Fix deep list argument error under Windows in os:cmd/1

Because of leeway in implementing os:cmd/1 under different OS there is
a difference in results when calling it with deep list
argument. os:cmd/1 specifies io_lib:chars() type for its argument and
io_lib functions can produce deep lists inspite of io_lib:chars()
result type specification. This commit flattens the argument for
erlang:open_port/2 (which is used under Windows) and expands the
os_SUITE to regress the bug.

2 files changed, 20 insertions, 2 deletions

diff --git a/lib/kernel/src/os.erl b/lib/kernel/src/os.erl
index 742c000cc1..2bded77fc4 100644
--- a/lib/kernel/src/os.erl
+++ b/lib/kernel/src/os.erl
@@ -187,11 +187,14 @@ cmd(Cmd) ->
 	{unix, _} ->
 	    unix_cmd(Cmd);
 	{win32, Wtype} ->
-	    Command = case {os:getenv("COMSPEC"),Wtype} of
+	    Command0 = case {os:getenv("COMSPEC"),Wtype} of
 			  {false,windows} -> lists:concat(["command.com /c", Cmd]);
 			  {false,_} -> lists:concat(["cmd /c", Cmd]);
 			  {Cspec,_} -> lists:concat([Cspec," /c",Cmd])
 		      end,
+            %% open_port/2 awaits string() in Command, but io_lib:chars() can be
+            %% deep lists according to io_lib module description.
+            Command = lists:flatten(Command0),
 	    Port = open_port({spawn, Command}, [stream, in, eof, hide]),
 	    get_data(Port, [])
     end.
diff --git a/lib/kernel/test/os_SUITE.erl b/lib/kernel/test/os_SUITE.erl
index 382fd6f6a9..e302bf7378 100644
--- a/lib/kernel/test/os_SUITE.erl
+++ b/lib/kernel/test/os_SUITE.erl
@@ -29,7 +29,8 @@ suite() -> [{ct_hooks,[ts_install_cth]}].
 
 all() -> 
     [space_in_cwd, quoting, space_in_name, bad_command,
-     find_executable, unix_comment_in_command, evil].
+     find_executable, unix_comment_in_command, deep_list_command,
+     evil].
 
 groups() -> 
     [].
@@ -237,6 +238,20 @@ unix_comment_in_command(Config) when is_list(Config) ->
     ?line test_server:timetrap_cancel(Dog),
     ok.
 
+deep_list_command(doc) ->
+    "Check that a deep list in command works equally on unix and on windows.";
+deep_list_command(suite) -> [];
+deep_list_command(Config) when is_list(Config) ->
+    %% As a 'io_lib' module description says: "There is no guarantee that the
+    %% character lists returned from some of the functions are flat, they can
+    %% be deep lists."
+    %% That's why os:cmd/1 can have arguments that are deep lists.
+    %% It is not a problem for unix, but for windows it is (in R15B02 for ex.).
+    ?line os:cmd([$e, $c, "ho"]),
+    %% FYI: [$e, $c, "ho"] =:= io_lib:format("ec~s", ["ho"])
+    ok.
+
+
 -define(EVIL_PROCS, 100).
 -define(EVIL_LOOPS, 100).
 -define(PORT_CREATOR, os_cmd_port_creator).