[ADD] forwardport: test on resuming fw by hand

Hit issues where this didn't seem to work after deactivating 17.2 and
trying to recover from the autoport being broken (see previous
commits), but apparently this says everything works just fine so
╮(￣▽￣"")╭

Fixes #1052

forwardport/tests/test_weird.py

@@ -1284,3 +1284,77 @@ def test_duplicate_manual_port(env, config, make_repo, users):
         'source': 'fp',
     })
     env.run_crons()
+
+@pytest.mark.parametrize('triggered', range(4))
+@pytest.mark.parametrize('kind', ['merge', 'fp'])
+def test_resume_manual_detached(env, config, make_repo, users, triggered, kind):
+    """In case of detached interrupted forward ports, check where and how they
+    can be manually resumed from.
+
+    Turns out it always works, not sure why on the mergebot there seemingly
+    have been cases where creating a batch from the source batch with source=fp
+    sometimes didn't work...
+    """
+    # region setup
+    prod, _ = make_basic(env, config, make_repo, statuses='default')
+    with prod:
+        prod.make_commits('a', Commit('c', tree={'x': '0'}), ref="heads/abranch")
+        pr1 = prod.make_pr(target='a', head='abranch')
+        prod.post_status('abranch', 'success')
+        pr1.post_comment('hansen r+', config['role_reviewer']['token'])
+
+        prod.make_commits('a', Commit('cc', tree={'y': '0'}), ref="heads/bbranch")
+        pr2 = prod.make_pr(target='a', head='bbranch')
+        prod.post_status('bbranch', 'success')
+        pr2.post_comment('hansen r+', config['role_reviewer']['token'])
+    env.run_crons()
+
+    with prod:
+        prod.post_status('staging.a', 'success')
+    env.run_crons()
+
+    pr1_a_id, pr2_a_id, pr1_b_id, pr2_b_id = prs = env['runbot_merge.pull_requests'].search([], order='number')
+    assert pr1_b_id.source_id == pr1_a_id
+    assert pr2_b_id.source_id == pr2_a_id
+    pr1_b_id.write({
+        'parent_id': False,
+        'detach_reason': 'whatever',
+    })
+
+    proj = env['runbot_merge.project'].search([])
+    proj.write({
+        'branch_ids': [
+            (1, pr1_b_id.target.id, {'active': False}),
+        ]
+    })
+    fw_batches = env['forwardport.batches'].search([])
+    assert len(fw_batches) == 2
+    fw_batches.unlink()
+
+    env.run_crons()
+    assert env['runbot_merge.pull_requests'].search_count([]) == 4
+    # endregion
+
+    # At this point we have two merged source PRs to A and two forward ports
+    # to the now disabled B, one detached and the other not.
+    #
+    # The port was interrupted because reasons even though the branch being
+    # disabled should have forced ports to C (it's happened live for a few
+    # reasons we have added guards for, still we want to handle recovery if a
+    # new issue sneaks in).
+    #
+    # We want to see if creating fw batches by hand puts us back into gear.
+    pr = prs[triggered]
+    env['forwardport.batches'].create({'source': kind, 'batch_id': pr.id})
+    env.run_crons()
+
+    new_prs = env['runbot_merge.pull_requests'].search([], order='number')[len(prs):]
+    assert len(new_prs) == 1, f"{pr.display_name} ({kind}) => no port (expected one)"
+    assert new_prs.source_id == (pr.source_id or pr)
+
+    env['forwardport.batches'].create([
+        {'source': 'merge', 'batch_id': pr.id},
+        {'source': 'fp', 'batch_id': pr.id},
+    ])
+    env.run_crons()
+    assert not env['runbot_merge.pull_requests'].search([], order='number')[len(prs)+1:]