[PATCH] Add a VFSFromYAML class and a parser to create it

[Ben Langmuir]

On Feb 20, 2014, at 4:11 PM, Ben Langmuir <blangmuir at apple.com> wrote:

> 
> On Feb 20, 2014, at 11:22 AM, Argyrios Kyrtzidis <kyrtzidis at apple.com> wrote:
> 
>> On Feb 20, 2014, at 10:02 AM, Ben Langmuir <blangmuir at apple.com> wrote:
>> 
>>> 
>>>> I think it is better to move the YAML VFS description to a new file under 'docs/'. This file format is API, and should be documented.
>>> 
>>> Can this wait until we have more practical experience with the file format? Things in docs/ tend to have better documentation that what I've written here, and I don't want to put a lot of effort into this until we're sure this is the right format.
>> 
>> +1, we are far from the point of committing to API, this is still in flux.
>> 
>>> 
>>>> Unrelated to this patch, but how do we keep track of the current working directory? Or we don't just yet?
>>> 
>>> We don't :)  I'll look at whether that is simple to do now, or can wait.  It won't be exercised until we use the VFS outside of FileManager, since FileManager always creates absolute paths I think.
>> 
>> FileManager has FileSystemOptions which has the “-working-directory” option, we should probably take advantage of that.
>> 
>>> 
>>> ================
>>> Comment at: lib/Basic/VirtualFileSystem.cpp:260
>>> @@ +259,3 @@
>>> +/// Possible configuration settings are
>>> +///   'case-sensitive': <boolean>
>>> +///
>>> ----------------
>>> Dmitri Gribenko wrote:
>>>> Is it optional?  If so, what is the default?
>>>> 
>>>> Please also add a mandatory version field, and refuse to load files with incorrect version.  I hope we will never have to bump the version and evolve the format in a compatible way, but who knows...
>>> It is optional, which is mentioned above.  I will specify its default value.
>>> 
>>> The version is going to make my unit tests ugly, but I see your point.
>> 
>> Do we need something standard at the beginning (something equivalent to a "<?xml version="1.0" encoding="UTF-8”?>”) that we can sniff out to figure out if it is json or binary format ?
>> I would prefer that if we move to binary format, the build system would need no changes at all (e.g. not require that the build system changes the file extension).
>> 
> 
> We could use the YAML version string
> %YAML 1.2

Actually, if we go this route we should encode our own version number in the same place for compactness.  In YAML, we could use a tag for this

%TAG ! tag:vfs-yaml-file,version:1234

Where 1234 is a made up version number for our vfs format.

Ben

> 
> It’s not legal JSON, but I don’t see any reason to be strict about JSON conformance as long as our parser works.
> 
> Ben