Ensure files determiner works on PRs and new branches

Author: Adam Duncan

lib/files-changed-determiner.js

@@ -3,11 +3,20 @@ const getCommit = gh => async data => {
   let commitData = null
   const options = {
     user: data.repo.namespace,
-    repo: data.repo.name,
-    base: data.build.before,
-    head: data.build.after
+    repo: data.repo.name
   }
-  const comparison = await promisify(gh.repos.compareCommits)(options)
+
+  let action = 'compareCommits'
+  // github sends this in some instances: first commit on a new branch?
+  if (!data.build.before || data.build.before === '0000000000000000000000000000000000000000') {
+    options.sha = data.build.after
+    action = 'getCommit'
+  } else {
+    options.base = data.build.before
+    options.head = data.build.after
+  }
+
+  const comparison = await promisify(gh.repos[action])(options)
   return comparison.files.map(f => f.filename)
 }