PATH defaults now act more like GNU and POSIX

When PATH is unset or empty, use the system default,
to be consistent with GNU/Linux and with POSIX.
If there is no system default do not default to "."
as that can be dangerous.
* src/callproc.c (init_callproc_1, init_callproc):
Default PATH to the null pointer, not the empty string.
* src/emacs.c (default_PATH): New function.
(find_emacs_executable, decode_env_path): Be consistent with POSIX
and with glibc about what to do when PATH is unset or empty.

2 files changed, 3 insertions, 2 deletions

diff --git a/doc/emacs/cmdargs.texi b/doc/emacs/cmdargs.texi
index 00167056be1..79ae2d064d1 100644
--- a/doc/emacs/cmdargs.texi
+++ b/doc/emacs/cmdargs.texi
@@ -695,6 +695,7 @@ The name of the organization to which you belong.  Used for setting the
 A colon-separated list of directories containing executable files.
 This is used to initialize the variable @code{exec-path}
 (@pxref{Shell}).
+If unset or empty, an implementation-dependent default is used.
 @item PWD
 @vindex PWD@r{, environment variable}
 If set, this should be the default directory when Emacs was started.
diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index 88b7bfc7049..2c2c710eea4 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -753,8 +753,8 @@ available.
 (either in the @var{cmd} argument to one of the above commands, or in
 other contexts), Emacs searches for the program in the directories
 specified by the variable @code{exec-path}.  The value of this
-variable must be a list of directories; the default value is
-initialized from the environment variable @env{PATH} when Emacs is
+variable must be a list of directories; the default value
+depends on the environment variable @env{PATH} when Emacs is
 started (@pxref{General Variables}).
 
   @kbd{M-x eshell} invokes a shell implemented entirely in Emacs.  It