4 files changed, 788 insertions, 0 deletions
diff --git a/tools/github-sync/converter.py b/tools/github-sync/converter.py
new file mode 100755
index 0000000000..57db9286c1
--- /dev/null
+++ b/tools/github-sync/converter.py
@@ -0,0 +1,481 @@
+#!/usr/bin/env python3
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import os
+import re
+import subprocess
+import sys
+
+import hglib
+import pygit2
+
+DEBUG = False
+
+
+def eprint(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
+def debugprint(*args, **kwargs):
+    if DEBUG:
+        eprint(*args, **kwargs)
+
+
+class HgCommit:
+    def __init__(self, parent1, parent2):
+        self.parents = []
+        if parent1 == NULL_PARENT_REV:
+            raise Exception(
+                "Encountered a hg changeset with no parents! We don't handle this...."
+            )
+        self.parents.append(parent1)
+        if parent2 != NULL_PARENT_REV:
+            self.parents.append(parent2)
+        self.touches_sync_code = False
+        self.children = []
+
+    def add_child(self, rev):
+        self.children.append(rev)
+
+
+class GitCommit:
+    def __init__(self, hg_rev, commit_obj):
+        self.hg_rev = hg_rev
+        self.commit_obj = commit_obj
+
+
+def load_git_repository():
+    commit_map = dict()
+    # First, scan the tags for "mozilla-xxx" that keep track of manually synchronized changes
+    sync_tags = filter(
+        lambda ref: ref.startswith("refs/tags/mozilla-"),
+        list(downstream_git_repo.references),
+    )
+    for desc in sync_tags:
+        commit = downstream_git_repo.lookup_reference(desc).peel()
+        # cut out the revision hash from the output
+        hg_rev = desc[18:]
+        commit_map[hg_rev] = GitCommit(hg_rev, commit)
+        debugprint("Loaded pre-existing tag hg %s -> git %s" % (hg_rev, commit.oid))
+
+    # Next, scan the commits for a specific message format
+    re_commitmsg = re.compile(
+        r"^\[(ghsync|wrupdater)\] From https://hg.mozilla.org/mozilla-central/rev/([0-9a-fA-F]+)$",
+        re.MULTILINE,
+    )
+    for commit in downstream_git_repo.walk(downstream_git_repo.head.target):
+        m = re_commitmsg.search(commit.message)
+        if not m:
+            continue
+        hg_rev = m.group(2)
+        commit_map[hg_rev] = GitCommit(hg_rev, commit)
+        debugprint("Loaded pre-existing commit hg %s -> git %s" % (hg_rev, commit.oid))
+    return commit_map
+
+
+def timeof(git_commit):
+    return git_commit.commit_obj.commit_time + git_commit.commit_obj.commit_time_offset
+
+
+def find_newest_commit(commit_map):
+    newest_hg_rev = None
+    newest_commit_time = None
+
+    for hg_rev, git_commit in commit_map.items():
+        if newest_hg_rev is None or timeof(git_commit) > newest_commit_time:
+            newest_hg_rev = hg_rev
+            newest_commit_time = timeof(git_commit)
+
+    return newest_hg_rev
+
+
+def get_single_rev(revset):
+    output = subprocess.check_output(
+        ["hg", "log", "-r", revset, "--template", "{node}"]
+    )
+    output = str(output, "ascii")
+    return output
+
+
+def get_multiple_revs(revset, template):
+    output = subprocess.check_output(
+        ["hg", "log", "-r", revset, "--template", template + "\\n"]
+    )
+    for line in output.splitlines():
+        yield str(line, "ascii")
+
+
+def get_base_hg_rev(commit_map):
+    base_hg_rev = find_newest_commit(commit_map)
+    eprint("Using %s as base hg revision" % base_hg_rev)
+    return base_hg_rev
+
+
+def load_hg_commits(commits, query):
+    for cset in get_multiple_revs(query, "{node} {p1node} {p2node}"):
+        tokens = cset.split()
+        commits[tokens[0]] = HgCommit(tokens[1], tokens[2])
+    return commits
+
+
+def get_real_base_hg_rev(hg_data, commit_map):
+    # Some of the HG commits we want to port to github may have landed on codelines
+    # that branched off central prior to base_hg_rev. So when we create the git
+    # equivalents, they will have parents that are not the HEAD of the git repo,
+    # but instead will be descendants of older commits in the git repo. In order
+    # to do this correctly, we need to find the hg-equivalents of all of those
+    # possible git parents. So first we identify all the "tail" hg revisions in
+    # our hg_data set (think "tail" as in opposite of "head" which is the tipmost
+    # commit). The "tail" hg revisions are the ones for which we don't have their
+    # ancestors in hg_data.
+    tails = []
+    for (rev, cset) in hg_data.items():
+        for parent in cset.parents:
+            if parent not in hg_data:
+                tails.append(rev)
+    eprint("Found hg tail revisions %s" % tails)
+    # Then we find their common ancestor, which will be some ancestor of base_hg_rev
+    # from which those codelines.
+    if len(tails) == 0:
+        common_ancestor = get_single_rev(".")
+    else:
+        common_ancestor = get_single_rev("ancestor(" + ",".join(tails) + ")")
+    eprint("Found common ancestor of tail revisions: %s" % common_ancestor)
+
+    # And then we find the newest git commit whose hg-equivalent is an ancestor of
+    # that common ancestor, to make sure we are starting from a known hg/git
+    # commit pair.
+    for git_commit in sorted(commit_map.values(), key=timeof, reverse=True):
+        new_base = get_single_rev(
+            "ancestor(" + common_ancestor + "," + git_commit.hg_rev + ")"
+        )
+        if new_base == common_ancestor:
+            eprint(
+                "Pre-existing git commit %s from hg rev %s is descendant of common ancestor; %s"
+                % (
+                    git_commit.commit_obj.id,
+                    git_commit.hg_rev,
+                    "walking back further...",
+                )
+            )
+            continue
+        if new_base != git_commit.hg_rev:
+            eprint(
+                "Pre-existing git commit %s from hg rev %s is on sibling branch"
+                " of common ancestor; %s"
+                % (
+                    git_commit.commit_obj.id,
+                    git_commit.hg_rev,
+                    "walking back further...",
+                )
+            )
+            continue
+        eprint(
+            "Pre-existing git commit %s from hg rev %s is sufficiently old; stopping walk"
+            % (git_commit.commit_obj.id, git_commit.hg_rev)
+        )
+        common_ancestor = new_base
+        break
+
+    return common_ancestor
+
+
+# Now we prune out all the uninteresting changesets from hg_commits. The
+# uninteresting ones are ones that don't touch the target code, are not merges,
+# and are not referenced by mozilla tags in the git repo.
+# We do this by rewriting the parents to the "interesting" ancestor.
+def prune_boring(rev):
+    while rev in hg_commits:
+        parent_pruned = False
+        for i in range(len(hg_commits[rev].parents)):
+            parent_rev = hg_commits[rev].parents[i]
+            if parent_rev not in hg_commits:
+                continue
+            if hg_commits[parent_rev].touches_sync_code:
+                continue
+            if len(hg_commits[parent_rev].parents) > 1:
+                continue
+            if parent_rev in hg_to_git_commit_map:
+                continue
+
+            # If we get here, then `parent_rev` is a boring revision and we can
+            # prune it. Connect `rev` to its grandparent, and prune the parent
+            grandparent_rev = hg_commits[parent_rev].parents[0]
+            hg_commits[rev].parents[i] = grandparent_rev
+            # eprint("Pruned %s as boring parent of %s, using %s now" %
+            #    (parent_rev, rev, grandparent_rev))
+            parent_pruned = True
+
+        if parent_pruned:
+            # If we pruned a parent, process `rev` again as we might want to
+            # prune more parents
+            continue
+
+        # Collapse identical parents, because if the parents are identical
+        # we don't need to keep multiple copies of them.
+        hg_commits[rev].parents = list(dict.fromkeys(hg_commits[rev].parents))
+
+        # If we get here, all of `rev`s parents are interesting, so we can't
+        # prune them. Move up to the parent rev and start processing that, or
+        # if we have multiple parents then recurse on those nodes.
+        if len(hg_commits[rev].parents) == 1:
+            rev = hg_commits[rev].parents[0]
+            continue
+
+        for parent_rev in hg_commits[rev].parents:
+            prune_boring(parent_rev)
+        return
+
+
+class FakeCommit:
+    def __init__(self, oid):
+        self.oid = oid
+
+
+def fake_commit(hg_rev, parent1, parent2):
+    if parent1 is None:
+        eprint("ERROR: Trying to build on None")
+        exit(1)
+    oid = "githash_%s" % hash(parent1)
+    eprint("Fake-built %s" % oid)
+    return FakeCommit(oid)
+
+
+def build_tree(builder, treedata):
+    for (name, value) in treedata.items():
+        if isinstance(value, dict):
+            subbuilder = downstream_git_repo.TreeBuilder()
+            build_tree(subbuilder, value)
+            builder.insert(name, subbuilder.write(), pygit2.GIT_FILEMODE_TREE)
+        else:
+            (filemode, contents) = value
+            blob_oid = downstream_git_repo.create_blob(contents)
+            builder.insert(name, blob_oid, filemode)
+
+
+def author_to_signature(author):
+    pieces = author.strip().split("<")
+    if len(pieces) != 2 or pieces[1][-1] != ">":
+        # We could probably handle this better
+        return pygit2.Signature(author, "")
+    name = pieces[0].strip()
+    email = pieces[1][:-1].strip()
+    return pygit2.Signature(name, email)
+
+
+def real_commit(hg_rev, parent1, parent2):
+    filetree = dict()
+    manifest = mozilla_hg_repo.manifest(rev=hg_rev)
+    for (nodeid, permission, executable, symlink, filename) in manifest:
+        if not filename.startswith(relative_path.encode("utf-8")):
+            continue
+        if symlink:
+            filemode = pygit2.GIT_FILEMODE_LINK
+        elif executable:
+            filemode = pygit2.GIT_FILEMODE_BLOB_EXECUTABLE
+        else:
+            filemode = pygit2.GIT_FILEMODE_BLOB
+        filecontent = mozilla_hg_repo.cat([filename], rev=hg_rev)
+        subtree = filetree
+        for component in filename.split(b"/")[2:-1]:
+            subtree = subtree.setdefault(component.decode("latin-1"), dict())
+        filename = filename.split(b"/")[-1]
+        subtree[filename.decode("latin-1")] = (filemode, filecontent)
+
+    builder = downstream_git_repo.TreeBuilder()
+    build_tree(builder, filetree)
+    tree_oid = builder.write()
+
+    parent1_obj = downstream_git_repo.get(parent1)
+    if parent1_obj.tree_id == tree_oid:
+        eprint("Early-exit; tree matched that of parent git commit %s" % parent1)
+        return parent1_obj
+
+    if parent2 is not None:
+        parent2_obj = downstream_git_repo.get(parent2)
+        if parent2_obj.tree_id == tree_oid:
+            eprint("Early-exit; tree matched that of parent git commit %s" % parent2)
+            return parent2_obj
+
+    hg_rev_obj = mozilla_hg_repo.log(revrange=hg_rev, limit=1)[0]
+    commit_author = hg_rev_obj[4].decode("latin-1")
+    commit_message = hg_rev_obj[5].decode("latin-1")
+    commit_message += (
+        "\n\n[ghsync] From https://hg.mozilla.org/mozilla-central/rev/%s" % hg_rev
+        + "\n"
+    )
+
+    parents = [parent1]
+    if parent2 is not None:
+        parents.append(parent2)
+    commit_oid = downstream_git_repo.create_commit(
+        None,
+        author_to_signature(commit_author),
+        author_to_signature(commit_author),
+        commit_message,
+        tree_oid,
+        parents,
+    )
+    eprint("Built git commit %s" % commit_oid)
+    return downstream_git_repo.get(commit_oid)
+
+
+def try_commit(hg_rev, parent1, parent2=None):
+    if False:
+        return fake_commit(hg_rev, parent1, parent2)
+    else:
+        return real_commit(hg_rev, parent1, parent2)
+
+
+def build_git_commits(rev):
+    debugprint("build_git_commit(%s)..." % rev)
+    if rev in hg_to_git_commit_map:
+        debugprint("  maps to %s" % hg_to_git_commit_map[rev].commit_obj.oid)
+        return hg_to_git_commit_map[rev].commit_obj.oid
+
+    if rev not in hg_commits:
+        debugprint("  not in hg_commits")
+        return None
+
+    if len(hg_commits[rev].parents) == 1:
+        git_parent = build_git_commits(hg_commits[rev].parents[0])
+        if not hg_commits[rev].touches_sync_code:
+            eprint(
+                "WARNING: Found rev %s that is non-merge and not related to the target"
+                % rev
+            )
+            return git_parent
+        eprint("Building git equivalent for %s on top of %s" % (rev, git_parent))
+        commit_obj = try_commit(rev, git_parent)
+        hg_to_git_commit_map[rev] = GitCommit(rev, commit_obj)
+        debugprint("  built %s as %s" % (rev, commit_obj.oid))
+        return commit_obj.oid
+
+    git_parent_1 = build_git_commits(hg_commits[rev].parents[0])
+    git_parent_2 = build_git_commits(hg_commits[rev].parents[1])
+    if git_parent_1 is None or git_parent_2 is None or git_parent_1 == git_parent_2:
+        git_parent = git_parent_1 if git_parent_2 is None else git_parent_2
+        if not hg_commits[rev].touches_sync_code:
+            debugprint(
+                "  %s is merge with no parents or doesn't touch WR, returning %s"
+                % (rev, git_parent)
+            )
+            return git_parent
+
+        eprint(
+            "WARNING: Found merge rev %s whose parents have identical target code"
+            ", but modifies the target" % rev
+        )
+        eprint("Building git equivalent for %s on top of %s" % (rev, git_parent))
+        commit_obj = try_commit(rev, git_parent)
+        hg_to_git_commit_map[rev] = GitCommit(rev, commit_obj)
+        debugprint("  built %s as %s" % (rev, commit_obj.oid))
+        return commit_obj.oid
+
+    # An actual merge
+    eprint(
+        "Building git equivalent for %s on top of %s, %s"
+        % (rev, git_parent_1, git_parent_2)
+    )
+    commit_obj = try_commit(rev, git_parent_1, git_parent_2)
+    hg_to_git_commit_map[rev] = GitCommit(rev, commit_obj)
+    debugprint("  built %s as %s" % (rev, commit_obj.oid))
+    return commit_obj.oid
+
+
+def pretty_print(rev, cset):
+    desc = "  %s" % rev
+    desc += " parents: %s" % cset.parents
+    if rev in hg_to_git_commit_map:
+        desc += " git: %s" % hg_to_git_commit_map[rev].commit_obj.oid
+    if rev == hg_tip:
+        desc += " (tip)"
+    return desc
+
+
+if len(sys.argv) < 3:
+    eprint("Usage: %s <local-checkout-path> <repo-relative-path>" % sys.argv[0])
+    eprint("Current dir must be the mozilla hg repo")
+    exit(1)
+
+local_checkout_path = sys.argv[1]
+relative_path = sys.argv[2]
+mozilla_hg_path = os.getcwd()
+NULL_PARENT_REV = "0000000000000000000000000000000000000000"
+
+downstream_git_repo = pygit2.Repository(pygit2.discover_repository(local_checkout_path))
+mozilla_hg_repo = hglib.open(mozilla_hg_path)
+hg_to_git_commit_map = load_git_repository()
+base_hg_rev = get_base_hg_rev(hg_to_git_commit_map)
+if base_hg_rev is None:
+    eprint("Found no sync commits or 'mozilla-xxx' tags")
+    exit(1)
+
+hg_commits = load_hg_commits(dict(), "only(.," + base_hg_rev + ")")
+eprint("Initial set has %s changesets" % len(hg_commits))
+base_hg_rev = get_real_base_hg_rev(hg_commits, hg_to_git_commit_map)
+eprint("Using hg rev %s as common ancestor of all interesting changesets" % base_hg_rev)
+
+# Refresh hg_commits with our wider dataset
+hg_tip = get_single_rev(".")
+wider_range = "%s::%s" % (base_hg_rev, hg_tip)
+hg_commits = load_hg_commits(hg_commits, wider_range)
+eprint("Updated set has %s changesets" % len(hg_commits))
+
+if DEBUG:
+    eprint("Graph of descendants of %s" % base_hg_rev)
+    output = subprocess.check_output(
+        [
+            "hg",
+            "log",
+            "--graph",
+            "-r",
+            "descendants(" + base_hg_rev + ")",
+            "--template",
+            "{node} {desc|firstline}\\n",
+        ]
+    )
+    for line in output.splitlines():
+        eprint(line.decode("utf-8", "ignore"))
+
+# Also flag any changes that touch the project
+query = "(" + wider_range + ') & file("glob:' + relative_path + '/**")'
+for cset in get_multiple_revs(query, "{node}"):
+    debugprint("Changeset %s modifies %s" % (cset, relative_path))
+    hg_commits[cset].touches_sync_code = True
+eprint(
+    "Identified %s changesets that touch the target code"
+    % sum([1 if v.touches_sync_code else 0 for (k, v) in hg_commits.items()])
+)
+
+prune_boring(hg_tip)
+
+# hg_tip itself might be boring
+if not hg_commits[hg_tip].touches_sync_code and len(hg_commits[hg_tip].parents) == 1:
+    new_tip = hg_commits[hg_tip].parents[0]
+    eprint("Pruned tip %s as boring, using %s now" % (hg_tip, new_tip))
+    hg_tip = new_tip
+
+eprint("--- Interesting changesets ---")
+for (rev, cset) in hg_commits.items():
+    if cset.touches_sync_code or len(cset.parents) > 1 or rev in hg_to_git_commit_map:
+        eprint(pretty_print(rev, cset))
+if DEBUG:
+    eprint("--- Other changesets (not really interesting) ---")
+    for (rev, cset) in hg_commits.items():
+        if not (
+            cset.touches_sync_code
+            or len(cset.parents) > 1
+            or rev in hg_to_git_commit_map
+        ):
+            eprint(pretty_print(rev, cset))
+
+git_tip = build_git_commits(hg_tip)
+if git_tip is None:
+    eprint("No new changesets generated, exiting.")
+else:
+    downstream_git_repo.create_reference("refs/heads/github-sync", git_tip, force=True)
+    eprint("Updated github-sync branch to %s, done!" % git_tip)
diff --git a/tools/github-sync/read-json.py b/tools/github-sync/read-json.py
new file mode 100755
index 0000000000..87264d7df4
--- /dev/null
+++ b/tools/github-sync/read-json.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import json
+import sys
+
+j = json.load(sys.stdin)
+components = sys.argv[1].split("/")
+
+
+def next_match(json_fragment, components):
+    if len(components) == 0:
+        yield json_fragment
+    else:
+        component = components[0]
+        if type(json_fragment) == list:
+            if component == "*":
+                for item in json_fragment:
+                    yield from next_match(item, components[1:])
+            else:
+                component = int(component)
+                if component >= len(j):
+                    sys.exit(1)
+                yield from next_match(json_fragment[component], components[1:])
+        elif type(json_fragment) == dict:
+            if component == "*":
+                for key in sorted(json_fragment.keys()):
+                    yield from next_match(json_fragment[key], components[1:])
+            elif component not in json_fragment:
+                sys.exit(1)
+            else:
+                yield from next_match(json_fragment[component], components[1:])
+
+
+for match in list(next_match(j, components)):
+    if type(match) == dict:
+        print(" ".join(match.keys()))
+    else:
+        print(match)
diff --git a/tools/github-sync/readme.md b/tools/github-sync/readme.md
new file mode 100644
index 0000000000..d691071336
--- /dev/null
+++ b/tools/github-sync/readme.md
@@ -0,0 +1,106 @@
+# Github synchronization scripts
+
+This tool aims to help synchronizing changes from mozilla-central to Github on pushes.
+This is useful for Gecko sub-projects that have Github mirrors, like `gfx/wr` linking to `https://github.com/servo/webrender`.
+Originally, the tools were developed in `https://github.com/staktrace/wrupdater`,
+then got moved under `gfx/wr/ci-scripts/wrupdater`,
+and finally migrated here while also abstracting away from WebRender specifically.
+
+The main entry point is the `sync-to-github.sh` script that is called with the following arguments:
+  1. name of the project, matching the repository under `https://github.com/moz-gfx` user (e.g. `webrender`)
+  2. relative folder in mozilla-central, which is the upstream for the changes (e.g. `gfx/wr`)
+  3. downstream repository specified as "organization/project-name" (e.g. `servo/webrender`)
+  4. name to call for auto-approving the pull request (e.g. `bors` or `@bors-servo`)
+
+It creates a staging directory at `~/.ghsync` if one doesn't already exist,
+and clones the the downstream repo into it.
+The script also requires the `GECKO_PATH` environment variable
+to point to a mercurial clone of `mozilla-central`, and access to the
+taskcluster secrets service to get a Github API token.
+
+The `sync-to-github.sh` script does some setup steps but the bulk of the actual work
+is done by the `converter.py` script. This script scans the mercurial
+repository for new changes to the relative folder in m-c,
+and adds commits to the git repository corresponding to those changes.
+There are some details in the implementation that make it more robust
+than simply exporting patches and attempting to reapply them;
+in particular it builds a commit tree structure that mirrors what is found in
+the `mozilla-central` repository with respect to branches and merges.
+So if conflicting changes land on autoland and inbound, and then get
+merged, the git repository commits will have the same structure with
+a fork/merge in the commit history. This was discovered to be
+necessary after a previous version ran into multiple cases where
+the simple patch approach didn't really work.
+
+One of the actions the `converter.py` takes is to find the last sync point
+between Github and mozilla-central. This is done based on the following markers:
+  - commit message containing the string "[ghsync] From https://hg.mozilla.org/mozilla-central/rev/xxx"
+  - commit message containing the string "[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/xxx"
+  - commit with tag "mozilla-xxx"
+(where xxx is always a mozilla-central hg revision identifier).
+
+Once the converter is done converting, the `sync-to-github.sh` script
+finishes the process by pushing the new commits to the `github-sync` branch
+of the `https://github.com/moz-gfx/<project-name>` repository,
+and generating a pull request against the downstream repository. It also
+leaves a comment on the PR that triggers testing and automatic merge of the PR.
+If there is already a pull request (perhaps from a previous run) the
+pre-existing PR is force-updated instead. This allows for graceful
+handling of scenarios where the PR failed to get merged (e.g. due to
+CI failures on the Github side).
+
+The script is intended to by run by taskcluster for any changes that
+touch the relative folder that land on `mozilla-central`. This may mean
+that multiple instances of this script run concurrently, or even out
+of order (i.e. the task for an older m-c push runs after the task for
+a newer m-c push). The script was written with these possibilities in
+mind and should be able to eventually recover from any such scenario
+automatically (although it may take additional changes to mozilla-central
+for such recovery to occur). That being said, the number of pathological
+scenarios here is quite large and they were not really tested.
+
+## Ownership and access
+
+When this tool is run in Firefox CI, it needs to have push permissions to
+the `moz-gfx` github user's account. It gets this permission via a secret token
+stored in the Firefox CI taskcluster secrets service. If you need to update
+the token, you need to find somebody who is a member of the
+[webrender-ci access group](https://people.mozilla.org/a/webrender-ci/). The
+Google Drive associated with that access group has additional documentation
+on the `moz-gfx` github user and the secret token.
+
+## Debugging
+
+To debug the converter.py script, you need to have a hg checkout of
+mozilla-central, let's assume it's at $MOZILLA. First create a virtualenv
+with the right dependencies installed:
+
+```
+mkdir -p $HOME/.ghsync
+virtualenv --python=python3 $HOME/.ghsync/venv
+source $HOME/.ghsync/venv/bin/activate
+pip3 install -r $MOZILLA/taskcluster/docker/github-sync/requirements.txt
+```
+
+Also create a checkout of the downstream github repo and set up a `github-sync`
+branch to the point where you want port commits to. For example, for WebRender
+you'd do:
+
+```
+cd $HOME/.ghsync
+git clone https://github.com/servo/webrender
+cd webrender
+git checkout -b github-sync master
+```
+
+(You can set the github-sync branch to a past revision if you want to replicate
+a failure that already got committed).
+
+Then run the converter from your hg checkout:
+
+```
+cd $MOZILLA
+tools/github-sync/converter.py $HOME/.ghsync/webrender gfx/wr
+```
+
+You can set the DEBUG variable in the script to True to get more output.
diff --git a/tools/github-sync/sync-to-github.sh b/tools/github-sync/sync-to-github.sh
new file mode 100755
index 0000000000..d677649748
--- /dev/null
+++ b/tools/github-sync/sync-to-github.sh
@@ -0,0 +1,159 @@
+#!/usr/bin/env bash
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+# Do NOT set -x here, since that will expose a secret API token!
+set -o errexit
+set -o nounset
+set -o pipefail
+
+if [[ "$(uname)" != "Linux" ]]; then
+    echo "Error: this script must be run on Linux due to readlink semantics"
+    exit 1
+fi
+
+# GECKO_PATH should definitely be set
+if [[ -z "${GECKO_PATH}" ]]; then
+    echo "Error: GECKO_PATH must point to a hg clone of mozilla-central"
+    exit 1
+fi
+
+# Internal variables, don't fiddle with these
+MYSELF=$(readlink -f ${0})
+MYDIR=$(dirname "${MYSELF}")
+WORKDIR="${HOME}/.ghsync"
+TMPDIR="${WORKDIR}/tmp"
+
+NAME="$1"
+RELATIVE_PATH="$2"
+DOWNSTREAM_REPO="$3"
+BORS="$4"
+BRANCH="github-sync"
+
+mkdir -p "${TMPDIR}"
+
+# Bring the project clone to a known good up-to-date state
+if [[ ! -d "${WORKDIR}/${NAME}" ]]; then
+    echo "Setting up ${NAME} repo..."
+    git clone "https://github.com/${DOWNSTREAM_REPO}" "${WORKDIR}/${NAME}"
+    pushd "${WORKDIR}/${NAME}"
+    git remote add moz-gfx https://github.com/moz-gfx/${NAME}
+    popd
+else
+    echo "Updating ${NAME} repo..."
+    pushd "${WORKDIR}/${NAME}"
+    git checkout master
+    git pull
+    popd
+fi
+
+if [[ -n "${GITHUB_SECRET:-}" ]]; then
+    echo "Obtaining github API token..."
+    # Be careful, GITHUB_TOKEN is secret, so don't log it (or any variables
+    # built using it).
+    GITHUB_TOKEN=$(
+        curl -sSfL "$TASKCLUSTER_PROXY_URL/secrets/v1/secret/${GITHUB_SECRET}" |
+        ${MYDIR}/read-json.py "secret/token"
+    )
+    AUTH="moz-gfx:${GITHUB_TOKEN}"
+    CURL_AUTH="Authorization: bearer ${GITHUB_TOKEN}"
+fi
+
+echo "Pushing base ${BRANCH} branch..."
+pushd "${WORKDIR}/${NAME}"
+git fetch moz-gfx
+git checkout -B ${BRANCH} moz-gfx/${BRANCH} || git checkout -B ${BRANCH} master
+
+if [[ -n "${GITHUB_SECRET:-}" ]]; then
+    # git may emit error messages that contain the URL, so let's sanitize them
+    # or we might leak the auth token to the task log.
+    git push "https://${AUTH}@github.com/moz-gfx/${NAME}" \
+        "${BRANCH}:${BRANCH}" 2>&1 | sed -e "s/${AUTH}/_SANITIZED_/g"
+    # Re-fetch to update the remote moz-gfx/$BRANCH branch in the local repo;
+    # normally the push does this but we use a fully-qualified URL for
+    # pushing so it doesn't happen.
+    git fetch moz-gfx
+fi
+popd
+
+# Run the converter
+echo "Running converter..."
+pushd "${GECKO_PATH}"
+"${MYDIR}/converter.py" "${WORKDIR}/${NAME}" "${RELATIVE_PATH}"
+popd
+
+# Check to see if we have changes that need pushing
+echo "Checking for new changes..."
+pushd "${WORKDIR}/${NAME}"
+PATCHCOUNT=$(git log --oneline moz-gfx/${BRANCH}..${BRANCH}| wc -l)
+if [[ ${PATCHCOUNT} -eq 0 ]]; then
+    echo "No new patches found, aborting..."
+    exit 0
+fi
+
+# Log the new changes, just for logging purposes
+echo "Here are the new changes:"
+git log --graph --stat moz-gfx/${BRANCH}..${BRANCH}
+
+# Collect PR numbers of PRs opened on Github and merged to m-c
+set +e
+FIXES=$(
+    git log master..${BRANCH} |
+    grep "\[import_pr\] From https://github.com/${DOWNSTREAM_REPO}/pull" |
+    sed -e "s%.*pull/% Fixes #%" |
+    uniq |
+    tr '\n' ','
+)
+echo "${FIXES}"
+set -e
+
+if [[ -z "${GITHUB_SECRET:-}" ]]; then
+    echo "Running in try push, exiting now"
+    exit 0
+fi
+
+echo "Pushing new changes to moz-gfx..."
+# git may emit error messages that contain the URL, so let's sanitize them
+# or we might leak the auth token to the task log.
+git push "https://${AUTH}@github.com/moz-gfx/${NAME}" +${BRANCH}:${BRANCH} \
+    2>&1 | sed -e "s/${AUTH}/_SANITIZED_/g"
+
+CURL_HEADER="Accept: application/vnd.github.v3+json"
+CURL=(curl -sSfL -H "${CURL_HEADER}" -H "${CURL_AUTH}")
+# URL extracted here mostly to make servo-tidy happy with line lengths
+API_URL="https://api.github.com/repos/${DOWNSTREAM_REPO}"
+
+# Check if there's an existing PR open
+echo "Listing pre-existing pull requests..."
+"${CURL[@]}" "${API_URL}/pulls?head=moz-gfx:${BRANCH}" |
+    tee "${TMPDIR}/pr.get"
+set +e
+COMMENT_URL=$(cat "${TMPDIR}/pr.get" | ${MYDIR}/read-json.py "0/comments_url")
+HAS_COMMENT_URL="${?}"
+set -e
+
+if [[ ${HAS_COMMENT_URL} -ne 0 ]]; then
+    echo "Pull request not found, creating..."
+    # The PR doesn't exist yet, so let's create it
+    (   echo -n '{ "title": "Sync changes from mozilla-central '"${RELATIVE_PATH}"'"'
+        echo -n ', "body": "'"${FIXES}"'"'
+        echo -n ', "head": "moz-gfx:'"${BRANCH}"'"'
+        echo -n ', "base": "master" }'
+    ) > "${TMPDIR}/pr.create"
+    "${CURL[@]}" -d "@${TMPDIR}/pr.create" "${API_URL}/pulls" |
+        tee "${TMPDIR}/pr.response"
+    COMMENT_URL=$(
+        cat "${TMPDIR}/pr.response" |
+        ${MYDIR}/read-json.py "comments_url"
+    )
+fi
+
+# At this point COMMENTS_URL should be set, so leave a comment to tell bors
+# to merge the PR.
+echo "Posting r+ comment to ${COMMENT_URL}..."
+echo '{ "body": "'"$BORS"' r=auto" }' > "${TMPDIR}/bors_rplus"
+"${CURL[@]}" -d "@${TMPDIR}/bors_rplus" "${COMMENT_URL}"
+
+echo "All done!"