Fix non-existent branch issues on closed PRs edge case

__tests__/functions/prechecks.test.js

@@ -3674,3 +3674,210 @@ test('runs prechecks and finds the PR is NOT behind the stable branch (HAS_HOOKS
     'beefdead'
   )
 })
+
+// Tests for branch existence checks
+class NotFoundError extends Error {
+  constructor(message) {
+    super(message)
+    this.status = 404
+  }
+}
+
+class UnexpectedError extends Error {
+  constructor(message) {
+    super(message)
+    this.status = 500
+  }
+}
+
+test('fails prechecks when the branch does not exist (deleted branch)', async () => {
+  // Mock getBranch to throw a 404 error for the PR branch check
+  octokit.rest.repos.getBranch = vi
+    .fn()
+    // First call: stable branch check (succeeds)
+    .mockReturnValueOnce({
+      data: {
+        commit: {sha: 'deadbeef', commit: {tree: {sha: 'beefdead'}}},
+        name: 'main'
+      },
+      status: 200
+    })
+    // Second call: base branch check (succeeds)
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'deadbeef'}, name: 'main'},
+      status: 200
+    })
+    // Third call: PR branch check (fails with 404)
+    .mockRejectedValueOnce(new NotFoundError('Reference does not exist'))
+
+  const result = await prechecks(context, octokit, data)
+
+  expect(result.status).toBe(false)
+  expect(result.message).toContain('Cannot proceed with deployment')
+  expect(result.message).toContain('ref: `test-ref`')
+  expect(result.message).toContain(
+    'The branch for this pull request no longer exists'
+  )
+  expect(warningMock).toHaveBeenCalledWith('branch does not exist: test-ref')
+})
+
+test('passes prechecks when branch exists (normal deployment)', async () => {
+  // Mock getBranch to succeed for all calls
+  octokit.rest.repos.getBranch = vi
+    .fn()
+    // First call: stable branch check
+    .mockReturnValueOnce({
+      data: {
+        commit: {sha: 'deadbeef', commit: {tree: {sha: 'beefdead'}}},
+        name: 'main'
+      },
+      status: 200
+    })
+    // Second call: base branch check
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'deadbeef'}, name: 'main'},
+      status: 200
+    })
+    // Third call: PR branch check (succeeds)
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'abc123'}, name: 'test-ref'},
+      status: 200
+    })
+
+  const result = await prechecks(context, octokit, data)
+
+  expect(result.status).toBe(true)
+  expect(result.ref).toBe('test-ref')
+  expect(debugMock).toHaveBeenCalledWith('checking if branch exists: test-ref')
+  expect(infoMock).toHaveBeenCalledWith('✅ branch exists: test-ref')
+})
+
+test('skips branch existence check when deploying to stable branch', async () => {
+  data.environmentObj.stable_branch_used = true
+
+  // Mock getBranch - should only be called twice (not three times)
+  octokit.rest.repos.getBranch = vi
+    .fn()
+    .mockReturnValueOnce({
+      data: {
+        commit: {sha: 'deadbeef', commit: {tree: {sha: 'beefdead'}}},
+        name: 'main'
+      },
+      status: 200
+    })
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'deadbeef'}, name: 'main'},
+      status: 200
+    })
+
+  const result = await prechecks(context, octokit, data)
+
+  expect(result.status).toBe(true)
+  // Verify the branch existence check was skipped (only 2 getBranch calls, not 3)
+  expect(octokit.rest.repos.getBranch).toHaveBeenCalledTimes(2)
+  expect(debugMock).not.toHaveBeenCalledWith(
+    'checking if branch exists: test-ref'
+  )
+})
+
+test('skips branch existence check when deploying an exact SHA', async () => {
+  data.environmentObj.sha = 'abc123def456'
+  data.inputs.allow_sha_deployments = true
+
+  octokit.rest.repos.getBranch = vi
+    .fn()
+    .mockReturnValueOnce({
+      data: {
+        commit: {sha: 'deadbeef', commit: {tree: {sha: 'beefdead'}}},
+        name: 'main'
+      },
+      status: 200
+    })
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'deadbeef'}, name: 'main'},
+      status: 200
+    })
+
+  const result = await prechecks(context, octokit, data)
+
+  expect(result.status).toBe(true)
+  // Verify the branch existence check was skipped
+  expect(octokit.rest.repos.getBranch).toHaveBeenCalledTimes(2)
+  expect(debugMock).not.toHaveBeenCalledWith(
+    'checking if branch exists: test-ref'
+  )
+})
+
+test('skips branch existence check when PR is from a fork', async () => {
+  // Mock the PR as a fork
+  octokit.rest.pulls.get = vi.fn().mockReturnValue({
+    data: {
+      head: {
+        ref: 'test-ref',
+        sha: 'abc123',
+        repo: {
+          fork: true
+        },
+        label: 'fork:test-ref'
+      },
+      base: {
+        ref: 'main'
+      },
+      draft: false
+    },
+    status: 200
+  })
+
+  octokit.rest.repos.getBranch = vi
+    .fn()
+    .mockReturnValueOnce({
+      data: {
+        commit: {sha: 'deadbeef', commit: {tree: {sha: 'beefdead'}}},
+        name: 'main'
+      },
+      status: 200
+    })
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'deadbeef'}, name: 'main'},
+      status: 200
+    })
+
+  const result = await prechecks(context, octokit, data)
+
+  expect(result.status).toBe(true)
+  expect(result.isFork).toBe(true)
+  // Verify the branch existence check was skipped for forks
+  expect(octokit.rest.repos.getBranch).toHaveBeenCalledTimes(2)
+  expect(debugMock).not.toHaveBeenCalledWith(
+    'checking if branch exists: abc123'
+  )
+})
+
+test('fails prechecks when branch check encounters unexpected error', async () => {
+  // Mock getBranch to throw a non-404 error
+  octokit.rest.repos.getBranch = vi
+    .fn()
+    .mockReturnValueOnce({
+      data: {
+        commit: {sha: 'deadbeef', commit: {tree: {sha: 'beefdead'}}},
+        name: 'main'
+      },
+      status: 200
+    })
+    .mockReturnValueOnce({
+      data: {commit: {sha: 'deadbeef'}, name: 'main'},
+      status: 200
+    })
+    .mockRejectedValueOnce(new UnexpectedError('Internal server error'))
+
+  const result = await prechecks(context, octokit, data)
+
+  // Should fail and not continue
+  expect(result.status).toBe(false)
+  expect(result.message).toContain('Cannot proceed with deployment')
+  expect(result.message).toContain('ref: `test-ref`')
+  expect(result.message).toContain(
+    'An unexpected error occurred while checking if the branch exists'
+  )
+  expect(result.message).toContain('Internal server error')
+})

src/functions/prechecks.js

@@ -381,6 +381,37 @@ export async function prechecks(context, octokit, data) {
   core.saveState('review_decision', reviewDecision)
   core.saveState('approved_reviews_count', approvedReviewsCount)
 
+  // Check if the branch exists before proceeding with deployment
+  // Skip this check if:
+  // 1. We're deploying to the stable branch (e.g., `.deploy main`)
+  // 2. We're deploying an exact SHA (allow_sha_deployments is enabled and a SHA was provided)
+  // 3. The PR is from a fork (we use SHA for forks, not branch names)
+  if (
+    data.environmentObj.stable_branch_used !== true &&
+    data.environmentObj.sha === null &&
+    isFork === false
+  ) {
+    core.debug(`checking if branch exists: ${ref}`)
+    try {
+      await octokit.rest.repos.getBranch({
+        ...context.repo,
+        branch: ref,
+        headers: API_HEADERS
+      })
+      core.info(`✅ branch exists: ${ref}`)
+    } catch (error) {
+      if (error.status === 404) {
+        message = `### ⚠️ Cannot proceed with deployment\n\n- ref: \`${ref}\`\n\nThe branch for this pull request no longer exists. This can happen if the branch was deleted after the PR was merged or closed. If you need to deploy, you can:\n- Use the stable branch deployment (e.g., \`${data.inputs.trigger} ${data.inputs.stable_branch}\`)\n- Use an exact SHA deployment if enabled (e.g., \`${data.inputs.trigger} ${sha}\`)\n\n> If you are running this command on a closed pull request, you can also try reopening the pull request to restore the branch for a deployment.`
+        core.warning(`branch does not exist: ${ref}`)
+        return {message: message, status: false}
+      }
+      // If it's not a 404 error, it's unexpected - hard stop
+      message = `### ⚠️ Cannot proceed with deployment\n\n- ref: \`${ref}\`\n\n> An unexpected error occurred while checking if the branch exists: \`${error.message}\``
+      core.error(`unexpected error checking if branch exists: ${error.message}`)
+      return {message: message, status: false}
+    }
+  }
+
   // Always allow deployments to the "stable" branch regardless of CI checks or PR review
   if (data.environmentObj.stable_branch_used === true) {
     message = `✅ deployment to the ${COLORS.highlight}stable${COLORS.reset} branch requested`