bug#27781: LIBOBJS should depend on LIBOBJDIR

[Michael Haubenwallner]

On 08/22/2017 12:40 AM, Mathieu Lirzin wrote:
> Michael Haubenwallner <address@hidden> writes:
> 
>> In this case let me come up with attached patch for now
>> (without deeper knowledge of automake internals though).
> 
> I have tested this patch, and confirm that it fixes the bug.  However I
> have on question regarding the added code.
> 
>> From c3d51adb53400fc8bf65c0e003d810b2e7166d0d Mon Sep 17 00:00:00 2001
>> From: Michael Haubenwallner <address@hidden>
>> Date: Wed, 16 Aug 2017 18:16:12 +0200
>> Subject: [PATCH] automake: Depend on LIBOBJDIR for LIBOBJS.
>>
>> This change fixes automake bug#27781.
>>
>> * bin/automake.in: Add Makefile dependency on LIBOBJDIR/dirstamp for
>> each LIBOBJS/ALLOCA variable used.
>> ---
>>  bin/automake.in | 11 ++++++++++-
>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/bin/automake.in b/bin/automake.in
>> index 9c4cb86..b82e8c5 100644
>> --- a/bin/automake.in
>> +++ b/bin/automake.in
>> @@ -2153,10 +2153,19 @@ sub handle_LIBOBJS_or_ALLOCA
>>        $dir = backname ($relative_dir) . "/$dir"
>>          if $relative_dir ne '.';
>>        define_variable ('LIBOBJDIR', "$dir", INTERNAL);
>> +      my $dirstamp = '';
>> +      # Abusing $clean_files{"$(VAR)"} as indicator for whether
>> +      # we have added the "$(VAR): $dirstamp" dependency already.
> 
> I am not sure to understand what this comment really means.  Can you
> explain it in other words?
>         
>> +      $dirstamp = require_build_directory ($dir)

Thing is, $dirstamp is calculated only when ...

>> +    if ! defined $clean_files{"\$($var)"};

... $clean_files{} was defined, which is done ...

>>        $clean_files{"\$($var)"} = MOSTLY_CLEAN;

... here. Subsequently, $output_rules is extended only when $dirstamp was
calculated:

>> +      $output_rules .= "\$($var): $dirstamp\n" if ($dirstamp);

But the name "clean_files" feels somewhat unrelated to the dirstamp dependency
(as in causing a different output by itself), because I use it to make sure
the dirstamp rule is added only once to $output_rules:
Within flex, I've seen handle_LIBOBJS_or_ALLOCA to be called thrice, but this
dirstamp rule is enough once, as "\$($var)" holds all three object files.
While I have also thought about adding this dependency for each explicit
object file separately - which would not need the "clean_files" indicator,
I've failed to identify where to get the correct object file name from.

>>        # If LTLIBOBJS is used, we must also clear LIBOBJS (which might
>>        # be created by libtool as a side-effect of creating LTLIBOBJS).
>> -      $clean_files{"\$($var)"} = MOSTLY_CLEAN if $var =~ s/^LT//;
>> +      if ($var =~ s/^LT//) {
>> +    $clean_files{"\$($var)"} = MOSTLY_CLEAN;
>> +    $output_rules .= "\$($var): $dirstamp\n" if ($dirstamp);
>> +      }
>>      }
>>  
>>    return $dir;

Another thought about the final "$(LIBOBJS): .../.dirstamp" Makefile line:
If I remember correctly, there have been (non-GNU) make implementations that
choke on this rule when LIBOBJS is an empty variable:
Am I wrong here, or is GNU make required anyway these days?

Thanks!
/haubi/