[FIX] forwardport: ask github what the PR's commits are

Attempts to use rev-list seem to work locally but they fail *a lot*
when live. The previous attempt to fix it in
0f4c22490c made things worse rather than
better once deployed.

Give up on that (at least for now?), and just ask github what the PR's
commits are then cherrypick exactly that.

forwardport/models/project.py

@@ -18,16 +18,16 @@ import json
 import logging
 import os
 import pathlib
+import re
 import subprocess
 import tempfile
 
-import re
 import requests
 
-from odoo.exceptions import UserError
-from odoo.tools.appdirs import user_cache_dir
-
 from odoo import _, models, fields, api
+from odoo.exceptions import UserError
+from odoo.tools import topological_sort
+from odoo.tools.appdirs import user_cache_dir
 from odoo.addons.runbot_merge import utils
 from odoo.addons.runbot_merge.models.pull_requests import RPLUS
 
@@ -302,6 +302,32 @@ class PullRequests(models.Model):
             if branch.fp_enabled
         ), None)
 
+    def _commits_lazy(self):
+        for page in itertools.count(1):
+            r = requests.get('https://api.github.com/repos/{}/pulls/{}/commits'.format(
+                self.repository.name,
+                self.number
+            ), params={'page': page})
+            r.raise_for_status()
+            yield from r.json()
+            if not r.links.get('next'):
+                return
+
+    def commits(self):
+        """ Returns a PR's commits oldest first (that's what GH does &
+        is what we want)
+        """
+        commits = list(self._commits_lazy())
+        # map shas to the position the commit *should* have
+        idx =  {
+            c: i
+            for i, c in enumerate(topological_sort({
+                c['sha']: [p['sha'] for p in c['parents']]
+                for c in commits
+            }))
+        }
+        return sorted(commits, key=lambda c: idx[c['sha']])
+
     def _iter_descendants(self):
         pr = self
         while True:
@@ -513,7 +539,6 @@ More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port
         working_copy.checkout(b=fp_branch_name)
 
         root = self._get_root()
-        working_copy.branch(root.target.name, 'origin/' + root.target.name)
         try:
             root._cherry_pick(working_copy)
         except CherrypickError as e:
@@ -523,22 +548,20 @@ More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port
             # when forward-porting) it'll just do nothing to the working copy
             # so the "conflict commit" will be empty
             # switch to a squashed-pr branch
-            root_base, root_branch = root._reference_branches()
+            root_branch = 'origin/pull/%d' % root.number
             working_copy.checkout('-bsquashed', root_branch)
-            root_commits = list(
+            root_commits = root.commits()
-                working_copy.lazy().stdout()
+
-                    .rev_list('--reverse', '%s..%s' % (root_base, root_branch))
+            # squash to a single commit: reset to the first parent of the pr's
-                    .stdout
+            # first commit
-            )
+            working_copy.reset('--soft', root_commits[0]['parents'][0]['sha'])
-            # squash the PR to a single commit
-            working_copy.reset('--soft', 'HEAD~%d' % len(root_commits))
             working_copy.commit(a=True, message="temp")
             squashed = working_copy.stdout().rev_parse('HEAD').stdout.strip().decode()
 
             # switch back to the PR branch
             working_copy.checkout(fp_branch_name)
             # cherry-pick the squashed commit
-            working_copy.with_config(check=False).cherry_pick(squashed)
+            working_copy.with_params('merge.renamelimit=0').with_config(check=False).cherry_pick(squashed)
 
             working_copy.commit(
                 a=True, allow_empty=True,
@@ -565,31 +588,25 @@ stderr:
         # original head so we can reset
         h = working_copy.stdout().rev_parse('HEAD').stdout
 
-        commits_range = self._reference_branches()
+        commits = self.commits()
-        # need to cherry-pick commit by commit because `-n` doesn't yield
+        logger.info("%s: %s commits in %s", self, len(commits), h.decode())
-        # back control on each op. `-e` with VISUAL=false kinda works but
+        for c in commits:
-        # doesn't seem to provide a good way to know when we're done
+            logger.debug('- %s (%s)', c['sha'], c['commit']['message'])
-        # cherrypicking
+
-        rev_list = working_copy.lazy().stdout()\
-            .rev_list('--reverse', '%s..%s' % commits_range)
-        commits = list(rev_list.stdout)
-        logger.info("%s: %d commits in %s..%s on %s", self, len(commits), commits_range[0], commits_range[1], h.decode())
         for commit in commits:
-            commit = commit.decode().strip()
+            commit_sha = commit['sha']
             r = working_copy.with_params('merge.renamelimit=0').with_config(
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
                 check=False,
-            ).cherry_pick(commit)
+            ).cherry_pick(commit_sha)
 
             if r.returncode: # pick failed, reset and bail
-                logger.info("%s: failed", commit)
+                logger.info("%s: failed", commit_sha)
                 working_copy.reset('--hard', h.decode().strip())
-                raise CherrypickError(commit, r.stdout.decode(), r.stderr.decode())
+                raise CherrypickError(commit_sha, r.stdout.decode(), r.stderr.decode())
 
-            original_msg = working_copy.stdout().show('-s', '--format=%B', commit).stdout.decode()
+            msg = self._parse_commit_message(commit['commit']['message'])
-
-            msg = self._parse_commit_message(original_msg)
 
             # original signed-off-er should be retained but didn't necessarily
             # sign off here, so convert signed-off-by to something else
@@ -601,22 +618,14 @@ stderr:
                     for v in sob
                 )
             # write the *merged* commit as "original", not the PR's
-            msg.headers['x-original-commit'] = cmap.get(commit, commit)
+            msg.headers['x-original-commit'] = cmap.get(commit_sha, commit_sha)
 
             # replace existing commit message with massaged one
             working_copy\
                 .with_config(input=str(msg).encode())\
                 .commit(amend=True, file='-')
             new = working_copy.stdout().rev_parse('HEAD').stdout.decode()
-            logger.info('%s: success -> %s', commit, new)
+            logger.info('%s: success -> %s', commit_sha, new)
-
-    def _reference_branches(self):
-        """
-        :returns: (PR target, PR branch)
-        """
-        ancestor_branch = 'origin/pull/%d' % self.number
-        source_target = self.target.name
-        return source_target, ancestor_branch
 
     def _get_local_directory(self):
         repos_dir = pathlib.Path(user_cache_dir('forwardport'))