Auto codespace reviews (#54675)

2025-12-19 18:10:59 -05:00 · 2025-03-05 10:14:17 -08:00
parent 70f09d91d0
commit 2b462c8894
5 changed files with 481 additions and 23 deletions
--- a/.github/workflows/codespace-review-check.yml
+++ b/.github/workflows/codespace-review-check.yml
@@ -0,0 +1,126 @@
+name: Codespace review - Check
+
+# **What it does**: Check on a regular basis for if a codespace is about to shut down, and comment on the pull request.
+# **Why we have it**: We want to notify contributors when their codespace is about to shut down.
+# **Who does it impact**: Contributors who open a pull request.
+
+on:
+  schedule:
+    - cron: '20,35,50,5 * * * *' # Check every 15 minutes, without hitting the top of the hour
+  pull_request:
+    paths:
+      - '.github/workflows/codespace-review-check.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  codespace-review-check-find:
+    runs-on: ubuntu-latest
+    if: ${{ github.repository == 'github/docs-internal' }}
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+
+      - name: Check codespaces
+        id: set-matrix
+        env:
+          GH_TOKEN: ${{ secrets.DOCS_BOT_PAT_CODESPACE }}
+          LOGIN: docs-bot
+          REPO: github/docs-internal
+        run: |
+          ago=$(date -d '225 minutes ago' -Iseconds)
+          echo "- Ago: $ago"
+          # on mac: date -v-225M -Iseconds
+          #   -v-225M means 225 minutes ago, 4 * 60 - 15 = 225
+          # -Iseconds means ISO 8601 format, to seconds
+          branches=$(
+            gh codespace list \
+              --repo "$REPO" \
+              --limit 1000 \
+              --json name,owner,lastUsedAt,gitStatus \
+              --jq ".[] | select(.owner == \"$LOGIN\" and .lastUsedAt < \"$ago\") | .gitStatus.ref" \
+          )
+          echo "- Branches:"
+          echo "$(echo "$branches" | sed 's/^/    /')"
+          count=$(echo "$branches" | sed '/^\s*$/d' | wc -l)
+          echo "- Count: $count"
+
+          if [[ $count -gt 0 ]]
+          then
+            echo "Codespaces found that are idle or soon to idle"
+          else
+            echo "Codespaces not found, exiting..."
+            exit 0
+          fi
+
+          # https://stackoverflow.com/a/70716837
+          # This might not need `| sed 's/"/\\"/g'`
+          matrix=$(echo "$branches" | jq -scR 'split("\n") | map(select(. != ""))' | sed 's/"/\\"/g')
+          echo "- Matrix: $matrix"
+          echo "matrix=$matrix" >> $GITHUB_OUTPUT
+
+      - uses: ./.github/actions/slack-alert
+        if: ${{ failure() && github.event_name != 'workflow_dispatch' }}
+        with:
+          slack_channel_id: ${{ secrets.DOCS_ALERTS_SLACK_CHANNEL_ID }}
+          slack_token: ${{ secrets.SLACK_DOCS_BOT_TOKEN }}
+
+  codespace-review-check-comment:
+    needs:
+      - codespace-review-check-find
+    strategy:
+      matrix:
+        value: ${{ fromJSON(needs.codespace-review-check-find.outputs.matrix) }}
+    runs-on: ubuntu-latest
+    if: ${{ github.repository == 'github/docs-internal' }}
+    env:
+      repo: github/docs-internal
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+
+      - name: Find the pull request
+        id: findPr
+        run: |
+          echo "Looking up pull request"
+          echo "- Branch: ${{ matrix.value }}"
+          number=$(gh pr view "${{ matrix.value }}" --json number --jq '.number')
+          echo "- Number: $number"
+          echo "pr-number=$number" >> $GITHUB_OUTPUT
+
+      - name: Find code changes comment
+        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e
+        id: findComment
+        with:
+          issue-number: ${{ steps.findPr.outputs.pr-number }}
+          comment-author: 'github-actions[bot]'
+          body-includes: '<!-- AUTO_CODESPACE -->'
+
+      - name: Update comment
+        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043
+        with:
+          comment-id: ${{ steps.findComment.outputs.comment-id }}
+          issue-number: ${{ steps.findPr.outputs.pr-number }}
+          edit-mode: replace
+          body: |
+            <!-- AUTO_CODESPACE -->
+
+            ### Review this PR in a codespace 📦
+
+            Your codespace is no longer active.
+            You’ve reached the 4 hour limit.
+            In order to reactivate your codespace, please update your pull request by adding the https://github.com/${{ env.REPO }}/labels/extend-codespace label.
+            If the label is already applied, you can remove and reapply the label to reactivate your codespace.
+
+            🤖 This comment is [automatically generated][workflow].
+
+            [workflow]: ${{ github.server_url }}/${{ github.repository }}/blob/${{ github.sha }}/.github/workflows/codespace-review-check.yml
+
+      - uses: ./.github/actions/slack-alert
+        if: ${{ failure() && github.event_name != 'workflow_dispatch' }}
+        with:
+          slack_channel_id: ${{ secrets.DOCS_ALERTS_SLACK_CHANNEL_ID }}
+          slack_token: ${{ secrets.SLACK_DOCS_BOT_TOKEN }}
--- a/.github/workflows/codespace-review-down.yml
+++ b/.github/workflows/codespace-review-down.yml
@@ -0,0 +1,84 @@
+name: Codespace review - Down
+
+# **What it does**: When closing or merging a pull request, if there are any associated codespaces, to shut them down.
+# **Why we have it**: To conserve resources.
+# **Who does it impact**: Contributors who open a pull request.
+
+on:
+  pull_request:
+    types:
+      - closed
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  codespace-review-down:
+    runs-on: ubuntu-latest
+    if: ${{ github.repository == 'github/docs-internal' }}
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+      - name: Delete codespace
+        env:
+          GH_TOKEN: ${{ secrets.DOCS_BOT_PAT_CODESPACE }}
+          BRANCH_NAME: ${{ github.head_ref || github.ref_name }}
+          LOGIN: docs-bot
+          REPO: github/docs-internal
+        run: |
+          echo "Checking if there's codespaces for this PR..."
+          names=$( \
+            gh codespace list \
+              --repo "$REPO" \
+              --limit 1000 \
+              --json "name,gitStatus,owner" \
+              --jq ".[] | select(.owner == \"$LOGIN\" and .gitStatus.ref == \"$BRANCH_NAME\") | .name" \
+          )
+          echo "- Names:"
+          echo "$(echo "$names" | sed 's/^/    /')"
+          count=$(echo "$names" | sed '/^\s*$/d' | wc -l)
+          echo "- Count: $count"
+
+          if [[ $count -gt 0 ]]
+          then
+            echo "Codespaces found for this PR"
+          else
+            echo "Codespaces not found, exiting..."
+            exit 0
+          fi
+
+          echo "Shutting down the codespaces..."
+          echo "$names" | while read -r name
+          do
+            echo "Deleting $name..."
+            gh codespace delete --codespace "$name"
+            echo "Deleted $name"
+          done
+          echo "Shut down the codespaces"
+
+      - name: Find code changes comment
+        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e
+        id: findComment
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          comment-author: 'github-actions[bot]'
+          body-includes: '<!-- AUTO_CODESPACE -->'
+
+      - name: Update comment
+        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043
+        if: ${{ steps.findComment.outputs.comment-id }} # only update if it exists
+        with:
+          comment-id: ${{ steps.findComment.outputs.comment-id }}
+          issue-number: ${{ github.event.pull_request.number }}
+          edit-mode: replace
+          body: |
+            <!-- AUTO_CODESPACE -->
+
+            ### Review this PR in a codespace 📦
+
+            Your pull request is now merged or closed, so I've removed all automatically created codespaces.
+
+            🤖 This comment is [automatically generated][workflow].
+
+            [workflow]: ${{ github.server_url }}/${{ github.repository }}/blob/${{ github.sha }}/.github/workflows/codespace-review-down.yml
--- a/.github/workflows/codespace-review-up.yml
+++ b/.github/workflows/codespace-review-up.yml
@@ -0,0 +1,233 @@
+name: Codespace review - Up
+
+# **What it does**: On opening or updating a pull request, creates a new codespace to review changes and comments to the user with next steps. Or it will rebuild the codespace if it already exists and is idle.
+# **Why we have it**: We want to provide contributors with a way to review their changes in a codespace before merging.
+# **Who does it impact**: Contributors who open a pull request.
+
+on:
+  pull_request:
+    types:
+      - assigned
+      - unassigned
+      - labeled
+      - unlabeled
+      - opened
+      - edited
+      # - closed
+      - reopened
+      - synchronize
+      - converted_to_draft
+      - ready_for_review
+      # - locked
+      # - unlocked
+      # - milestoned
+      # - demilestoned
+      - review_requested
+      - review_request_removed
+      # - auto_merge_enabled
+      - auto_merge_disabled
+      # - enqueued
+      - dequeued
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  codespace-review-up:
+    runs-on: ubuntu-latest
+    if: >-
+      ${{ github.repository == 'github/docs-internal'
+          && contains( github.event.pull_request.labels.*.name, 'auto-codespace') }}
+    env:
+      GH_TOKEN: ${{ secrets.DOCS_BOT_PAT_CODESPACE }}
+      BRANCH_NAME: ${{ github.head_ref || github.ref_name }}
+      LOGIN: docs-bot
+      REPO: github/docs-internal
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+
+      - name: Check for existing codespace
+        id: check-codespace
+        run: |
+          echo "Checking if there's already a codespace for this pull request..."
+          names=$( \
+            gh codespace list \
+              --repo "$REPO" \
+              --limit 1000 \
+              --json "name,gitStatus,owner" \
+              --jq ".[] | select(.owner == \"$LOGIN\" and .gitStatus.ref == \"$BRANCH_NAME\") | .name" \
+          )
+          echo "- Names:"
+          echo "$(echo "$names" | sed 's/^/    /')"
+          count=$(echo "$names" | sed '/^\s*$/d' | wc -l)
+          echo "- Count: $count"
+          if [[ $count -gt 0 ]]
+          then
+            echo "Codespace found for this pull request"
+            echo "has-codespace=yes" >> $GITHUB_OUTPUT
+          else
+            echo "Codespace not found for this pull request"
+            echo "has-codespace=no" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Clean up old codespaces if needed
+        if: ${{ steps.check-codespace.outputs.has-codespace == 'no' }}
+        run: |
+          echo "Checking if there are more than 95 codespaces..."
+          spaces=$( \
+            gh codespace list \
+              --repo "$REPO" \
+              --limit 1000 \
+              --json "name,lastUsedAt,gitStatus,owner" \
+              --jq "sort_by(.lastUsedAt) | reverse | .[] | select(.owner == \"$LOGIN\") | [.name,.gitStatus.ref] | @tsv" \
+          )
+          echo "- Spaces:"
+          echo "$(echo "$spaces" | sed 's/^/    /')"
+          count=$(echo "$spaces" | sed '/^\s*$/d' | wc -l)
+          echo "- Count: $count"
+
+          if [[ $count -gt 95 ]]
+          then
+            tocut=$((count - 95))
+            echo "$count codespaces found. Deleting the oldest $tocut..."
+            oldest=$(echo "$spaces" | tail -n $tocut)
+            echo "- Oldest:"
+            echo "$(echo "$oldest" | sed 's/^/    /')"
+            echo "$oldest" | while read -r name branch
+            do
+              echo "Deleting $name..."
+              gh codespace delete --codespace "$name"
+              echo "Deleted $name"
+
+              echo "Commenting on branch $branch"
+              # We could move this to a matrix and update the AUTO_CODESPACE comment instead
+              # but that's significantly more code for a scenario I'm not sure will actually happen
+              gh pr comment \
+                "$branch" \
+                --repo "$REPO" \
+                --body "Thank you for your pull request. I deleted the oldest codespaces to make room for a new one. You can make a new codespace by updating your pull request or closing and reopening your pull request."
+              echo "Commented on branch $branch"
+            done
+            echo "Deleted the oldest $tocut codespaces"
+          else
+            echo "$count codespaces found. No deletes needed."
+          fi
+
+      - name: Create a new codespace
+        if: ${{ steps.check-codespace.outputs.has-codespace == 'no' }}
+        run: |
+          echo "Creating a new codespace..."
+          # Machine types: gh api /repos/github/docs-internal/codespaces/machines
+          name=$( \
+            gh codespace create \
+              --repo "$REPO" \
+              --branch "$BRANCH_NAME" \
+              --idle-timeout "4h" \
+              --retention-period "720h" \
+              --default-permissions \
+              --machine "standardLinux32gb" \
+          )
+          echo "- Name: $name"
+          echo "Created a new codespace"
+
+          echo "Updating port visibility..."
+          gh codespace ports visibility \
+            --codespace "$name" \
+            4000:public
+          echo "Updated port visibility"
+
+          echo "APP_URL=https://$name-4000.app.github.dev" >> $GITHUB_ENV
+
+      - name: Rebuild existing codespace
+        if: ${{ steps.check-codespace.outputs.has-codespace == 'yes' }}
+        run: |
+          echo "Checking if the codespace is in idle mode..."
+          spaces=$( \
+            gh codespace list \
+              --repo "$REPO" \
+              --limit 1000 \
+              --json "name,gitStatus,owner,state" \
+              --jq ".[] | select(.owner == \"$LOGIN\" and .gitStatus.ref == \"$BRANCH_NAME\") | [.name,.state] | @tsv" \
+          )
+          echo "- Spaces:"
+          echo "$(echo "$spaces" | sed 's/^/    /')"
+          echo "$spaces" | while read -r name state
+          do
+            echo "Codespace $name is in state $state"
+            if [[ $state == "Shutdown" ]]
+            then
+              echo "Codespace $name is in idle mode"
+              echo "Rebuilding the codespace to kick it out of idle mode..."
+              gh codespace rebuild --codespace "$name"
+              echo "Rebuilt the codespace to kick it out of idle mode"
+
+              echo "Updating port visibility..."
+              gh codespace ports visibility \
+                --codespace "$name" \
+                4000:public
+              echo "Updated port visibility"
+            else
+              echo "Codespace $name is active"
+            fi
+            echo "APP_URL=https://$name-4000.app.github.dev" >> $GITHUB_ENV
+          done
+
+      - uses: ./.github/actions/node-npm-setup
+
+      - name: Get changes table
+        id: changes
+        timeout-minutes: 30
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+          APP_URL: ${{ env.APP_URL }}
+        run: npm run content-changes-table-comment
+
+      - name: Find code changes comment
+        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e
+        id: findComment
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          comment-author: 'github-actions[bot]'
+          body-includes: '<!-- AUTO_CODESPACE -->'
+
+      - name: Update comment
+        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043
+        with:
+          comment-id: ${{ steps.findComment.outputs.comment-id }}
+          issue-number: ${{ github.event.pull_request.number }}
+          edit-mode: replace
+          body: |
+            <!-- AUTO_CODESPACE -->
+
+            ### Review this PR in a codespace 📦
+
+            Your codespace will be ready in two to three minutes and you can review changes at:
+            ${{ env.APP_URL }}
+            Your codespace will be automatically deleted once your pull request is closed or merged.
+
+            #### Your codespace will idle after 4 hours of inactivity
+
+            After 4 hours, you can reactivate your codespace by applying the https://github.com/${{ env.REPO }}/labels/extend-codespace label to the pull request.
+            If the label is already applied, you can remove and reapply the label to reactivate your codespace.
+
+            #### Maximum of 100 _active_ codespaces per user
+
+            Your codespace may be deleted if the limit is reached.
+
+            <details><summary>Table of review links</summary>
+
+            ${{ steps.changes.outputs.changesTable && 'The table shows the files in the `content` directory that were changed in this pull request. This helps you review your changes on the review server. Changes to the `data` directory are not included in this table.' || '' }}
+
+            ${{ steps.changes.outputs.changesTable || '_This pull request contains code changes, so we will not generate a table of review links._' }}
+
+            ${{ steps.changes.outputs.changesTable && 'Key: **fpt**: Free, Pro, Team; **ghec**: GitHub Enterprise Cloud; **ghes**: GitHub Enterprise Server' || '' }}
+
+            </details>
+
+            🤖 This comment is [automatically generated][workflow].
+
+            [workflow]: ${{ github.server_url }}/${{ github.repository }}/blob/${{ github.sha }}/.github/workflows/codespace-review-up.yml
--- a/.github/workflows/review-comment.yml
+++ b/.github/workflows/review-comment.yml
@@ -26,7 +26,7 @@ permissions:

 # This allows a subsequently queued workflow run to interrupt previous runs
 concurrency:
-  group: '${{ github.workflow }} @ ${{ github.event.pull_request.head.label || github.head_ref || github.ref }}'
+  group: '${{ github.workflow }} @ ${{ github.event.pull_request.head.label || github.head_ref || github.ref }} x ${{ github.event_name }}'
  cancel-in-progress: true

 jobs:
@@ -60,6 +60,7 @@ jobs:
        timeout-minutes: 30
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          REVIEW_SERVER: o
          REVIEW_SERVER_ACCESS_TOKEN: ${{ secrets.REVIEW_SERVER_ACCESS_TOKEN }}
          APP_URL: ${{ env.APP_URL }}
          BASE_SHA: ${{ github.event.pull_request.base.sha }}
@@ -71,7 +72,7 @@ jobs:
        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043
        with:
          comment-id: ${{ steps.findComment.outputs.comment-id }}
-          issue-number: ${{ github.event.pull_request.number || inputs.PR_NUMBER }}
+          issue-number: ${{ github.event.pull_request.number }}
          edit-mode: replace
          body: |
            <!-- REVIEW_COMMENT -->
@@ -83,10 +84,7 @@ jobs:
            * [Set up a local development environment][local]
            ${{ github.repository == 'github/docs-internal' && '* Message `#docs-engineering` on Slack for a staging server.' || '' }}

-            [codespace]: ${{ github.repository == 'github/docs' && 'https://docs.github.com/en/contributing/setting-up-your-environment-to-work-on-github-docs/working-on-github-docs-in-a-codespace' || 'https://github.com/github/docs-team/blob/main/contributing-to-docs/use-a-codespace-to-review.md' }}
-            [local]: https://docs.github.com/en/contributing/setting-up-your-environment-to-work-on-github-docs/creating-a-local-environment#setting-up-your-local-environment
-
-            ${{ github.repository == 'github/docs' && 'A Hubber will need to deploy your changes internally to review.' || '' }}
+            ${{ fromJSON('["A Hubber will need to deploy your changes internally to review.",""]')[github.repository == 'github/docs-internal'] }}

            <details><summary>Table of review links</summary>

@@ -100,4 +98,8 @@ jobs:

            </details>

-            🤖 This comment is [automatically generated](https://github.com/${{ github.repository }}/blob/${{ github.sha }}/.github/workflows/review-comment.yml).
+            🤖 This comment is [automatically generated][workflow].
+
+            [workflow]: ${{ github.server_url }}/${{ github.repository }}/blob/${{ github.sha }}/.github/workflows/review-comment.yml
+            [codespace]: ${{ github.repository == 'github/docs-internal' && 'https://github.com/github/docs-team/blob/main/contributing-to-docs/use-a-codespace-to-review.md' || 'https://docs.github.com/en/contributing/setting-up-your-environment-to-work-on-github-docs/working-on-github-docs-in-a-codespace' }}
+            [local]: https://docs.github.com/en/contributing/setting-up-your-environment-to-work-on-github-docs/creating-a-local-environment#setting-up-your-local-environment
--- a/src/workflows/content-changes-table-comment.ts
+++ b/src/workflows/content-changes-table-comment.ts
@@ -24,7 +24,15 @@ import { allVersionShortnames } from '@/versions/lib/all-versions.js'
 import readFrontmatter from '@/frame/lib/read-frontmatter.js'
 import { inLiquid } from './lib/in-liquid'

-const { GITHUB_TOKEN, REVIEW_SERVER_ACCESS_TOKEN, APP_URL } = process.env
+const {
+  GITHUB_TOKEN,
+  REVIEW_SERVER,
+  REVIEW_SERVER_ACCESS_TOKEN,
+  APP_URL,
+  HEAD_BRANCH,
+  BASE_SHA,
+  HEAD_SHA,
+} = process.env
 const context = github.context

 // the max size of the comment (in bytes)
@@ -46,8 +54,8 @@ if (import.meta.url.endsWith(process.argv[1])) {
  const baseOwner = context.payload.pull_request!.base.repo.owner.login
  const baseRepo = context.payload.pull_request!.base.repo.name

-  const baseSHA = process.env.BASE_SHA || context.payload.pull_request!.base.sha
-  const headSHA = process.env.HEAD_SHA || context.payload.pull_request!.head.sha
+  const baseSHA = BASE_SHA || context.payload.pull_request!.base.sha
+  const headSHA = HEAD_SHA || context.payload.pull_request!.head.sha

  const markdownTable = await main(baseOwner, baseRepo, baseSHA, headSHA, {
    isFork,
@@ -70,7 +78,6 @@ async function main(
  if (!APP_URL) {
    throw new Error(`APP_URL environment variable not set`)
  }
-  const headBranch = process.env.HEAD_BRANCH

  const RetryingOctokit = Octokit.plugin(retry)
  const octokit = new RetryingOctokit({
@@ -78,21 +85,27 @@ async function main(
  })

  // we'll attach the branch or sha right after this
-  const searchParams = new URLSearchParams({
-    'review-server-repository': isFork ? `${headOwner}/${headRepo}` : `${owner}/${repo}`,
-  })
+  let queryParams = ''
+  if (REVIEW_SERVER) {
+    const searchParams = new URLSearchParams({
+      'review-server-repository': isFork ? `${headOwner}/${headRepo}` : `${owner}/${repo}`,
+    })

-  // this token will be available in the internal repo only, skip it for the open source repo
-  if (REVIEW_SERVER_ACCESS_TOKEN)
-    searchParams.append('review-server-access-token', REVIEW_SERVER_ACCESS_TOKEN)
+    // this token will be available in the internal repo only, skip it for the open source repo
+    if (REVIEW_SERVER_ACCESS_TOKEN) {
+      searchParams.append('review-server-access-token', REVIEW_SERVER_ACCESS_TOKEN)
+    }

-  // this script compares with SHAs only, so this allows us
-  // to surface the branch name for the review server bar
-  headBranch
-    ? searchParams.append('review-server-branch', headBranch)
-    : searchParams.append('review-server-sha', headSHA)
+    // this script compares with SHAs only, so this allows us
+    // to surface the branch name for the review server bar
+    if (HEAD_BRANCH) {
+      searchParams.append('review-server-branch', HEAD_BRANCH)
+    } else if (headSHA) {
+      searchParams.append('review-server-sha', headSHA)
+    }

-  const queryParams = `?${searchParams.toString()}`
+    queryParams = `?${searchParams.toString()}`
+  }

  // get the list of file changes from the PR
  // this works even if the head commit is from a fork