master 34e0a232cd: Allow symlink creation on MS-Windows without Administrator privileges

[Eli Zaretskii]

branch: master
commit 34e0a232cd0e7b38a33bc9134134c47665aeb185
Author: Kien Nguyen <kien.n.quang@gmail.com>
Commit: Eli Zaretskii <eliz@gnu.org>

    Allow symlink creation on MS-Windows without Administrator privileges
    
    * src/w32.c (symlink): Use the
    SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE flag when available.
    (Bug#57386)
---
 src/w32.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/w32.c b/src/w32.c
index cbcfcdd4f6..44c279602c 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -5992,12 +5992,22 @@ sys_umask (int mode)
 #ifndef SYMBOLIC_LINK_FLAG_DIRECTORY
 #define SYMBOLIC_LINK_FLAG_DIRECTORY 0x1
 #endif
+#ifndef SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
+#define SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE 0x2
+#endif
 
 int
 symlink (char const *filename, char const *linkname)
 {
   char linkfn[MAX_UTF8_PATH], *tgtfn;
-  DWORD flags = 0;
+  /* The SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE flag is
+     supported from Windows 10 build 14972.  It is only supported if
+     Developer Mode is enabled, and is ignored if it isn't.  */
+  DWORD flags =
+    (os_subtype == OS_SUBTYPE_NT
+     && (w32_major_version > 10
+        || (w32_major_version == 10 && w32_build_number >= 14972)))
+    ? SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE : 0;
   int dir_access, filename_ends_in_slash;
 
   /* Diagnostics follows Posix as much as possible.  */
@@ -6055,7 +6065,7 @@ symlink (char const *filename, char const *linkname)
      directory.  */
   filename_ends_in_slash = IS_DIRECTORY_SEP (filename[strlen (filename) - 1]);
   if (dir_access == 0 || filename_ends_in_slash)
-    flags = SYMBOLIC_LINK_FLAG_DIRECTORY;
+    flags |= SYMBOLIC_LINK_FLAG_DIRECTORY;
 
   tgtfn = (char *)map_w32_filename (filename, NULL);
   if (filename_ends_in_slash)