Ambiguous if and else branches: Is the behaviour defined?

Question

I recently came accross some C++ code like the following:

if(test_1)
    if(test_2)
    {
         // Do stuff
    }
    else
       exit(0);

Answer 1

Yes its not ambiguous, as the rules state where it is applied, but my GCC C++ compiler still gives a warning stating it is :

/brainModule/BrainModule.cpp: In function ‘void failExpiredPendingAndRunning()’: ../brainModule/BrainModule.cpp:158:16: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if (job->isExpired() == false)

g++ (Raspbian 6.3.0-18+rpi1+deb9u1) 6.3.0 20170516