Fix Janino classloader issue when analytics-engine is parent plugin

Calcite's EnumerableInterpretable.getBindable() hardcodes
EnumerableInterpretable.class.getClassLoader() for Janino compilation.
When analytics-engine is the parent classloader via extendedPlugins,
this returns the parent classloader which cannot see SQL plugin classes,
causing CompileException for any Enumerable code generation.

Override implement() in OpenSearchCalcitePreparingStmt to use our own
compileWithPluginClassLoader() which does the same code generation but
uses CalciteToolsHelper.class.getClassLoader() (SQL plugin's child
classloader) so Janino can resolve both parent and child classes.

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

core/src/main/java/org/opensearch/sql/calcite/utils/CalciteToolsHelper.java

@@ -358,7 +358,140 @@ public Type getElementType() {
           }
         };
       }
-      return super.implement(root);
+      return implementEnumerable(root);
+    }
+
+    /**
+     * Implements the Enumerable path with classloader fix for Janino compilation. Calcite's {@code
+     * EnumerableInterpretable.getBindable()} hardcodes {@code
+     * EnumerableInterpretable.class.getClassLoader()} as the parent classloader for Janino. When
+     * analytics-engine is the parent classloader (via extendedPlugins), this returns the
+     * analytics-engine classloader which cannot see SQL plugin classes. This method replicates the
+     * Calcite implementation but uses this class's classloader (SQL plugin, child) which can see
+     * both parent and child classes.
+     */
+    private PreparedResult implementEnumerable(RelRoot root) {
+      Hook.PLAN_BEFORE_IMPLEMENTATION.run(root);
+      RelDataType resultType = root.rel.getRowType();
+      boolean isDml = root.kind.belongsTo(SqlKind.DML);
+      EnumerableRel enumerable = (EnumerableRel) root.rel;
+
+      if (!root.isRefTrivial()) {
+        List<RexNode> projects = new java.util.ArrayList<>();
+        final RexBuilder rexBuilder = enumerable.getCluster().getRexBuilder();
+        for (java.util.Map.Entry<Integer, String> field : root.fields) {
+          projects.add(rexBuilder.makeInputRef(enumerable, field.getKey()));
+        }
+        org.apache.calcite.rex.RexProgram program =
+            org.apache.calcite.rex.RexProgram.create(
+                enumerable.getRowType(), projects, null, root.validatedRowType, rexBuilder);
+        enumerable =
+            org.apache.calcite.adapter.enumerable.EnumerableCalc.create(enumerable, program);
+      }
+
+      // Access the internalParameters map via reflection. This map is shared with the
+      // DataContext so stashed values (e.g., table scan references) are available at execution.
+      java.util.Map<String, Object> parameters;
+      try {
+        java.lang.reflect.Field f =
+            CalcitePrepareImpl.CalcitePreparingStmt.class.getDeclaredField("internalParameters");
+        f.setAccessible(true);
+        @SuppressWarnings("unchecked")
+        java.util.Map<String, Object> p = (java.util.Map<String, Object>) f.get(this);
+        parameters = p;
+      } catch (ReflectiveOperationException e) {
+        throw new RuntimeException("Failed to access internalParameters", e);
+      }
+
+      CatalogReader.THREAD_LOCAL.set(catalogReader);
+      final Bindable bindable;
+      try {
+        bindable = compileWithPluginClassLoader(enumerable, parameters);
+      } finally {
+        CatalogReader.THREAD_LOCAL.remove();
+      }
+
+      return new PreparedResultImpl(
+          resultType,
+          requireNonNull(parameterRowType, "parameterRowType"),
+          requireNonNull(fieldOrigins, "fieldOrigins"),
+          root.collation.getFieldCollations().isEmpty()
+              ? ImmutableList.of()
+              : ImmutableList.of(root.collation),
+          root.rel,
+          mapTableModOp(isDml, root.kind),
+          isDml) {
+        @Override
+        public String getCode() {
+          throw new UnsupportedOperationException();
+        }
+
+        @Override
+        public Bindable getBindable(Meta.CursorFactory cursorFactory) {
+          return bindable;
+        }
+
+        @Override
+        public Type getElementType() {
+          return resultType.getFieldList().size() == 1 ? Object.class : Object[].class;
+        }
+      };
+    }
+
+    /**
+     * Compiles an EnumerableRel to a Bindable using the SQL plugin's classloader. This is
+     * equivalent to {@code EnumerableInterpretable.toBindable()} + {@code getBindable()} but uses
+     * this class's classloader instead of {@code EnumerableInterpretable.class.getClassLoader()}.
+     */
+    private static Bindable compileWithPluginClassLoader(
+        EnumerableRel rel, java.util.Map<String, Object> parameters) {
+      try {
+        org.apache.calcite.adapter.enumerable.EnumerableRelImplementor relImplementor =
+            new org.apache.calcite.adapter.enumerable.EnumerableRelImplementor(
+                rel.getCluster().getRexBuilder(), parameters);
+        org.apache.calcite.linq4j.tree.ClassDeclaration expr =
+            relImplementor.implementRoot(rel, EnumerableRel.Prefer.ARRAY);
+        String s =
+            org.apache.calcite.linq4j.tree.Expressions.toString(
+                expr.memberDeclarations, "\n", false);
+        Hook.JAVA_PLAN.run(s);
+
+        // Use this class's classloader (SQL plugin) instead of
+        // EnumerableInterpretable.class.getClassLoader() (analytics-engine parent).
+        // commons-compiler is in the parent classloader at runtime, so we use reflection.
+        ClassLoader classLoader = CalciteToolsHelper.class.getClassLoader();
+        Class<?> factoryFactoryClass =
+            classLoader.loadClass("org.codehaus.commons.compiler.CompilerFactoryFactory");
+        Object compilerFactory =
+            factoryFactoryClass
+                .getMethod("getDefaultCompilerFactory", ClassLoader.class)
+                .invoke(null, classLoader);
+        Object compiler =
+            compilerFactory.getClass().getMethod("newSimpleCompiler").invoke(compilerFactory);
+        compiler
+            .getClass()
+            .getMethod("setParentClassLoader", ClassLoader.class)
+            .invoke(compiler, classLoader);
+
+        String fullCode =
+            "public final class "
+                + expr.name
+                + " implements "
+                + Bindable.class.getName()
+                + ", "
+                + org.apache.calcite.runtime.Typed.class.getName()
+                + " {\n"
+                + s
+                + "\n}\n";
+        compiler.getClass().getMethod("cook", String.class).invoke(compiler, fullCode);
+        ClassLoader compiledClassLoader =
+            (ClassLoader) compiler.getClass().getMethod("getClassLoader").invoke(compiler);
+        @SuppressWarnings("unchecked")
+        Class<Bindable> clazz = (Class<Bindable>) compiledClassLoader.loadClass(expr.name);
+        return clazz.getDeclaredConstructors()[0].newInstance() instanceof Bindable b ? b : null;
+      } catch (Exception e) {
+        throw org.apache.calcite.util.Util.throwAsRuntime(e);
+      }
     }
 
     @Override