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Re: GOP-PROP 5: build system output (update)

From: Graham Percival
Subject: Re: GOP-PROP 5: build system output (update)
Date: Fri, 15 Jul 2011 08:43:34 -0700
User-agent: Mutt/1.5.20 (2009-06-14)

On Fri, Jul 15, 2011 at 02:20:51PM +0100, Phil Holmes wrote:
> ----- Original Message ----- From: "Graham Percival"
> >   * All output will be saved to various log files. (including
> >     output from make(1))
> >   * We will still display the output of make(1) on the console.
> I read these as mutually exclusive.  Are you saying we'll send the
> output of make both to a console and a log file?  Why?

Yes.  (well, "proposing" rather than "saying that we will")

- package maintainers (evidently) want to see the normal output of
  make(1).  Also, it anybody doesn't want to see that, they can
  trivially avoid it by doing make --silent.
- we'll still have tons of output, and some terminals only save
  1000 lines (for example).  If something goes wrong and I want
  to see exactly what commands were run, it'll be much easier to
  look at those commands if they were dumped verbatim into a
  test file.

I'm not certain if it's possible to cause make(1) to automatically
put its output into a logfile in addition to the console.  If not,
or if it looks really finicky to do this, then I'm quite willing
to withdraw this aspect of the proposal.  But if we're discussing
our ideal for the build system, mine would include this.

> >   * No other output will be displayed on the console, with one
> >     exception: if a build fails, we might display some
> >     portion(s) of log file(s) which give useful clues about the
> >     reason for the failure.
> I think there should be an option to turn it all back on if you want
> - a sort of inverse of QUIET_BUILD.  We should also get rid of the
> QUIET_BUILD variable completely.

Agreed.  Maybe using the V=1 thing that Jan was talking about?

> >   * Both stderr and stdout will be saved in *.log. The order of
> >     lines from these streams must be preserved.
> I do not believe this is possible, given the buffered nature of
> stdout.  See the font of all Unix knowledge, Wikipedia, when
> discussing sending both streams to the same file:
> "Messages appear in the same order as the program writes them,
> unless buffering is involved. (For example, a common situation is
> when the standard error stream is unbuffered but the standard output
> stream is line-buffered; in this case, text written to standard
> error later may appear on the terminal earlier, if the standard
> output stream's buffer is not yet full.)"

Hmm.  I've heard people talking about this, but I can't recall
ever running into this problem in lilypond development.  That
said, I almost always do multi-cpu builds, so I'm never surprised
when I see error messages apparently out of order -- but the
errors always make sense when I try a second make(1) call without

Can we change the buffering on streams?  I wouldn't be surprised
if we could do that.  Or maybe this is an argument in favor of
always using stderr, since that (apparently) guarantees unbuffered

At the moment, I'm thinking that we should acknowledge this as a
theoretical possibility, leave it in the policy as an "intended
behavior", and then go on with life.  If we have a bug report
about the actual behavior not following the intended behavior,
then we'll look at the technical issues in that bug, and if the
technical issues are unsurmountable, we can modify the policy.

> >   * Ideally, a failing build should provide hints about the
> >     reason why it failed, or at least hints about which log
> >     file(s) to examine.
> Seems a repeat of bullet point 3?

I think there's miscommunication here.  I see bullet point 3 as "
Logfiles from calling lilypond... all other logfiles will go

That bullet point is talking about informing the user of *which*
logfile to examine (we'll have a lot of logfiles, so guesswork
wouldn't be fun!), and possibly even output to console a portion
of the relevant logfile.

How could I clarify the language in those bullet points, or did
you mean a different bullet point?

- Graham

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