erts: Fix UNC path handling on Windows

This is unlikely to be the last of the path problems seen after
OTP 21, and I'm starting to regret my decision to unconditionally
use long paths. The idea to hit all long-path problems all the time
was good in theory as it makes such bugs far more visible, but
there just aren't enough people who test pre-release versions on
Windows, making this the world's slowest game of whack-a-mole.

1 files changed, 28 insertions, 3 deletions

diff --git a/lib/kernel/test/file_SUITE.erl b/lib/kernel/test/file_SUITE.erl
index e784c06865..a51025cba6 100644
--- a/lib/kernel/test/file_SUITE.erl
+++ b/lib/kernel/test/file_SUITE.erl
@@ -100,7 +100,7 @@
 
 -export([unicode_mode/1]).
 
--export([volume_relative_paths/1]).
+-export([volume_relative_paths/1,unc_paths/1]).
 
 -export([tiny_writes/1, tiny_writes_delayed/1,
          large_writes/1, large_writes_delayed/1,
@@ -129,7 +129,7 @@ suite() ->
 
 all() -> 
     [unicode, altname, read_write_file, {group, dirs},
-     {group, files}, delete, rename, names, volume_relative_paths,
+     {group, files}, delete, rename, names, volume_relative_paths, unc_paths,
      {group, errors}, {group, compression}, {group, links}, copy,
      delayed_write, read_ahead, segment_read, segment_write,
      ipread, pid2name, interleaved_read_write, otp_5814, otp_10852,
@@ -2182,6 +2182,30 @@ volume_relative_paths(Config) when is_list(Config) ->
             {skip, "This test is Windows-specific."}
     end.
 
+unc_paths(Config) when is_list(Config) ->
+    case os:type() of
+        {win32, _} ->
+            %% We assume administrative shares are set up and reachable, and we
+            %% settle for testing presence as some of the returned data is
+            %% different.
+            {ok, _} = file:read_file_info("C:\\Windows\\explorer.exe"),
+            {ok, _} = file:read_file_info("\\\\localhost\\c$\\Windows\\explorer.exe"),
+
+            {ok, Cwd} = file:get_cwd(),
+
+            try
+                ok = file:set_cwd("\\\\localhost\\c$\\Windows\\"),
+                {ok, _} = file:read_file_info("explorer.exe")
+            after
+                file:set_cwd(Cwd)
+            end,
+
+            [] = flush(),
+            ok;
+        _ ->
+            {skip, "This test is Windows-specific."}
+    end.
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 
@@ -2210,7 +2234,8 @@ e_delete(Config) when is_list(Config) ->
     case os:type() of
 	{win32, _} ->
 	    %% Remove a character device.
-	    {error, eacces} = ?FILE_MODULE:delete("nul");
+	    expect({error, eacces}, {error, einval},
+                   ?FILE_MODULE:delete("nul"));
 	_ ->
 	    ?FILE_MODULE:write_file_info(
 	       Base, #file_info {mode=0}),