Re: AC_CONFIG_FILES assumes that build directories have sibling in the source tree

[Alexandre Duret-Lutz]

>>> "Akim" == Akim Demaille <address@hidden> writes:

[...]

 Akim> Nope, it does not "work fine": it contains a hidden failure:

 Akim> rm -Rf test
 Akim> mkdir test
 Akim> cd test
 Akim> cat >configure.in <<EOF
 Akim> AC_INIT
 Akim> AC_OUTPUT(sub/foo:in/sub.in)
 Akim> EOF
 Akim> mkdir in
 Akim> echo '@srcdir@' >in/sub.in       # <<<===
 Akim> autoconf2.13                     # <<<===
 Akim> mkdir _build
 Akim> cd _build
 Akim> ../configure
 Akim> cat sub/foo                      # <<<===

 Akim> => ../../sub

This looks correct to me.

[...]

 >> I believe it would be fine for ./config.status to ignore this
 >> `cd' error, since it make no sense for the user to use
 >> @abs_srcdir@ in such a file.

 Akim> That's an option.  AFAICS there are three sounds options:

 Akim> 1. ignore and do as 2.13: output junk
 Akim> 2. ignore but ac_subst @srcdir@ as "" (or NONE?  or don't ac_subst it?)
 Akim> 3. recognize case and output "in/" as srcdir

 Akim> 3 of course "fails" when there are more that one source file.  But
 Akim> that's the common case.

 Akim> Opinions?

We seems to disagree about what @srcdir@ means.  For me, it's a
relative path from the current build directory to its twin
source directory.  Especially, this become `.' when in non-VPATH
builds.  The value of this variable is global to a directory,
and independent on how files are constructed.  This rules out
option 3.

When the source directory corresponding to the current build
directory does not exist, there is a problem.  (The converse
cannot happen, because config.status always creates missing
build directories.)  Admittedly the @srcdir@ variable is of
little value when the directory does not exists.  Even though,
it's still possible to define @srcdir@ as relative path from the
current build directory to its (possibly nonexistent) twin
source directory.  Autoconf does this very well presently.

My complaint is about @abs_srcdir@, not @address@hidden  While
@srcdir@ can be computed without assuming the existence of the
source directory, @abs_srcdir@ cannot, because this involves a
cd into this directory (and creating a directory into the source
tree for the sake of this cd is not an option).

I can see only two options to define @abs_srcdir@ when the
source directory does not exist:

 1. define @abs_srcdir@ as junk
 2. compute @abs_srcdir@ without using cd

I've suggested option 1 in my previous mail because that seems
the easier to implement, and I can't see why one would want to
use this variable when the source directory does not exist.

Not AC_SUBSTing @abs_srcdir@ in this case does not seem very
sensible, because it will be impossible for tools which trace
AC_SUBST to know which AC_SUBSTs are substituted and which are
not.  (However if what you meant was to never AC_SUBST
@abs_srcdir@, then I'm all for it.  IMHO all the abs_
substitutions are evil.)
-- 
Alexandre Duret-Lutz