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Thu, 30 Jul 2020 11:51:11 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 18D621132FD2; Thu, 30 Jul 2020 13:51:10 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH] schemas: Add vim modeline References: <20200729185024.121766-1-abologna@redhat.com> <87ime52wxd.fsf@dusky.pond.sub.org> <20200730093732.GB3477223@redhat.com> Date: Thu, 30 Jul 2020 13:51:10 +0200 In-Reply-To: <20200730093732.GB3477223@redhat.com> ("Daniel P. =?utf-8?Q?B?= =?utf-8?Q?errang=C3=A9=22's?= message of "Thu, 30 Jul 2020 10:37:32 +0100") Message-ID: <87k0ylz0ep.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/30 03:59:04 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , qemu-block@nongnu.org, Juan Quintela , Jason Wang , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Yuval Shaia , Gerd Hoffmann , Andrea Bolognani , Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , John Snow , Michael Roth , "Dr. David Alan Gilbert" , Stefan Berger Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Daniel P. Berrang=C3=A9 writes: > On Thu, Jul 30, 2020 at 11:07:26AM +0200, Markus Armbruster wrote: >> Andrea Bolognani writes: >>=20 >> > 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 > > 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. Berrang=C3=A9 > > >> 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. >>=20 >> 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. >>=20 >> 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=20 > 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=20 > files straight into the python intepretor as code, and not parse=20 > 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= =20 > parsing our files which would actually be a concatenation of multiple=20 > 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.