Add initial transpiler setup

.github/workflows/transpile.yml

+name: Transpile
+
+on:
+  push:
+    branches: [upstream-patched]
+
+jobs:
+  transpile:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 10.x
+      - uses: actions/cache@v2
+        with:
+          path: ~/.npm
+          key: npm-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: npm-
+      - run: npm ci
+      - run: bash scripts/transpile.sh

buidler/env-artifacts.js

+const { BuidlerError } = require('@nomiclabs/buidler/internal/core/errors');
+
+extendEnvironment(env => {
+  const { artifacts } = env;
+
+  env.artifacts = {
+    ...artifacts,
+    require (name) {
+      try {
+        return artifacts.require(name + 'UpgradeSafeWithInit');
+      } catch (e) {
+        if (BuidlerError.isBuidlerError(e) && e.number === 700) {
+          return artifacts.require(name + 'UpgradeSafe');
+        } else {
+          throw e;
+        }
+      }
+    },
+  };
+});

buidler/task-test-get-files.js

+const { internalTask } = require('@nomiclabs/buidler/config');
+
+const { TASK_TEST_GET_TEST_FILES } = require('@nomiclabs/buidler/builtin-tasks/task-names');
+const glob = require('glob');
+const path = require('path');
+const { promisify } = require('util');
+
+internalTask(TASK_TEST_GET_TEST_FILES)
+  .setAction(async ({ testFiles }, { config }) => {
+    if (testFiles.length !== 0) {
+      return testFiles;
+    }
+    return await promisify(glob)(
+      path.join(config.paths.tests, '**/*.js'),
+      { ignore: [path.join(config.paths.tests, 'proxy/**/*')] },
+    );
+  });

scripts/transpile.sh

+#!/usr/bin/env bash
+
+set -euo pipefail -x
+
+npm run compile
+
+npx @openzeppelin/upgrade-safe-transpiler -D
+
+COMMIT="$(git rev-parse --short HEAD)"
+
+git config user.name 'github-actions'
+git config user.email '41898282+github-actions[bot]@users.noreply.github.com'
+
+git add contracts
+git reset --soft master
+git checkout master
+git commit -m "Transpile $COMMIT"
+git push origin master