Add fallback for git branch calculation (#871)

In some ci's, the git branch will not be present in the environment with
the default that env-ci uses, so we need to provide a fallback. The
fallback is either the PR's branch if present or the .git branch. This
branch is used inside of the Engine frontend to display more information
about the schema changes.

See https://github.com/pvdlg/env-ci#caveats for a longer list of cases
when the branch will not be present in the ci environment

packages/apollo/src/__tests__/git.test.ts

@@ -0,0 +1,15 @@
+import { gitInfo } from "../git";
+
+describe("Git integration", () => {
+  it("Returns commit, branch, message, committer, and remoteUrl", async () => {
+    // Currently these tests are too granular and would be better as
+    // service:push tests when they are uncommented
+    const info = await gitInfo();
+
+    expect(info.commit).toBeDefined();
+    expect(info.committer).toBeDefined();
+    expect(info.remoteUrl).toBeDefined();
+    expect(info.message).toBeDefined();
+    expect(info.branch).toBeDefined();
+  });
+});

packages/apollo/src/git.ts

@@ -35,14 +35,24 @@ export interface GitContext {
 }
 
 export const gitInfo = async (): Promise<GitContext | undefined> => {
-  const { isCi, commit, branch, slug, root } = ci();
+  // Occasionally `branch` will be undefined depending on the environment, so
+  // we need to fallback on `prBranch`. However in some cases, we are not able
+  // to get to the branch at all. For more information, see
+  // https://github.com/pvdlg/env-ci#caveats
+  //
+  // slug is formatted as follows: ${organization}/${repository name}
+  const { isCi, commit, branch: ciBranch, slug, root, prBranch } = ci();
   const gitLoc = root ? root : findGitRoot();
 
   if (!commit) return;
 
   let committer;
+  let branch = ciBranch || prBranch;
   let remoteUrl = slug;
   let message;
+
+  // In order to use git-parse and git-rev-sync, we must ensure that a git context is
+  // accessible. Without this check, the commands would throw
   if (gitLoc) {
     const { authorName, authorEmail, ...commit } = await gitToJs(gitLoc)
       .then((commits: Commit[]) =>
@@ -63,10 +73,25 @@ export const gitInfo = async (): Promise<GitContext | undefined> => {
         remoteUrl = git.remoteUrl();
       } catch (e) {}
     }
+
+    // The ci and pr branches pulled from the ci's environment can be undefined,
+    // so we fallback on the git context.
+    //
+    // See https://github.com/pvdlg/env-ci#caveats for a detailed list of when
+    // branch can be undefined
+    if (!branch) {
+      branch = git.branch();
+    }
   }
 
   return pickBy(
-    { committer, commit, remoteUrl, message, branch },
+    {
+      committer,
+      commit,
+      remoteUrl,
+      message,
+      branch
+    },
     identity
   ) as GitContext;
 };