GROOVY-11959: multi-assignment failure for singleton primitives

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

@@ -477,6 +477,13 @@ public void evaluateEqual(final BinaryExpression expression, final boolean defin
             return;
         }
 
+        // GROOVY-11959: box primitive RHS so the temp slot holds an object reference
+        // (the multi-assignment path ALOADs it for IF_ACMPEQ and dispatches iterator/getAt on it)
+        if (!singleAssignment && ClassHelper.isPrimitiveType(rhsType)) {
+            operandStack.box();
+            rhsType = operandStack.getTopOperand();
+        }
+
         int rhsValueId = compileStack.defineTemporaryVariable("$rhs", rhsType, true);
         // TODO: if RHS is already a VariableSlotLoader, then skip creating a new one
         Expression rhsValueLoader = new VariableSlotLoader(rhsType, rhsValueId, operandStack);

src/test/groovy/gls/statements/MultipleAssignmentDeclarationTest.groovy

@@ -151,6 +151,38 @@ final class MultipleAssignmentDeclarationTest {
         '''
     }
 
+    @Test // GROOVY-11959
+    void testMultiAssignFromInteger() {
+        shouldFail MissingMethodException, '''
+            Integer z = 42
+            def (x, y) = z
+        '''
+    }
+
+    @Test // GROOVY-11959
+    void testMultiAssignFromPrimitiveInt() {
+        shouldFail MissingMethodException, '''
+            int z = 42
+            def (x, y) = z
+        '''
+    }
+
+    @Test // GROOVY-11959
+    void testMultiAssignFromPrimitiveLong() {
+        shouldFail MissingMethodException, '''
+            long z = 42L
+            def (x, y) = z
+        '''
+    }
+
+    @Test // GROOVY-11959
+    void testMultiAssignFromPrimitiveDouble() {
+        shouldFail MissingMethodException, '''
+            double z = 4.2d
+            def (x, y) = z
+        '''
+    }
+
     @Test
     void testMultiAssignFromCalendar() {
         assertScript '''