Empty elements in EMACSLOADPATH now stand for the default

* src/lread.c (load_path_check): Take path to check as argument.
(load_path_default): New, split from init_lread.
(init_lread): Move calc of default load-path to load_path_default.
Empty elements in EMACSLOADPATH now stand for the default.
(load-path): Doc fix.

* src/emacs.c (decode_env_path): Add option to treat empty elements
as nil rather than ".".

* src/callproc.c (init_callproc_1, init_callproc):
* src/image.c (Vx_bitmap_file_path):
* src/lisp.h (decode_env_path):
* lread.c (Vsource_directory):
Update for new argument spec of decode_env_path.

* leim/Makefile.in (RUN_EMACS): Empty EMACSLOADPATH rather than unsetting.

* lisp/Makefile.in (emacs): Empty EMACSLOADPATH rather than unsetting.

* test/automated/Makefile.in (emacs):
Empty EMACSLOADPATH rather than unsetting.

* doc/emacs/cmdargs.texi (General Variables):
Empty elements in EMACSLOADPATH now mean the default load-path.

* doc/lispref/loading.texi (Library Search):
Empty elements in EMACSLOADPATH now mean the default load-path.

* etc/NEWS: Mention this.

Fixes: debbugs:12100

4 files changed, 38 insertions, 16 deletions

diff --git a/doc/emacs/ChangeLog b/doc/emacs/ChangeLog
index 229929d132d..a0d5344641e 100644
--- a/doc/emacs/ChangeLog
+++ b/doc/emacs/ChangeLog
@@ -1,3 +1,8 @@
+2013-11-23  Glenn Morris  <rgm@gnu.org>
+
+        * cmdargs.texi (General Variables):
+        Empty elements in EMACSLOADPATH now mean the default load-path.
+
 2013-11-21  Glenn Morris  <rgm@gnu.org>
 
         * cmdargs.texi (Action Arguments): Use path-separator with -L.
diff --git a/doc/emacs/cmdargs.texi b/doc/emacs/cmdargs.texi
index 92861c443f1..4294f775e5e 100644
--- a/doc/emacs/cmdargs.texi
+++ b/doc/emacs/cmdargs.texi
@@ -455,13 +455,16 @@ This is used to initialize the variable @code{data-directory}.
 Directory for the documentation string file, which is used to
 initialize the Lisp variable @code{doc-directory}.
 @item EMACSLOADPATH
-A colon-separated list of directories@footnote{ Here and below,
+A colon-separated list of directories@footnote{Here and below,
 whenever we say ``colon-separated list of directories'', it pertains
 to Unix and GNU/Linux systems.  On MS-DOS and MS-Windows, the
 directories are separated by semi-colons instead, since DOS/Windows
-file names might include a colon after a drive letter.}  to search for
-Emacs Lisp files.  If set, it overrides the usual initial value of the
-@code{load-path} variable (@pxref{Lisp Libraries}).
+file names might include a colon after a drive letter.} to search for
+Emacs Lisp files.  If set, it modifies the usual initial value of the
+@code{load-path} variable (@pxref{Lisp Libraries}).  An empty element
+stands for the default value of @code{load-path}; e.g., using
+@samp{EMACSLOADPATH="/tmp:"} adds @file{/tmp} to the front of
+the default @code{load-path}.
 @item EMACSPATH
 A colon-separated list of directories to search for executable files.
 If set, Emacs uses this in addition to @env{PATH} (see below) when
diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 8a082a851c9..5251efec3e4 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2013-11-23  Glenn Morris  <rgm@gnu.org>
+
+        * loading.texi (Library Search):
+        Empty elements in EMACSLOADPATH now mean the default load-path.
+
 2013-11-22  Glenn Morris  <rgm@gnu.org>
 
         * loading.texi (Library Search): Minor clarification.
diff --git a/doc/lispref/loading.texi b/doc/lispref/loading.texi
index 38a73b4e296..aae92de99cb 100644
--- a/doc/lispref/loading.texi
+++ b/doc/lispref/loading.texi
@@ -310,25 +310,34 @@ directories, if they exist.  Normally these directories do not contain
 @file{site-lisp} directories.)
 
 @cindex @env{EMACSLOADPATH} environment variable
-If the environment variable @env{EMACSLOADPATH} is set, it overrides
-the above initialization procedure.  That is, Emacs initializes
-@code{load-path} based solely on the value of the environment
-variable.  You must therefore include the directory containing the
-standard Lisp files, else Emacs will not function.  In most
-situations, it is better to use the @option{-L} command-line option
-(see below) to add elements to @code{load-path}.
+If the environment variable @env{EMACSLOADPATH} is set, it modifies
+the above initialization procedure.  Emacs initializes
+@code{load-path} based on the value of the environment variable.
 
 The syntax of @env{EMACSLOADPATH} is the same as used for @code{PATH};
 directory names are separated by @samp{:} (or @samp{;}, on some
-operating systems), and @samp{.} stands for the current default
-directory.  Here is an example of how to set @env{EMACSLOADPATH}
-variable (from a @command{sh}-style shell):
+operating systems).
+@ignore
+@c AFAICS, does not (yet) work right to specify non-absolute elements.
+and @samp{.} stands for the current default directory.
+@end ignore
+Here is an example of how to set @env{EMACSLOADPATH} variable (from a
+@command{sh}-style shell):
 
 @example
-export EMACSLOADPATH
-EMACSLOADPATH=/home/foo/.emacs.d/lisp:/usr/local/emacs/24.3/lisp
+export EMACSLOADPATH=/home/foo/.emacs.d/lisp:
 @end example
 
+An empty element in the value of the environment variable, whether
+trailing (as in the above example), leading, or embedded, is replaced
+by the default value of @code{load-path} as determined by the standard
+initialization procedure.  If there are no such empty elements, then
+@env{EMACSLOADPATH} specifies the entire @code{load-path}.  You must
+include either an empty element, or the explicit path to the directory
+containing the standard Lisp files, else Emacs will not function.
+(Another way to modify @code{load-path} is to use the @option{-L}
+command-line option when starting Emacs; see below.)
+
   For each directory in @code{load-path}, Emacs then checks to see if
 it contains a file @file{subdirs.el}, and if so, loads it.  The
 @file{subdirs.el} file is created when Emacs is built/installed,