[PATCH] D13801: [Support] Extend sys::path with user_cache_directory function.

[Rafael Espíndola via llvm-commits]

> and the above would be replaced with:
> ```
> if (sys::path::user_cache_directory(Dir, "LLVM", "Kaleidoscope")) {
>   sys::path::append(Dir, CacheFileName);
> }
> ```
>
> Which one is better?

The second one if at least the first argument is mandatory. That way
we make sure we never write directly to the top level folder.

> ================
> Comment at: lib/Support/Unix/Path.inc:636
> @@ -585,3 +635,3 @@
>
>  void system_temp_directory(bool ErasedOnReboot, SmallVectorImpl<char> &Result) {
>    Result.clear();
> ----------------
> rafael wrote:
>> Should we drop the EraseOnReboot argument from this function? We would now have
>>
>>  user_cache_directory
>>  system_temp_directory(true
>>  system_temp_directory(false
>>
>> When should each one be used?
> user_cache_directory is similar to system_temp_directory(false) (level of similarity is OS-specific). We can drop system_temp_directory(false) then, but because it is the API change it's probably bad idea to do it at once.
>
> In the end I would like to have:
> user_cache_directory
> system_temp_directory
> and maybe user_temp_directory
>
> I think that needs to be discussed. And we can agree on the final solution I'm happy to implement it.

Awesome. Yes, multiple patches are better.

Cheers,
Rafael