[CALCITE-7772] ModelHandler.addFunctions should defer UDF class initialization until after shape validation

core/src/main/java/org/apache/calcite/model/ModelHandler.java

@@ -227,10 +227,10 @@
     filter.check(className);
     final Class<?> clazz;
     try {
-      clazz = Class.forName(className);
+      // Defer class initialization until it is checked to be a valid function (see below)
+      clazz = Class.forName(className, false, ModelHandler.class.getClassLoader());
     } catch (ClassNotFoundException e) {
-      throw new RuntimeException("UDF class '"
-          + className + "' not found");
+      throw new RuntimeException("UDF class '" + className + "' not found");
     }
     String methodNameOrDefault = Util.first(methodName, "eval");
     String actualFunctionName;

core/src/test/java/org/apache/calcite/model/ModelHandlerTest.java

@@ -36,6 +36,7 @@
 import java.sql.DriverManager;
 import java.util.Properties;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.is;
@@ -120,6 +121,33 @@ public class ModelHandlerTest {
     assertThat(e.getMessage(), containsString("javax.naming."));
   }
 
+  /** Set by {@link NotAFunction}'s static initializer. */
+  static final AtomicBoolean NOT_A_FUNCTION_INITIALIZED = new AtomicBoolean(false);
+
+  /** Not a valid function class; records whether its static initializer ran. */
+  public static class NotAFunction {
+    static {
+      NOT_A_FUNCTION_INITIALIZED.set(true);
+    }
+  }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7772">[CALCITE-7772] ModelHandler
+   * addFunctions should defer UDF class initialization until after shape validation</a>.
+   * A class that passes the name filter but fails the function-shape
+   * checks must be rejected without its static initializer running. */
+  @Test void testRejectedUdfClassIsNotInitialized() {
+    SchemaPlus root = CalciteSchema.createRootSchema(false, false).plus();
+    ClassNameFilter permissive = ClassNameFilter.of("", "org.apache.calcite.");
+    RuntimeException e =
+        assertThrows(RuntimeException.class, () ->
+            ModelHandler.addFunctions(permissive, root, "f",
+                NotAFunction.class.getName(), null, false));
+    assertThat(e.getMessage(), containsString("Not a valid function class"));
+    assertThat("static initializer of a rejected UDF class must not run",
+        NOT_A_FUNCTION_INITIALIZED.get(), is(false));
+  }
+
   @Test void testDenyFactory() {
     String model = "inline:{"
         + "  version: '1.0',"