recent debian perl tests failures without . in @INC

[Patrice Dumas]

Hello,

Recent perl in debian do not have . in @INC anymore, and it will be
upstream in perl 5.26.
https://lists.debian.org/debian-devel-announce/2016/08/msg00013.html

As a consequence some tests now fail, even with top_srcdir set:  

top_srcdir=../
export top_srcdir
perl t/accents.t
Can't locate Texinfo/ModulePath.pm in @INC (you may need to install the 
Texinfo::ModulePath module) (@INC contains: 
/home/dumas/perl5/lib/perl5//x86_64-linux-gnu-thread-multi 
/home/dumas/perl5/lib/perl5/ /etc/perl 
/usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 
/usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 
/usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 
/usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at t/accents.t 
line 4.

Other tests, such as t/01use.t work, though only if top_srcdir is set.

Using -I . option to perl makes the test work again (even if 
top_srcdir is not set), like:
  perl -I . t/accents.t

It seems to me that the difference between tests that work and tests 
that do not is the presence or not, in BEGIN block of 
 if (defined($ENV{'top_srcdir'})) {unshift @INC, 
File::Spec->catdir($ENV{'top_srcdir'}, 'tp');

It seems to me that Texinfo/ModulePath.pm is generated so will be in the
build directory, and that it can set top_srcdir carefully, not
overwriting it if not needed.  It would also probably be good to have
tests working even if top_srcdir is not set.

One possibility could be to add something like the following in every
test:
 BEGIN { 
  if (not (grep {$_ eq '.'} @INC)) {push @INC, '.';} 
 }

And maybe the line: 
 if (defined($ENV{'top_srcdir'})) {unshift @INC, 
File::Spec->catdir($ENV{'top_srcdir'}, 'tp');
could be removed, but maybe with a comment stating that it will only
work for out of source builds if Texinfo/ModulePath.pm is generated in
the build tree.

-- 
Pat