Fix handling of skipped directories when autoloading functions

Fix a bug in autoloading functions. Directories in the path search
list which should be skipped (e.g. because they don't exist) did
not interact correctly with autoloaded functions, so that a
function to autoload was not always found.

Details:
att#1454

Fix backported (and cleaned up) from:
att@3bc58164

src/cmd/ksh93/sh/path.c:
- path_opentype(): Fix the path search loop so that entries marked
  with PATH_SKIP are handled correctly.

src/cmd/ksh93/tests/functions.sh:
- Add regression test verifying an autoloaded function with a PATH
  that triggered the bug.
  The bug in path_opentype() fixed by this commit may affect other
  scenarios but we know it affects autoloaded functions. Hence the
  test for that scenario.

(cherry picked from commit a27903165775309f4f032de5d42ec1785f14cfbc)

NEWS

@@ -4,6 +4,14 @@ For full details, see the git log at:
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-05-31:
+
+- Fix a bug in autoloading functions. Directories in the path search list
+  which should be skipped (e.g. because they don't exist) did not interact
+  correctly with autoloaded functions, so that a function to autoload was
+  not always found correctly.
+  Details: https://github.com/att/ast/issues/1454
+
 2020-05-30:
 
 - Fix POSIX compliance of 'test'/'[' exit status on error. The command now

src/cmd/ksh93/include/version.h

@@ -17,4 +17,4 @@
 *                  David Korn <[email protected]>                   *
 *                                                                      *
 ***********************************************************************/
-#define SH_RELEASE	"93u+m 2020-05-30"
+#define SH_RELEASE	"93u+m 2020-05-31"

src/cmd/ksh93/sh/path.c

@@ -508,20 +508,24 @@ static int	path_opentype(Shell_t *shp,const char *name, register Pathcomp_t *pp,
 {
 	register int fd= -1;
 	struct stat statb;
-	Pathcomp_t *oldpp;
+	Pathcomp_t *nextpp;
+
 	if(!pp && !shp->pathlist)
 		path_init(shp);
 	if(!fun && strchr(name,'/'))
 	{
 		if(sh_isoption(SH_RESTRICTED))
 			errormsg(SH_DICT,ERROR_exit(1),e_restricted,name);
 	}
+
+	nextpp = pp;
 	do
 	{
-		pp = path_nextcomp(shp,oldpp=pp,name,0);
-		while(oldpp && (oldpp->flags&PATH_SKIP))
-			oldpp = oldpp->next;
-		if(fun && (!oldpp || !(oldpp->flags&PATH_FPATH)))
+		pp = nextpp;
+		nextpp = path_nextcomp(shp,pp,name,0);
+		if(pp && (pp->flags&PATH_SKIP))
+			continue;
+		if(fun && (!pp || !(pp->flags&PATH_FPATH)))
 			continue;
 		if((fd = sh_open(path_relative(shp,stakptr(PATH_OFFSET)),O_RDONLY,0)) >= 0)
 		{
@@ -533,7 +537,8 @@ static int	path_opentype(Shell_t *shp,const char *name, register Pathcomp_t *pp,
 			}
 		}
 	}
-	while( fd<0 && pp);
+	while(fd<0 && nextpp);
+
 	if(fd>=0 && (fd = sh_iomovefd(fd)) > 0)
 	{
 		fcntl(fd,F_SETFD,FD_CLOEXEC);

src/cmd/ksh93/tests/functions.sh

@@ -1213,4 +1213,33 @@ rc=$?
 exp=$((256+$(kill -l TERM) ))
 [[  $rc == "$exp" ]] || err_exit "expected exitval $exp got $rc"
 
+# ======
+# Verify that directories in the path search list which should be skipped
+# (e.g. because they don't exist) interact correctly with autoloaded functions.
+# See https://github.com/att/ast/issues/1454
+expect="Func cd called with |$tmp/usr|
+$tmp/usr"
+actual=$(
+	set -- wrong args passed
+	mkdir -p "$tmp/usr/bin"
+	print 'echo "wrong file executed ($*)"' >"$tmp/usr/bin/cd"
+	prefix=$tmp/ksh.$$
+
+	FPATH=$prefix/bad:$prefix/functions
+	mkdir -p "$prefix/functions"
+	print 'function cd { echo "Func cd called with |$*|"; command cd "$@"; }' >"$prefix/functions/cd"
+	typeset -fu cd
+
+	PATH=$tmp/arglebargle:$PATH:$tmp/usr/bin:$tmp/bin
+	cd "$tmp/usr"
+	pwd
+)
+actual_status=$?
+expect_status=0
+[[ $actual_status == "$expect_status" ]] ||
+    err_exit "autoload function skipped dir test wrong status (expected $expect_status, got $actual_status)"
+[[ $actual == "$expect" ]] ||
+    err_exit "autoload function skipped dir test wrong output (expected $(printf %q "$expect"), got $(printf %q "$actual"))"
+
+# ======
 exit $((Errors<125?Errors:125))