is_admin: doesn't require MEX

Can also use Java on Unix-like or .Net on Windows

Author: scivision

+stdlib/is_admin.m

@@ -1,8 +1,23 @@
 %% IS_ADMIN is the process run as root / admin
-% requires: mex
+% optional: mex
+
+function y = is_admin()
+
+if ispc()
+  % com.sun.security.auth.module.NTSystem().getGroupIDs();
+  % Administrator group SID (S-1-5-32-544) is not an appropriate check .getGroupIDs because it
+  % only tells if a user is *allowed* to run as admin, not if they are currently running as admin.
+
+  % Use .NET System.Security.Principal to check for admin privileges
+  identity = System.Security.Principal.WindowsIdentity.GetCurrent();
+  principal = System.Security.Principal.WindowsPrincipal(identity);
+  y = principal.IsInRole(System.Security.Principal.WindowsBuiltInRole.Administrator);
+elseif stdlib.isoctave()
+  y = getuid() == 0;
+else
+  y = com.sun.security.auth.module.UnixSystem().getUid() == 0;
+end
 
-function is_admin()
-error("buildtool mex")
 end
 
 %!testif 0

test/TestFileImpure.m

@@ -60,6 +60,13 @@ function test_get_pid(tc)
 end
 
 
+function test_is_admin(tc)
+  tc.assumeTrue(ispc() || stdlib.has_java() || stdlib.is_mex_fun("stdlib.is_admin"))
+
+  tc.verifyClass(stdlib.is_admin(), "logical")
+end
+
+
 function test_handle2filename(tc, ph)
 tc.verifyEqual(stdlib.handle2filename(ph{1}), ph{2})
 end

test/TestMex.m

@@ -14,11 +14,6 @@ function test_is_char_device(tc)
 end
 
 
-function test_is_admin(tc)
-tc.verifyClass(stdlib.is_admin(), "logical")
-end
-
-
 function test_remove_file(tc)
 tc.assertTrue(stdlib.is_mex_fun("stdlib.remove"))