improve test

core/src/execution/datafusion/expressions/regexp.rs

@@ -115,6 +115,8 @@ impl PhysicalExpr for RLike {
                 )
             }
         } else {
+            // this should be unreachable because Spark will evaluate regex expressions against
+            // literal strings as part of query planning
             Err(CometError::Internal("Only columnar inputs are supported".to_string()).into())
         }
     }

spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala

@@ -1100,6 +1100,16 @@ object QueryPlanSerde extends Logging with ShimQueryPlanSerde with CometExprShim
           // in Rust, or even transpile the pattern to work around differences between the JVM
           // and Rust regular expression engines
           if (CometConf.COMET_REGEXP_ALLOW_INCOMPATIBLE.get()) {
+
+            // we currently only support scalar regex patterns
+            right match {
+              case Literal(_, DataTypes.StringType) =>
+              // supported
+              case _ =>
+                withInfo(expr, "Only scalar patterns are supported")
+                return None
+            }
+
             val leftExpr = exprToProtoInternal(left, inputs)
             val rightExpr = exprToProtoInternal(right, inputs)
 

spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala

@@ -601,6 +601,12 @@ class CometExpressionSuite extends CometTestBase with AdaptiveSparkPlanHelper {
       withSQLConf(CometConf.COMET_REGEXP_ALLOW_INCOMPATIBLE.key -> "true") {
         val query = sql(s"select id from $table where name rlike 'R[a-z]+s [Rr]ose'")
         checkSparkAnswerAndOperator(query)
+
+        // test that we fall back to Spark if the pattern is not a scalar value
+        val query2 = sql(s"select id from $table where name rlike name")
+        val (sparkPlan, cometPlan) = checkSparkAnswer(query2)
+        val explain = new ExtendedExplainInfo().generateExtendedInfo(cometPlan)
+        assert(explain == "Only scalar patterns are supported")
       }
     }
   }