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Re: [PATCH] build: use automake's new $(AM_V_GEN) and $(AM_V_at) variabl

From: Ralf Wildenhues
Subject: Re: [PATCH] build: use automake's new $(AM_V_GEN) and $(AM_V_at) variables
Date: Sat, 25 Apr 2009 08:58:02 +0200
User-agent: Mutt/1.5.18 (2008-05-17)

Hi Jim,

* Jim Meyering wrote on Sat, Apr 25, 2009 at 08:04:36AM CEST:
> Ralf Wildenhues wrote:
> > Jim Meyering writes:
> >> +  $(AM_V_GEN)
> >> +  $(AM_V_at)rm -f $@ address@hidden

> > Thanks for using these.  Note the $(AM_V_GEN) will expand to the empty 
> > string
> > with V=1 or --disable-silent-rules.  I am actually not sure whether any make
> > implementation fails hard upon empty rule commands, but a couple of them 
> > will
> > output a warning, such as FreeBSD:

> How about making AM_V_GEN expand to ":;" rather than the empty string?
> That would seem slightly more symmetric.
> Fewer pitfalls for users, too.

Yes, I'm still considering that as an alternative.  There are two minor
draw-backs of using ":;" over the empty string:

- the verbose output from 'make' will contain the ":;", and users might
  wonder about that; on a more aesthetic note (but still quite able to
  turn a pretty bikeshed color into an ugly one), this makes the verbose
  output from packages using 'silent-rules' differ ever so slightly more
  from the output from packages not using the 'silent-rules' option in
  the first place.

- GNU make has this minor optimization that, when a rule doesn't contain
  any characters special to the shell, then it can go ahead and exec the
  command directly, rather than going through another fork&exec with
    sh -c "command ..."

  The ":;" would prevent this optimization.


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