From bug-octave-request at bevo dot che dot wisc dot edu  Fri Oct 23 12:54:42 1998
Subject: [patch] extra colon feature + problem with default loadpath
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Rafael Laboissiere <rafael at icp dot inpg dot fr>
Cc: bug-octave at bevo dot che dot wisc dot edu, Dirk Eddelbuettel <edd@debian.org>
Date: Fri, 23 Oct 1998 12:54:18 -0500

On 23-Oct-1998, Rafael Laboissiere <rafael at icp dot inpg dot fr> wrote:

| The solution found, implied changing a couple of files in version
| 2.0.13.  (BTW, guys, reading the Octave source is a great pleasure, and
| making modifications to it are quite straightforward; Congrats!)
| Essentially, what I did was to transfer the burden of default path
| expansion from file src/defaults.cc to the method dir_path::init() [in
| file liboctave/pathsearch.cc].  A new global variable Vload_path_default
| is defined , that stores the default path.

One problem with this solution is that it puts an Octave-specific
variable (Vload_path_default) in liboctave.  It also assumes that the
dir_path class is only going to be used to expand LOADPATH, but it is
also used to search files in other PATH-like variables.  Automatically
inserting the value of Vload_path_default in them is probably not right.

| A new builtin function
| Fload_path_default() was also created, which prints the default path
| (this addition is fully optional, but is the only way that I could
| imagine to get access to the value of the default path from the Octave
| prompt).

It would have also been possible to define a new built-in variable
using DEFVAR.

| The default value for Vload_path (and hence LOADPATH at startup) is set
| to ":".  This adds a nice feature to Octave, namely, that
| initializations of LOADPATH in octave.conf or ~/.octaverc can safely
| append/prepend values to LOADPATH, and the default path is still there.
| As a counterexemple, the file /etc/octave.conf in a Debian system (Salut
| Dirk !) has the line:
| 
| LOADPATH = [ ":/usr/local/share/octave/site-m//", LOADPATH ];
| 
| With the current version of Octave, after initialization we get the
| following value for LOADPATH:
| 
| :/usr/local/share/octave/site-m//.:/usr/lib/octave/site/oct/i386-pc-linux-gnu//:/usr/share/octave/site/m//:/usr/lib/octave/2.0.13/oct/i386-pc-linux-gnu//:/usr/share/octave/2.0.13/m//
| 
| whose second element is wrong (more on that below).

I'm getting a bit confused here.

| First, the bug: the environment variable OCTAVE_PATH, if it exists, is
| intended to replace the default path (defined by #define
| OCTAVE_FCNFILEPATH).

I think there is some misunderstanding here.  OCTAVE_PATH is not
intended to provide a way to override the value of OCTAVE_FCNFILEPATH.
It is just intended to be another way to specify the default value of
LOADPATH from the environment.

| However, as the function
| maybe_add_default_load_path() uses the value OCTAVE_FCNFILEPATH, the
| environment variable OCTAVE_PATH is useless.  My design solves the
| problem and allow the user to _really_ overriden the builtin default
| path.

I think the real problem is that if OCTAVE_PATH is found in the
environment, maybe_add_default_load_path is not called on its value.
Here is a fix for that:

Fri Oct 23 12:07:32 1998  John W. Eaton  <jwe at bevo dot che dot wisc dot edu>

	* defaults.cc (set_default_path): If OCTAVE_PATH is set in the
	environment, call maybe_add_default_load_path on it.

*** defaults.cc~	Tue Oct 20 20:57:45 1998
--- defaults.cc	Fri Oct 23 12:19:09 1998
***************
*** 192,198 ****
  
    char *oct_path = getenv ("OCTAVE_PATH");
  
!   Vload_path = oct_path ? string (oct_path) : std_path;
  
    Vload_path_dir_path = dir_path (Vload_path);
  }
--- 192,198 ----
  
    char *oct_path = getenv ("OCTAVE_PATH");
  
!   Vload_path = oct_path ? maybe_add_default_load_path (oct_path) : std_path;
  
    Vload_path_dir_path = dir_path (Vload_path);
  }

| The bad feature is illustrated above: at initialization, if LOADPATH
| has leading or trailing colons, the default path is inserted in it.
| With my new design, no insertion happens, the default path is kept
| hidden, thanks to Vload_path_default.  This means that the user gets
| the value of LOADPATH that she asked for.

Keeping the default path hidden may seem like a nice feature, but it
will cause problems for things like this:

  file_in_path (LOADPATH, "foo")

because file_in_path doesn't know that LOADPATH is special, so it
can't know to insert the default path at the appropriate places.

Thanks,

jwe