"fly execute --exclude-ignored" broken for mercurial resource #1244

[chendrix]

cc @marco-m Moved from concourse/concourse#1244

---

With a pipeline using the mercurial resource

resources:
- name: concourse-native
  type: hg
  source:
    uri: https://bitbucket.com/me/myrepo
    branch: default

The checked out repo will have a directory named .hg (the equivalent of .git).

When doing a one-off build with fly execute, it will upload the whole repo history, inside the .hg directory.

If I try to avoid uploading the .hg directory with --exclude-ignored, fly prints an error message and stays stuck uploading (have to hit Ctrl-C):

 concourse-native> fly -t tutorial execute --exclude-ignored --config ci/build-task.yml
 executing build 34
 could not determine ignored files: exit status 128
   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                  Dload  Upload   Total   Spent    Left  Speed
   0     0    0     0    0     0      0      0 --:--:--  0:00:24 --:--:--     0^C

I just double-tested the exact setup but with a git repository and the .git directory is not uploaded and the upload succeeds.

• Concourse version: 3.1.1
• Infrastructure/IaaS: Vagrant
• Did this used to work? First time I tried