[RFC] Throwing an exception with null pointers

[Richard (Rikki) Andrew Cattermole]

On 17/04/2025 10:54 AM, Derek Fawcus wrote:
> On Wednesday, 16 April 2025 at 22:43:24 UTC, Derek Fawcus wrote:
>> ```
>> $ clang-14 -Wall -Wnullable-to-nonnull-conversion -c ttt.c
>> ttt.c:37:8: warning: implicit conversion from nullable pointer 'int * 
>> _Nullable' to non-nullable pointer type 'int * _Nonnull' [-Wnullable- 
>> to-nonnull-conversion]
>>         ptr = arg3;
>>               ^
>> ttt.c:41:20: warning: implicit conversion from nullable pointer 'int * 
>> _Nullable' to non-nullable pointer type 'int * _Nonnull' [-Wnullable- 
>> to-nonnull-conversion]
>>         a += *someNonNull(arg3);
>>                           ^
>> ttt.c:29:16: warning: variable 'ptr' set but not used [-Wunused-but- 
>> set-variable]
>>         int * NONNULL ptr;
>>                       ^
>> 3 warnings generated.
>> ```
> 
> Having now got this to complain in the desired fashion, I'll now be 
> applying it to some code at work.  More help in quashing sources of bugs.

After a quick play, I would suggest also passing ``--analyze`` if you 
are not already doing so.

It covers the case where you are not assuming non-null.

I.e. it can see the difference between:

```c++
void test(int *p) {
   if (!p)
     *p = 0; // warn
}
```

and

```c++
void test2(int *p) {
   if (p)
     *p = 0; // ok
}
```

This is definitely DFA.