SQL: Verify Full-Text Search functions not allowed in SELECT

Add a verification that full-text search functions are not
allowed in the SELECT clause, so that a nice error message is
returned to the user early instead of an "ugly" exception.

Fixes: elastic#47446

Author: matriv

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/analysis/analyzer/Verifier.java

@@ -22,6 +22,7 @@
 import org.elasticsearch.xpack.ql.expression.function.aggregate.AggregateFunction;
 import org.elasticsearch.xpack.ql.expression.function.grouping.GroupingFunction;
 import org.elasticsearch.xpack.ql.expression.function.scalar.ScalarFunction;
+import org.elasticsearch.xpack.ql.expression.predicate.fulltext.FullTextPredicate;
 import org.elasticsearch.xpack.ql.plan.logical.Aggregate;
 import org.elasticsearch.xpack.ql.plan.logical.Filter;
 import org.elasticsearch.xpack.ql.plan.logical.Limit;
@@ -215,8 +216,16 @@ Collection<Failure> verify(LogicalPlan plan) {
         // if there are no (major) unresolved failures, do more in-depth analysis
 
         if (failures.isEmpty()) {
+            Set<Failure> localFailures = new LinkedHashSet<>();
             final Map<Attribute, Expression> collectRefs = new LinkedHashMap<>();
 
+            // Full-Text search function are not allowed in the SELECT clause
+            plan.forEachUp(p -> p.forEachExpressionsUp(e -> {
+                if (e instanceof FullTextPredicate) {
+                    localFailures.add(fail(e, "Cannot use a Full-Text search functions in the SELECT clause"));
+                }
+            }), Project.class);
+
             // collect Attribute sources
             // only Aliases are interesting since these are the only ones that hide expressions
             // FieldAttribute for example are self replicating.
@@ -242,8 +251,6 @@ Collection<Failure> verify(LogicalPlan plan) {
                     return;
                 }
 
-                Set<Failure> localFailures = new LinkedHashSet<>();
-
                 checkGroupingFunctionInGroupBy(p, localFailures);
                 checkFilterOnAggs(p, localFailures, attributeRefs);
                 checkFilterOnGrouping(p, localFailures, attributeRefs);

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/analysis/analyzer/VerifierErrorMessagesTests.java

@@ -511,7 +511,7 @@ public void testUnsupportedTypeInHierarchy() {
         assertEquals("1:8: Cannot use field [x.y] with unsupported type [foobar]", error("SELECT x.y FROM test"));
     }
 
-    public void testTermEqualitOnInexact() {
+    public void testTermEqualityOnInexact() {
         assertEquals("1:26: [text = 'value'] cannot operate on first argument field of data type [text]: " +
                 "No keyword/multi-field defined exact matches for [text]; define one or use MATCH/QUERY instead",
             error("SELECT * FROM test WHERE text = 'value'"));
@@ -712,6 +712,13 @@ public void testInvalidTypeForRLikeMatch() {
             error("SELECT * FROM test WHERE text RLIKE 'foo'"));
     }
 
+    public void testFullTextFunctionsNotAllowedInSelect() {
+        assertEquals("1:8: Cannot use a Full-Text search functions in the SELECT clause",
+                error("SELECT MATCH(text, 'foo') FROM test"));
+        assertEquals("1:38: Cannot use a Full-Text search functions in the SELECT clause",
+                error("SELECT int > 10 AND (bool = false OR QUERY('foo*')) FROM test"));
+    }
+
     public void testAllowCorrectFieldsInIncompatibleMappings() {
         assertNotNull(incompatibleAccept("SELECT languages FROM \"*\""));
     }