bug#57386: 29.0.50; support make-symbolic-link without admin priviledge on Windows

["Kiên Nguyễn Quang" <kien.n.quang@gmail.com>]

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Oops. Here it is.

On Thu, Aug 25, 2022 at 6:57 PM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Kiên Nguyễn Quang <kien.n.quang@gmail.com>
> > Date: Thu, 25 Aug 2022 18:51:30 +0900
> > Cc: 57386@debbugs.gnu.org
> >
> > > When you call an API with a parameter that is invalid, you are risking
> > > an exception, depending on the API and the build (debug or not).  This
> > > has various unpleasant consequences; in the worst case, the Emacs
> > > process could be terminated.  As documented, the problem is limited to
> > > CRT functions, but our general policy is to avoid that even when using
> > > the Win32 APIs.  And version check is a simple enough way of avoiding
> > > that, so I see no reason not to do it here.
> >
> > Okay, that makes sense. Although I think that's the problem of CRT APIs
> only, as API should never throw
> > exceptions, which is a foreign concept to ABI and requires an exact
> library match to handle correctly
> >
> > The new patch is attached.
>
> Thanks, but I think you sent a wrong patch?
>


-- 
 Nguyen Quang Kien - グエン クアン キエン
 Software Developer @ MSD

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From d108561e58a3a5117b259bf03cb790db1407e670 Mon Sep 17 00:00:00 2001
From: Kien Nguyen <kien.n.quang@gmail.com>
Date: Wed, 24 Aug 2022 23:19:35 +0900
Subject: [PATCH] symlink: allow w32 non-admin user to create symlink

* src/w32.c (symlink): allow w32 user to create symlink without admin privileged

---
 src/w32.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/w32.c b/src/w32.c
index cbcfcdd4f..5e5ed980f 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -5992,12 +5992,17 @@ 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 new flag is supported from build 14972 */
+  DWORD flags = (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 +6060,7 @@ 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)
-- 
2.37.0.windows.1