*** Bug 16101 has been marked as a duplicate of this bug. ***

Also did an:
1) apply patch
2) perl -cw C4/AuthoritiesMarc.pm
   -- no issues
3) checked out master
4) repeat step 2
   -- expected failures.

Pushed to Master - Should be in the May 2016 Release.  Thanks!

Patch pushed to 3.22.x, will be in 3.22.6

(In reply to Jonathan Druart from comment #1)

> QA note: this may have an impact on performance but I have not found any
> other workarounds.

This

   if ( can_load( modules => { 'Cache::Memory' => undef, nocache => 1 } ) ) {

is not a right syntax for 'noncache' parameter.. If called that way, can_load() tries to load Cache::Memory and (nonexisting) 'nocache' module (version >= 1.0), and fails - so it simply prevents Cache::Memory loading (hence no more warnings). This has and enormous impact on performance in all setups which do not use memcached as a caching system; after that, memchached is the only caching system still working in Koha.

It also causes 'prove t/Cache.t' to fail in the default setup (w/o memcached).

I found another workaround:

+can_load( modules => { 'Cache::Memory' => undef } ) && Cache::Memory->new();
our %L1_cache;

-    if ( can_load( modules => { 'Cache::Memory' => undef, nocache => 1 } ) ) {
+    if ( can_load( modules => { 'Cache::Memory' => undef } ) ) {

which seems to work (?, "perl -wc C4/AuthoritiesMarc.pm" does not emit any warnings) without introducing noticeable performance issues, but I have no idea how exactly/why it works.. I have a feeling that it only hides the problem (whatever it really is) instead of fixing it properly.

(In reply to Jacek Ablewicz from comment #8)
> This
> 
>    if ( can_load( modules => { 'Cache::Memory' => undef, nocache => 1 } ) ) {
> 
> is not a right syntax for 'noncache' parameter.. If called that way,
> can_load() tries to load Cache::Memory and (nonexisting) 'nocache' module
> (version >= 1.0), and fails - so it simply prevents Cache::Memory loading
> (hence no more warnings). This has and enormous impact on performance in all
> setups which do not use memcached as a caching system; after that,
> memchached is the only caching system still working in Koha.

Erk! You are right, I misread the doc :-/

@RM please revert this patch

(In reply to Jonathan Druart from comment #10)
> @RM please revert this patch

ping!

Above all, it fails 2 tests in t/db_dependent/Context.t

(In reply to Jonathan Druart from comment #11)
> (In reply to Jonathan Druart from comment #10)
> > @RM please revert this patch
> 
> ping!
> 
> Above all, it fails 2 tests in t/db_dependent/Context.t

And t/db_dependent/sysprefs.t

Patch reverted in 3.22.x

Created attachment 51088 [details] [review]
Revert "Bug 16104: Remove warnings "used only once: possible typo""

This reverts commit 6b319a2d487257e8a08bc26af9c6b2e7fa2ece2c.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Tested with memcached and without MEMCACHED_SERVERS.
Cache.t, Context.t and sysprefs.t pass now.

Revert pushed to master

Revert will be in 3.22.7

If you compile (perl -cw) a script or module now that contains a use C4::Context, you have the following warnings:

Name "Tie::Hash::FIELDS" used only once: possible typo at /usr/share/perl/5.22/fields.pm line 135.
Name "Cache::RemovalStrategy::LRU::FIELDS" used only once: possible typo at /usr/share/perl/5.22/fields.pm line 135.
Name "Cache::RemovalStrategy::FIELDS" used only once: possible typo 
at /usr/share/perl/5.22/fields.pm line 135.

[ PS koha-qa does the same. ]

Are these warnings somehow related to perl's Cache module containing things like below?

use base qw(Tie::Hash);

my $strategy = $args->{removal_strategy} || 'Cache::RemovalStrategy::LRU';

(In reply to Marcel de Rooy from comment #18)
> If you compile (perl -cw) a script or module now that contains a use
> C4::Context, you have the following warnings:
> 
> Name "Tie::Hash::FIELDS" used only once: possible typo at
> /usr/share/perl/5.22/fields.pm line 135.
> Name "Cache::RemovalStrategy::LRU::FIELDS" used only once: possible typo at
> /usr/share/perl/5.22/fields.pm line 135.
> Name "Cache::RemovalStrategy::FIELDS" used only once: possible typo 
> at /usr/share/perl/5.22/fields.pm line 135.
> 
> [ PS koha-qa does the same. ]
> 
> Are these warnings somehow related to perl's Cache module containing things
> like below?
> 
> use base qw(Tie::Hash);
> 
> my $strategy = $args->{removal_strategy} || 'Cache::RemovalStrategy::LRU';

Yes, more or less, but I have never managed to track down completely the problem.
There is something weird happening...
To recreate easily, see bug 11998 comment 62

Hm, this has been reverted - changing status.

FYI I have added a temporary fix to the qa tools
  commit d73431289d4c72d7751b006137f518851d2ee605
    Do not consider "used only once: possible typo" as a warning (and make the tests pass!)

*** Bug 17238 has been marked as a duplicate of this bug. ***

History here is a little confusing and I am not sure how to test if these warning still occur. Is this still valid?