Resolve simultaneous deployments with rebase

__tests__/execute.test.ts

@@ -13,8 +13,10 @@ describe('execute', () => {
     expect(exec).toBeCalledWith('echo Montezuma', [], {
       cwd: './',
       silent: true,
+      ignoreReturnCode: false,
       listeners: {
-        stdout: expect.any(Function)
+        stdout: expect.any(Function),
+        stderr: expect.any(Function)
       }
     })
   })
@@ -28,8 +30,10 @@ describe('execute', () => {
     expect(exec).toBeCalledWith('echo Montezuma', [], {
       cwd: './',
       silent: false,
+      ignoreReturnCode: false,
       listeners: {
-        stdout: expect.any(Function)
+        stdout: expect.any(Function),
+        stderr: expect.any(Function)
       }
     })
   })

__tests__/git.test.ts

@@ -30,7 +30,7 @@ jest.mock('@actions/io', () => ({
 jest.mock('../src/execute', () => ({
   // eslint-disable-next-line @typescript-eslint/naming-convention
   __esModule: true,
-  execute: jest.fn()
+  execute: jest.fn(() => ({stdout: '', stderr: ''}))
 }))
 
 describe('git', () => {

__tests__/main.test.ts

@@ -15,7 +15,7 @@ import {setFailed, exportVariable} from '@actions/core'
 const originalAction = JSON.stringify(action)
 
 jest.mock('../src/execute', () => ({
-  execute: jest.fn()
+  execute: jest.fn(() => ({stdout: '', stderr: ''}))
 }))
 
 jest.mock('@actions/io', () => ({

__tests__/ssh.test.ts

@@ -33,7 +33,7 @@ jest.mock('@actions/core', () => ({
 }))
 
 jest.mock('../src/execute', () => ({
-  execute: jest.fn()
+  execute: jest.fn(() => ({stdout: '', stderr: ''}))
 }))
 
 describe('configureSSH', () => {

__tests__/worktree.error.test.ts

@@ -5,7 +5,7 @@ import {generateWorktree} from '../src/worktree'
 jest.mock('../src/execute', () => ({
   // eslint-disable-next-line @typescript-eslint/naming-convention
   __esModule: true,
-  execute: jest.fn()
+  execute: jest.fn(() => ({stdout: '', stderr: ''}))
 }))
 
 describe('generateWorktree', () => {

__tests__/worktree.test.ts

@@ -104,7 +104,7 @@ describe('generateWorktree', () => {
         path.join(workspace, 'worktree'),
         true
       )
-      expect(commitMessages).toBe('gh1')
+      expect(commitMessages.stdout).toBe('gh1')
     })
   })
   describe('with missing branch and new commits', () => {
@@ -132,7 +132,7 @@ describe('generateWorktree', () => {
         path.join(workspace, 'worktree'),
         true
       )
-      expect(commitMessages).toBe('Initial no-pages commit')
+      expect(commitMessages.stdout).toBe('Initial no-pages commit')
     })
   })
   describe('with existing branch and singleCommit', () => {

action.yml

@@ -60,6 +60,11 @@ inputs:
     description: 'Do not actually push back, but use `--dry-run` on `git push` invocations insead.'
     required: false
 
+  force:
+    description: 'Whether to force-push and overwrite any existing deployment. Setting this to false will attempt to rebase simultaneous deployments. This option is on by default and can be toggled off by setting it to false.'
+    required: false
+    default: true
+
   git-config-name:
     description: 'Allows you to customize the name that is attached to the GitHub config which is used when pushing the deployment commits. If this is not included it will use the name in the GitHub context, followed by the name of the action.'
     required: false

src/constants.ts

@@ -33,6 +33,8 @@ export interface ActionInterface {
   folder: string
   /** The auto generated folder path. */
   folderPath?: string
+  /** Whether to force-push or attempt to merge existing changes. */
+  force?: boolean
   /** Determines test scenarios the action is running in. */
   isTest: TestFlag
   /** The git config name. */
@@ -85,6 +87,9 @@ export const action: ActionInterface = {
   dryRun: !isNullOrUndefined(getInput('dry-run'))
     ? getInput('dry-run').toLowerCase() === 'true'
     : false,
+  force: !isNullOrUndefined(getInput('force'))
+    ? getInput('force').toLowerCase() === 'true'
+    : true,
   clean: !isNullOrUndefined(getInput('clean'))
     ? getInput('clean').toLowerCase() === 'true'
     : false,

src/execute.ts

@@ -1,37 +1,58 @@
 import {exec} from '@actions/exec'
 import buffer from 'buffer'
 
-let output = ''
+type ExecuteOutput = {
+  stdout: string
+  stderr: string
+}
+
+const output: ExecuteOutput = {stdout: '', stderr: ''}
 
 /** Wrapper around the GitHub toolkit exec command which returns the output.
  * Also allows you to easily toggle the current working directory.
  *
  * @param {string} cmd - The command to execute.
  * @param {string} cwd - The current working directory.
  * @param {boolean} silent - Determines if the in/out should be silenced or not.
+ * @param {boolean} ignoreReturnCode - Determines whether to throw an error
+ * on a non-zero exit status or to leave implementation up to the caller.
  */
 export async function execute(
   cmd: string,
   cwd: string,
-  silent: boolean
-): Promise<string> {
-  output = ''
+  silent: boolean,
+  ignoreReturnCode = false
+): Promise<ExecuteOutput> {
+  output.stdout = ''
+  output.stderr = ''
 
   await exec(cmd, [], {
     // Silences the input unless the INPUT_DEBUG flag is set.
     silent,
     cwd,
-    listeners: {
-      stdout
-    }
+    listeners: {stdout, stderr},
+    ignoreReturnCode
   })
 
   return Promise.resolve(output)
 }
 
 export function stdout(data: Buffer | string): void {
   const dataString = data.toString().trim()
-  if (output.length + dataString.length < buffer.constants.MAX_STRING_LENGTH) {
-    output += dataString
+  if (
+    output.stdout.length + dataString.length <
+    buffer.constants.MAX_STRING_LENGTH
+  ) {
+    output.stdout += dataString
+  }
+}
+
+export function stderr(data: Buffer | string): void {
+  const dataString = data.toString().trim()
+  if (
+    output.stderr.length + dataString.length <
+    buffer.constants.MAX_STRING_LENGTH
+  ) {
+    output.stderr += dataString
   }
 }

src/git.ts

@@ -108,11 +108,15 @@ export async function deploy(action: ActionInterface): Promise<Status> {
     // Checks to see if the remote exists prior to deploying.
     const branchExists =
       action.isTest & TestFlag.HAS_REMOTE_BRANCH ||
-      (await execute(
-        `git ls-remote --heads ${action.repositoryPath} refs/heads/${action.branch}`,
-        action.workspace,
-        action.silent
-      ))
+      Boolean(
+        (
+          await execute(
+            `git ls-remote --heads ${action.repositoryPath} refs/heads/${action.branch}`,
+            action.workspace,
+            action.silent
+          )
+        ).stdout
+      )
 
     await generateWorktree(action, temporaryDeploymentDirectory, branchExists)
 
@@ -186,11 +190,15 @@ export async function deploy(action: ActionInterface): Promise<Status> {
 
     const hasFilesToCommit =
       action.isTest & TestFlag.HAS_CHANGED_FILES ||
-      (await execute(
-        checkGitStatus,
-        `${action.workspace}/${temporaryDeploymentDirectory}`,
-        true // This output is always silenced due to the large output it creates.
-      ))
+      Boolean(
+        (
+          await execute(
+            checkGitStatus,
+            `${action.workspace}/${temporaryDeploymentDirectory}`,
+            true // This output is always silenced due to the large output it creates.
+          )
+        ).stdout
+      )
 
     if (
       (!action.singleCommit && !hasFilesToCommit) ||
@@ -216,12 +224,67 @@ export async function deploy(action: ActionInterface): Promise<Status> {
       `${action.workspace}/${temporaryDeploymentDirectory}`,
       action.silent
     )
-    if (!action.dryRun) {
+
+    if (action.dryRun) {
+      info(`Dry run complete`)
+      return Status.SUCCESS
+    }
+
+    if (action.force) {
+      // Force-push our changes, overwriting any changes that were added in
+      // the meantime
+      info(`Force-pushing changes...`)
       await execute(
         `git push --force ${action.repositoryPath} ${temporaryDeploymentBranch}:${action.branch}`,
         `${action.workspace}/${temporaryDeploymentDirectory}`,
         action.silent
       )
+    } else {
+      // Attempt to push our changes, but fetch + rebase if there were
+      // other changes added in the meantime
+      const ATTEMPT_LIMIT = 3
+      let attempt = 0
+      // Keep track of whether the most recent attempt was rejected
+      let rejected = false
+      do {
+        attempt++
+        if (attempt > ATTEMPT_LIMIT) throw new Error(`Attempt limit exceeded`)
+
+        // Handle rejection for the previous attempt first such that, on
+        // the final attempt, time is not wasted rebasing it when it will
+        // not be pushed
+        if (rejected) {
+          info(`Fetching upstream ${action.branch}...`)
+          await execute(
+            `git fetch ${action.repositoryPath} ${action.branch}:${action.branch}`,
+            `${action.workspace}/${temporaryDeploymentDirectory}`,
+            action.silent
+          )
+          info(`Rebasing this deployment onto ${action.branch}...`)
+          await execute(
+            `git rebase ${action.branch} ${temporaryDeploymentBranch}`,
+            `${action.workspace}/${temporaryDeploymentDirectory}`,
+            action.silent
+          )
+        }
+
+        info(`Pushing changes... (attempt ${attempt} of ${ATTEMPT_LIMIT})`)
+        const pushResult = await execute(
+          `git push --porcelain ${action.repositoryPath} ${temporaryDeploymentBranch}:${action.branch}`,
+          `${action.workspace}/${temporaryDeploymentDirectory}`,
+          action.silent,
+          true // Ignore non-zero exit status
+        )
+
+        rejected =
+          pushResult.stdout.includes(`[rejected]`) ||
+          pushResult.stdout.includes(`[remote rejected]`)
+        if (rejected) info('Updates were rejected')
+
+        // If the push failed for any reason other than being rejected,
+        // there is a problem
+        if (!rejected && pushResult.stderr) throw new Error(pushResult.stderr)
+      } while (rejected)
     }
 
     info(`Changes committed to the ${action.branch} branch… 📦`)