mingw: provide details about unsafe directories' ownership

When Git refuses to use an existing repository because it is owned by
someone else than the current user, it can be a bit tricky on Windows to
figure out what is going on.

Let's help with that by providing more detailed information.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

compat/mingw.c

@@ -1,6 +1,7 @@
 #include "../git-compat-util.h"
 #include "win32.h"
 #include <aclapi.h>
+#include <sddl.h>
 #include <conio.h>
 #include <wchar.h>
 #include "../strbuf.h"
@@ -2720,6 +2721,29 @@ int is_path_owned_by_current_sid(const char *path, struct strbuf *report)
 		    IsValidSid(current_user_sid) &&
 		    EqualSid(sid, current_user_sid))
 			result = 1;
+		else if (report) {
+			LPSTR str1, str2, to_free1 = NULL, to_free2 = NULL;
+
+			if (ConvertSidToStringSidA(sid, &str1))
+				to_free1 = str1;
+			else
+				str1 = "(inconvertible)";
+
+			if (!current_user_sid)
+				str2 = "(none)";
+			else if (!IsValidSid(current_user_sid))
+				str2 = "(invalid)";
+			else if (ConvertSidToStringSidA(current_user_sid, &str2))
+				to_free2 = str2;
+			else
+				str2 = "(inconvertible)";
+			strbuf_addf(report,
+				    "'%s' is owned by:\n"
+				    "\t'%s'\nbut the current user is:\n"
+				    "\t'%s'\n", path, str1, str2);
+			LocalFree(to_free1);
+			LocalFree(to_free2);
+		}
 	}
 
 	/*