A script for using gh and copilot to create PR descriptions out of their git diff

copilot-creates-pr-summary.sh

#!/usr/bin/env bash
# pr-summarise: Generate and apply a PR description using GitHub Models.
# Usage: pr-summarise [PR number]
#        If no PR number is given, uses the current branch's open PR.
#
# Required tools:
#   gh    - GitHub CLI (https://cli.github.com), authenticated via `gh auth login`
#   curl  - HTTP client, used to call the GitHub Models API
#   jq    - JSON processor (https://jqlang.org)

set -euo pipefail

# ── Config ────────────────────────────────────────────────────────────────────
MODEL="${PR_SUMMARISE_MODEL:-openai/gpt-4.1}"
MAX_DIFF_CHARS="${PR_SUMMARISE_MAX_DIFF_CHARS:-28000}"
ENDPOINT="${PR_SUMMARISE_ENDPOINT:-https://models.github.ai/inference/chat/completions}"
# For org attribution, set:
# export PR_SUMMARISE_ENDPOINT="https://models.github.ai/orgs/<ORG>/inference/chat/completions"

# ── Resolve PR number ─────────────────────────────────────────────────────────
if [[ $# -ge 1 ]]; then
  PR="$1"
else
  if ! PR=$(gh pr view --json number -q '.number' 2>/dev/null); then
    echo "Error: no PR number given and no open PR found for the current branch." >&2
    exit 1
  fi
fi

# ── Fetch existing PR description ─────────────────────────────────────────────
EXISTING_BODY=$(gh pr view "$PR" --json body -q '.body // ""')
MARKER="<!-- pr-summarise -->"

if [[ -n "$EXISTING_BODY" && "$EXISTING_BODY" != *"$MARKER"* ]]; then
  echo "PR #$PR already has a human-written description. Skipping." >&2
  echo ""
  echo "$EXISTING_BODY"
  exit 0
fi

# ── Fetch diff ────────────────────────────────────────────────────────────────
echo "Fetching diff for PR #$PR..."
FULL_DIFF=$(gh pr diff "$PR" --patch)
DIFF="${FULL_DIFF:0:$MAX_DIFF_CHARS}"

if [[ -z "$DIFF" ]]; then
  echo "Error: no diff found for PR #$PR." >&2
  exit 1
fi

# ── Call GitHub Models ────────────────────────────────────────────────────────
echo "Generating summary via GitHub Models ($MODEL)..."
RESPONSE=$(curl -sS -L "$ENDPOINT" \
  -H "Authorization: Bearer $(gh auth token)" \
  -H "Accept: application/vnd.github+json" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  -H "Content-Type: application/json" \
  -d "$(jq -n \
    --arg model "$MODEL" \
    --arg diff  "$DIFF" \
    '{
      model: $model,
      temperature: 0.2,
      max_tokens: 500,
      messages: [{
        role: "user",
        content:
          "Write a concise GitHub PR description in Markdown for this diff.\n" +
          "Format:\n" +
          "1) One short summary paragraph.\n" +
          "2) A \"## Changes\" section with bullet points.\n" +
          "3) A \"## Notes for reviewers\" section (optional, only if useful).\n" +
          "Output only Markdown, nothing else.\n\n" + $diff
      }]
    }')")

SUMMARY=$(echo "$RESPONSE" | jq -r '.choices[0].message.content')

if [[ -z "$SUMMARY" || "$SUMMARY" == "null" ]]; then
  echo "Error: empty response from GitHub Models. Raw response:" >&2
  echo "$RESPONSE" >&2
  exit 1
fi

# ── Compose final body ────────────────────────────────────────────────────────
FINAL_BODY="${SUMMARY}"$'\n\n'"${MARKER}"

# ── Review and confirm ────────────────────────────────────────────────────────
echo ""
echo "──── Generated description ────────────────────────────────────────────────"
echo "$FINAL_BODY"
echo "───────────────────────────────────────────────────────────────────────────"
echo ""
read -r -p "Apply this description to PR #$PR? [y/N] " confirm

if [[ "$confirm" =~ ^[Yy]$ ]]; then
  gh pr edit "$PR" --body "$FINAL_BODY"
  echo "PR #$PR description updated."
else
  echo "Aborted. No changes made."
fi