GROOVY-11982: Default methods in interface throw IncompatibleClassCha…

src/main/java/org/codehaus/groovy/classgen/AsmClassGenerator.java

@@ -1467,8 +1467,12 @@ public void visitVariableExpression(final VariableExpression expression) {
     }
 
     protected void createInterfaceSyntheticStaticFields() {
-        if (referencedClasses.isEmpty()) return;
         var icl = controller.getInterfaceClassLoadingClass();
+        // GROOVY-11982: also materialise the helper when there are call sites
+        // (e.g. dynamic code in default methods under indy=false), otherwise
+        // CallSiteWriter routes INVOKESTATIC at a class that was never emitted
+        boolean hasCallSites = !controller.getCallSiteWriter().getCallSites().isEmpty();
+        if (referencedClasses.isEmpty() && !hasCallSites) return;
         addInnerClass(icl);
         for (Map.Entry<String, ClassNode> entry : referencedClasses.entrySet()) {
             // generate a field node

src/main/java/org/codehaus/groovy/classgen/asm/CallSiteWriter.java

@@ -115,7 +115,10 @@ public void makeSiteEntry() {
         if (controller.isNotClinit()) {
             MethodVisitor mv = controller.getMethodVisitor();
             mv.visitInsn(NOP); // GROOVY-9076: need this for debugger to support step into
-            mv.visitMethodInsn(INVOKESTATIC, controller.getInternalClassName(), GET_CALLSITE_METHOD, GET_CALLSITE_DESC, false);
+            // GROOVY-11982: for an interface, route to the helper inner class which
+            // owns $getCallSiteArray (interfaces themselves never have it, and an
+            // INVOKESTATIC Methodref against an interface owner throws ICCE)
+            mv.visitMethodInsn(INVOKESTATIC, controller.getClassName(), GET_CALLSITE_METHOD, GET_CALLSITE_DESC, false);
             controller.getOperandStack().push(CALLSITE_ARRAY_TYPE);
             callSiteArrayVarIndex = controller.getCompileStack().defineTemporaryVariable("$local$callSiteArray", CALLSITE_ARRAY_TYPE, true);
         }

src/test/groovy/bugs/Groovy11982.groovy

@@ -0,0 +1,96 @@
+/*
+ *  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 bugs
+
+import org.codehaus.groovy.control.CompilerConfiguration
+import org.junit.jupiter.api.Test
+
+/**
+ * An interface default method whose body uses dynamic Groovy features (e.g. a
+ * {@code GString} or a dynamic method call) needs the call-site array. Under
+ * {@code indy=false} the bytecode prologue emitted at the top of the method
+ * is {@code INVOKESTATIC $getCallSiteArray()}; the owner of that call must be
+ * the synthetic helper class (not the interface itself), and the helper must
+ * actually be materialised. Otherwise the JVM throws
+ * {@code IncompatibleClassChangeError} at first invocation because a
+ * {@code Methodref} cannot resolve to an interface owner.
+ */
+final class Groovy11982 {
+
+    @Test
+    void testInterfaceDefaultMethodWithGStringNonIndy() {
+        CompilerConfiguration config = new CompilerConfiguration()
+        config.optimizationOptions.put('indy', false)
+        new GroovyShell(config).evaluate '''
+            interface IConfig {
+                String getName()
+                default String getDescription() {
+                    "config[name=${getName()}]"
+                }
+            }
+            class ConfigImpl implements IConfig {
+                String getName() { 'impl' }
+            }
+            assert new ConfigImpl().description == 'config[name=impl]'
+        '''
+    }
+
+    @Test
+    void testInterfaceDefaultMethodCallingOtherDefaultNonIndy() {
+        CompilerConfiguration config = new CompilerConfiguration()
+        config.optimizationOptions.put('indy', false)
+        new GroovyShell(config).evaluate '''
+            interface IConfig {
+                String getName()
+                default String getDescription() {
+                    "config[name=${getName()}]"
+                }
+                default String greet() {
+                    "greeted as ${getDescription()}"
+                }
+            }
+            class ConfigImpl implements IConfig {
+                String getName() { 'impl' }
+            }
+            assert new ConfigImpl().greet() == 'greeted as config[name=impl]'
+        '''
+    }
+
+    @Test
+    void testStaticConsumerCallsDefaultMethodNonIndy() {
+        CompilerConfiguration config = new CompilerConfiguration()
+        config.optimizationOptions.put('indy', false)
+        new GroovyShell(config).evaluate '''
+            interface IConfig {
+                String getName()
+                default String getDescription() {
+                    "config[name=${getName()}]"
+                }
+            }
+            class ConfigImpl implements IConfig {
+                String getName() { 'impl' }
+            }
+            @groovy.transform.CompileStatic
+            class StaticConsumer {
+                static String describe(IConfig c) { c.description }
+            }
+            assert StaticConsumer.describe(new ConfigImpl()) == 'config[name=impl]'
+        '''
+    }
+}