gcc -I- feature

[nmake Technical Support <nmake at lucent dot com>]

This is to request reinstatement of the -I- command line directory
search option.  Sorry for the late request, we only recently became
aware that -I- is deprecated in gcc 4.0.

The Lucent(R) nmake tool (http://www.bell-labs.com/project/nmake/)
relies on -I- to implement the Lucent(R) nmake viewpathing feature
which allows developers to have copies of only the code they are
modifying in their private build area while picking up the rest of
the code from shared, common base areas.  Lucent(R) nmake viewpathing
requires the ability to override searching the directory of the
including file for #include "..." style includes.

The example below shows a development node "dev" viewpathed through
an official node "off".  The developer has a modified version of a.h
which is included from a.c in the official node.  There is also an
official version of a.h in off.  When compiling a.c from the dev
directory, the developer needs to pick up the official version of a.c
and the development version of a.h.  It is not clear how to use the
suggested replacement option -iquote to achieve the needed effect.

See http://www.bell-labs.com/project/nmake/impact/viewpath.html
and http://www.bell-labs.com/project/nmake/tutorial/s10.html for
more on Lucent(R) nmake viewpathing.  See the 2 pages linked from
http://www.bell-labs.com/project/nmake/manual/cpp.html for an
explanation of the Lucent(R) nmake cpp -I- feature.

We also read in a mailing list archive some concern that suppressing
the directory containing the current file tends to break system headers
(see http://gcc.gnu.org/ml/gcc-patches/2004-05/msg00154.html.)
We believe that a companion feature, "prefixinclude", may address
this concern by extending -I- to reasonably handle the case of
include paths with a directory prefix.

See http://www.bell-labs.com/project/nmake/manual/cppfeatures.html for
a description of prefixinclude.  gcc historically implemented -I- but
not prefixinclude, so while useful it gets us only part of the way
there.  prefixinclude support may eliminate problems encountered with
-I-.  At some point we would also like to see prefixinclude support in
gcc.
 
Other data points related to this request:

- -I- with prefixinclude has a proven, long history of use in large
   Lucent(R) nmake-based projects.

- HP aC++ and ANSI C implement -I- and prefixinclude
  http://docs.hp.com/en/5187-0137/5187-0137.html

- Sun Studio 10 implements -I-
  http://docs.sun.com/source/819-0494/sun.specific.html#60446


Let us know what you think or if you have any additional questions.
We would very much like to see -I- supported again in gcc.

Thanks.

nmake Development
Gary Selzer
Rich Brack


____________________
$ uname -a
Linux phoebe 2.6.12-1-686 #1 Tue Aug 9 13:00:08 UTC 2005 i686 GNU/Linux
$ cat /etc/debian_version
testing/unstable
$ type gcc-4.0
gcc-4.0 is /usr/bin/gcc-4.0
$ gcc-4.0 -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --enable-nls --without-included-gettext --enable-threads=posix --program-suffix=-4.0 --enable-__cxa_atexit --enable-libstdcxx-allocator=mt --enable-clocale=gnu --enable-libstdcxx-debug --enable-java-gc=boehm --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr --disable-werror --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.0.2 20050806 (prerelease) (Debian 4.0.1-4)
$ pwd
/home/gms/ms/050049
$ ls -lR
.:
total 16
drwxr-xr-x  2 gms gms 4096 2005-08-23 10:23 dev
-rwxr-xr-x  1 gms gms  249 2005-08-22 17:26 mk
drwxr-xr-x  2 gms gms 4096 2005-08-22 17:30 off

./dev:
total 0
-rw-r--r--  1 gms gms 27 2005-08-22 16:28 a.h

./off:
total 4
-rw-r--r--  1 gms gms 88 2005-08-22 17:07 a.c
-rw-r--r--  1 gms gms 24 2005-08-22 16:27 a.h
$ cat off/a.c
#include <stdio.h>
#include "a.h"

int
main()
{
  printf("sval: %s version\n", sval);
}
$ cat off/a.h
#define sval "official"
$ cat dev/a.h
#define sval "development"
$ cd dev
$ gcc-4.0 -o a -iquote . ../off/a.c
$ ./a
sval: official version
$ gcc-4.0 -o a -I. -I- ../off/a.c
cc1: note: obsolete option -I- used, please use -iquote instead
$ ./a
sval: development version