[Bug c++/62181] [C/C++] Expected new warning: "adding 'char' to a string does not append to the string" [-Wstring-plus-int]

[ryxi at stu dot xidian.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62181

--- Comment #7 from Xi Ruoyao <ryxi at stu dot xidian.edu.cn> ---
(In reply to Martin Sebor from comment #6)
> With constant arguments (or those whose value or range is known), GCC should
> warn on the first declaration in comment #0 (copied below) not necessarily
> because the addition doesn't append 'c' to "aa" (i.e., with
> -Wstring-plus-char warns) but mainly because it results in an invalid
> pointer.
> 
>   const char *a = "aa" + 'c';
> 
> GCC should warn for a constant operand that results in an out-of-bounds
> pointer regardless of its type, such as the following:
> 
>   const char *a = "aa" + 4;
> 

Clang-5.0 is doing this now for -Wstring-plus-int.  I'll try to do this.

> GCC could (and, in my view, should) also warn on the following where the
> value of i isn't known but where its range is such that the addition will
> never result in a valid pointer:
> 
>   void f (int i)
>   {
>     if (i < 4) return;
>     const char *a = "aa" + i;
>     ...
>   }

We should make a new PR requesting for clang -Warray-bounds as well.  It's
a part of meta-bug PR30334.