branch-4.1: [fix](fe) Fix alias function with cast outermost expr and reject illegal expressions #63254

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/functions/udf/AliasUdf.java

@@ -20,7 +20,6 @@
 import org.apache.doris.catalog.AliasFunction;
 import org.apache.doris.catalog.Env;
 import org.apache.doris.catalog.FunctionSignature;
-import org.apache.doris.nereids.analyzer.UnboundFunction;
 import org.apache.doris.nereids.parser.NereidsParser;
 import org.apache.doris.nereids.trees.expressions.Expression;
 import org.apache.doris.nereids.trees.expressions.functions.ExplicitlyCastableSignature;
@@ -42,23 +41,15 @@
  * alias function
  */
 public class AliasUdf extends ScalarFunction implements ExplicitlyCastableSignature {
-    private final UnboundFunction unboundFunction;
+    private final Expression unboundFunction;
     private final List<String> parameters;
     private final List<DataType> argTypes;
     private final Map<String, String> sessionVariables;
 
-    /**
-     * constructor
-     */
-    public AliasUdf(String name, List<DataType> argTypes, UnboundFunction unboundFunction,
-            List<String> parameters, Expression... arguments) {
-        this(name, argTypes, unboundFunction, parameters, null, arguments);
-    }
-
     /**
      * constructor with session variables
      */
-    public AliasUdf(String name, List<DataType> argTypes, UnboundFunction unboundFunction,
+    public AliasUdf(String name, List<DataType> argTypes, Expression unboundFunction,
             List<String> parameters, Map<String, String> sessionVariables, Expression... arguments) {
         super(name, arguments);
         this.argTypes = argTypes;
@@ -76,7 +67,7 @@ public List<String> getParameters() {
         return parameters;
     }
 
-    public UnboundFunction getUnboundFunction() {
+    public Expression getUnboundFunction() {
         return unboundFunction;
     }
 
@@ -107,7 +98,7 @@ public static void translateToNereidsFunction(String dbName, AliasFunction funct
         AliasUdf aliasUdf = new AliasUdf(
                 function.functionName(),
                 Arrays.stream(function.getArgs()).map(DataType::fromCatalogType).collect(Collectors.toList()),
-                ((UnboundFunction) parsedFunction),
+                parsedFunction,
                 function.getParameters(),
                 sessionVariables);
 

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/CreateFunctionCommand.java

@@ -67,10 +67,15 @@
 import org.apache.doris.nereids.trees.expressions.IntegralDivide;
 import org.apache.doris.nereids.trees.expressions.Mod;
 import org.apache.doris.nereids.trees.expressions.Multiply;
+import org.apache.doris.nereids.trees.expressions.Placeholder;
 import org.apache.doris.nereids.trees.expressions.Slot;
 import org.apache.doris.nereids.trees.expressions.SlotReference;
+import org.apache.doris.nereids.trees.expressions.SubqueryExpr;
 import org.apache.doris.nereids.trees.expressions.Subtract;
+import org.apache.doris.nereids.trees.expressions.WindowExpression;
 import org.apache.doris.nereids.trees.expressions.functions.BoundFunction;
+import org.apache.doris.nereids.trees.expressions.functions.scalar.GroupingScalarFunction;
+import org.apache.doris.nereids.trees.expressions.functions.table.TableValuedFunction;
 import org.apache.doris.nereids.trees.plans.PlanType;
 import org.apache.doris.nereids.trees.plans.commands.info.FunctionArgTypesInfo;
 import org.apache.doris.nereids.trees.plans.logical.LogicalEmptyRelation;
@@ -1025,7 +1030,7 @@ private Expr translateToLegacyExpr(Expression expression, ConnectContext ctx) th
                 ConnectContext.get().getStatementContext().getNextRelationId(), new ArrayList<>());
         CascadesContext cascadesContext = CascadesContext.initContext(ctx.getStatementContext(), plan,
                 PhysicalProperties.ANY);
-        Map<String, DataType> argTypeMap = new CaseInsensitiveMap();
+        Map<String, DataType> argTypeMap = new CaseInsensitiveMap<>();
         List<DataType> argTypes = argsDef.getArgTypeDefs();
         if (!parameters.isEmpty()) {
             if (parameters.size() != argTypes.size()) {
@@ -1039,6 +1044,13 @@ private Expr translateToLegacyExpr(Expression expression, ConnectContext ctx) th
         ExpressionAnalyzer analyzer = new CustomExpressionAnalyzer(cascadesContext, argTypeMap);
         expression = analyzer.analyze(expression);
 
+        if (expression.containsType(
+                org.apache.doris.nereids.trees.expressions.functions.agg.AggregateFunction.class,
+                GroupingScalarFunction.class, WindowExpression.class, Placeholder.class,
+                TableValuedFunction.class, SubqueryExpr.class)) {
+            throw new AnalysisException("Alias function only supports scalar functions.");
+        }
+
         PlanTranslatorContext translatorContext = new PlanTranslatorContext(cascadesContext);
         ExpressionToExpr translator = new ExpressionToExpr();
         return expression.accept(translator, translatorContext);

fe/fe-core/src/test/java/org/apache/doris/nereids/trees/expressions/UdfTest.java

@@ -188,6 +188,37 @@ public void testParameterUseMoreThanOneTime() throws Exception {
                 );
     }
 
+    @Test
+    public void testAliasFunctionWithCastOutermostExpression() throws Exception {
+        // Bug fix: when the outermost expression of an alias function body is a Cast,
+        // AliasUdf.translateToNereidsFunction previously cast parsedFunction to UnboundFunction,
+        // causing ClassCastException. After the fix, parsedFunction is kept as Expression.
+        createFunction(
+                "create alias function f_cast_varchar(int) with parameter(n) as cast(n as varchar(20))");
+
+        Assertions.assertEquals(1, Env.getCurrentEnv().getFunctionRegistry()
+                .findUdfBuilder(connectContext.getDatabase(), "f_cast_varchar").size());
+
+        // Verify the function can be used in a query without error
+        PlanChecker.from(connectContext)
+                .analyze("select f_cast_varchar(42)")
+                .matches(
+                        logicalOneRowRelation()
+                                .when(oneRow -> oneRow.getProjects().size() == 1)
+                );
+    }
+
+    @Test
+    public void testAliasFunctionWithIllegalExpressionsRejected() throws Exception {
+        // Bug fix: before the fix, alias functions containing aggregate functions in their body
+        // could be created successfully, which is incorrect behavior.
+        // After the fix, they are rejected with a clear error message.
+        Exception e = Assertions.assertThrows(Exception.class, () ->
+                createFunction(
+                        "create alias function f_agg_rejected(int) with parameter(n) as sum(n)"));
+        Assertions.assertTrue(e.getMessage().contains("Alias function only supports scalar functions."));
+    }
+
     @Test
     public void testReadFromStream() throws Exception {
         createFunction("create global alias function f8(int) with parameter(n) as hours_add(now(3), n)");