Re: [PATCH 5/5] gdbsupport: add path_join function

[Simon Marchi <simon.marchi@polymtl.ca>]

> On 2022-04-18 15:09, Pedro Alves wrote:
>> On 2022-04-18 19:43, Simon Marchi via Gdb-patches wrote:
>>>> One implementation could be:
>>>>
>>>>     /* The real worker can be compiled in a .cc file if you wish.  */
>>>>     extern std::string path_join_1 (std::string a, std::string b);
>>>>
>>>>     template <typename ...Args)
>>>>     std::string
>>>>     path_join (std::string a, std::string b, Args... comps)
>>>>     {
>>>>       return path_join (path_join (a, b), comps...);
>>>>     }
>>>>
>>>>     template <>
>>>>     std::string
>>>>     path_join (std::string a, std::string b)
>>>>     {
>>>>       return path_join_1 (a, b);
>>>>     }
>>>>
>>>> I do not pretend this is optimal (it is not).  In this POC I pass all
>>>> arguments as std::string and by value, this is probably not what you
>>>> want to do in a production grade implementation, but this just gives the
>>>> overall idea.
>>>>
>>>> What do you think?
>>> If you can make it work using gdb::string_view or const char *, I think
>>> it would be ok.  I'll give it a try.  But otherwise, I am personally
>>> fine with the sentinel nullptr, given that the compiler gives you a
>>> warning if you forget it.
>>
>> I think it would just work as is you replace std::string with const char *
>> in Lancelot's snippet above.  FWIW, I had the same thought as Lancelot
>> about using variable templates instead of varargs.
>>
>> OOC, is there any place in GDB that wants to pass more than two components
>> to path_join?  I skimmed the patch and didn't notice one.
> 
> I am not aware of one, I'd be happy to make path_join just have two
> parameters and be done with it.

Actually, I have one use for it in my upcoming DWARF reader changes,
where I join the CU's compilation directory, the directory (from the
line header directory table) and the file name.

I like Tom's proposal, here:

  https://sourceware.org/pipermail/gdb-patches/2022-April/188016.html

It seems efficient (no extraneous string copies) and type-safe.  I
successfully changed my patch to use it.

Simon