If the last component of the directory name is a symlink followed by a
slash, rmdir should fail, even if the symlink resolves to an existing
empty directory.

mkdir was similarly fixed in 2009 in commit
52dba6a5c45e8d8ba1e237a15213311dc11d91fb.  Modify a comment to clarify
the purpose of that commit.

Addresses https://cygwin.com/ml/cygwin/2019-09/msg00221.html.
---
 winsup/cygwin/dir.cc | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/dir.cc b/winsup/cygwin/dir.cc
index b757851d5..0e0535891 100644
--- a/winsup/cygwin/dir.cc
+++ b/winsup/cygwin/dir.cc
@@ -305,15 +305,14 @@ mkdir (const char *dir, mode_t mode)
 
   __try
     {
-      /* POSIX says mkdir("symlink-to-missing/") should create the
-        directory "missing", but Linux rejects it with EEXIST.  Copy
-        Linux behavior for now.  */
-
       if (!*dir)
        {
          set_errno (ENOENT);
          __leave;
        }
+      /* Following Linux, do not resolve the last component of DIR if
+        it is a symlink, even if DIR has a trailing slash.  Achieve
+        this by stripping trailing slashes or backslashes.  */
       if (isdirsep (dir[strlen (dir) - 1]))
        {
          /* This converts // to /, but since both give EEXIST, we're okay.  */
@@ -351,9 +350,29 @@ rmdir (const char *dir)
 {
   int res = -1;
   fhandler_base *fh = NULL;
+  tmp_pathbuf tp;
 
   __try
     {
+      if (!*dir)
+       {
+         set_errno (ENOENT);
+         __leave;
+       }
+
+      /* Following Linux, do not resolve the last component of DIR if
+        it is a symlink, even if DIR has a trailing slash.  Achieve
+        this by stripping trailing slashes or backslashes.  */
+      if (isdirsep (dir[strlen (dir) - 1]))
+       {
+         /* This converts // to /, but since both give ENOTEMPTY,
+            we're okay.  */
+         char *buf;
+         char *p = stpcpy (buf = tp.c_get (), dir) - 1;
+         dir = buf;
+         while (p > dir && isdirsep (*p))
+           *p-- = '\0';
+       }
       if (!(fh = build_fh_name (dir, PC_SYM_NOFOLLOW)))
        __leave;   /* errno already set */;
 
-- 
2.21.0

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