mingw: use Unicode functions explicitly

Many Win32 API functions actually exist in two variants: one with
the `A` suffix that takes ANSI parameters (`char *` or `const char *`)
and one with the `W` suffix that takes Unicode parameters (`wchar_t *`
or `const wchar_t *`).

The ANSI variant assumes that the strings are encoded according to
whatever is the current locale. This is not what Git wants to use on
Windows: we assume that `char *` variables point to strings encoded in
UTF-8.

There is a pseudo UTF-8 locale on Windows, but it does not work
as one might expect. In addition, if we overrode the user's locale, that
would modify the behavior of programs spawned by Git (such as editors,
difftools, etc), therefore we cannot use that pseudo locale.

Further, it is actually highly encouraged to use the Unicode versions
instead of the ANSI versions, so let's do precisely that.

Note: when calling the Win32 API functions _without_ any suffix, it
depends whether the `UNICODE` constant is defined before the relevant
headers are #include'd. Without that constant, the ANSI variants are
used. Let's be explicit and avoid that ambiguity.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.c

@@ -1407,7 +1407,7 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	do_unset_environment_variables();
 
 	/* Determine whether or not we are associated to a console */
-	cons = CreateFile("CONOUT$", GENERIC_WRITE,
+	cons = CreateFileW(L"CONOUT$", GENERIC_WRITE,
 			FILE_SHARE_WRITE, NULL, OPEN_EXISTING,
 			FILE_ATTRIBUTE_NORMAL, NULL);
 	if (cons == INVALID_HANDLE_VALUE) {

compat/poll/poll.c

@@ -150,7 +150,7 @@ win32_compute_revents (HANDLE h, int *p_sought)
       if (!once_only)
 	{
 	  NtQueryInformationFile = (PNtQueryInformationFile)
-	    GetProcAddress (GetModuleHandle ("ntdll.dll"),
+	    GetProcAddress (GetModuleHandleW (L"ntdll.dll"),
 			    "NtQueryInformationFile");
 	  once_only = TRUE;
 	}

compat/winansi.c

@@ -599,7 +599,7 @@ int winansi_isatty(int fd)
 void winansi_init(void)
 {
 	int con1, con2;
-	char name[32];
+	wchar_t name[32];
 
 	/* check if either stdout or stderr is a console output screen buffer */
 	con1 = is_console(1);
@@ -619,13 +619,15 @@ void winansi_init(void)
 	}
 
 	/* create a named pipe to communicate with the console thread */
-	xsnprintf(name, sizeof(name), "\\\\.\\pipe\\winansi%lu", GetCurrentProcessId());
-	hwrite = CreateNamedPipe(name, PIPE_ACCESS_OUTBOUND,
+	if (swprintf(name, ARRAY_SIZE(name) - 1, L"\\\\.\\pipe\\winansi%lu",
+		     GetCurrentProcessId()) < 0)
+		die("Could not initialize winansi pipe name");
+	hwrite = CreateNamedPipeW(name, PIPE_ACCESS_OUTBOUND,
 		PIPE_TYPE_BYTE | PIPE_WAIT, 1, BUFFER_SIZE, 0, 0, NULL);
 	if (hwrite == INVALID_HANDLE_VALUE)
 		die_lasterr("CreateNamedPipe failed");
 
-	hread = CreateFile(name, GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);
+	hread = CreateFileW(name, GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);
 	if (hread == INVALID_HANDLE_VALUE)
 		die_lasterr("CreateFile for named pipe failed");