[Automake-NG] [FYI 2/2] built sources: avoid fork bomb in $(BUILT_SOURCES) handling

[Stefano Lattarini]

Due to how the handling of $(BUILT_SOURCES) was implemented in Automake-NG,
a recursive make call in the recipe of any $(BUILT_SOURCES) (or of any of
its prerequisites) would have caused an infinite recursion (complete with
fork bomb, yuck).  Work around the issue.

See:
<http://lists.gnu.org/archive/html/help-smalltalk/2012-08/msg00027.html>
<http://lists.gnu.org/archive/html/automake-patches/2012-08/msg00052.html>

* lib/am/common-targets.mk: Here, with the help of ...
(am.hack.making-built-sources): ... this new internal variable.
* Makefile.am (XFAIL_TESTS): Remove 't/built-sources-fork-bomb.sh'.

Signed-off-by: Stefano Lattarini <address@hidden>
---
 Makefile.am              | 1 -
 lib/am/common-targets.mk | 8 ++++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Makefile.am b/Makefile.am
index e19f3fd..656ebac 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -338,7 +338,6 @@ perl_fake_XFAIL_TESTS = \
 
 XFAIL_TESTS = \
   t/all.sh \
-  t/built-sources-fork-bomb.sh \
   t/override-suggest-local.sh \
   t/comments-in-var-def.sh \
   t/cond17.sh \
diff --git a/lib/am/common-targets.mk b/lib/am/common-targets.mk
index b9eb64f..da8e16c 100644
--- a/lib/am/common-targets.mk
+++ b/lib/am/common-targets.mk
@@ -159,8 +159,16 @@ ifeq ($(am.make.dry-run),true)
 # completely accurate.
 all check install: | $(am.built-early)
 else
+# Also, with this implementation, a recursive make call in the recipe
+# of any $(BUILT_SOURCES) (or any of its prerequisites) could cause an
+# infinite recursion (complete with fork bomb, yuck), if we are not
+# careful.  The following hack takes care of the problem.
+$(am.built-early): am.hack.making-built-sources = yes
+export am.hack.making-built-sources
+ifndef am.hack.making-built-sources
 $(foreach x,$(am.built-early),$(eval -include .am/built-sources/$(x)))
 .am/built-sources/%: | %
        @$(am.cmd.ensure-target-dir-exists)
        @touch $@
 endif
+endif
-- 
1.7.12