The build problem reported by Tim has been solved, and I'd like
to thank him for reporting it and for the tests he did at my request.
A workaround should be implemented in the future version of the build
system of POV-Ray for Unix.  This message is meant to serve as reference
in the mean time.


	Short version:

The problem is _not_ due to the build system in POV-Ray for Unix
per se, but rather to the combination of:
- a particular setting in one environment variable
- a (seemingly) buggy behavior of the compiler used -- here gcc,
   possibly affecting all versions.

The build failure is due to having the environment variable
C_INCLUDE_PATH set with a "." (current directory) in the list of
include paths, and gcc wrongly removing all duplicate "." entries.

Workaround: do not set C_INCLUDE_PATH (or any similar environment
variable used by the compiler) with the "." path.  An (untested)
alternative is to build POV-Ray in a different directory than in
its source tree; see section 4.1.3 of the INSTALL file.


	Long version:

Facts:

1) The build failure in the unix/ directory is the consequence of
    unix/config.h not being read; the definitions contained therein
    are thus missing and lead to compilation errors in other files.

2) Instead, a config.h file is read in another directory (here in
    the 3rd-party zlib library in ../libraries/zlib).  Using this
    config.h file generates the warnings that appear before the
    make errors.

Causes:

1) The C_INCLUDE_PATH environment variable is set for the user
    (e.g. in his $HOME/.bash_profile configuration file) with
    something like
      C_INCLUDE_PATH=.:/home/user/include
    where the first dot means the current directory.  These paths
    are normally used by the compiler to search for header files
    included in C sources.

2) For compiling POV-Ray, several include paths are specified on
    the compiler command-line using -Ipath flags.  These flags are
    normally prepended to the list of paths used to search for
    include files.  The compiler then searches for include files
    in the following order:
      1) all -Ipath specified at the command-line, in the given order;
      2) paths specified through environment variables specified by
         the user, in the given order;
      3) default (system) search paths (unless the compiler is asked
         not to search in system paths), in a system-specific order.
    The -I. compiler flag is usually used when compiling each
    source file.

3) For some unknown reason, the gcc (g++) compiler does the following
    when compiling a C++ source file:

    (tested in the unix/ directory using the -v compiler option,
simplified output)

g++ -I. -I. -I..  -I.. -I../source -I../source/base -I../source/frontend
     -I../source -I../libraries/zlib -I../libraries/png -I../libraries/tiff/libtiff
     -I../libraries/tiff/libtiff  -I/usr/X11R6/include  -v -c -o svga.o
    `test -f 'svga.cpp' || echo './'`svga.cpp
<snip>
ignoring nonexistent directory "/usr/i386-redhat-linux/include"
ignoring duplicate directory "."
   as it is a non-system directory that duplicates a system directory
ignoring duplicate directory "."
   as it is a non-system directory that duplicates a system directory
ignoring duplicate directory ".."
ignoring duplicate directory "../source"
ignoring duplicate directory "../libraries/tiff/libtiff"
#include "..." search starts here:
#include <...> search starts here:
  ..
  ../source
  ../source/base
  ../source/frontend
  ../libraries/zlib
  ../libraries/png
  ../libraries/tiff/libtiff
  /usr/X11R6/include
  .
  /home/user/include
  /usr/include/c++/3.2.2
  /usr/include/c++/3.2.2/i386-redhat-linux
  /usr/include/c++/3.2.2/backward
  /usr/local/include
  /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/include
  /usr/include
End of search list.

	Note that gcc decides to completely remove the "." directory from
the search list of include files, while -I. was specified as the first
path to be searched (here twice: the second -I. is due to the fact that
the user builds POV-Ray directly in its source tree).
	Apparently gcc removes "." because it considers that the "." given
in C_INCLUDE_PATH (here right before /home/user/include) is a system directory.
Also in principle C_INCLUDE_PATH should be ignored when compiling a C++ source
(the preprocessor should use CPLUS_INCLUDE_PATH instead).
	As a result, the ./config.h file is not found for the C++ source file.
Instead the first config.h file found in the list above (in ../libraries/zlib
in this case) is used instead.  The "." found in the search list is too low
in the list to be useful here.  (On systems where compiling the 3rd-party
libraries is not required, the build could eventually succeed.)

Conclusion:

A possible workaround is to remove "." from the search list in C_INCLUDE_PATH.
Alternatively, one can build the POV-Ray source in another directory so as to
have gcc use a -Ipath refering to the unix/ directory by something else but
the "." path.


	- NC

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