[FIX] runbot_merge: ensure all staging branches are built/tested

Before this change, when staging batches only affecting one repo (of n)
the unaffected repositories would get a staging branch exactly matching
the target.

As a result, either runbot_merge or runbot would simply return the
result of an unrelated build, potentially providing incorrect
information and either failing a staging which should have succeeded
(e.g. change in repo A broke B, PR is making a change in repo A which
fixes B, but B's state is reported as the previous broken build) or
succeeding a staging which should have failed (change in repo A breaking
B except a previous build of the exact same B succeeded with a different
A and is returned).

To fix this issue, create a dummy commit at the head of each staging
branch. Because commit dates are included in the hash and have a second
precision it's pretty unlikely that we can get built duplicates, but
just to be completely sure some random bits are added to the commit
message as well.

Various tests fixed to correctly handle the extra dummy commit on
staging branches.

fixes #35

runbot_merge/models/pull_requests.py

@@ -1,7 +1,9 @@
+import base64
 import collections
 import datetime
 import json
 import logging
+import os
 import pprint
 import re
 
@@ -77,9 +79,14 @@ class Project(models.Model):
                     updated = []
                     try:
                         for repo_name, head in staging_heads.items():
+                            if repo_name.endswith('^'):
+                                continue
+
+                            # if the staging has a $repo^ head, merge that,
+                            # otherwise merge the regular (CI'd) head
                             gh[repo_name].fast_forward(
                                 staging.target.name,
-                                head
+                                staging_heads.get(repo_name + '^') or head
                             )
                             updated.append(repo_name)
                     except exceptions.FastForwardError:
@@ -171,18 +178,31 @@ class Project(models.Model):
                     staged |= Batch.stage(meta, batch)
 
                 if staged:
+                    heads = {}
+                    for repo, it in meta.items():
+                        tree = it['gh'].commit(it['head'])['tree']
+                        # ensures staging branches are unique and always
+                        # rebuilt
+                        r = base64.b64encode(os.urandom(12)).decode('ascii')
+                        dummy_head = it['gh']('post', 'git/commits', json={
+                            'message': 'force rebuild\n\nuniquifier: %s' % r,
+                            'tree': tree['sha'],
+                            'parents': [it['head']],
+                        }).json()
+
+                        # $repo is the head to check, $repo^ is the head to merge
+                        heads[repo.name + '^'] = it['head']
+                        heads[repo.name] = dummy_head['sha']
+
                     # create actual staging object
                     st = self.env['runbot_merge.stagings'].create({
                         'target': branch.id,
                         'batch_ids': [(4, batch.id, 0) for batch in staged],
-                        'heads': json.dumps({
-                            repo.name: it['head']
-                            for repo, it in meta.items()
-                        })
+                        'heads': json.dumps(heads)
                     })
                     # create staging branch from tmp
                     for r, it in meta.items():
-                        it['gh'].set_ref('staging.{}'.format(branch.name), it['head'])
+                        it['gh'].set_ref('staging.{}'.format(branch.name), heads[r.name])
 
                     # creating the staging doesn't trigger a write on the prs
                     # and thus the ->staging taggings, so do that by hand
@@ -757,13 +777,13 @@ class Stagings(models.Model):
     def _validate(self):
         Commits = self.env['runbot_merge.commit']
         for s in self:
-            heads = list(json.loads(s.heads).values())
+            heads = [
+                head for repo, head in json.loads(s.heads).items()
+                if not repo.endswith('^')
+            ]
             commits = Commits.search([
                 ('sha', 'in', heads)
             ])
-            if len(commits) < len(heads):
-                s.state = 'pending'
-                continue
 
             reqs = [r.strip() for r in s.target.project_id.required_statuses.split(',')]
             st = 'success'
@@ -776,6 +796,13 @@ class Stagings(models.Model):
                         st = 'pending'
                     else:
                         assert v == 'success'
+
+            # mark failure as soon as we find a failed status, but wait until
+            # all commits are known & not pending to mark a success
+            if st == 'success' and len(commits) < len(heads):
+                s.state = 'pending'
+                continue
+
             s.state = st
 
     def cancel(self, reason, *args):
@@ -825,6 +852,9 @@ class Stagings(models.Model):
 
         # try inferring which PR failed and only mark that one
         for repo, head in json.loads(self.heads).items():
+            if repo.endswith('^'):
+                continue
+
             commit = self.env['runbot_merge.commit'].search([
                 ('sha', '=', head)
             ])
@@ -959,8 +989,6 @@ class Batch(models.Model):
         # update meta to new heads
         for pr, head in new_heads.items():
             meta[pr.repository]['head'] = head
-            if not self.env['runbot_merge.commit'].search([('sha', '=', head)]):
-                self.env['runbot_merge.commit'].create({'sha': head})
         return self.create({
             'target': prs[0].target.id,
             'prs': [(4, pr.id, 0) for pr in prs],

runbot_merge/tests/test_basic.py

@@ -1,9 +1,12 @@
 import datetime
+import re
 
 import pytest
 
 import odoo
 
+from test_utils import re_matches
+
 @pytest.fixture
 def repo(make_repo):
     return make_repo('repo')
@@ -46,6 +49,7 @@ def test_trivial_flow(env, repo):
     staging_head = repo.commit('heads/staging.master')
     repo.post_status(staging_head.id, 'success', 'ci/runbot')
     repo.post_status(staging_head.id, 'success', 'legal/cla')
+    assert re.match('^force rebuild', staging_head.message)
 
     env['runbot_merge.project']._check_progress()
     assert pr.state == 'merged'
@@ -539,11 +543,14 @@ class TestMergeMethod:
         staging = repo.commit('heads/staging.master')
         assert not repo.is_ancestor(prx.head, of=staging.id),\
             "the pr head should not be an ancestor of the staging branch in a squash merge"
-        assert staging.parents == [m2],\
-            "the previous master's tip should be the sole parent of the staging commit"
+        assert re.match('^force rebuild', staging.message)
         assert repo.read_tree(staging) == {
             'm': b'c1', 'm2': b'm2',
         }, "the tree should still be correctly merged"
+        [actual_sha] = staging.parents
+        actual = repo.commit(actual_sha)
+        assert actual.parents == [m2],\
+            "dummy commit aside, the previous master's tip should be the sole parent of the staging commit"
 
         repo.post_status(staging.id, 'success', 'legal/cla')
         repo.post_status(staging.id, 'success', 'ci/runbot')
@@ -641,13 +648,26 @@ class TestMergeMethod:
         # then compare to the dag version of the right graph
         nm2 = node('M2', node('M1', node('M0')))
         nb1 = node('B1', node('B0', nm2))
-        expected = (
+        merge_head = (
             'title\n\nbody\n\ncloses {}#{}'.format(repo.name, prx.number),
             frozenset([nm2, nb1])
         )
+        expected = (re_matches('^force rebuild'), frozenset([merge_head]))
         assert staging == expected
 
-        final_tree = repo.read_tree(repo.commit('heads/staging.master'))
+        repo.post_status('heads/staging.master', 'success', 'legal/cla')
+        repo.post_status('heads/staging.master', 'success', 'ci/runbot')
+        env['runbot_merge.project']._check_progress()
+
+        assert env['runbot_merge.pull_requests'].search([
+            ('repository.name', '=', repo.name),
+            ('number', '=', prx.number),
+        ]).state == 'merged'
+
+        # check that the dummy commit is not in the final master
+        master = log_to_node(repo.log('heads/master'))
+        assert master == merge_head
+        final_tree = repo.read_tree(repo.commit('heads/master'))
         assert final_tree == {'m': b'2', 'b': b'1'}, "sanity check of final tree"
 
     @pytest.mark.skip(reason="what do if the PR contains merge commits???")

runbot_merge/tests/test_multirepo.py

@@ -9,6 +9,8 @@ import json
 
 import pytest
 
+from test_utils import re_matches
+
 @pytest.fixture
 def repo_a(make_repo):
     return make_repo('a')
@@ -138,11 +140,17 @@ def test_sub_match(env, project, repo_a, repo_b, repo_c):
     # should be part of the same staging
     assert pr_c.staging_id == pr_b.staging_id, \
         "branch-matched PRs should be part of the same staging"
+
     st = pr_b.staging_id
+    b_staging = repo_b.commit('heads/staging.master')
+    c_staging = repo_c.commit('heads/staging.master')
     assert json.loads(st.heads) == {
-        repo_a.name: repo_a.commit('heads/master').id,
-        repo_b.name: repo_b.commit('heads/staging.master').id,
-        repo_c.name: repo_c.commit('heads/staging.master').id,
+        repo_a.name: repo_a.commit('heads/staging.master').id,
+        repo_a.name + '^': repo_a.commit('heads/master').id,
+        repo_b.name: b_staging.id,
+        repo_b.name + '^': b_staging.parents[0],
+        repo_c.name: c_staging.id,
+        repo_c.name + '^': c_staging.parents[0],
     }
 
 def test_merge_fail(env, project, repo_a, repo_b, users):
@@ -182,8 +190,14 @@ def test_merge_fail(env, project, repo_a, repo_b, users):
     ]
     other = to_pr(env, pr1a)
     assert not other.staging_id
-    assert len(list(repo_a.log('heads/staging.master'))) == 2,\
-        "root commit + squash-merged PR commit"
+    assert [
+        c['commit']['message']
+        for c in repo_a.log('heads/staging.master')
+    ] == [
+        re_matches('^force rebuild'),
+        'commit_A2_00\n\ncloses %s#2' % repo_a.name,
+        'initial'
+    ], "dummy commit + squash-merged PR commit + root commit"
 
 def test_ff_fail(env, project, repo_a, repo_b):
     """ In a matched-branch scenario, fast-forwarding one of the repos fails

runbot_merge/tests/test_utils.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+import re
+
+
+class re_matches:
+    def __init__(self, pattern, flags=0):
+        self._r = re.compile(pattern, flags)
+
+    def __eq__(self, text):
+        return self._r.match(text)
+
+    def __repr__(self):
+        return '~' + self._r.pattern + '~'