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I set my torrc to be the same as in #5610 (moved), restarted my Tor, and it wanted to fetch a microdesc.

Apr 13 18:54:04.000 [info] launch_descriptor_downloads(): Launching 1 request for 1 router, 4 at a time
Apr 13 18:54:04.000 [debug] smartlist_choose_node_by_bandwidth_weights(): Choosing node for rule weight as directory based on weights Wg=0.307700 Wm=1.000000 We=0.000000 Wd=0.128000 with total bw 571593023.800000
Apr 13 18:54:04.000 [debug] directory_initiate_command_rend(): anonymized 0, use_begindir 1.
Apr 13 18:54:04.000 [debug] directory_initiate_command_rend(): Initiating microdescriptor fetch
Apr 13 18:54:04.000 [info] connection_ap_make_link(): Making internal direct tunnel to 188.138.82.143:443 ...
Apr 13 18:54:04.000 [debug] connection_add_impl(): new conn type Socks, socket -1, address (Tor_internal), n_conns 3.
Apr 13 18:54:04.000 [warn] Requested exit point '$2BC7B25AFFACBB861872248D3E19D77EE71CE1CE' is excluded or would refuse request. Closing.
Apr 13 18:54:04.000 [warn] Making tunnel to dirserver failed.

Looks like launch_descriptor_downloads() calls initiate_descriptor_downloads() which calls directory_get_from_dirserver() which calls router_pick_directory_server() which does not exclude exits.

I believe we don't want to exclude exits in this case. Quoting from ChangeLog,

        . "Exit", in the context of ExitNodes and ExcludeExitNodes, means
          a node that delivers user traffic outside the Tor network.

So I think the bug is in connection_ap_can_use_exit(). Probably where it says

  if (routerset_contains_node(options->_ExcludeExitNodesUnion, exit)) {
    /* Not a suitable exit. Refuse it. */
    return 0;
  }

without checking if conn->use_begindir.