whence -v/-a: report path to autoloadable functions

Since at least 1999, whence -v on pdksh (and its successor mksh)
reports the path where an autoloadable function may be found:

  $ mkdir ~/fun; FPATH=~/fun
  $ echo 'myfn() { echo hi; }' >~/fun/myfn
  $ whence -v myfn
  myfn is a undefined (autoload from /home/user/fun/myfn) function

Whereas ksh93 only reports, rather uselessly:

  myfn is an undefined function

As of this commit, whence -v/-a on ksh 93u+m does the same as
pdksh, but with correct grammar:

  myfn is an undefined function (autoload from /home/user/fun/myfn)

This may be a small violation of my own "no new features" policy
for 93u+m, but I couldn't resist. This omission has been annoying
me, and it's just embarrassing to lack a pdksh feature :)

src/cmd/ksh93/include/path.h,
src/cmd/ksh93/data/msg.c:
- Add e_autoloadfrom[] = " (autoload from %s)" message.

src/cmd/ksh93/bltins/whence.c: whence():
- Report the path (if any) when reporting an undefined function.
  This needs to be done in two places:
  1. When a function has been explicitly marked undefined with
     'autoload', we need to do a quick path_search() loop to find
     the path. (These undefined functions take precedence over
     regular commands, so are reported first.)
  2. When a function is not explicitly autoloaded but merely
     available in $FPATH, that path search was already done, so all
     we need to do is report it. (These are reported last.)
  Note that the output remains as on 93u+ if no function definition
  file is found on $FPATH. This is also like pdksh/mksh.

src/cmd/ksh93/data/builtins.c:
- Bump 'whence' version date. The inline docs never detailed very
  exactly what 'whence -v' reports, so no need for further edits.

src/cmd/ksh93/tests/path.sh:
- Regress-test the new whence behaviour plus actual autoloading,
  including the command override behaviour of autoloaded functions.

NEWS

@@ -5,6 +5,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 
 2020-09-25:
 
+- whence -v/-a now reports the path to the file that an "undefined" (i.e.
+  autoloadable) function will be loaded from when invoked, if found in $FPATH.
+
 - When ksh invoked a shell script that does not have a leading
   #!/hashbang/path, 'ps' and /proc/<PID>/cmdline showed corrupted output if
   the new script's command line was shorter than that of the invoking script.

src/cmd/ksh93/bltins/whence.c

@@ -139,7 +139,7 @@ static int whence(Shell_t *shp,char **argv, register int flags)
 	register const char *msg;
 	Namval_t *nq;
 	char *notused;
-	Pathcomp_t *pp=0;
+	Pathcomp_t *pp;
 	if(flags&Q_FLAG)
 		flags &= ~A_FLAG;
 	while(name= *argv++)
@@ -179,16 +179,24 @@ static int whence(Shell_t *shp,char **argv, register int flags)
 	bltins:
 		if(!(flags&F_FLAG) && (np = nv_bfsearch(name, shp->fun_tree, &nq, &notused)) && !is_abuiltin(np))
 		{
-			if(flags&V_FLAG)
-				if(nv_isnull(np))
-					cp = sh_translate(is_ufunction);
-				else
-					cp = sh_translate(is_function);
-			else
-				cp = "";
 			if(flags&Q_FLAG)
 				continue;
-			sfprintf(sfstdout,"%s%s\n",name,cp);
+			sfputr(sfstdout,name,-1);
+			if(flags&V_FLAG)
+			{
+				if(nv_isnull(np))
+				{
+					sfprintf(sfstdout,sh_translate(is_ufunction));
+					pp = 0;
+					while(!path_search(shp,name,&pp,3) && pp && (pp = pp->next))
+						;
+					if(*stakptr(PATH_OFFSET)=='/')
+						sfprintf(sfstdout,sh_translate(e_autoloadfrom),sh_fmtq(stakptr(PATH_OFFSET)));
+				}
+				else
+					sfprintf(sfstdout,sh_translate(is_function));
+			}
+			sfputc(sfstdout,'\n');
 			if(!aflag)
 				continue;
 			aflag++;
@@ -210,6 +218,7 @@ static int whence(Shell_t *shp,char **argv, register int flags)
 			aflag++;
 		}
 	search:
+		pp = 0;
 		do
 		{
 			int maybe_undef_fn = 0;  /* flag for possible undefined (i.e. autoloadable) function */
@@ -246,7 +255,10 @@ static int whence(Shell_t *shp,char **argv, register int flags)
 					/* Undefined/autoloadable function on FPATH */
 					sfputr(sfstdout,sh_fmtq(cp),-1);
 					if(flags&V_FLAG)
-						sfputr(sfstdout,sh_translate(is_ufunction),-1);
+					{
+						sfprintf(sfstdout,sh_translate(is_ufunction));
+						sfprintf(sfstdout,sh_translate(e_autoloadfrom),sh_fmtq(stakptr(PATH_OFFSET)));
+					}
 					sfputc(sfstdout,'\n');
 				}
 			}

src/cmd/ksh93/data/builtins.c

@@ -1988,7 +1988,7 @@ _JOB_
 ;
 
 const char sh_optwhence[] =
-"[-1c?\n@(#)$Id: whence (AT&T Research/ksh93) 2020-07-20 $\n]"
+"[-1c?\n@(#)$Id: whence (AT&T Research/ksh93) 2020-09-25 $\n]"
 USAGE_LICENSE
 "[+NAME?whence, type - locate a command and describe its type]"
 "[+DESCRIPTION?Without \b-v\b, \bwhence\b writes on standard output an "

src/cmd/ksh93/data/msg.c

@@ -141,6 +141,7 @@ const char is_alias[]		= "%s is an alias for ";
 const char is_talias[]		= "is a tracked alias for";
 const char is_function[]	= " is a function";
 const char is_ufunction[]	= " is an undefined function";
+const char e_autoloadfrom[]	= " (autoload from %s)";
 #ifdef JOBS
 #   ifdef SIGTSTP
 	const char e_newtty[]	= "Switching to new tty driver...";

src/cmd/ksh93/include/path.h

@@ -129,6 +129,7 @@ extern const char is_reserved[];
 extern const char is_talias[];
 extern const char is_function[];
 extern const char is_ufunction[];
+extern const char e_autoloadfrom[];
 #ifdef SHELLMAGIC
     extern const char e_prohibited[];
 #endif /* SHELLMAGIC */

src/cmd/ksh93/tests/path.sh

@@ -29,6 +29,7 @@ Command=${0##*/}
 integer Errors=0
 
 [[ -d $tmp && -w $tmp && $tmp == "$PWD" ]] || { err\_exit "$LINENO" '$tmp not set; run this from shtests. Aborting.'; exit 1; }
+PATH_orig=$PATH
 
 type /xxxxxx > out1 2> out2
 [[ -s out1 ]] && err_exit 'type should not write on stdout for not found case'
@@ -417,6 +418,8 @@ ${.sh.version}
 END
 ) || err_exit '${.sh.xxx} variables causes cat not be found'
 
+PATH=$PATH_orig
+
 # ======
 # Check that 'command -p' searches the default OS utility PATH.
 expect=/dev/null
@@ -448,6 +451,39 @@ actual=$(PATH=$tmp; redirect 2>&1; hash ls; command -p -v ls)
 [[ $actual == "$expect" ]] || err_exit "'command -p -v' fails to search default path if tracked alias exists" \
 	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
 
+# ======
+# Unlike pdksh, ksh93 didn't report the path to autoloadable functions, which was an annoying omission.
+if	((.sh.version >= 20200925))
+then	fundir=$tmp/whencefun
+	mkdir $fundir
+	echo "whence_FPATH_test() { echo I\'m just on FPATH; }" >$fundir/whence_FPATH_test
+	echo "whence_autoload_test() { echo I was explicitly autoloaded; }" >$fundir/whence_autoload_test
+	echo "function chmod { echo Hi, I\'m your new chmod!; }" >$fundir/chmod
+	echo "function ls { echo Hi, I\'m your new ls!; }" >$fundir/ls
+	hash -r
+	actual=$("$SHELL" -c 'FPATH=$1
+			autoload chmod whence_autoload_test
+			whence -a chmod whence_FPATH_test whence_autoload_test ls cp
+			whence_FPATH_test
+			whence_autoload_test
+			cp --totally-invalid-option 2>/dev/null
+			ls --totally-invalid-option 2>/dev/null
+			chmod --totally-invalid-option' \
+		whence_autoload_test "$fundir" 2>&1)
+	expect="chmod is an undefined function (autoload from $fundir/chmod)"
+	expect+=$'\n'"chmod is ${ whence -p chmod; }"
+	expect+=$'\n'"whence_FPATH_test is an undefined function (autoload from $fundir/whence_FPATH_test)"
+	expect+=$'\n'"whence_autoload_test is an undefined function (autoload from $fundir/whence_autoload_test)"
+	expect+=$'\n'"ls is a tracked alias for ${ whence -p ls; }"
+	expect+=$'\n'"ls is an undefined function (autoload from $fundir/ls)"
+	expect+=$'\n'"cp is a tracked alias for ${ whence -p cp; }"
+	expect+=$'\n'"I'm just on FPATH"
+	expect+=$'\n'"I was explicitly autoloaded"
+	expect+=$'\n'"Hi, I'm your new chmod!"
+	[[ $actual == "$expect" ]] || err_exit "failure in reporting or running autoloadable functions" \
+		"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
+fi
+
 # ======
 exit $((Errors<125?Errors:125))