pr-welcome-comment.yml

# Post a welcome comment on new PRs telling the author who owns
# the docs areas they're changing (derived from .github/OWNERS).
#
# NOTE: This uses `pull_request_target` so it has write access to
# comment on PRs from forks. The script only reads OWNERS from
# the base branch and lists changed files — no untrusted code is executed.

name: PR Welcome Comment

on:
  pull_request_target:
    types: [opened, ready_for_review]

jobs:
  welcome-comment:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    # Skip draft PRs — the comment will be posted when marked ready
    if: ${{ !github.event.pull_request.draft }}

    steps:
      - name: Post welcome comment with owners
        uses: actions/github-script@v8
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const { owner, repo } = context.repo;
            const pr = context.payload.pull_request;
            const author = pr.user.login;

            // --- Fetch OWNERS from the base branch ---
            let ownersContent;
            try {
              const { data } = await github.rest.repos.getContent({
                owner, repo,
                path: '.github/OWNERS',
                ref: pr.base.ref
              });
              ownersContent = Buffer.from(data.content, 'base64').toString();
            } catch (error) {
              console.log('Could not read .github/OWNERS:', error.message);
              return;
            }

            // --- Parse OWNERS rules (CODEOWNERS syntax) ---
            const rules = [];
            for (const line of ownersContent.split('\n')) {
              const trimmed = line.trim();
              if (!trimmed || trimmed.startsWith('#')) continue;
              const parts = trimmed.split(/\s+/);
              const pattern = parts[0];
              const owners = parts.slice(1).filter(o => o.startsWith('@'));
              if (owners.length > 0) rules.push({ pattern, owners });
            }

            // Last matching rule wins (same as GitHub CODEOWNERS behavior)
            function findOwners(filepath) {
              let matched = null;
              for (const rule of rules) {
                let pat = rule.pattern.startsWith('/') ? rule.pattern.slice(1) : rule.pattern;
                let matches = false;
                if (pat === '*') {
                  matches = true;
                } else if (pat.endsWith('/')) {
                  matches = filepath.startsWith(pat);
                } else if (pat.includes('*')) {
                  const re = new RegExp(
                    '^' + pat.replace(/[.+?^${}()|[\]\\]/g, '\\$&').replace(/\*/g, '.*')
                  );
                  matches = re.test(filepath);
                } else {
                  matches = filepath === pat;
                }
                if (matches) matched = rule;
              }
              return matched ? matched.owners : [];
            }

            // --- Map file paths to human-readable product names ---
            function getProductName(filepath) {
              const map = [
                ['src/langsmith/fleet/', 'LangSmith Fleet'],
                ['src/langsmith/', 'LangSmith'],
                ['src/oss/deepagents/', 'Deep Agents'],
                ['src/oss/langgraph/', 'LangGraph'],
                ['src/oss/langchain/', 'LangChain'],
                ['src/oss/python/integrations/', 'Python integrations'],
                ['src/oss/javascript/integrations/', 'JavaScript integrations'],
                ['src/oss/', 'open source'],
              ];
              for (const [prefix, name] of map) {
                if (filepath.startsWith(prefix)) return name;
              }
              return null;
            }

            // --- Get changed files ---
            const files = await github.paginate(github.rest.pulls.listFiles, {
              owner, repo, pull_number: pr.number, per_page: 100
            });

            // --- Group by product, merging owners across files ---
            const productOwners = new Map();
            let authorIsOwner = false;
            for (const file of files) {
              const owners = findOwners(file.filename);
              const ownerNames = owners.map(o => o.replace(/^@/, ''));

              if (ownerNames.some(o => o.toLowerCase() === author.toLowerCase())) {
                authorIsOwner = true;
              }

              const product = getProductName(file.filename);
              if (!product || owners.length === 0) continue;

              // Skip areas where the author is already an owner
              if (ownerNames.some(o => o.toLowerCase() === author.toLowerCase())) continue;

              if (!productOwners.has(product)) {
                productOwners.set(product, new Set());
              }
              for (const o of ownerNames) {
                productOwners.get(product).add(o);
              }
            }

            if (productOwners.size === 0) {
              // Skip fallback if author owns any of the changed files
              if (authorIsOwner || author.toLowerCase() === 'lnhsingh') return;
              productOwners.set('General changes', new Set(['lnhsingh']));
            }

            // --- Format the comment ---
            function formatOwners(ownerSet) {
              const mentions = [...ownerSet].map(o => `\`@${o}\``);
              if (mentions.length === 1) return mentions[0];
              if (mentions.length === 2) return `${mentions[0]} or ${mentions[1]}`;
              return mentions.slice(0, -1).join(', ') + `, or ${mentions[mentions.length - 1]}`;
            }

            const areas = [...productOwners.entries()];
            const lines = areas.map(([product, owners]) =>
              `- ${formatOwners(owners)} (${product})`
            );
            const body = [
              `Thanks for opening a docs PR, @${author}! When it's ready for review, please add the relevant reviewers:\n`,
              lines.join('\n')
            ].join('\n');

            await github.rest.issues.createComment({
              owner, repo,
              issue_number: pr.number,
              body
            });

            console.log(`Posted welcome comment on PR #${pr.number}`);