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Thu, 8 Oct 2020 07:56:44 +0200 (CEST) From: Markus Armbruster To: John Snow Subject: Re: [PATCH v5 03/36] qapi-gen: Separate arg-parsing from generation References: <20201005195158.2348217-1-jsnow@redhat.com> <20201005195158.2348217-4-jsnow@redhat.com> <87imbntvw9.fsf@dusky.pond.sub.org> <69effb8e-3d83-a2e7-c484-feea8ed850b9@redhat.com> <87h7r6jws4.fsf@dusky.pond.sub.org> <65c2a120-e29e-b572-680a-ee6d141ff9c8@redhat.com> Date: Thu, 08 Oct 2020 07:56:44 +0200 In-Reply-To: <65c2a120-e29e-b572-680a-ee6d141ff9c8@redhat.com> (John Snow's message of "Wed, 7 Oct 2020 10:52:54 -0400") Message-ID: <87h7r545wj.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/08 01:56:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.742, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-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: qemu-devel@nongnu.org, Eduardo Habkost , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 10/7/20 3:54 AM, Markus Armbruster wrote: >> John Snow writes: >> >>> On 10/6/20 7:51 AM, Markus Armbruster wrote: >>>> John Snow writes: >>>> >>>>> This is a minor re-work of the entrypoint script. It isolates a >>>>> generate() method from the actual command-line mechanism. >>>>> >>>>> Signed-off-by: John Snow >>>>> Reviewed-by: Eduardo Habkost >>>>> Reviewed-by: Cleber Rosa >>>>> Tested-by: Cleber Rosa >>>>> --- >>>>> scripts/qapi-gen.py | 85 +++++++++++++++++++++++++++++++++------------ >>>>> 1 file changed, 62 insertions(+), 23 deletions(-) >>>>> >>>>> diff --git a/scripts/qapi-gen.py b/scripts/qapi-gen.py >>>>> index 541e8c1f55d..117b396a595 100644 >>>>> --- a/scripts/qapi-gen.py >>>>> +++ b/scripts/qapi-gen.py >>>>> @@ -1,30 +1,77 @@ >>>>> #!/usr/bin/env python3 >>>>> -# QAPI generator >>>>> -# >>>>> + >>>>> # This work is licensed under the terms of the GNU GPL, version 2 or later. >>>>> # See the COPYING file in the top-level directory. >>>>> +""" >>>>> +QAPI Generator >>>>> + >>>>> +This script is the main entry point for generating C code from the QAPI schema. >>>>> +""" >>>>> import argparse >>>>> import re >>>>> import sys >>>>> from qapi.commands import gen_commands >>>>> +from qapi.error import QAPIError >>>>> from qapi.events import gen_events >>>>> from qapi.introspect import gen_introspect >>>>> -from qapi.schema import QAPIError, QAPISchema >>>>> +from qapi.schema import QAPISchema >>>>> from qapi.types import gen_types >>>>> from qapi.visit import gen_visit >>>> Unrelated cleanup. Okay. >>>> >>>>> -def main(argv): >>>>> +DEFAULT_OUTPUT_DIR = '' >>>>> +DEFAULT_PREFIX = '' >>>>> + >>>>> + >>>>> +def generate(schema_file: str, >>>>> + output_dir: str, >>>>> + prefix: str, >>>>> + unmask: bool = False, >>>>> + builtins: bool = False) -> None: >>>>> + """ >>>>> + generate uses a given schema to produce C code in the target directory. >>>>> + >>>>> + :param schema_file: The primary QAPI schema file. >>>>> + :param output_dir: The output directory to store generated code. >>>>> + :param prefix: Optional C-code prefix for symbol names. >>>>> + :param unmask: Expose non-ABI names through introspection? >>>>> + :param builtins: Generate code for built-in types? >>>>> + >>>>> + :raise QAPIError: On failures. >>>>> + """ >>>>> + match = re.match(r'([A-Za-z_.-][A-Za-z0-9_.-]*)?', prefix) >>>>> + if match.end() != len(prefix): >>>>> + msg = "funny character '{:s}' in prefix '{:s}'".format( >>>>> + prefix[match.end()], prefix) >>>>> + raise QAPIError('', None, msg) >>>> Uh... >>>> $ python3 scripts/qapi-gen.py --prefix=@ x >>>> scripts/qapi-gen.py: : funny character '@' in prefix '@' >>>> Unwanted " :". >>>> This is due to a hack: you pass '' for info (*quack*). Everything >>>> else >>>> passes QAPISourceInfo (I believe). >>>> >>> >>> Quack indeed - why does our base error class require so much >>> information from a specific part of the generation process? >> Because it's not "a base error class", it's a base error class for >> the >> QAPI schema compiler frontend. >> > > Well. It's the base for every error we /had/. You asked why the class has the init it has, and I answered :) >>> Ah, someone changes this in part 4 so that we have a more generic >>> error class to use as a base when we are missing such information. >> Evolving it to satisfy a need for a more widely usable error class >> is >> okay. >> > > Yep. It's helpful to keep a very generic form on which we grow other > errors from, so that things like the entry point can be written > legibly. If you have a non-trivial error message format convention, you have a use for a function formatting error messages. If you have a separation between diagnose and report of errors, you you have a use for a transport from diagnose to report. In Python, that's raise. The existing error message in main() has neither. The existing error class QAPIError caters for the existing users. >>> You are witnessing some more future-bleed. >>>> Is it really a good idea to do this in generate? It's not about >>>> generating code, it's about validating a CLI option. >>>> >>> >>> One might also ask: Is it a good idea to only validate this on a >>> frontend, and not in the implementation? >> Yes, because that's where you can emit the better error message more >> easily. >> $ python3 scripts/qapi-gen.py --prefix=@ x >> scripts/qapi-gen.py: 'funny character '@' in argument of --prefix >> is better than >> $ python3 scripts/qapi-gen.py --prefix=@ x >> scripts/qapi-gen.py: funny character '@' in prefix '@' >> In generate(), the knowledge where the offending prefix value comes >> from >> is no longer available. >> To emit this error message, you'd have to raise a sufficiently >> distinct >> error in generate, catch it in main(), then put the error message >> together somehow. Bah. >> Aside: there's a stray ' in the old error message. >> >>> The idea here was to create a function that could be used in a script >>> (for tests, debugging interfaces, other python packages) to do all of >>> the same things that the CLI tool did, just sans the actual CLI. >> YAGNI. >> > > It's useful for testing and debugging to be able to just call it > outside of the CLI, though. Maybe you won't use it, but I will. For testing and debugging, treating "prefix is sane" as a precondition is fine. I wouldn't even bother checking it. A check would catch accidents, and these accidents seem vanishingly unlikely to me. Evidence: we did without *any* prefix checking for *years*. I added it in commit 1cf47a15f18 just for completeness. > I could always add the prefix check into a tiny function and give the > good error message in main(), and just assert in generate() if you > insist on the slightly more specific error message from the CLI script. If you genuinely think a check is needed there, that's the way to go. >>> Wouldn't make sense to allow garbage to flow in from one interface but >>> not the other; so the check is here. >> "@prefix is sane" is a precondition of generate(). >> When there's a real risk of preconditions getting violated, or >> readers >> getting confused about preconditions, check them with assert. [...]