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Re: [PATCH] schemas: Add vim modeline
From: |
Markus Armbruster |
Subject: |
Re: [PATCH] schemas: Add vim modeline |
Date: |
Thu, 30 Jul 2020 13:51:10 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) |
Daniel P. Berrangé <berrange@redhat.com> writes:
> On Thu, Jul 30, 2020 at 11:07:26AM +0200, Markus Armbruster wrote:
>> Andrea Bolognani <abologna@redhat.com> writes:
>>
>> > The various schemas included in QEMU use a JSON-based format which
>> > is, however, strictly speaking not valid JSON.
>> >
>> > As a consequence, when vim tries to apply syntax highlight rules
>> > for JSON (as guessed from the file name), the result is an unreadable
>> > mess which mostly consist of red markers pointing out supposed errors
>> > in, well, pretty much everything.
>> >
>> > Using Python syntax highlighting produces much better results, and
>> > in fact these files already start with specially-formatted comments
>> > that instruct Emacs to process them as if they were Python files.
>> >
>> > This commit adds the equivalent special comments for vim.
>> >
>> > Signed-off-by: Andrea Bolognani <abologna@redhat.com>
>
> Given that we already have emacs mode-lines, I see no reason to
> not also have vim mode-lines, so regardless of the deeper discussion
> I think this is patch is fine to merge in the short term
>
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
>
>
>> Naming QAPI schema files .json even though their contents isn't was a
>> mistake. Correcting it would be a pain. If we correct it, then the
>> sooner the better.
>>
>> Renaming them to .py gives decent editor support out of the box. Their
>> contents isn't quite Python, though: true vs. True, false vs. False. Do
>> we care? Only a few dozen occurences; they could be adjusted.
>>
>> Renaming them to .qapi would perhaps be less confusing, for the price of
>> "out of the box".
>
> IMHO, the critical rule is that if you a pick a particular file extension
> associated with an existing language, you absolutely MUST BE compliant
> with that language.
Can't argue with that :)
> We fail at compliance with both JSON and Python because we're actually
> using our own DSL (domain specific language).
>
> IOW if we're going to stick with our current file format, then we should
> be naming them .qapi. We can still use an editor mode line if we want to
> claim we're approximately equiv to another language, but we can't be
> surprised if editors get upset.
>
>
> The bigger question is whether having our own DSL is justified ?
>
> I'm *really* sceptical that it is.
To be precise: our own DSL *syntax*. Semantics is a separate question
to be skeptical about.
> We can't use JSON because it lacks comments. So we invented our own
> psuedo-JSON parser that supported comments, and used ' instead of "
> for some reason. We also needed to be able to parse a sequence of
> multiple JSON documents in one file. We should have just picked a
> different language because JSON clearly didn't do what we eneeded.
JSON is a exceptionally poor choice for a DSL, or even a configuration
language.
Correcting our mistake involves a flag day and a re-learn. We need to
weigh costs against benefits.
The QAPI schema language has two layers:
* JSON, with a lexical and a syntactical sub-layer (both in parser.py)
* QAPI, with a context-free and a context-dependend sub-layer (in
expr.py and schema.py, respectively)
Replacing the JSON layer is possible as long as the replacement is
sufficiently expressive (not a tall order).
> You suggest naming them .py. If we do that, we must declare that they
> are literally Python code
Agree.
> 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.
> While JSON doesn't do what we need, its second-cousin YAML is a more
> flexible format. Taking one example
>
> ---
> ##
> # @ImageInfoSpecificQCow2:
> #
> # @compat: compatibility level
> #
> # ...snip...
> #
> # Since: 1.7
> ##
> struct: ImageInfoSpecificQCow2
> data:
> compat: str
> "*data-file": str
> "*data-file-raw": bool
> "*lazy-refcounts": bool
> "*corrupt": bool
> refcount-bits: int
> "*encrypt": ImageInfoSpecificQCow2Encryption
> "*bitmaps":
> - Qcow2BitmapInfo
> compression-type: Qcow2CompressionType
>
>
> Then we could use a regular off the shelf YAML parser in python.
>
> 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 hate having to quote identifiers. There's a reason we don't write
'int'
'main'('int', 'argc', 'char' *'argv'[])
{
'printf'("hello world\n");
return 0;
}
> struct: ImageInfoSpecificQCow2
> data:
> "compat": "str"
> "*data-file": "str"
> "*data-file-raw": "bool"
> "*lazy-refcounts": "bool"
> "*corrupt": "bool"
> "refcount-bits": "int"
> "*encrypt": "ImageInfoSpecificQCow2Encryption"
> "*bitmaps":
> - "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()
> method.
Required reading on YAML:
https://www.arp242.net/yaml-config.html
Some of the criticism there doesn't matter for our use case.
- [PATCH] schemas: Add vim modeline, Andrea Bolognani, 2020/07/29
- Re: [PATCH] schemas: Add vim modeline, Markus Armbruster, 2020/07/30
- Re: [PATCH] schemas: Add vim modeline, Markus Armbruster, 2020/07/31
- Re: [PATCH] schemas: Add vim modeline, Daniel P . Berrangé, 2020/07/31
- Re: [PATCH] schemas: Add vim modeline, John Snow, 2020/07/31
- Re: [PATCH] schemas: Add vim modeline, Daniel P . Berrangé, 2020/07/31
- Re: [PATCH] schemas: Add vim modeline, Paolo Bonzini, 2020/07/31
- Re: [PATCH] schemas: Add vim modeline, Dr. David Alan Gilbert, 2020/07/31