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).

1 files changed, 57 insertions, 9 deletions

diff --git a/src/fileio.c b/src/fileio.c
index 66010b68783..c91af36fdf6 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;
           }