Merge pull request #102 from danger/package-json-yarn-lock-warning

Warn if changes to package.json and not yarn.lock

dangerfile.js

@@ -1,16 +1,26 @@
 // import { danger, warn } from "danger"
 import fs from "fs"
+import includes from "lodash.includes"
 
 // Request a CHANGELOG entry if not declared #trivial
-const hasChangelog = danger.git.modified_files.includes("changelog.md")
-const isTrivial = (danger.github.pr.body + danger.github.pr.title).includes("#trivial")
+const hasChangelog = includes(danger.git.modified_files, "changelog.md")
+const isTrivial = includes((danger.github.pr.body + danger.github.pr.title), "#trivial")
 if (!hasChangelog && !isTrivial) {
   warn("Please add a changelog entry for your changes.")
 
   // Politely ask for their name on the entry too
   const changelogDiff = danger.git.diffForFile("changelog.md")
   const contributorName = danger.github.pr.user.login
-  if (changelogDiff && changelogDiff.indexOf(contributorName) === -1) {
+  if (changelogDiff && !includes(changelogDiff, contributorName)) {
     warn("Please add your GitHub name to the changelog entry, so we can attribute you.")
   }
 }
+
+// Warns if there are changes to package.json without changes to yarn.lock.
+const packageChanged = includes(danger.git.modified_files, "package.json")
+const lockfileChanged = includes(danger.git.modified_files, "yarn.lock")
+if (packageChanged && !lockfileChanged) {
+  const message = "Changes were made to package.json, but not to yarn.lock"
+  const idea = "Perhaps you need to run `yarn install`?"
+  warn(`${message} - <i>${idea}</i>`)
+}