Add support for looking at a specific file's diff

changelog.md

@@ -4,6 +4,15 @@
 
 * The env vars `DANGER_TEST_REPO` and `DANGER_TEST_PR` will allow you initialize the FakeCI with a repo of your choice. See README.md for more info
 * Improved error messaging around not including a `DANGER_GITHUB_API_TOKEN` in the ENV - nsfmc / orta
+* Adds support for getting the diff for a specific file from git: e.g. 
+  ```js
+// 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) {
+  warn("Please add your GitHub name to the changelog entry, so we can attribute you.")
+}
+  ```
 
 ### 0.6.3
 

source/platforms/GitHub.js

@@ -8,6 +8,8 @@ import parseDiff from "parse-diff"
 import fetch from "node-fetch"
 import "babel-polyfill"
 
+import os from "os"
+
 // This pattern of re-typing specific strings has worked well for Artsy in Swift
 // so, I'm willing to give it a shot here.
 
@@ -59,7 +61,11 @@ export class GitHub {
       diffForFile: (name: string) => {
         const diff = fileDiffs.find((diff) => diff.from === name || diff.to === name)
         if (!diff) { return null }
-        return diff.chunks.reduce((chunk) => chunk.content.reduce((content) => content.join("")))
+
+        const changes = diff.chunks.map((c) => { return c.changes })
+                            .reduce((a, b) => a.concat(b), [])
+        const lines = changes.map((c) => { return c.content })
+        return lines.join(os.EOL)
       }
     }
   }

source/platforms/_tests/GitHub.test.js

@@ -1,4 +1,5 @@
 // @flow
+/*eslint-disable */
 
 import { GitHub } from "../GitHub"
 import Fake from "../../ci_source/Fake"
@@ -80,9 +81,10 @@ describe("with fixtured data", () => {
       expect(gitDSL.deleted_files).toEqual(["lib/components/artist/related_artists/index.js", "lib/components/artist/related_artists/related_artist.js", "lib/components/gene/about_gene.js"])
     })
 
+    // sorry windows users - I guess this test will fail for you
     it("shows the diff for a specific file", async () => {
       const gitDSL:GitDSL = await github.getReviewDiff()
-      expect(gitDSL.diffForFile("CHANGELOG.md")).toEqual("sads")
+      expect(gitDSL.diffForFile("CHANGELOG.md")).toEqual(` - [dev] Updates Flow to 0.32 - orta\n - [dev] Updates React to 0.34 - orta\n - [dev] Turns on \"keychain sharing\" to fix a keychain bug in sim - orta\n+- GeneVC now shows about information, and trending artists - orta\n \n ### 1.1.0-beta.2\n `)
     })
   })
 })