From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B737C4361B for ; Wed, 16 Dec 2020 17:55:04 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 74EF5251B6 for ; Wed, 16 Dec 2020 17:55:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 74EF5251B6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54570 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kpb0w-0007IC-7A for qemu-devel@archiver.kernel.org; Wed, 16 Dec 2020 12:55:02 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:55336) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kpazd-0006Hq-Nn for qemu-devel@nongnu.org; Wed, 16 Dec 2020 12:53:41 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:57289) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kpazZ-00053W-Hg for qemu-devel@nongnu.org; Wed, 16 Dec 2020 12:53:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608141216; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rQqQoXu1znNQE6GTCwWeD1gp6pQ9piVz/xMRYp+YPPQ=; b=AW+AZVgK2tKVFwuw46QNHXYuPept79EukMwzjqXhZGyec/OYo0m7/BVn78svMTzBEwqCQM /KcqyQF0Ia7G36WXZvgBEE0Ub0rn8hifuIcPCaEy00V1mG7/z84CYWFfcLpS2o+SZ7j4zD 2Fia6kEuQun4Weu7p11y4BJFlI7na1g= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-487-9X1QXrQNNX2VtqVUgW0-jQ-1; Wed, 16 Dec 2020 12:53:34 -0500 X-MC-Unique: 9X1QXrQNNX2VtqVUgW0-jQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E19AE8030B0 for ; Wed, 16 Dec 2020 17:53:33 +0000 (UTC) Received: from [10.10.120.103] (ovpn-120-103.rdu2.redhat.com [10.10.120.103]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0AE0918993; Wed, 16 Dec 2020 17:53:29 +0000 (UTC) Subject: Re: [PATCH 06/12] qapi/source: Add builtin null-object sentinel To: Markus Armbruster References: <20201214235327.1007124-1-jsnow@redhat.com> <20201214235327.1007124-7-jsnow@redhat.com> <87r1nqrtp7.fsf@dusky.pond.sub.org> From: John Snow Message-ID: Date: Wed, 16 Dec 2020 12:53:29 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <87r1nqrtp7.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jsnow@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=jsnow@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=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: =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , qemu-devel@nongnu.org, Eduardo Habkost , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 12/16/20 4:22 AM, Markus Armbruster wrote: > John Snow writes: > >> We use None to represent an object that has no source information >> because it's a builtin. This complicates interface typing, since many >> interfaces expect that there is an info object available to print errors >> with. >> >> Introduce a special QAPISourceInfo that represents these built-ins so >> that if an error should so happen to occur relating to one of these >> builtins that we will be able to print its information, and interface >> typing becomes simpler: you will always have a source info object. > > Two aspects mixed up: > > 1. Represent "no source info" as special QAPISourceInfo instead of > None > > This is what de-complicates interface typing. > Yup. > 2. On error with "no source info", don't crash. > > I have my doubts on this one. > > Such an error means the QAPI code generator screwed up, at least in > theory. Crashing is only proper. It gets the screwup fixed. > > In practice, errors due to interactions between built-in stuff and > user-defined stuff could conceivably escape testing. I can't > remember such a case offhand. > > Will the "no source info" error be more useful than a crash? > Possibly. Will it get the screwup fixed? Maybe not. > > Can we separate the two aspects? > We can add an intentional assertion, if you'd like, that makes such cases obvious -- but if we are already in the error printer, QAPI is likely already in the process of crashing and printing an error. So, Is this really an issue? >> >> This object will evaluate as False, so "if info" is a valid idiomatic >> construct. > > Suggest s/is a valid/remains a valid/. > > Not 100% sure we'll want to keep this idiom, but now is not the time to > worry about that. > OK. >> >> NB: It was intentional to not allow empty constructors or similar to >> create "empty" source info objects; callers must explicitly invoke >> 'builtin()' to pro-actively opt into using the sentinel. This should >> prevent use-by-accident. >> >> Signed-off-by: John Snow >> --- >> scripts/qapi/source.py | 20 +++++++++++++++++++- >> 1 file changed, 19 insertions(+), 1 deletion(-) >> >> diff --git a/scripts/qapi/source.py b/scripts/qapi/source.py >> index d7a79a9b8aee..64af7318cb67 100644 >> --- a/scripts/qapi/source.py >> +++ b/scripts/qapi/source.py >> @@ -11,7 +11,12 @@ >> >> import copy >> import sys >> -from typing import List, Optional, TypeVar >> +from typing import ( >> + List, >> + Optional, >> + Type, >> + TypeVar, >> +) >> >> >> class QAPISchemaPragma: >> @@ -41,6 +46,17 @@ def __init__(self, fname: str, line: int, >> self.defn_meta: Optional[str] = None >> self.defn_name: Optional[str] = None >> >> + @classmethod >> + def builtin(cls: Type[T]) -> T: >> + """ >> + Create a SourceInfo object corresponding to a builtin definition. > > Let's spell it built-in for consistency with existing comments. > > Could perhaps shorten "a SourceInfo object" to "an instance". > OK. >> + """ >> + return cls('', -1, None) > > No users? Peeking ahead... aha, they are in Patch 08. Any particular > reason for putting PATCH 07 between the two? Could PATCH 08 be squashed > into this one? > Too much soup in one pot: this patch highlights the "trick" and the subsequent patch shows the adoption of it. Seemed safe. Goofy ordering, though. I've pushed the genc/genh patch downwards instead; you can squash them on commit if you'd like. >> + >> + def __bool__(self) -> bool: >> + # "if info: ..." is false if info is the builtin sentinel. >> + return bool(self.fname) > > Nitpicking... "The builtin sentinel" suggests there is just one. PATCH > 08 creates several. I don't mind, but let's say something like "if > @info corresponds to a built-in definition". > Fair enough. I don't mind nitpicks on comments and docstrings so much if it helps make things clearer for more people. (And they don't cause me rebase pain as much as other nitpicks ;) >> + >> def set_defn(self, meta: str, name: str) -> None: >> self.defn_meta = meta >> self.defn_name = name >> @@ -73,4 +89,6 @@ def include_path(self) -> str: >> return ret >> >> def __str__(self) -> str: >> + if not bool(self): >> + return '[builtin]' >> return self.include_path() + self.in_defn() + self.loc() > > Looks like we can separate the two aspects easily: > > def __str__(self) -> str: > + assert not bool(self) > return self.include_path() + self.in_defn() + self.loc() > Feels like abusing __str__ to prevent application logic we don't like elsewhere and unrelated to this class; I am still leaning on "If we are printing this, it's likely we're already crashing" unless you have news to the contrary for me.