[PATCH 2/3] getpwuid(mingw): provide a better default for the user name

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schinde...@gmx.de>

We do have the excellent GetUserInfoEx() function to obtain more
detailed information of the current user (if the user is part of a
Windows domain); Let's use it.

Suggested by Lutz Roeder.

To avoid the cost of loading Secur32.dll (even lazily, loading DLLs
takes a non-neglibile amount of time), we use the established technique
to load DLLs only when, and if, needed.

Signed-off-by: Johannes Schindelin <johannes.schinde...@gmx.de>
---
 compat/mingw.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/compat/mingw.c b/compat/mingw.c
index 597781b370..623ff5daf5 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -5,6 +5,7 @@
 #include "../strbuf.h"
 #include "../run-command.h"
 #include "../cache.h"
+#include "win32/lazyload.h"
 
 #define HCAST(type, handle) ((type)(intptr_t)handle)
 
@@ -1798,6 +1799,33 @@ int mingw_getpagesize(void)
        return si.dwAllocationGranularity;
 }
 
+/* See https://msdn.microsoft.com/en-us/library/windows/desktop/ms724435.aspx 
*/
+enum EXTENDED_NAME_FORMAT {
+       NameDisplay = 3,
+       NameUserPrincipal = 8
+};
+
+static char *get_extended_user_info(enum EXTENDED_NAME_FORMAT type)
+{
+       DECLARE_PROC_ADDR(secur32.dll, BOOL, GetUserNameExW,
+               enum EXTENDED_NAME_FORMAT, LPCWSTR, PULONG);
+       static wchar_t wbuffer[1024];
+       DWORD len;
+
+       if (!INIT_PROC_ADDR(GetUserNameExW))
+               return NULL;
+
+       len = ARRAY_SIZE(wbuffer);
+       if (GetUserNameExW(type, wbuffer, &len)) {
+               char *converted = xmalloc((len *= 3));
+               if (xwcstoutf(converted, wbuffer, len) >= 0)
+                       return converted;
+               free(converted);
+       }
+
+       return NULL;
+}
+
 struct passwd *getpwuid(int uid)
 {
        static unsigned initialized;
@@ -1816,7 +1844,9 @@ struct passwd *getpwuid(int uid)
 
        p = xmalloc(sizeof(*p));
        p->pw_name = user_name;
-       p->pw_gecos = "unknown";
+       p->pw_gecos = get_extended_user_info(NameDisplay);
+       if (!p->pw_gecos)
+               p->pw_gecos = "unknown";
        p->pw_dir = NULL;
 
        initialized = 1;
-- 
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