master 7d58072: Revert recent expand-file-name changes if DOS_NT

[Paul Eggert]

branch: master
commit 7d5807277ff614a337c7e4530bb8d0e0188c189b
Author: Paul Eggert <eggert@cs.ucla.edu>
Commit: Paul Eggert <eggert@cs.ucla.edu>

    Revert recent expand-file-name changes if DOS_NT
    
    * src/fileio.c (Fexpand_file_name): Restore pre-August-26
    behavior, if DOS_NT.  This should fix the recently-introduced
    expand-file-name bugs on DOS_NT (Bug#26911).
---
 src/fileio.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 57 insertions(+), 9 deletions(-)

diff --git a/src/fileio.c b/src/fileio.c
index 66010b6..c91af36 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -1372,6 +1372,14 @@ the root directory.  */)
 
   length = newdirlim - newdir;
 
+#ifdef DOS_NT
+  /* Ignore any slash at the end of newdir, unless newdir is
+     just "/" or "//".  */
+  while (length > 1 && IS_DIRECTORY_SEP (newdir[length - 1])
+        && ! (length == 2 && IS_DIRECTORY_SEP (newdir[0])))
+    length--;
+#endif
+
   /* Now concatenate the directory and name to new space in the stack frame.  
*/
   tlen = length + file_name_as_directory_slop + (nmlim - nm) + 1;
   eassert (tlen >= file_name_as_directory_slop + 1);
@@ -1388,22 +1396,40 @@ the root directory.  */)
 
   if (newdir)
     {
-      if (!collapse_newdir)
+#ifndef DOS_NT
+      bool treat_as_absolute = !collapse_newdir;
+#else
+      bool treat_as_absolute = !nm[0] || IS_DIRECTORY_SEP (nm[0]);
+#endif
+      if (treat_as_absolute)
        {
-         /* With ~ or ~user, leave NEWDIR as-is to avoid transforming
-            it from a symlink (or a regular file!) into a directory.  */
-         memcpy (target, newdir, length);
-         nbytes = length;
+#ifdef DOS_NT
+         /* If newdir is effectively "C:/", then the drive letter will have
+            been stripped and newdir will be "/".  Concatenating with an
+            absolute directory in nm produces "//", which will then be
+            incorrectly treated as a network share.  Ignore newdir in
+            this case (keeping the drive letter).  */
+         if (!(drive && nm[0] && IS_DIRECTORY_SEP (newdir[0])
+               && newdir[1] == '\0'))
+#endif
+           {
+             /* With ~ or ~user, leave NEWDIR as-is to avoid transforming
+                it from a symlink (or a regular file!) into a directory.  */
+             memcpy (target, newdir, length);
+             nbytes = length;
+           }
        }
       else
        nbytes = file_name_as_directory (target, newdir, length, multibyte);
 
+#ifndef DOS_NT
       /* If TARGET ends in a directory separator, omit leading
         directory separators from NM so that concatenating a TARGET "/"
         to an NM "/foo" does not result in the incorrect "//foo".  */
       if (nbytes && IS_DIRECTORY_SEP (target[nbytes - 1]))
        while (IS_DIRECTORY_SEP (nm[0]))
          nm++;
+#endif
     }
 
   memcpy (target + nbytes, nm, nmlim - nm + 1);
@@ -1420,6 +1446,7 @@ the root directory.  */)
          {
            *o++ = *p++;
          }
+#ifndef DOS_NT
        else if (p[1] == '.' && IS_DIRECTORY_SEP (p[2]))
          {
            /* Replace "/./" with "/".  */
@@ -1432,6 +1459,18 @@ the root directory.  */)
            *o++ = *p;
            p += 2;
          }
+#else
+       else if (p[1] == '.'
+                && (IS_DIRECTORY_SEP (p[2])
+                    || p[2] == 0))
+         {
+           /* If "/." is the entire filename, keep the "/".  Otherwise,
+              just delete the whole "/.".  */
+           if (o == target && p[2] == '\0')
+             *o++ = *p;
+           p += 2;
+         }
+#endif
        else if (p[1] == '.' && p[2] == '.'
                 /* `/../' is the "superroot" on certain file systems.
                    Turned off on DOS_NT systems because they have no
@@ -1445,9 +1484,7 @@ the root directory.  */)
 #endif
                 && (IS_DIRECTORY_SEP (p[3]) || p[3] == 0))
          {
-#ifdef WINDOWSNT
-           char *prev_o = o;
-#endif
+#ifndef DOS_NT
            while (o != target)
              {
                o--;
@@ -1459,11 +1496,22 @@ the root directory.  */)
                    break;
                  }
              }
-#ifdef WINDOWSNT
+#else
+# ifdef WINDOWSNT
+           char *prev_o = o;
+# endif
+           while (o != target && (--o, !IS_DIRECTORY_SEP (*o)))
+             continue;
+# ifdef WINDOWSNT
            /* Don't go below server level in UNC filenames.  */
            if (o == target + 1 && IS_DIRECTORY_SEP (*o)
                && IS_DIRECTORY_SEP (*target))
              o = prev_o;
+           else
+# endif
+           /* Keep initial / only if this is the whole name.  */
+           if (o == target && IS_ANY_SEP (*o) && p[3] == 0)
+             ++o;
 #endif
            p += 3;
          }