feat: Add generic CI support

Closes greenkeeperio#245

README.md

@@ -53,6 +53,7 @@ Read all about it here: https://blog.greenkeeper.io/announcing-native-lockfile-s
 * ✅ Drone.io _Thank you [@donny-dont](https://github.com/greenkeeperio/greenkeeper-lockfile/pull/141) 👏_
 * ✅ AppVeyor _Thank you [@patkub](https://github.com/greenkeeperio/greenkeeper-lockfile/pull/142) 👏_
 * ✅ GitLab CI _Thank you [@baer95](https://github.com/greenkeeperio/greenkeeper-lockfile/pull/227) 👏_
+* ✅ [Any generic CI](#generic-setup) 
 
 
 * 🙏 [Contribute your own](#contributing-a-ci-service)
@@ -160,6 +161,20 @@ the following environment variables:
 - VCS_ROOT_URL from the vcsroot.<vcsrootid>.url parameter
 - VCS_ROOT_BRANCH from the teamcity.build.branch parameter
 
+## Generic Setup
+
+A generic CI setup allows greenkeeper-lockfile to function in any CI by getting all the data from environment variables.
+All the environment variables are required; boolean values should be provided as the string "true" or "false".
+
+| **Variable**                     | **Description**                                                                               | **Type** | **Example**                      |
+|----------------------------------|-----------------------------------------------------------------------------------------------|----------|----------------------------------|
+| GK_LOCK_GENERIC_CI               | Set this to `true` to trigger generic CI                                                      | boolean  | true                             |
+| GK_LOCK_GENERIC_CI_REPO_SLUG     | Your GitHub repo slug                                                                         | string   | greenkeeper/greenkeeper-lockfile |
+| GK_LOCK_GENERIC_CI_BRANCH_NAME   | Name of the current branch                                                                    | string   | greenkeeper/lodash-4.0.0         |
+| GK_LOCK_GENERIC_CI_FIRST_PUSH    | Whether this is the first push to the branch or not                                           | boolean  | true                             |
+| GK_LOCK_GENERIC_CI_CORRECT_BUILD | Is this a regular build (not a pull request for example)                                      | boolean  | false                            |
+| GK_LOCK_GENERIC_CI_UPLOAD_BUILD  | Should the lockfile be uploaded from this build (relevant for testing multiple node versions) | boolean  | true                             |
+
 ## Configuration options
 
 | Environment Variable  | default value | what is it for? |

ci-services/generic.js

@@ -0,0 +1,33 @@
+'use strict';
+
+const forEach = require('lodash/forEach');
+const env = process.env;
+
+const _export = {
+  // The GitHub repo slug
+  repoSlug: env.GK_LOCK_GENERIC_CI_REPO_SLUG,
+  // The name of the current branch
+  branchName: env.GK_LOCK_GENERIC_CI_BRANCH_NAME,
+  // Is this the first push of the build
+  firstPush: env.GK_LOCK_GENERIC_CI_FIRST_PUSH,
+  // Is this a regular build
+  correctBuild: env.GK_LOCK_GENERIC_CI_CORRECT_BUILD,
+  // Should the lockfile be uploaded from this build
+  uploadBuild: env.GK_LOCK_GENERIC_CI_UPLOAD_BUILD
+};
+
+let hasMissingVars = false;
+forEach(_export, (value, key) => {
+  if (!value) {
+    console.error(`${key} missing`);
+    hasMissingVars = true;
+  }
+});
+
+if (!hasMissingVars) {
+  for (const k of ['firstPush', 'correctBuild', 'uploadBuild']) {
+    _export[k] = _export[k] === 'true';
+  }
+
+  module.exports = _export;
+}

ci-services/tests.js

@@ -17,5 +17,6 @@ module.exports = {
   appveyor: () => env.APPVEYOR === 'True' || env.APPVEYOR === 'true',
   gitlab: () => env.GITLAB_CI === 'true',
   buddyworks: () => env.BUDDY_EXECUTION_ID !== undefined,
-  cirrus: () => env.CIRRUS_CI === 'true'
+  cirrus: () => env.CIRRUS_CI === 'true',
+  generic: () => env.GK_LOCK_GENERIC_CI === 'true'
 }