.index.query.QueryBuilder;
+import org.elasticsearch.index.query.functionscore.FunctionScoreQueryBuilder;
 import org.elasticsearch.tasks.CancellableTask;
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.tasks.TaskId;
@@ -268,9 +274,53 @@ public final class FieldCapabilitiesRequest extends LegacyActionRequest implemen
         if (fields == null || fields.length == 0) {
             validationException = ValidateActions.addValidationError("no fields specified", validationException);
         }
+
+        // Band-aid fix for https://github.com/elastic/elasticsearch/issues/116106.
+        // Semantic queries are high-recall queries, making them poor filters and effectively the same as an exists query when used in that
+        // context.
+        if (containsSemanticQuery(indexFilter)) {
+            validationException = ValidateActions.addValidationError(
+                "index filter cannot contain semantic queries. Use an exists query instead.",
+                validationException
+            );
+        }
+
         return validationException;
     }
 
+    /**
+     * Recursively checks if a query builder contains any semantic queries
+     */
+    private static boolean containsSemanticQuery(QueryBuilder queryBuilder) {
+        boolean containsSemanticQuery = false;
+
+        if (queryBuilder == null) {
+            return containsSemanticQuery;
+        }
+
+        if ("semantic".equals(queryBuilder.getWriteableName())) {
+            containsSemanticQuery = true;
+        } else if (queryBuilder instanceof BoolQueryBuilder boolQuery) {
+            containsSemanticQuery = boolQuery.must().stream().anyMatch(FieldCapabilitiesRequest::containsSemanticQuery)
+                || boolQuery.mustNot().stream().anyMatch(FieldCapabilitiesRequest::containsSemanticQuery)
+                || boolQuery.should().stream().anyMatch(FieldCapabilitiesRequest::containsSemanticQuery)
+                || boolQuery.filter().stream().anyMatch(FieldCapabilitiesRequest::containsSemanticQuery);
+        } else if (queryBuilder instanceof DisMaxQueryBuilder disMaxQuery) {
+            containsSemanticQuery = disMaxQuery.innerQueries().stream().anyMatch(FieldCapabilitiesRequest::containsSemanticQuery);
+        } else if (queryBuilder instanceof NestedQueryBuilder nestedQuery) {
+            containsSemanticQuery = containsSemanticQuery(nestedQuery.query());
+        } else if (queryBuilder instanceof BoostingQueryBuilder boostingQuery) {
+            containsSemanticQuery = containsSemanticQuery(boostingQuery.positiveQuery())
+                || containsSemanticQuery(boostingQuery.negativeQuery());
+        } else if (queryBuilder instanceof ConstantScoreQueryBuilder constantScoreQuery) {
+            containsSemanticQuery = containsSemanticQuery(constantScoreQuery.innerQuery());
+        } else if (queryBuilder instanceof FunctionScoreQueryBuilder functionScoreQuery) {
+            containsSemanticQuery = containsSemanticQuery(functionScoreQuery.query());
+        }
+
+        return containsSemanticQuery;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

x-pack/plugin/inference/src/test/java/org/elasticsearch/action/fieldcaps/FieldCapabilitiesRequestSemanticIndexFilterTests.java

@@ -0,0 +1,136 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.action.fieldcaps;
+
+import org.apache.lucene.search.join.ScoreMode;
+import org.elasticsearch.action.ActionRequestValidationException;
+import org.elasticsearch.index.query.BoolQueryBuilder;
+import org.elasticsearch.index.query.BoostingQueryBuilder;
+import org.elasticsearch.index.query.ConstantScoreQueryBuilder;
+import org.elasticsearch.index.query.DisMaxQueryBuilder;
+import org.elasticsearch.index.query.MatchAllQueryBuilder;
+import org.elasticsearch.index.query.NestedQueryBuilder;
+import org.elasticsearch.index.query.QueryBuilder;
+import org.elasticsearch.index.query.TermQueryBuilder;
+import org.elasticsearch.index.query.functionscore.FunctionScoreQueryBuilder;
+import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.xpack.inference.queries.SemanticQueryBuilder;
+
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.notNullValue;
+
+public class FieldCapabilitiesRequestSemanticIndexFilterTests extends ESTestCase {
+    private static final String EXPECTED_ERROR_MESSAGE = "index filter cannot contain semantic queries. Use an exists query instead.";
+
+    public void testValidateWithoutIndexFilter() {
+        FieldCapabilitiesRequest request = new FieldCapabilitiesRequest();
+        request.fields("field1", "field2");
+
+        ActionRequestValidationException validationException = request.validate();
+        assertNull(validationException);
+    }
+
+    public void testValidateWithNonSemanticIndexFilter() {
+        FieldCapabilitiesRequest request = new FieldCapabilitiesRequest();
+        request.fields("field1", "field2");
+        request.indexFilter(randomNonSemanticQuery());
+
+        ActionRequestValidationException validationException = request.validate();
+        assertNull(validationException);
+    }
+
+    public void testValidateWithDirectSemanticQuery() {
+        FieldCapabilitiesRequest request = new FieldCapabilitiesRequest();
+        request.fields("field1", "field2");
+        request.indexFilter(randomSemanticQuery());
+
+        ActionRequestValidationException validationException = request.validate();
+        assertThat(validationException, notNullValue());
+        assertThat(validationException.getMessage(), containsString(EXPECTED_ERROR_MESSAGE));
+    }
+
+    public void testValidateWithRandomCompoundQueryContainingSemantic() {
+        for (int i = 0; i < 100; i++) {
+            FieldCapabilitiesRequest request = new FieldCapabilitiesRequest();
+            request.fields("field1", "field2");
+
+            // Create a randomly structured compound query containing semantic query
+            QueryBuilder randomCompoundQuery = randomCompoundQueryWithSemantic(randomIntBetween(1, 3));
+            request.indexFilter(randomCompoundQuery);
+
+            ActionRequestValidationException validationException = request.validate();
+            assertThat(validationException, notNullValue());
+            assertThat(validationException.getMessage(), containsString(EXPECTED_ERROR_MESSAGE));
+        }
+    }
+
+    private static SemanticQueryBuilder randomSemanticQuery() {
+        return new SemanticQueryBuilder(randomAlphaOfLength(5), randomAlphaOfLength(10));
+    }
+
+    private static QueryBuilder randomNonSemanticQuery() {
+        return switch (randomIntBetween(0, 2)) {
+            case 0 -> new TermQueryBuilder(randomAlphaOfLength(5), randomAlphaOfLength(5));
+            case 1 -> new MatchAllQueryBuilder();
+            case 2 -> {
+                BoolQueryBuilder boolQuery = new BoolQueryBuilder();
+                boolQuery.must(new TermQueryBuilder(randomAlphaOfLength(5), randomAlphaOfLength(5)));
+                yield boolQuery;
+            }
+            default -> throw new IllegalStateException("Unexpected value");
+        };
+    }
+
+    private static QueryBuilder randomCompoundQueryWithSemantic(int depth) {
+        if (depth <= 0) {
+            return randomSemanticQuery();
+        }
+
+        return switch (randomIntBetween(0, 5)) {
+            case 0 -> {
+                BoolQueryBuilder boolQuery = new BoolQueryBuilder();
+                QueryBuilder clauseQuery = randomCompoundQueryWithSemantic(depth - 1);
+                switch (randomIntBetween(0, 3)) {
+                    case 0 -> boolQuery.must(clauseQuery);
+                    case 1 -> boolQuery.mustNot(clauseQuery);
+                    case 2 -> boolQuery.should(clauseQuery);
+                    case 3 -> boolQuery.filter(clauseQuery);
+                    default -> throw new IllegalStateException("Unexpected value");
+                }
+
+                if (randomBoolean()) {
+                    boolQuery.should(randomNonSemanticQuery());
+                }
+
+                yield boolQuery;
+            }
+            case 1 -> {
+                DisMaxQueryBuilder disMax = new DisMaxQueryBuilder();
+                disMax.add(randomCompoundQueryWithSemantic(depth - 1));
+                if (randomBoolean()) {
+                    disMax.add(randomNonSemanticQuery());
+                }
+                yield disMax;
+            }
+            case 2 -> new NestedQueryBuilder(randomAlphaOfLength(5), randomCompoundQueryWithSemantic(depth - 1), ScoreMode.Max);
+            case 3 -> {
+                boolean positiveSemanticQuery = randomBoolean();
+                QueryBuilder semanticQuery = randomCompoundQueryWithSemantic(depth - 1);
+                QueryBuilder nonSemanticQuery = randomNonSemanticQuery();
+
+                yield new BoostingQueryBuilder(
+                    positiveSemanticQuery ? semanticQuery : nonSemanticQuery,
+                    positiveSemanticQuery ? nonSemanticQuery : semanticQuery
+                );
+            }
+            case 4 -> new ConstantScoreQueryBuilder(randomCompoundQueryWithSemantic(depth - 1));
+            case 5 -> new FunctionScoreQueryBuilder(randomCompoundQueryWithSemantic(depth - 1));
+            default -> throw new IllegalStateException("Unexpected value");
+        };
+    }
+}