[cfe-dev] RFC: A virtual file system for clang

[Manuel Klimek]

On Fri, Feb 7, 2014 at 9:13 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com>wrote:

>
> On Feb 7, 2014, at 11:09 AM, Manuel Klimek <klimek at google.com> wrote:
>
> On Fri, Feb 7, 2014 at 6:39 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com>wrote:
>
>> Hi Manuel,
>>
>> On Feb 7, 2014, at 1:01 AM, Manuel Klimek <klimek at google.com> wrote:
>>
>>
>>> Some non-goals (at least for a first iteration):
>>> 1) File system modification operations (create_directory, rename, etc.).
>>>  Clients will continue to use the real file system for these operations,
>>> and we don’t intend to detect any conflicts this might create.
>>> 2) Completely virtual file buffers that do not exist on disk.
>>>
>>
>> I'd vote for making that an explicit goal; two reasons:
>> 1. I don't think it'll make a first iteration harder to implement
>> 2. saying that we'll do things like that later will almost certainly make
>> it super-hard to do later
>>
>>
>> We don’t have the bandwidth to design / implement / test fully virtual
>> files.
>>
>
> I'm curious why you think it will be a lot more effort; my gut feeling
> would be that this is probably going to be less effort (depending on what
> exactly you want to use the VFS layer for)
>
>
> You can always prove me wrong, after we have the simpler case (mapping
> virtual paths to real paths) working ;-)
>
> I just want to make clear that we are going to focus on what we need,
> which is to get modules for ObjC user frameworks working and fully
> supported. Virtual file buffers is not something we need at the moment (but
> to reiterate, we don’t want to prohibit either).
>

Ok :) I'm probably mainly confused because I think it'll be hard to *not*
support virtual file buffers with any design I can think of, so I was
concerned when you said that it's an explicit non-goal (as opposed to being
just not a primary goal).


>
> if we don't want to break all of the Tooling layers in the process.
>
>
> Not sure why they would break, if these are based on the FileManager. Also
> as long as the related “vfs” option is not passed to a compiler invocation
> to introduce a virtual layout via a configuration file, there should be no
> behavior change anywhere.
>

Sounds good.


>
>
>
>> We also don’t have uses for them (apart from replacing the remapping of
>> buffers in the SourceManager) so I think this should be driven by someone
>> that actually needs this and is going to dogfood it.
>>
>> Apart from that, we are definitely trying to make sure we will not do
>> anything that will make adding virtual files prohibitively difficult, we
>> think it can be added on top with maybe some refinements on the interface.
>> While we are implementing the VFS if you think we are doing something
>> that will make virtual file buffers “super-hard to do later” please let us
>> know.
>>
>
> Will do.
>
> Cheers,
> /Manuel
>
>
>
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