* lib/am/remake-hdr.am ($(srcdir)/%CONFIG_HIN%): Erase %STAMP%.

* tests/Makefile.am (TESTS): Add autohdr3.test
* tests/autohdr3.test: New file.

1 files changed, 32 insertions, 1 deletions

diff --git a/lib/am/remake-hdr.am b/lib/am/remake-hdr.am
index 1ae7c0f27..067c34844 100644
--- a/lib/am/remake-hdr.am
+++ b/lib/am/remake-hdr.am
@@ -38,7 +38,38 @@
 if %?FIRST_CONFIG_HIN%
 $(srcdir)/%CONFIG_HIN%: %MAINTAINER-MODE% $(am__configure_deps) %FILES%
 	cd $(top_srcdir) && $(AUTOHEADER)
-## Autoheader has the bad habit of not changing the time stamp if
+## Whenever $(AUTOHEADER) has run, we must make sure that
+## ./config.status will rebuild config.h.  The dependency from %STAMP%
+## on %CONFIG_H_DEPS% (which contains config.hin) is not enough to
+## express his.
+##
+## There are some tricky cases where this rule will build a
+## config.hin which has the same timestamp as %STAMP%, in which case
+## ./config.status will not be rerun (meaning that users will use in
+## out-of-date config.h without knowing it).  One situation where this
+## can occurs is the following:
+## 1. the user updates some configure dependency (let's say foo.m4)
+##    and run `make'
+## 2. the rebuild rules detect that a foo.m4 has changed,
+##    run aclocal, autoconf, automake, and then run ./config.status.
+##    (Note that autoheader hasn't been called yet, so ./config.status
+##    outputs a config.h from an obsolete config.hin.)
+## 3. Once Makefile has been regenerated, make continues, and
+##    discover that config.h is a dependency of the `all' rule.
+##    Because config.h depends on stamp-h1, stamp-h1 depends on
+##    config.hin, and config.hin depends on aclocal.m4, make runs
+##    autoheader to rebuild config.hin.
+## Now make ought to call ./config.status once again to rebuild
+## config.h from the new config.hin, but if you have a sufficiently
+## fast box, steps 2 and 3 will occur within the same second: the
+## config.h/stamp-h1 generated from the outdated config.hin will have
+## the same mtime as the new config.hin.  Hence make will think that
+## config.h is up to date.
+##
+## A solution is to erase %STAMP% here so that the %STAMP% rule
+## is always triggered after the this one.
+	rm -f %STAMP%
+## Autoheader has the bad habit of not changing the timestamp if
 ## config.hin is unchanged, which breaks Make targets.  Since what
 ## must not changed gratuitously is config.h, which is already handled
 ## by config.status, there is no reason to make things complex for