yuqi1129 commented on code in PR #13142:
URL: https://github.com/apache/gravitino/pull/13142#discussion_r4013357665


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trino-connector/trino-connector/src/main/java/org/apache/gravitino/trino/connector/util/TrinoRoutineSpecification.java:
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@@ -0,0 +1,133 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.gravitino.trino.connector.util;
+
+import io.trino.spi.TrinoException;
+import io.trino.spi.type.Type;
+import java.util.Arrays;
+import java.util.stream.Collectors;
+import org.apache.gravitino.function.Function;
+import org.apache.gravitino.function.FunctionDefinition;
+import org.apache.gravitino.trino.connector.GravitinoErrorCode;
+
+/**
+ * Builds the SQL routine specification Trino expects for a language function 
from a Gravitino
+ * function definition and its stored SQL body:
+ *
+ * <pre>FUNCTION name(params) RETURNS type [NOT] DETERMINISTIC SECURITY 
INVOKER body</pre>
+ *
+ * <p>The stored body is either a bare expression, which is wrapped in a 
{@code RETURN} statement,
+ * or a control statement ({@code RETURN ...} / {@code BEGIN ... END}) that is 
used as-is. {@code
+ * SECURITY INVOKER} is always declared because the function has no owner 
identity for Trino's
+ * {@code SECURITY DEFINER} default.
+ *
+ * <p>Identifiers are always quoted. Trino resolves routine and parameter 
names case-insensitively
+ * regardless of quoting, so this is equivalent to plain identifiers while 
also covering reserved
+ * words and names with special characters.
+ */
+public final class TrinoRoutineSpecification {
+
+  private TrinoRoutineSpecification() {}
+
+  /**
+   * Builds the routine specification for one definition of a function.
+   *
+   * @param function the Gravitino function
+   * @param definition the definition whose parameters and return type 
describe the routine
+   * @param sql the stored SQL body
+   * @param typeTransformer converts Gravitino types to Trino types
+   * @return the complete routine specification
+   * @throws TrinoException if the definition or body is not supported or a 
type cannot be mapped
+   */
+  public static String build(
+      Function function,
+      FunctionDefinition definition,
+      String sql,
+      GeneralDataTypeTransformer typeTransformer) {
+    if (definition.returnType() == null) {
+      throw new TrinoException(
+          GravitinoErrorCode.GRAVITINO_ILLEGAL_ARGUMENT,
+          "Function " + function.name() + " has a definition without a return 
type");
+    }
+    String body = stripLeadingComments(sql);
+    if (startsWithKeyword(body, "FUNCTION")) {
+      throw new TrinoException(
+          GravitinoErrorCode.GRAVITINO_ILLEGAL_ARGUMENT,
+          "The SQL body of function "
+              + function.name()
+              + " must be an expression or a RETURN/BEGIN statement, not a 
full FUNCTION"
+              + " specification");
+    }
+
+    String parameters =
+        Arrays.stream(definition.parameters())
+            .map(
+                param ->
+                    quoteIdentifier(param.name())
+                        + " "
+                        + 
formatType(typeTransformer.getTrinoType(param.dataType())))
+            .collect(Collectors.joining(", ", "(", ")"));
+    String statement =
+        startsWithKeyword(body, "RETURN") || startsWithKeyword(body, "BEGIN")
+            ? body
+            : "RETURN " + body;

Review Comment:
   [P2] Avoid classifying a bare expression solely by its first keyword.
   
   Trino allows `return`, `begin`, and `function` as unquoted identifiers. For 
a parameter named `return` and a bare SQL body `return + 1`, this branch emits 
`return + 1` unchanged instead of `RETURN return + 1`. I verified with the 
Trino 440 parser that the emitted routine contains `ReturnStatement{value=+1}`, 
whereas the expected routine contains `ReturnStatement{value=(return + 1)}`. 
This silently returns a constant instead of using the argument.
   
   Similarly, `begin + 1` is mistaken for a block, and `function + 1` is 
rejected by the earlier full-specification check. Could we disambiguate 
expression bodies from statements and add regression tests for these parameter 
names, including an assertion that the parameter reference is preserved?



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