Received: (at 6740) by debbugs.gnu.org; 19 Nov 2020 04:26:08 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Nov 18 23:26:08 2020 Received: from localhost ([127.0.0.1]:37487 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1kfbWG-0003qA-Pa for submit <at> debbugs.gnu.org; Wed, 18 Nov 2020 23:26:08 -0500 Received: from mail-ej1-f42.google.com ([209.85.218.42]:41198) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <stefankangas@HIDDEN>) id 1kfbWE-0003pL-EM for 6740 <at> debbugs.gnu.org; Wed, 18 Nov 2020 23:26:03 -0500 Received: by mail-ej1-f42.google.com with SMTP id gj5so5956175ejb.8 for <6740 <at> debbugs.gnu.org>; Wed, 18 Nov 2020 20:26:02 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:in-reply-to:references:user-agent :mime-version:date:message-id:subject:to:cc; bh=6FMNB6oqEEIr7plNReAEPDCLros+ZREFuXllrYKFtw8=; b=MqZT2ynqC+Xa7VFYTEbzhYTpAMqqmU+FufFlVAN9/Kj6I6UsOQwTSox8wI1THXTD3C MLeEeH9j21a7KqcVCnt9K69pjxEOlpoHz3xpIa/isLcBv+mdEI1PgP7nAYcChljXUGhD 43xNkZbsZpUhnSho0Lfq7bQeHjhTuXUxRbGXr61+vGvKmus2LuG00PF2RDrzAdLd1I7d J6dCus8GypaL/tuaQc4aZCAt140prtlDsLO5xT0X9RdnlKn0D+0ZTmPD4JvUfpH8Xuyh CMHmMnDtS82reH5DJvdYzzi5Iw1Rij4JlRmQ2brGCmqBIAw5MjLICK10mrmFlre5o4hQ g9CA== X-Gm-Message-State: AOAM5309P0iV4YovLPfcwUCqFUCIz1krxf5Lk6KaE9xW6tDjx+T2ajq8 btJQv9Fjc/QtYY1SNskk1FTBjj7Sv3uEGqVpWpZA9n0Z/UI= X-Google-Smtp-Source: ABdhPJyGe7a1uXG3UgOUFN+GNGtIMp++jGBaL3M67xsNk2PjcpG3AepqhUz3gjepcyN3JCsGo01xEv6xq7XeyCsK0tE= X-Received: by 2002:a17:906:a00c:: with SMTP id p12mr28086190ejy.249.1605759956804; Wed, 18 Nov 2020 20:25:56 -0800 (PST) Received: from 753933720722 named unknown by gmailapi.google.com with HTTPREST; Wed, 18 Nov 2020 20:25:56 -0800 From: Stefan Kangas <stefan@HIDDEN> In-Reply-To: <jwvvd80iozu.fsf-monnier+emacs@HIDDEN> (Stefan Monnier's message of "Tue, 27 Jul 2010 23:40:50 +0200") References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN> <jwvvd80iozu.fsf-monnier+emacs@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) MIME-Version: 1.0 Date: Wed, 18 Nov 2020 20:25:56 -0800 Message-ID: <CADwFkmkFAAo9HDhi+Po_0VoyXNdZyFPi3-w2BZwCGZE8cvV1sA@HIDDEN> Subject: Re: bug#6740: Spurious byte compiler warnings To: Stefan Monnier <monnier@HIDDEN> Content-Type: text/plain; charset="UTF-8" X-Spam-Score: 0.5 (/) X-Debbugs-Envelope-To: 6740 Cc: Dan Nicolaescu <dann@HIDDEN>, 6740 <at> debbugs.gnu.org, Alan Mackenzie <acm@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -0.5 (/) Stefan Monnier <monnier@HIDDEN> writes: >>> Warning: value returned from (featurep (quote cc-fix)) is unused >>> Warning: value returned from (featurep (quote cc-fix)) is unused >>> >>> It is obvious that that value is indeed used. This is a bug. > >> The byte compiler knows that (featurep 'xemacs) is false, so >> (and (not (featurep 'cc-fix)) ... ) >> will be false, so the featurep result is indeed unused. > >> If you use (and (featurep 'xemacs) (not (featurep 'cc-fix) ... >> the warning will go away. > > It's one of those cases where the warning is the result of a check done > "too late" (i.e. after some optimization), which means the check is not > performed on the code the user sees, but on some massaged version of it. > It's difficult to avoid them, short of removing all "code > improvement" warnings. (That was 10 years ago.) I think this is a very minor issue that is likely not worth spending any time on. In any case, it's not even clear what the fix would be or if a different behavior would improve the situation. Does anyone object to closing this as wontfix?
bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
Full text available.Received: (at 6740) by debbugs.gnu.org; 29 Jul 2010 20:36:32 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Thu Jul 29 16:36:32 2010 Received: from localhost ([127.0.0.1] helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1OeZqB-0006X9-Ey for submit <at> debbugs.gnu.org; Thu, 29 Jul 2010 16:36:31 -0400 Received: from mail-bw0-f44.google.com ([209.85.214.44]) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <lekktu@HIDDEN>) id 1OeZq9-0006X4-SO for 6740 <at> debbugs.gnu.org; Thu, 29 Jul 2010 16:36:30 -0400 Received: by bwz7 with SMTP id 7so489524bwz.3 for <6740 <at> debbugs.gnu.org>; Thu, 29 Jul 2010 13:36:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:mime-version:received:in-reply-to :references:from:date:message-id:subject:to:cc:content-type :content-transfer-encoding; bh=/U2CGrPi7cVwjj2HLu3o0khKMI1voUIhVRJc2CK4yYw=; b=ppr75RUBJtj+foUehMPUtpdnkdY2rcRFHbcoIAsckCDUDxNd6snj/wN1ucPNPlU6RM /ipZl3UclBNalLlmJ8Qsz4/63do2gHvYehegg+ttNFejRAcFmfsUvo8hbC2NuXgUgQNH P3CcEfIG+aNKOOLeKT3wS3UsXm0DO3NecK+9o= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=OCSah8oOayMEoI6EPM0WGjs1A54o5jZ/qXUPkRreseFW+rIG7MYXBagEjJtxFiN9OC 8uWTV88uwzEYBZanmJF4PE+f31nYCb+PEwOVPovRixIRbFkCEOxdYZ1ziw9pASxxUESb 0YEcK2Qkne1NR8fRwlLZMcGx5lzqE2sknNOCo= Received: by 10.204.76.205 with SMTP id d13mr448098bkk.93.1280435803257; Thu, 29 Jul 2010 13:36:43 -0700 (PDT) MIME-Version: 1.0 Received: by 10.204.180.136 with HTTP; Thu, 29 Jul 2010 13:36:23 -0700 (PDT) In-Reply-To: <20100729202420.GB2459@HIDDEN> References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN> <20100727212328.GD2280@HIDDEN> <AANLkTikdVKf70_nbaBbYPyjUE7iRZ1RXX8ybFJEvaXQe@HIDDEN> <20100728174933.GB2999@HIDDEN> <AANLkTinL9pYA-yg2kOvD_N0+jVX+=uJcoVbBCvQ_qN87@HIDDEN> <20100728194511.GD2999@HIDDEN> <AANLkTinPrue70-0fO0Z+S=594dok0CmzZfo5WKgf22xg@HIDDEN> <20100729202420.GB2459@HIDDEN> From: Juanma Barranquero <lekktu@HIDDEN> Date: Thu, 29 Jul 2010 22:36:23 +0200 Message-ID: <AANLkTik4xbU23rhOKqcunf3T+_k9-CygthVM3SzN191v@HIDDEN> Subject: Re: bug#6740: Spurious byte compiler warnings To: Alan Mackenzie <acm@HIDDEN> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -2.7 (--) X-Debbugs-Envelope-To: 6740 Cc: Dan Nicolaescu <dann@HIDDEN>, 6740 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.11 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <http://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <http://debbugs.gnu.org/pipermail/debbugs-submit> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <http://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Sender: debbugs-submit-bounces <at> debbugs.gnu.org Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org X-Spam-Score: -2.7 (--) On Thu, Jul 29, 2010 at 22:24, Alan Mackenzie <acm@HIDDEN> wrote: > No, sorry it isn't. =C2=A0It's a good hint that there's a bug in the byte > compiler, the tentative conclusion I came to after trying various things. No, of course not, because there's no bug (well, other than the duplicate message). The warning is obscure, yes. Warnings about optimized code often are. I agree that it'd be good to have better warnings and error messages (something like "optimization X has rendered code Y unused", perhaps). IIRC, there's published research about good error messages in the face of program transformations. > If it were such a good hint, I wouldn't have spent several hours of > bafflement trying to figure out what was wrong. =C2=A0Or is it just me wh= o's > uniquely stupid? It's not about being stupid, only about knowing a bit what the bytecompiler does, or not. You didn't, and you're *right* that the warning is difficult to interpret. > Is there anybody here listening in who's seen this > message and immediately understood it? Well, I did, but I remembered the (featurep 'xemacs) optimization so I had a head start. > Abstractly seen, the warning did not relate to my source code; it related > to an internal, transformed, different piece of source created by the > compiler. =C2=A0I think warning messages should always be wrt the origina= l > code. Agreed. > The cause of my confusion was that silent change to 'xemacs. > There are surely not too many situations where the compiler does this, > are there? Even if there aren't many, optimizations could be added later; for example, to statically determine that (=3D 0 0) is t, or even that (and (> x 0) (< x 0)) is nil. > Yes; I've already made that change, thanks! =C2=A0But what is the process= by > which I'm meant to come to sufficient understanding to be able figure > this out? That's a good question. > There's nothing suspicious about having (featurep 'xemacs) in the middle > of an `and' form. No, but the warning isn't about that. Is about unused side-effect-free code= . > I agree there would be something suspicious about > having a bare `nil' there. =C2=A0Can't the compiler figure out the differ= ence > between these two cases somehow? Yes, it could. Again, no one has bothered to implement it, because these kinds of problems aren't common (most warnings are relatively understandable withouth delving into the bytecompiler sources). > Oh, all right then. =C2=A0Can I ask you to come up with some form of warn= ing > which, several years ago, would have saved me all these hours of > frustration? Not me. I understand what the bytecompiler is doing (at least, I think I do) but I'll leave fixing it for the experts. =C2=A0 =C2=A0 Juanma
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
Full text available.Received: (at 6740) by debbugs.gnu.org; 29 Jul 2010 20:13:03 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Thu Jul 29 16:13:01 2010 Received: from localhost ([127.0.0.1] helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1OeZTR-0006MQ-LH for submit <at> debbugs.gnu.org; Thu, 29 Jul 2010 16:13:01 -0400 Received: from colin.muc.de ([193.149.48.1] helo=mail.muc.de) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <acm@HIDDEN>) id 1OeZTO-0006MK-8e for 6740 <at> debbugs.gnu.org; Thu, 29 Jul 2010 16:12:59 -0400 Received: (qmail 9692 invoked by uid 3782); 29 Jul 2010 20:13:11 -0000 Received: from acm.muc.de (pD9E530D8.dip.t-dialin.net [217.229.48.216]) by colin2.muc.de (tmda-ofmipd) with ESMTP; Thu, 29 Jul 2010 22:13:09 +0200 Received: (qmail 4002 invoked by uid 1000); 29 Jul 2010 20:24:20 -0000 Date: Thu, 29 Jul 2010 20:24:20 +0000 To: Juanma Barranquero <lekktu@HIDDEN> Subject: Re: bug#6740: Spurious byte compiler warnings Message-ID: <20100729202420.GB2459@HIDDEN> References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN> <20100727212328.GD2280@HIDDEN> <AANLkTikdVKf70_nbaBbYPyjUE7iRZ1RXX8ybFJEvaXQe@HIDDEN> <20100728174933.GB2999@HIDDEN> <AANLkTinL9pYA-yg2kOvD_N0+jVX+=uJcoVbBCvQ_qN87@HIDDEN> <20100728194511.GD2999@HIDDEN> <AANLkTinPrue70-0fO0Z+S=594dok0CmzZfo5WKgf22xg@HIDDEN> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <AANLkTinPrue70-0fO0Z+S=594dok0CmzZfo5WKgf22xg@HIDDEN> User-Agent: Mutt/1.5.9i X-Delivery-Agent: TMDA/1.1.5 (Fettercairn) From: Alan Mackenzie <acm@HIDDEN> X-Primary-Address: acm@HIDDEN X-Spam-Score: -1.7 (-) X-Debbugs-Envelope-To: 6740 Cc: Dan Nicolaescu <dann@HIDDEN>, 6740 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.11 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <http://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <http://debbugs.gnu.org/pipermail/debbugs-submit> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <http://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Sender: debbugs-submit-bounces <at> debbugs.gnu.org Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org X-Spam-Score: -2.6 (--) Hi, Juanma, On Wed, Jul 28, 2010 at 09:54:04PM +0200, Juanma Barranquero wrote: > On Wed, Jul 28, 2010 at 21:45, Alan Mackenzie <acm@HIDDEN> wrote: > > I'm doubting its adequacy. Without understanding that (featurep > > 'xemacs) has been optimised to nil, it's impossible to understand the > > current message > I think the message is a good hint that something is being statically > determined to be nil inside an `and'. No, sorry it isn't. It's a good hint that there's a bug in the byte compiler, the tentative conclusion I came to after trying various things. If it were such a good hint, I wouldn't have spent several hours of bafflement trying to figure out what was wrong. Or is it just me who's uniquely stupid? Is there anybody here listening in who's seen this message and immediately understood it? Abstractly seen, the warning did not relate to my source code; it related to an internal, transformed, different piece of source created by the compiler. I think warning messages should always be wrt the original code. > > If only there were a warning about 'xemacs, it would be plain and > > obvious. > But, as I've explained, there cannot (easily) be a warning about > `xemacs'; it would have to be about any code that statically evaluates > to nil in such a context. No. It would be about code which the _compiler_ had transformed to a static nil. The cause of my confusion was that silent change to 'xemacs. There are surely not too many situations where the compiler does this, are there? > I'm not sure how clean that would be to implement, and anyway no one > has been bothered enough to try it. :-) I know nothing of the byte compiler, but maybe I'll give it a go sometime. > > Does anybody care about it enough to want that message in this > > particular case? > Yes. You don't know whether a warning is relevant or not unless you > get it. In *this* particular case, all you need to quiet the > byte-compiler is > @@ -1,5 +1,5 @@ > (eval-when-compile > - (if (and (not (featurep 'cc-fix)) > - (featurep 'xemacs) > + (if (and (featurep 'xemacs) > + (not (featurep 'cc-fix)) > (progn > (require 'font-lock) Yes; I've already made that change, thanks! But what is the process by which I'm meant to come to sufficient understanding to be able figure this out? > > Couldn't the optimisation just be done quietly in the background, > > with no warning? > Why? The optimization is detecting something suspicious, and acting > accordingly. There's nothing suspicious about having (featurep 'xemacs) in the middle of an `and' form. I agree there would be something suspicious about having a bare `nil' there. Can't the compiler figure out the difference between these two cases somehow? > > Or couldn't there be a warning like > > "`(featurep 'xemacs)' has been translated to nil" > ???? > That's worse that what you're complaining now; every use of (featurep > 'xemacs) in the sources would produce warnings! Oh, all right then. Can I ask you to come up with some form of warning which, several years ago, would have saved me all these hours of frustration? > Juanma -- Alan Mackenzie (Nuremberg, Germany).
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
Full text available.Received: (at 6740) by debbugs.gnu.org; 28 Jul 2010 23:00:02 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jul 28 19:00:02 2010 Received: from localhost ([127.0.0.1] helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1OeFbV-0003sw-T5 for submit <at> debbugs.gnu.org; Wed, 28 Jul 2010 19:00:02 -0400 Received: from fencepost.gnu.org ([140.186.70.10]) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <dann@HIDDEN>) id 1OeFbU-0003sY-22 for 6740 <at> debbugs.gnu.org; Wed, 28 Jul 2010 19:00:00 -0400 Received: from dann by fencepost.gnu.org with local (Exim 4.69) (envelope-from <dann@HIDDEN>) id 1OeFbf-000697-A0; Wed, 28 Jul 2010 19:00:11 -0400 To: Juanma Barranquero <lekktu@HIDDEN> Subject: Re: bug#6740: Spurious byte compiler warnings References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN> <20100727212328.GD2280@HIDDEN> <AANLkTikdVKf70_nbaBbYPyjUE7iRZ1RXX8ybFJEvaXQe@HIDDEN> <20100728174933.GB2999@HIDDEN> <AANLkTinL9pYA-yg2kOvD_N0+jVX+=uJcoVbBCvQ_qN87@HIDDEN> <20100728194511.GD2999@HIDDEN> <AANLkTinPrue70-0fO0Z+S=594dok0CmzZfo5WKgf22xg@HIDDEN> From: Dan Nicolaescu <dann@HIDDEN> Date: Wed, 28 Jul 2010 19:00:11 -0400 In-Reply-To: <AANLkTinPrue70-0fO0Z+S=594dok0CmzZfo5WKgf22xg@HIDDEN> (Juanma Barranquero's message of "Wed\, 28 Jul 2010 21\:54\:04 +0200") Message-ID: <yxqfwz3tdok.fsf@HIDDEN> User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -6.5 (------) X-Debbugs-Envelope-To: 6740 Cc: Alan Mackenzie <acm@HIDDEN>, 6740 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.11 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <http://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <http://debbugs.gnu.org/pipermail/debbugs-submit> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <http://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Sender: debbugs-submit-bounces <at> debbugs.gnu.org Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org X-Spam-Score: -6.5 (------) Juanma Barranquero <lekktu@HIDDEN> writes: > On Wed, Jul 28, 2010 at 21:45, Alan Mackenzie <acm@HIDDEN> wrote: > >> >> =A0 =A0"`(featurep 'xemacs)' has been translated to nil" > > ???? > > That's worse that what you're complaining now; every use of (featurep > 'xemacs) in the sources would produce warnings! Exactly, and it would defeat the purpose of optimizing away=20 (featurp 'xemacs) (and (featurep 'emacs): being able to have a single sourc= e base that=20 works on both platforms, and it can be compiled warning free.
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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From: Juanma Barranquero <lekktu@HIDDEN>
Date: Wed, 28 Jul 2010 21:54:04 +0200
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Subject: Re: bug#6740: Spurious byte compiler warnings
To: Alan Mackenzie <acm@HIDDEN>
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On Wed, Jul 28, 2010 at 21:45, Alan Mackenzie <acm@HIDDEN> wrote:
> I'm doubting
> its adequacy. =C2=A0Without understanding that (featurep 'xemacs) has bee=
n
> optimised to nil, it's impossible to understand the current message
I think the message is a good hint that something is being statically
determined to be nil inside an `and'.
> (either of them).
Yes, that's a bug :-)
> If only there were a warning about 'xemacs, it would be plain
> and obvious.
But, as I've explained, there cannot (easily) be a waning about
`xemacs'; it would have to be about any code that statically evaluates
to nil in such a context. I'm not sure how clean that would be to
implement, and anyway no one has been bothered enough to try it.
> Does anybody care about
> it enough to want that message in this particular case?
Yes. You don't know whether a warning is relevant or not unless you
get it. In *this* particular case, all you need to quiet the
byte-compiler is
@@ -1,5 +1,5 @@
(eval-when-compile
- (if (and (not (featurep 'cc-fix))
- (featurep 'xemacs)
+ (if (and (featurep 'xemacs)
+ (not (featurep 'cc-fix))
(progn
(require 'font-lock)
> Couldn't the
> optimisation just be done quietly in the background, with no warning?
Why? The optimization is detecting something suspicious, and acting
accordingly.
> Or couldn't there be a warning like
>
> =C2=A0 =C2=A0"`(featurep 'xemacs)' has been translated to nil"
????
That's worse that what you're complaining now; every use of (featurep
'xemacs) in the sources would produce warnings!
=C2=A0 =C2=A0 Juanma
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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To: Juanma Barranquero <lekktu@HIDDEN>
Subject: Re: bug#6740: Spurious byte compiler warnings
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Hi, Juanma,
On Wed, Jul 28, 2010 at 07:56:32PM +0200, Juanma Barranquero wrote:
> > What use is this warning message? How could it prompt a hacker to
> > improve his code? (That's a genuine question, not a rhetorical one.)
> It's a warning about non-side-effects code whose result is discarded,
> so it obviously prompts the programmer to either check that it didn't
> make a mistake (like forgetting to assign the expression's result to a
> variable), or remove the code altogether if it is leftover code from a
> cut&paste or refactoring.
OK, thanks.
> > What do you mean by "generic" here? Is the same trick performed on
> > symbols other than 'xemacs?
> The warning has *nothing* to do with the xemacs symbol. It would still
> be there if you did "(and (not (featurep 'cc-fix)) nil ...)". It just
> happens to be triggered, in this particular case, by the byte-compiler
> optimizing (featurep 'xemacs) to nil. So the warning is entirely
> generic.
I'm not any more doubting the correctness of the message; I'm doubting
its adequacy. Without understanding that (featurep 'xemacs) has been
optimised to nil, it's impossible to understand the current message
(either of them). I've spent a long, long time puzzling over this error
message. If only there were a warning about 'xemacs, it would be plain
and obvious.
> > Does anybody actually care about "(featurep 'xemacs)" being optimised
> > away?
> IIRC, optimizing (featurep 'xemacs) => nil is done, *precisely*, to
> help compiling portable code.
Misunderstanding, sorry! I'm all in favour of this optimisation being
done. But I don't care about it, in the sense I don't want to have to
make sense of a confusing message about it. Does anybody care about
it enough to want that message in this particular case? Couldn't the
optimisation just be done quietly in the background, with no warning?
Or couldn't there be a warning like
"`(featurep 'xemacs)' has been translated to nil"
?
> Because you can have
> (if (featurep 'xemacs)
> ;; lots of code which would throw warnings or errors on Emacs
> ;; because of incompatible parameter profiles and such
> ;; else
> ;; code for emacs
> and compile it without getting warnings of errors in code that will
> never be executed on Emacs anyway.
OK, I can see that.
> Juanma
--
Alan Mackenzie (Nuremberg, Germany).
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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Subject: Re: bug#6740: Spurious byte compiler warnings
To: Alan Mackenzie <acm@HIDDEN>
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> But
> this discussion is most emphatically NOT about compiled code. =C2=A0It's =
about
> the process of compiling sources.
Warnings do not affect compatibility, so no problem there (though I
admit they are ugly).
> What use is this warning message? =C2=A0How could it prompt a hacker to
> improve his code? =C2=A0(That's a genuine question, not a rhetorical one.=
)
It's a warning about non-side-effects code whose result is discarded,
so it obviously prompts the programmer to either check that it didn't
make a mistake (like forgetting to assign the expression's result to a
variable), or remove the code altogether if it is leftover code from a
cut&paste or refactoring.
> What do you mean by "generic" here? =C2=A0Is the same trick performed on
> symbols other than 'xemacs?
The warning has *nothing* to do with the xemacs symbol. It would still
be there if you did "(and (not (featurep 'cc-fix)) nil ...)". It just
happens to be triggered, in this particular case, by the byte-compiler
optimizing (featurep 'xemacs) to nil. So the warning is entirely
generic.
> Surely it is a bug that "(featurep 'cc-fix)" appears in the message
> rather than "(featurep 'xemacs)". =C2=A0This situation is not about 'cc-f=
ix,
> it's about 'xemacs.
Absolutely no, as shown above. At the point the byte-compiler throws
the warning, it does not know (I think) where the relevant nil came
from. It is rightly complaining that (featurep 'cc-fix) does nothing
and returns a value that goes unused. It would be possible to store
the original code before optimization and pass it to the warning
generation code, but it is likely not worth it.
> Does
> anybody actually care about "(featurep 'xemacs)" being optimised away?
IIRC, optimizing (featurep 'xemacs) =3D> nil is done, *precisely*, to
help compiling portable code. Because you can have
(if (featurep 'xemacs)
;; lots of code which would throw warnings or errors on Emacs
;; because of incompatible parameter profiles and such
;; else
;; code for emacs
and compile it without getting warnings of errors in code that will
never be executed on Emacs anyway.
=C2=A0 =C2=A0 Juanma
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
Full text available.Received: (at 6740) by debbugs.gnu.org; 28 Jul 2010 17:38:18 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jul 28 13:38:18 2010 Received: from localhost ([127.0.0.1] helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1OeAaA-0001dq-4f for submit <at> debbugs.gnu.org; Wed, 28 Jul 2010 13:38:18 -0400 Received: from colin.muc.de ([193.149.48.1] helo=mail.muc.de) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <acm@HIDDEN>) id 1OeAa7-0001dk-GY for 6740 <at> debbugs.gnu.org; Wed, 28 Jul 2010 13:38:16 -0400 Received: (qmail 15504 invoked by uid 3782); 28 Jul 2010 17:38:25 -0000 Received: from acm.muc.de (pD9E527D0.dip.t-dialin.net [217.229.39.208]) by colin2.muc.de (tmda-ofmipd) with ESMTP; Wed, 28 Jul 2010 19:38:23 +0200 Received: (qmail 3406 invoked by uid 1000); 28 Jul 2010 17:49:33 -0000 Date: Wed, 28 Jul 2010 17:49:33 +0000 To: Juanma Barranquero <lekktu@HIDDEN> Subject: Re: bug#6740: Spurious byte compiler warnings Message-ID: <20100728174933.GB2999@HIDDEN> References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN> <20100727212328.GD2280@HIDDEN> <AANLkTikdVKf70_nbaBbYPyjUE7iRZ1RXX8ybFJEvaXQe@HIDDEN> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <AANLkTikdVKf70_nbaBbYPyjUE7iRZ1RXX8ybFJEvaXQe@HIDDEN> User-Agent: Mutt/1.5.9i X-Delivery-Agent: TMDA/1.1.5 (Fettercairn) From: Alan Mackenzie <acm@HIDDEN> X-Primary-Address: acm@HIDDEN X-Spam-Score: -2.5 (--) X-Debbugs-Envelope-To: 6740 Cc: Dan Nicolaescu <dann@HIDDEN>, 6740 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.11 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <http://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <http://debbugs.gnu.org/pipermail/debbugs-submit> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <http://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Sender: debbugs-submit-bounces <at> debbugs.gnu.org Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org X-Spam-Score: -2.5 (--) Hi, Juanma, On Wed, Jul 28, 2010 at 12:57:04AM +0200, Juanma Barranquero wrote: > On Tue, Jul 27, 2010 at 23:23, Alan Mackenzie <acm@HIDDEN> wrote: > > It's a bug that the error message is repeated, at the very least. > Yes, likely. > > And the message is most assuredly false because (featurep 'cc-fix) > > isn't always false - for example when it's run under XEmacs. > Not, in code byte-compiled for Emacs it is always false because > (featurep 'xemacs) is false. That means that optimized bytecode is not > portable to XEmacs. But I don't think it was before (for a long time). Optimised .elc isn't even compatible with earlier versions of Emacs. But this discussion is most emphatically NOT about compiled code. It's about the process of compiling sources. > > At the very least, emitting such arcane warnings is unhelpful. Are > > there any circumstances in which such a warning might help a hacker > > improve his code? Surely we aren't in the business of making it > > difficult to adapt code for XEmacs? > You make it appear as it if were an attempt to warn about using > XEmacs-specific code, but it is not, as Dan has pointed out. What use is this warning message? How could it prompt a hacker to improve his code? (That's a genuine question, not a rhetorical one.) > The warning is generic, the result of > (and X (featurep 'xemacs) Y Z...) => (prog (and X) nil) => (prog X > nil) ; IIUC the comments in byte-opt.el... Thanks for this explanation. What do you mean by "generic" here? Is the same trick performed on symbols other than 'xemacs? Surely it is a bug that "(featurep 'cc-fix)" appears in the message rather than "(featurep 'xemacs)". This situation is not about 'cc-fix, it's about 'xemacs. I would suggest that if I, a highly experienced Emacs hacker, remain baffled by this message over many months, so will lots of others. Does anybody actually care about "(featurep 'xemacs)" being optimised away? Again, who does this warning message help (other than the hackers who wrote the optimisation code in the first place, of course)? > from whence, "value returned from X is unused". > > I think it's clear, the only code containing (featurep 'xemacs) is > > portable code. > The code is portable. The .elc is not. Er, we're in strong agreement with this. > Juanma -- Alan Mackenzie (Nuremberg, Germany).
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
Full text available.Received: (at 6740) by debbugs.gnu.org; 27 Jul 2010 22:57:18 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Tue Jul 27 18:57:17 2010 Received: from localhost ([127.0.0.1] helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1Odt5J-0001df-DJ for submit <at> debbugs.gnu.org; Tue, 27 Jul 2010 18:57:17 -0400 Received: from mail-bw0-f44.google.com ([209.85.214.44]) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from <lekktu@HIDDEN>) id 1Odt5H-0001dZ-UB for 6740 <at> debbugs.gnu.org; Tue, 27 Jul 2010 18:57:16 -0400 Received: by bwz7 with SMTP id 7so3968114bwz.3 for <6740 <at> debbugs.gnu.org>; Tue, 27 Jul 2010 15:57:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:mime-version:received:in-reply-to :references:from:date:message-id:subject:to:cc:content-type :content-transfer-encoding; bh=OT4bTkiR6EhP33nlbLoSabYTwxBUNTRpGjT1vwdd1ew=; b=O0L7EQpOeaQXMCj3cu1BwVDR/QpqB+VnEpMx9oX6itISvg8M28VbTWfj+5h40HGzFv pZkCU4I5ef6hYE3nSNU/HbYqj5c2PckRMh5TgaiuUn8bEd/zjaJ5WhTO+KM2bV6iDRjv fu099/TaV8Dy9lz2O5ecFONmRDIKx+Zlg4wIU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=VT5jn0hqk3RBIObuSRw2bJlZvsE/DxChGtp9GR5iv/gOH2mwMcH/8+47mB9YsBz/BE bzAAGk6dT61Dbq+2cG/jD0uQlDUqMtHKeKDb4jFNTTk7u38NwDO0qfAZ7r8SQyGxY/rp g7xjOcrWl0AIT2nUTho1X3JeYWh3d6wJI3v4k= Received: by 10.204.140.219 with SMTP id j27mr7234054bku.153.1280271444228; Tue, 27 Jul 2010 15:57:24 -0700 (PDT) MIME-Version: 1.0 Received: by 10.204.180.136 with HTTP; Tue, 27 Jul 2010 15:57:04 -0700 (PDT) In-Reply-To: <20100727212328.GD2280@HIDDEN> References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN> <20100727212328.GD2280@HIDDEN> From: Juanma Barranquero <lekktu@HIDDEN> Date: Wed, 28 Jul 2010 00:57:04 +0200 Message-ID: <AANLkTikdVKf70_nbaBbYPyjUE7iRZ1RXX8ybFJEvaXQe@HIDDEN> Subject: Re: bug#6740: Spurious byte compiler warnings To: Alan Mackenzie <acm@HIDDEN> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -2.7 (--) X-Debbugs-Envelope-To: 6740 Cc: Dan Nicolaescu <dann@HIDDEN>, 6740 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.11 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <http://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <http://debbugs.gnu.org/pipermail/debbugs-submit> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <http://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Sender: debbugs-submit-bounces <at> debbugs.gnu.org Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org X-Spam-Score: -2.7 (--) On Tue, Jul 27, 2010 at 23:23, Alan Mackenzie <acm@HIDDEN> wrote: > It's a bug that the error message is repeated, at the very least. Yes, likely. > And > the message is most assuredly false because (featurep 'cc-fix) isn't > always false - for example when it's run under XEmacs. Not, in code byte-compiled for Emacs it is always false because (featurep 'xemacs) is false. That means that optimized bytecode is not portable to XEmacs. But I don't think it was before (for a long time). > At the very least, emitting such arcane warnings is unhelpful. =C2=A0Are = there > any circumstances in which such a warning might help a hacker improve his > code? =C2=A0Surely we aren't in the business of making it difficult to ad= apt > code for XEmacs? You make it appear as it if were an attempt to warn about using XEmacs-specific code, but it is not, as Dan has pointed out. The warning is generic, the result of (and X (featurep 'xemacs) Y Z...) =3D> (prog (and X) nil) =3D> (prog X nil) ; IIUC the comments in byte-opt.el... from whence, "value returned from X is unused". > I think it's clear, the only code containing (featurep 'xemacs) is > portable code. The code is portable. The .elc is not. =C2=A0 =C2=A0 Juanma
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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From: Stefan Monnier <monnier@HIDDEN>
To: Dan Nicolaescu <dann@HIDDEN>
Subject: Re: bug#6740: Spurious byte compiler warnings
Message-ID: <jwvvd80iozu.fsf-monnier+emacs@HIDDEN>
References: <20100727200619.GC2280@HIDDEN> <yxqmxtcwu1w.fsf@HIDDEN>
Date: Tue, 27 Jul 2010 23:40:50 +0200
In-Reply-To: <yxqmxtcwu1w.fsf@HIDDEN> (Dan Nicolaescu's message of
"Tue, 27 Jul 2010 16:26:03 -0400")
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>> Warning: value returned from (featurep (quote cc-fix)) is unused
>> Warning: value returned from (featurep (quote cc-fix)) is unused
>>
>> It is obvious that that value is indeed used. This is a bug.
> The byte compiler knows that (featurep 'xemacs) is false, so
> (and (not (featurep 'cc-fix)) ... )
> will be false, so the featurep result is indeed unused.
> If you use (and (featurep 'xemacs) (not (featurep 'cc-fix) ...
> the warning will go away.
It's one of those cases where the warning is the result of a check done
"too late" (i.e. after some optimization), which means the check is not
performed on the code the user sees, but on some massaged version of it.
It's difficult to avoid them, short of removing all "code
improvement" warnings.
Stefan
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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Date: Tue, 27 Jul 2010 21:23:28 +0000
To: Dan Nicolaescu <dann@HIDDEN>
Subject: Re: bug#6740: Spurious byte compiler warnings
Message-ID: <20100727212328.GD2280@HIDDEN>
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Hi, Dan,
On Tue, Jul 27, 2010 at 04:26:03PM -0400, Dan Nicolaescu wrote:
> Alan Mackenzie <acm@HIDDEN> writes:
> > Hi, Emacs!
> > (i) Start Emacs, even a most recent bzr version, with -Q.
> > (ii) Put the following into the *scratch* buffer:
> > (eval-when-compile
> > (if (and (not (featurep 'cc-fix))
> > (featurep 'xemacs)
> > (progn
> > (require 'font-lock)
> > (let (font-lock-keywords)
> > (font-lock-compile-keywords '("\\<\\>"))
> > font-lock-keywords)))
> > (cc-load "cc-fix")))
> > (This fragment is at the top level, and taken from cc-defs.el.).
> > (iii) do M-x compile-defun on this form.
> > The byte compiler then issues the following two identical error
> > messages:
> > Warning: value returned from (featurep (quote cc-fix)) is unused
> > Warning: value returned from (featurep (quote cc-fix)) is unused
> > It is obvious that that value is indeed used. This is a bug.
> The byte compiler knows that (featurep 'xemacs) is false, so
> (and (not (featurep 'cc-fix)) ... )
> will be false, so the featurep result is indeed unused.
Ah, thanks for the explanation! But .....
It's a bug that the error message is repeated, at the very least. And
the message is most assuredly false because (featurep 'cc-fix) isn't
always false - for example when it's run under XEmacs.
> If you use (and (featurep 'xemacs) (not (featurep 'cc-fix) ...
> the warning will go away.
At the very least, emitting such arcane warnings is unhelpful. Are there
any circumstances in which such a warning might help a hacker improve his
code? Surely we aren't in the business of making it difficult to adapt
code for XEmacs?
I think it's clear, the only code containing (featurep 'xemacs) is
portable code. Can we please remove this unhelpful warning?
--
Alan Mackenzie (Nuremberg, Germany).
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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To: Alan Mackenzie <acm@HIDDEN>
Subject: Re: bug#6740: Spurious byte compiler warnings
References: <20100727200619.GC2280@HIDDEN>
From: Dan Nicolaescu <dann@HIDDEN>
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Alan Mackenzie <acm@HIDDEN> writes:
> Hi, Emacs!
>
> (i) Start Emacs, even a most recent bzr version, with -Q.
> (ii) Put the following into the *scratch* buffer:
>
> (eval-when-compile
> (if (and (not (featurep 'cc-fix))
> (featurep 'xemacs)
> (progn
> (require 'font-lock)
> (let (font-lock-keywords)
> (font-lock-compile-keywords '("\\<\\>"))
> font-lock-keywords)))
> (cc-load "cc-fix")))
>
> (This fragment is at the top level, and taken from cc-defs.el.).
> (iii) do M-x compile-defun on this form.
>
> The byte compiler then issues the following two identical error
> messages:
>
> Warning: value returned from (featurep (quote cc-fix)) is unused
> Warning: value returned from (featurep (quote cc-fix)) is unused
>
> It is obvious that that value is indeed used. This is a bug.
The byte compiler knows that (featurep 'xemacs) is false, so
(and (not (featurep 'cc-fix)) ... )
will be false, so the featurep result is indeed unused.
If you use (and (featurep 'xemacs) (not (featurep 'cc-fix) ...
the warning will go away.
owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
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Date: Tue, 27 Jul 2010 20:06:19 +0000
To: bug-gnu-emacs@HIDDEN
Subject: Spurious byte compiler warnings
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From: Alan Mackenzie <acm@HIDDEN>
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Hi, Emacs!
(i) Start Emacs, even a most recent bzr version, with -Q.
(ii) Put the following into the *scratch* buffer:
(eval-when-compile
(if (and (not (featurep 'cc-fix))
(featurep 'xemacs)
(progn
(require 'font-lock)
(let (font-lock-keywords)
(font-lock-compile-keywords '("\\<\\>"))
font-lock-keywords)))
(cc-load "cc-fix")))
(This fragment is at the top level, and taken from cc-defs.el.).
(iii) do M-x compile-defun on this form.
The byte compiler then issues the following two identical error
messages:
Warning: value returned from (featurep (quote cc-fix)) is unused
Warning: value returned from (featurep (quote cc-fix)) is unused
It is obvious that that value is indeed used. This is a bug.
--
Alan Mackenzie (Nuremberg, Germany).
Alan Mackenzie <acm@HIDDEN>:bug-gnu-emacs@HIDDEN.
Full text available.owner <at> debbugs.gnu.org, bug-gnu-emacs@HIDDEN:bug#6740; Package emacs.
Full text available.
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