[ng] memoize: expose a serious bug (affecting GNU make < 3.83)

This is a follow-up to commit v1.12-217-gd55204f of 2012-05-12,
"[ng] vars: implement memoization of make variables (new 'am__memoize'
func)".

So, apparently, all our workarounds aimed at avoiding the subtle GNU
make bug affecting variable memoization:

  <http://lists.gnu.org/archive/html/bug-make/2012-05/msg00013.html>
  <https://savannah.gnu.org/patch/?7534>

have not been enough :-(

When trying to use 'am__memoize' in a non-trivial setup (to optimize
the new form of the parallel-tests harness implemented by the series
http://lists.gnu.org/archive/html/automake-ng/2012-05/msg00015.html),
we stumbled upon that bug again.  At this point, it's quite clear that
there is no safe way to safely avoid it, so we'll have to find a way
to enable memoization (that is just an optimization) only with GNU
make >= 3.83 (once that is out).

Here, we just enhance our testsuite to expose the (re)discovered
issue.

* t/memoize.tap: Enhance.  The new check fails with GNU make <= 3.82,
and passes with the development version of GNU make (which should
become GNU make 3.83 eventually).

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

diff --git a/t/memoize.tap b/t/memoize.tap
index 516d335fde5ba9b106ccb7b00ff85d202002aa3a..8bd56f766a47125804243987784c0495ddf083a7 100755 (executable)
--- a/t/memoize.tap
+++ b/t/memoize.tap
@@ -19,7 +19,7 @@
 am_create_testdir=empty
 . ./defs || Exit 1
 
-plan_ 12
+plan_ 13
 
 ocwd=`pwd` || fatal_ "couldn't get current working directory"
 
@@ -223,6 +223,25 @@ END
 
 #---------------------------------------------------------------------------
 
+# This usage has been known to cause problems with GNU make <= 3.82,
+# tickling this bug:
+# <http://lists.gnu.org/archive/html/bug-make/2012-05/msg00013.html>
+# <https://savannah.gnu.org/patch/?7534>
+
+T "known GNU make issue (https://savannah.gnu.org/patch/?7534)" <<'END'
+
+setup := $(shell mkdir -p t/pm && : > t/pm/Cond2.pl)
+
+TESTS = $(wildcard t/pm/Cond2.pl)
+memo/am__test_bases = $(TESTS)
+$(call am__memoize,am__test_bases)
+
+test:
+       test '$(am__test_bases)' = 't/pm/Cond2.pl'
+END
+
+#---------------------------------------------------------------------------
+
 # Try memoization with variables having a very long content.  Our first
 # (unpublished) memoization implementation didn't work in that case -- it
 # triggered errors like "*** unterminated variable reference.  Stop" when