[FIX] runbot_merge: update squash flag on reopen

While the head gets updated (properly), the squash flag did not which
could lead to odd results. Since a PR can only be reopened if it was
regular-pushed to (not after a force push) there are two scenarios:

* the PR updated to have 0 commits, closed, pushed to with one commit
  then reopened, after reopening the PR would be marked as !squash and
  would ask for a merge method (that's what happened with
  odoo/odoo#51763)
* the PR has a single commit, is closed, pushed to then reopened,
  after reopening the PR would still be marked a squash and potentially
  straight rebased without asking for a merge method

Nothing would break per-se but both scenarios are undesirable.

Close #373

runbot_merge/controllers/__init__.py

@@ -207,6 +207,7 @@ def handle_pr(env, event):
                 'state': 'opened',
                 # updating the head triggers a revalidation
                 'head': pr['head']['sha'],
+                'squash': pr['commits'] == 1,
             })
 
             return 'Reopened {}'.format(pr_obj.id)

runbot_merge/tests/test_basic.py

@@ -935,34 +935,6 @@ def test_ci_failure_after_review(env, repo, users, config):
         (users['user'], "'ci/runbot' failed on this reviewed PR.".format_map(users)),
     ]
 
-def test_reopen_state(env, repo):
-    """ The PR should be validated on opening and reopening in case there's
-    already a CI+ stored (as the CI might never trigger unless explicitly
-    re-requested)
-    """
-    with repo:
-        m = repo.make_commit(None, 'initial', None, tree={'m': 'm'})
-        repo.make_ref('heads/master', m)
-
-        c = repo.make_commit(m, 'fist', None, tree={'m': 'c1'})
-        repo.post_status(c, 'success', 'legal/cla')
-        repo.post_status(c, 'success', 'ci/runbot')
-        prx = repo.make_pr(title='title', body='body', target='master', head=c)
-
-    pr = env['runbot_merge.pull_requests'].search([
-        ('repository.name', '=', repo.name),
-        ('number', '=', prx.number),
-    ])
-    assert pr.state == 'validated', \
-        "if a PR is created on a CI'd commit, it should be validated immediately"
-
-    with repo: prx.close()
-    assert pr.state == 'closed'
-
-    with repo: prx.open()
-    assert pr.state == 'validated', \
-        "if a PR is reopened and had a CI'd head, it should be validated immediately"
-
 def test_reopen_merged_pr(env, repo, config, users):
     """ Reopening a *merged* PR should cause us to immediately close it again,
     and insult whoever did it
@@ -2147,6 +2119,10 @@ class TestPRUpdate(object):
             ('repository.name', '=', repo.name),
             ('number', '=', prx.number)
         ])
+        assert pr.state == 'opened'
+        assert pr.head == c
+        assert pr.squash
+
         with repo:
             prx.close()
 
@@ -2156,11 +2132,41 @@ class TestPRUpdate(object):
 
         assert pr.state == 'closed'
         assert pr.head == c
+        assert pr.squash
 
         with repo:
             prx.open()
         assert pr.state == 'opened'
         assert pr.head == c2
+        assert not pr.squash
+
+    def test_update_closed_revalidate(self, env, repo):
+        """ The PR should be validated on opening and reopening in case there's
+        already a CI+ stored (as the CI might never trigger unless explicitly
+        re-requested)
+        """
+        with repo:
+            m = repo.make_commit(None, 'initial', None, tree={'m': 'm'})
+            repo.make_ref('heads/master', m)
+
+            c = repo.make_commit(m, 'fist', None, tree={'m': 'c1'})
+            repo.post_status(c, 'success', 'legal/cla')
+            repo.post_status(c, 'success', 'ci/runbot')
+            prx = repo.make_pr(title='title', body='body', target='master', head=c)
+
+        pr = env['runbot_merge.pull_requests'].search([
+            ('repository.name', '=', repo.name),
+            ('number', '=', prx.number),
+        ])
+        assert pr.state == 'validated', \
+            "if a PR is created on a CI'd commit, it should be validated immediately"
+
+        with repo: prx.close()
+        assert pr.state == 'closed'
+
+        with repo: prx.open()
+        assert pr.state == 'validated', \
+            "if a PR is reopened and had a CI'd head, it should be validated immediately"
 
     @pytest.mark.xfail(reason="github doesn't allow reopening force-pushed PRs", strict=True)
     def test_force_update_closed(self, env, repo):