bug#8665: automake should offer APIs to honour silent-rules verbosity from shell code in Makefiles

[Jack Kelly]

On Fri, May 13, 2011 at 7:30 PM, Stefano Lattarini
<address@hidden> wrote:
> Hello Jack, thanks for the feedback.
>
> On Friday 13 May 2011, Jack Kelly wrote:
>> Comments inline, after some snipping.
>>
>> On Fri, May 13, 2011 at 6:27 AM, Stefano Lattarini
>> <address@hidden> wrote:
>> > -snip intro-
>> >
>> > I thus propose we add an API of this kind.  At first, this might be as
>> > simple as just defining two proper `AM_V_ECHO' and `AM_Q_ECHO' variables;
>> > `AM_V_ECHO' should be `echo' when silent rules are in effect, and `:'
>> > when they are not; viceversa for `AM_Q_ECHO'.
>> >
>> > To give a simplified example of what I'm proposing:
>> >
>> >  $ cat > Makefile.am <<'END'
>> >  headers:
>> >   address@hidden [commands defining a shell variable `$headers']; \
>> >     $(AM_V_ECHO) "cd somedir && generate-header --flag $$headers"; \
>> >     $(AM_Q_ECHO) "GEN headers"; \
>> >     cd somedir && generate-header --flag $$headers
>>
>> If you're just echoing "GEN headers", is there any reason you can't
>> use $(AM_V_GEN) here?
>>
> Well, first of all, assuming that $(AM_V_ECHO) and $(AM_Q_ECHO) aren't
> available, using just $(AM_V_GEN) wouldn't be enough to silence the
> "cd somedir && generate-header --flag $$headers" message echoed by the
> rule above, and this clearly defies the purpose of having silent rules
> in the first place.  Also in case the generation of headers uses a
> timestamp file, say ".headers_timestamp" (which would probably be the
> case in a real-world example), the use of $(AM_V_GEN) woul cause the
> displaying of a leass appealing and IMHO slightly less clear message
> "GEN .headers_timpestamp".

You do have $(AM_V_at), though. I am persuaded by your arguments for
the general case.

> Also, thinking about more general situations, we might want to display
> some trimmed-down versions of $headers instead of the constant string
> `headers'; for example, we might want to display the number of headers
> that are being generated (an information that is available only to the
> shell running the rule, and not to the make process):
>
> -snip example-

Agreed.

>> Maybe we should have a more general method of
>> declaring silencing variables (like the $(AM_V_GEN), but also the
>> others that echo 'CC' and friends. Then users who have unconventional
>> setups can silence things without echoing 'GEN' everywhere.
>>
> If I understand correctly what you're suggesting, then I think the current
> implementation already offers what you want; see the documentation for the
> 'silent-rules' option at:
>
>  <http://www.gnu.org/software/automake/manual/html_node/Options.html>
>
> (I know, that is, er, "suboptimally" placed; a patch to fix this is still
> pending).
>
> A relevant excerpt:
>
>  You can add your own variables, so strings of your own choice are shown.
>  The following snippet shows how you would define your own equivalent of
>  AM_V_GEN:
>     pkg_verbose = $(pkg_verbose_$(V))
>     pkg_verbose_ = $(pkg_verbose_$(AM_DEFAULT_VERBOSITY))
>     pkg_verbose_0 = @echo PKG-GEN $@;
>
>     foo: foo.in
>         (pkg_verbose)cp $(srcdir)/foo.in $@

Yes. I think it would be nice to make a Makefile.am declaration or m4
macro to generate this, the above was what I was looking for.

-- Jack