Automatically assign PR reviewers

.gitignore

@@ -11,3 +11,7 @@ node_modules
 # tests
 coverage
 npm-debug.log
+
+# editors
+.vscode
+.idea

src/actions/assign.ts

@@ -0,0 +1,122 @@
+import { Context, Octokit } from "probot"
+import { different } from "../utils"
+
+export default async function assignPullRequestReviewers(context: Context) {
+  const PRnumber = context.payload.number
+  const owner = context.payload.repository.owner.login
+  const repo = context.payload.repository.name
+
+  context.log.info("PR number:", PRnumber, ", owner:", owner, ", repo:", repo)
+
+  const oldReviewers: string[] = context.payload.pull_request.requested_reviewers.map(
+    (reviewer: { login: string }) => reviewer.login
+  )
+
+  const newReviewers = await reviewersOfPR(context, PRnumber, owner, repo)
+
+  // Check if old and new reviewers differ. Otherwise we can skip an API call
+  if (different(oldReviewers, newReviewers)) {
+    // Log reviewers replacement
+    context.log.info("Old reviewers:", oldReviewers)
+    context.log.info("New reviewers:", newReviewers)
+
+    const params = context.repo({ pull_number: PRnumber, reviewers: newReviewers })
+    const response = await context.github.pulls.createReviewRequest(params)
+    context.log.info("Status:", response.headers.status)
+  } else {
+    context.log.info("No reviewers changed")
+  }
+}
+
+interface CodeOwner {
+  path: string
+  username: string
+}
+
+function parseModifiedFiles(filesResponse: Octokit.PullsListFilesResponse): string[] {
+  const modifiedFiles: string[] = []
+
+  for (const file of filesResponse) {
+    modifiedFiles.push(file.filename)
+  }
+
+  return modifiedFiles
+}
+
+function parseCodeOwners(codeOwnersFile: string): CodeOwner[] {
+  const codeOwners: CodeOwner[] = []
+  for (const line of codeOwnersFile.split("\n")) {
+    // Ignore empty lines and comments
+    if (line.length === 0 || line.startsWith("#")) {
+      continue
+    }
+
+    let [path, owner] = line.split(" ")
+
+    // Allow only owners in the form of @username
+    if (!owner?.startsWith("@")) {
+      continue
+    }
+
+    const codeOwner: CodeOwner = {
+      path: path,
+      username: owner.slice(1) // Remove initial '@'
+    }
+
+    codeOwners.push(codeOwner)
+  }
+
+  return codeOwners
+}
+
+/**
+ * @return List of maintainers of the files that were modified in `PRnumber`
+ */
+async function reviewersOfPR(
+  context: Context,
+  PRnumber: number,
+  repoOwner: string,
+  repo: string
+): Promise<string[]> {
+  const reviewers: string[] = []
+
+  // Get list of modified files
+  const modifiedFilesResponse = await context.github.pulls.listFiles({
+    owner: repoOwner,
+    repo: repo,
+    pull_number: PRnumber,
+  })
+
+  const filesData: any = modifiedFilesResponse.data
+  const modifiedFiles = parseModifiedFiles(filesData)
+
+  // Get CODEOWNERS file contents
+  const codeOwnersResponse = await context.github.repos.getContents({
+    owner: repoOwner,
+    repo: repo,
+    path: ".github/CODEOWNERS",
+  })
+
+  const codeOwnersData: any = codeOwnersResponse.data
+  const codeOwnersFile = Buffer.from(codeOwnersData.content, "base64").toString()
+  const codeOwners = parseCodeOwners(codeOwnersFile)
+
+  // Assumptions:
+  // - There can be many files owned by the same owner
+  // - There can be many owners for the same file. For example:
+  //   /plugins/git/git.plugin.zsh could have 2 owners (for /plugins and for /plugins/git)
+  // - The number of codeOwners >> the number of modified files
+  for (const codeOwner of codeOwners) {
+    for (const path of modifiedFiles) {
+      if (path.includes(codeOwner.path)) {
+        context.log.info(`${path} was modified. ${codeOwner.username} owns ${codeOwner.path}`)
+        reviewers.push(codeOwner.username)
+        break // This user is a reviewer, let's look at the next one
+      }
+    }
+  }
+
+  return reviewers
+}
+
+export { parseModifiedFiles, parseCodeOwners, CodeOwner }

src/actions/triage.ts

@@ -1,13 +1,14 @@
 import { Context } from 'probot' // eslint-disable-line no-unused-vars
 import { execSync } from 'child_process'
+import { different } from "../utils"
 
 // List of labels determined *only* via the triage function.
 // The result of the triage function will have precedence
 // on these labels over a maintainer having applied them from
 // the GitHub web UI.
 import codeLabels from './labels.json'
 
-export = async function triage (context: Context) {
+export default async function triage (context: Context) {
   // Get PR number and current PR labels
   const PRNumber = context.payload.number
   const oldLabels: string[] = context.payload.pull_request.labels.map((label: { name: string }) => label.name)
@@ -21,9 +22,10 @@ export = async function triage (context: Context) {
   process.env['REPO_URL'] = repoURL
   process.env['REPO_DIR'] = `${process.cwd()}/github`
 
+  let newLabels: string[] = []
   try {
     // Get new PR labels
-    var newLabels = labelsOfPR(PRNumber)
+    newLabels = labelsOfPR(PRNumber)
   } catch (err) {
     context.log.error(err, 'Error in triage.zsh script call')
     return
@@ -45,6 +47,10 @@ export = async function triage (context: Context) {
   }
 }
 
+/**
+ * Executes the zsh script that assign labels to the PR of PRNumber.
+ * The zsh script assign the labels basing on the files that have been changed.
+ */
 function labelsOfPR (PRNumber: number): string[] {
   // Path to script based on app root
   const zshScript = `${process.cwd()}/src/actions/triage.zsh`
@@ -57,16 +63,3 @@ function labelsOfPR (PRNumber: number): string[] {
   // NOTE: this assumes there are no "s in the original string
   return JSON.parse(stdout.replace(/'/g, '"'))
 }
-
-function different (A: string[], B: string[]): boolean {
-  if (A.length !== B.length) return true
-
-  A.sort()
-  B.sort()
-
-  for (let i = 0; i < A.length; i++) {
-    if (A[i] !== B[i]) return true
-  }
-
-  return false
-}

src/index.ts

@@ -1,6 +1,8 @@
 import { Application } from 'probot' // eslint-disable-line no-unused-vars
 import triagePullRequest from './actions/triage'
+import assignPullRequestReviewers from './actions/assign'
 
 export = (app: Application) => {
   app.on(['pull_request.opened', 'pull_request.synchronize'], triagePullRequest)
+  app.on(['pull_request.opened', 'pull_request.synchronize'], assignPullRequestReviewers)
 }

src/utils.ts

@@ -0,0 +1,14 @@
+function different (A: string[], B: string[]): boolean {
+  if (A.length !== B.length) return true
+
+  A.sort()
+  B.sort()
+
+  for (let i = 0; i < A.length; i++) {
+    if (A[i] !== B[i]) return true
+  }
+
+  return false
+}
+
+export { different }

test/assign.test.ts

@@ -0,0 +1,30 @@
+import { promises as fs } from 'fs'
+import { parseModifiedFiles, parseCodeOwners, CodeOwner } from '../src/actions/assign' // eslint-disable-line no-unused-vars
+import modifiedFilesResponse from '../test/fixtures/modifiedFiles.json'
+
+describe('assigning PR reviewers', () => {
+  test('correctly parses modified files', async () => {
+    const expectedModifiedFiles = ['plugins/gitfast/update']
+    const modifiedFiles = await parseModifiedFiles(modifiedFilesResponse)
+
+    expect(modifiedFiles.sort()).toEqual(expectedModifiedFiles.sort())
+  })
+
+  test('correctly parses CODEOWNERS file', async () => {
+    const expectedCodeOwners: CodeOwner[] = [
+      {
+        path: 'plugins/gitfast/',
+        username: 'felipec'
+      },
+      {
+        path: 'plugins/sdk/',
+        username: 'rgoldberg'
+      }
+    ]
+
+    const codeOwnersFile = await fs.readFile('./test/fixtures/CODEOWNERS')
+    const codeOwners = await parseCodeOwners(codeOwnersFile.toString())
+
+    expect(codeOwners.sort()).toEqual(expectedCodeOwners.sort())
+  })
+})

test/fixtures/CODEOWNERS

@@ -0,0 +1,3 @@
+# Plugin owners
+plugins/gitfast/ @felipec
+plugins/sdk/ @rgoldberg

test/fixtures/modifiedFiles.json

@@ -0,0 +1,14 @@
+[
+  {
+    "sha": "40050a704603103d24d37a777cff345a530f34d9",
+    "filename": "plugins/gitfast/update",
+    "status": "modified",
+    "additions": 2,
+    "deletions": 0,
+    "changes": 2,
+    "blob_url": "https://github.com/bartekpacia/ohmyzsh/blob/5383477f0701be7802f356fbc5c5db118dc4edd8/plugins/gitfast/update",
+    "raw_url": "https://github.com/bartekpacia/ohmyzsh/raw/5383477f0701be7802f356fbc5c5db118dc4edd8/plugins/gitfast/update",
+    "contents_url": "https://api.github.com/repos/bartekpacia/ohmyzsh/contents/plugins/gitfast/update?ref=5383477f0701be7802f356fbc5c5db118dc4edd8",
+    "patch": "@@ -7,3 +7,5 @@ curl -s -o _git \"${url}/git-completion.zsh?h=v${version}\" &&\n curl -s -o git-completion.bash \"${url}/git-completion.bash?h=v${version}\" &&\n curl -s -o git-prompt.sh \"${url}/git-prompt.sh?h=v${version}\" &&\n git apply updates.patch\n+\n+echo \"This is an example change to a plugin!\"\n\\ No newline at end of file"
+  }
+]