mingw_rmdir: set errno=ENOTEMPTY when appropriate

On Windows, EACCES overrules ENOTEMPTY when calling rmdir(). But if the
directory is busy, we only want to retry deleting the directory if it
is empty, so test specifically for that case and set ENOTEMPTY rather
than EACCES.

Noticed by Greg Hazel.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -225,6 +225,30 @@ int mingw_unlink(const char *pathname)
 	return ret;
 }
 
+static int is_dir_empty(const char *path)
+{
+	struct strbuf buf = STRBUF_INIT;
+	WIN32_FIND_DATAA findbuf;
+	HANDLE handle;
+
+	strbuf_addf(&buf, "%s\\*", path);
+	handle = FindFirstFileA(buf.buf, &findbuf);
+	if (handle == INVALID_HANDLE_VALUE) {
+		strbuf_release(&buf);
+		return GetLastError() == ERROR_NO_MORE_FILES;
+	}
+
+	while (!strcmp(findbuf.cFileName, ".") ||
+			!strcmp(findbuf.cFileName, ".."))
+		if (!FindNextFile(handle, &findbuf)) {
+			strbuf_release(&buf);
+			return GetLastError() == ERROR_NO_MORE_FILES;
+		}
+	FindClose(handle);
+	strbuf_release(&buf);
+	return 0;
+}
+
 #undef rmdir
 int mingw_rmdir(const char *pathname)
 {
@@ -233,6 +257,10 @@ int mingw_rmdir(const char *pathname)
 	while ((ret = rmdir(pathname)) == -1 && tries < ARRAY_SIZE(delay)) {
 		if (!is_file_in_use_error(GetLastError()))
 			break;
+		if (!is_dir_empty(pathname)) {
+			errno = ENOTEMPTY;
+			break;
+		}
 		/*
 		 * We assume that some other process had the source or
 		 * destination file open at the wrong moment and retry.