test github actions

.github/actions/setup-opam/.gitattributes

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+*.exe binary

.github/actions/setup-opam/action.yml

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+name: Setup opam environment
+description: Installs opam
+runs:
+  using: 'node12'
+  main: 'index.js'

.github/actions/setup-opam/index.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const core = require('@actions/core');
+const exec = require('@actions/exec');
+const io = require('@actions/io');
+const tc = require('@actions/tool-cache');
+const path = require('path');
+const uuidV4 = require('uuid/v4');
+
+const CYGWIN_PACKAGES = [
+  'rsync',
+  'patch',
+  'diffutils',
+  'curl',
+  'make',
+  'unzip',
+  'git',
+  'm4',
+  'perl',
+  'mingw64-x86_64-gcc-core',
+];
+
+async function installWindows() {
+  // Install cygwin and the packages that opam needs.
+  //
+  // TODO: see if this might be faster:
+  //
+  //   const cygwinInstaller = await tc.downloadTool('https://cygwin.com/setup-x86_64.exe');
+  //   await exec.exec(cygwinInstaller, [
+  //     '--no-admin',
+  //     '--no-shortcuts',
+  //     '--packages',
+  //     ...CYGWIN_PACKAGES,
+  //     '--prune-install',
+  //     '--quiet-mode',
+  //   ]);
+  await exec.exec(`choco.exe install cygwin`);
+  await exec.exec(`choco.exe install ${CYGWIN_PACKAGES.join(' ')} --source=cygwin`);
+
+  // download opam installer
+  console.log(`Downloading opam`);
+  const opamInstaller = await tc.downloadTool('https://github.com/fdopen/opam-repository-mingw/releases/download/0.0.0.2/opam64.tar.xz');
+
+  // extract opam installer. tool-cache's extractTar almost works, except for
+  // actions/toolkit#165 and actions/toolkit#180, so we duplicate some of its
+  // functionality.
+  const tempDirectory = process.env['RUNNER_TEMP'] || path.join(process.env['USERPROFILE'] || 'C:\\', 'flow', 'temp');
+  const dest = path.join(tempDirectory, uuidV4());
+  await io.mkdirP(dest);
+  console.log(`Created temporary directory ${dest}`);
+  const tarPath = await io.which('tar', true);
+  await exec.exec(`"${tarPath}"`, ["-x", "--force-local", "-f", opamInstaller, "-C", dest.replace(/\\/g, '/')]);
+
+  // run opam installer
+  await exec.exec(
+    "c:\\tools\\cygwin\\bin\\bash.exe",
+    ["opam64/install.sh"],
+    {
+      cwd: dest,
+      env: {
+        ...process.env,
+        PATH: "c:\\tools\\cygwin\\bin",
+      },
+    }
+  );
+}
+
+async function installLinux() {
+  const url = 'https://github.com/ocaml/opam/releases/download/2.0.5/opam-2.0.5-x86_64-linux';
+  const exe = await tc.downloadTool(url);
+  // TODO: chmod +x, mv into PATH
+}
+
+async function installMac() {
+  const url = 'https://github.com/ocaml/opam/releases/download/2.0.5/opam-2.0.5-x86_64-macos';
+  const exe = await tc.downloadTool(url);
+  // TODO: chmod +x, mv into PATH
+}
+
+async function run() {
+  try {
+    switch (process.platform) {
+      case 'win32':
+        await installWindows();
+        break;
+      case 'linux':
+        await installLinux();
+        break;
+      case 'darwin':
+        await installMac();
+        break;
+      default:
+        core.setFailed(`Unsupported platform: ${process.platform}`);
+    }
+  } catch (error) {
+    core.setFailed(error.message);
+  }
+}
+
+run();