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Re: [PATCH] schemas: Add vim modeline

From: John Snow
Subject: Re: [PATCH] schemas: Add vim modeline
Date: Fri, 31 Jul 2020 02:45:54 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 7/30/20 9:24 AM, Daniel P. Berrangé wrote:
On Thu, Jul 30, 2020 at 01:51:10PM +0200, Markus Armbruster wrote:
Daniel P. Berrangé <berrange@redhat.com> writes:

                               modify them so that we can load the
files straight into the python intepretor as code, and not parse
them as data. I feel unhappy about treating data as code though.

Stress on *can* load.  Doesn't mean we should.

Ancient prior art: Lisp programs routinely use s-expressions as
configuration file syntax.  They don't load them as code, they read them
as data.

With Python, it's ast.parse(), I think.

Yes, that could work

I use a similar trick for parsing "Fuzzy JSON" inside of qmp-shell.

It's cute, and I'm not really proud of it.

struct: ImageInfoSpecificQCow2
   compat: str
   "*data-file": str
   "*data-file-raw": bool
   "*lazy-refcounts": bool
   "*corrupt": bool
   refcount-bits: int
   "*encrypt": ImageInfoSpecificQCow2Encryption
     - Qcow2BitmapInfo
   compression-type: Qcow2CompressionType

Then we could use a regular off the shelf YAML parser in python.

I have a prototype where I started this, but I use "---" as a document separator to allow us multiple definitions per file so that the nesting remains pleasant.

(YAML does not allow you to duplicate field names.)

The uglyiness with quotes is due to the use of "*". Slightly less ugly
if we simply declare that quotes are always used, even where they're
not strictly required.

StrictYAML insists on quotes.

I wouldn't suggest StrictYAML, just normal YAML is what pretty much
everyone uses.
 > If we came up with a different way to mark a field as optional
instead of using the magic "*" then we wouldn't need to quote

I have a YAML prototype branch where I use `?field` to indicate optional syntax. It works just fine, at the expense of being slightly new to people.

I tested with normal YAML, but I was thinking about adopting strict YAML because Markus wanted some assurance we wouldn't get lost in the weeds using complex feature of YAML.

(Or, shoot ourselves entirely by accident.)

My prototype doesn't use anything that Strict YAML prohibits, so I thought it was a good idea.

IF -- IF IF IF IF IF we decide that actually we need the crazy horsepower of standard YAML, or that strict YAML is too buggy -- we could always just replace it. No real big deal.

I hate having to quote identifiers.  There's a reason we don't write

     'main'('int', 'argc', 'char' *'argv'[])
         'printf'("hello world\n");
         return 0;

Fair enough ... but there's no special meaning to quoting or not quoting the RHS in YAML, so maybe it's best to avoid pretending like there's a structural semantic between an identifier and a string there.

(Since they're both just strings, and the semantic difference is picked up inside the QAPI generator post-parse.)

struct: ImageInfoSpecificQCow2
   "compat": "str"
   "*data-file": "str"
   "*data-file-raw": "bool"
   "*lazy-refcounts": "bool"
   "*corrupt": "bool"
   "refcount-bits": "int"
   "*encrypt": "ImageInfoSpecificQCow2Encryption"
     - "Qcow2BitmapInfo"
   "compression-type": "Qcow2CompressionType"

With the use of "---" to denote the start of document, we have no trouble
parsing our files which would actually be a concatenation of multiple
documents. The python YAML library provides the easy yaml.load_all()

Nevermind the earlier comment, then.

Required reading on YAML:

I don't think this is especially helpful to our evaluation. You can write
such blog posts about pretty much any thing if you want to pick holes in a
proposal. Certainly there's plenty of awful stuff you can write about
JSON, and Python.

Some of the criticism there doesn't matter for our use case.

Yeah, what matters is whether it can do the job we need in a way that is
better than what we have today, and whether there are any further options
to consider that might be viable alternatives.


I guess I'll dust off the work I have already to show the class.


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