fix #380: Fix skipping of nested if statements and loops in else branch

Author: adazem009

src/engine/virtualmachine_p.cpp

@@ -254,9 +254,20 @@ unsigned int *VirtualMachinePrivate::run(unsigned int *pos, bool reset)
     DISPATCH();
 
 do_else:
-    while (*pos != OP_ENDIF)
+    unsigned int ifCounter = 1;
+    while (!(*pos == OP_ENDIF && ifCounter == 0)) {
         pos += instruction_arg_count[*pos++];
 
+        if ((*pos == OP_IF) || (*pos == OP_FOREVER_LOOP) || (*pos == OP_REPEAT_LOOP) || (*pos == OP_UNTIL_LOOP))
+            ifCounter++;
+        else if ((*pos == OP_ENDIF) || (*pos == OP_LOOP_END)) {
+            assert(ifCounter > 0);
+            ifCounter--;
+        }
+
+        assert(!(*pos == OP_ELSE && ifCounter == 1));
+    }
+
 do_endif:
     DISPATCH();
 

test/virtual_machine/virtual_machine_test.cpp

@@ -1641,6 +1641,17 @@ TEST(VirtualMachineTest, NoCrashInNestedIfStatementsWithLoopAndIfElse)
 TEST(VirtualMachineTest, NoCrashInNestedLoopsInRepeatUntilLoop)
 {
     // Regtest for #379
+    static unsigned int bytecode[] = { OP_START, OP_NULL, OP_NOT, OP_IF, OP_ELSE, OP_NULL, OP_REPEAT_LOOP, OP_NULL, OP_IF, OP_ENDIF, OP_LOOP_END, OP_ENDIF, OP_HALT };
+
+    VirtualMachine vm(nullptr, nullptr, nullptr);
+    vm.setBytecode(bytecode);
+    vm.run();
+    ASSERT_EQ(vm.registerCount(), 0);
+}
+
+TEST(VirtualMachineTest, NoCrashInNestedLoopsInIfElseStatements)
+{
+    // Regtest for #380
     static unsigned int bytecode[] = { OP_START, OP_UNTIL_LOOP, OP_NULL, OP_NOT, OP_BEGIN_UNTIL_LOOP, OP_NULL, OP_REPEAT_LOOP, OP_LOOP_END, OP_LOOP_END, OP_HALT };
 
     VirtualMachine vm(nullptr, nullptr, nullptr);