Fix 'whence -a' to print correct path for tracked alias (#25)

'whence -a' bases the path for tracked aliases on the user's
current working directory if an enabled ksh builtin of the same
name is also available. The following example will claim 'cat'
is in the user's current working directory:

$ whence -a cat
cat is a tracked alias for /usr/bin/cat
$ builtin cat
$ whence -a cat
cat is a shell builtin
cat is /usr/bin/cat
cat is a tracked alias for /current/working/directory/cat

This patch from ksh2020 fixes this problem by properly saving the
path of the tracked alias for use with 'whence -a', since
'path_pwd' (as implied by the function's name) only gets the users
current working directory, not the location of tracked aliases.
Ref.: https://github.com/att/ast/issues/1049

This bug was originally reported by David Morano about two decades
ago to the AST team: https://github.com/att/ast/issues/954

src/cmd/ksh93/bltins/whence.c:
 - Print the actual path of a tracked alias, path_pwd doesn't
   have this functionality.

src/cmd/ksh93/include/name.h:
 - Add 'pathcomp' for saving the value of tracked aliases.

src/cmd/ksh93/sh/path.c:
 - Save the value of tracked aliases for use by whence.

src/cmd/ksh93/tests/builtins.sh:
 - Add a regression test for using 'whence -a' on tracked
   aliases with a builtin equivalent.

NEWS

@@ -3,6 +3,13 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-06-18:
+
+- A two decade old bug that caused 'whence -a' to base the path of
+  tracked aliases on the user's current working directory has been
+  fixed. Now the real path to the tracked aliases is shown when '-a'
+  is passed to the whence command.
+
 2020-06-17:
 
 - A bug in 'unset -f' was fixed that prevented shell functions from

src/cmd/ksh93/bltins/whence.c

@@ -249,7 +249,10 @@ static int whence(Shell_t *shp,char **argv, register int flags)
 					if(*cp!= '/')
 					{
 						if(!np && (np=nv_search(name,shp->track_tree,0)))
-							sfprintf(sfstdout,"%s %s %s/%s\n",name,sh_translate(is_talias),path_pwd(shp,0),cp);
+						{
+							const char *command_path = np->nvalue.pathcomp->name;
+							sfprintf(sfstdout,"%s %s %s/%s\n",name,sh_translate(is_talias),command_path,cp);
+						}
 						else if(!np || nv_isnull(np))
 							sfprintf(sfstdout,"%s%s\n",name,sh_translate(is_ufunction));
 						continue;

src/cmd/ksh93/include/name.h

@@ -32,6 +32,7 @@
 #include	<cdt.h>
 
 typedef int (*Nambfp_f)(int, char**, void*);
+struct pathcomp;
 
 /* Nodes can have all kinds of values */
 union Value
@@ -54,6 +55,7 @@ union Value
 	struct Namfun		*funp;	/* discipline pointer */
 	struct Namref		*nrp;	/* name reference */
 	Nambfp_f		bfp;	/* builtin entry point function pointer */
+	struct pathcomp *pathcomp;
 };
 
 #include	"nval.h"

src/cmd/ksh93/include/version.h

@@ -17,4 +17,4 @@
 *                  David Korn <dgk@research.att.com>                   *
 *                                                                      *
 ***********************************************************************/
-#define SH_RELEASE	"93u+m 2020-06-17"
+#define SH_RELEASE	"93u+m 2020-06-18"

src/cmd/ksh93/sh/path.c

@@ -1793,8 +1793,10 @@ void path_alias(register Namval_t *np,register Pathcomp_t *pp)
 	{
 		struct stat statb;
 		char *sp;
+		Pathcomp_t *old;
 		nv_offattr(np,NV_NOPRINT);
 		nv_stack(np,&talias_init);
+		old = np->nvalue.pathcomp;
 		np->nvalue.cp = (char*)pp;
 		pp->refcount++;
 		nv_setattr(np,NV_TAGGED|NV_NOFREE);

src/cmd/ksh93/tests/builtins.sh

@@ -702,5 +702,19 @@ printf '\\\000' | read -r -d ''
 foo=BUG command eval ':'
 [[ $foo == BUG ]] && err_exit '`command` fails to disable the special properties of special builtins'
 
+# ======
+# `whence -a` should not base the path of tracked aliases on the current directory
+run_whence()
+{
+	whence -a chmod >> /dev/null
+	builtin chmod
+	whence -a chmod
+}
+actual="$(run_whence)"
+expected="chmod is a shell builtin
+chmod is $(whence -p chmod)
+chmod is a tracked alias for $(whence -p chmod)"
+[[ $actual == $expected ]] || err_exit '`whence -a` does not work correctly with tracked aliases'
+
 # ======
 exit $((Errors<125?Errors:125))