name: Checkout

description: 'Checkout into trusted / untrusted / pinned folders consistently.'

inputs:
  merged-as-untrusted-at:
    description: "Whether and which SHA to checkout for the merge commit in the ./nixpkgs/untrusted folder."
  target-as-trusted-at:
    description: "Whether and which SHA to checkout for the target commit in the ./nixpkgs/trusted folder."
  untrusted-pin-bump:
    description: "Commit that bumps ci/pinned.json; when set, ./nixpkgs/untrusted and ./nixpkgs/untrusted-pinned are derived from this commit."

runs:
  using: composite
  steps:
    - uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
      env:
        MERGED_SHA: ${{ inputs.merged-as-untrusted-at }}
        TARGET_SHA: ${{ inputs.target-as-trusted-at }}
        PIN_BUMP_SHA: ${{ inputs.untrusted-pin-bump }}
      with:
        retries: 3
        script: |
          const { rm, writeFile } = require('node:fs/promises')
          const { spawn } = require('node:child_process')
          const { join } = require('node:path')

          async function run(cmd, ...args) {
            return new Promise((resolve, reject) => {
              const proc = spawn(cmd, args, {
                stdio: 'inherit'
              })
              proc.on('close', (code) => {
                if (code === 0) resolve()
                else reject(code)
              })
            })
          }

          // These are set automatically by the spare checkout for .github/actions.
          // Undo them, otherwise git fetch below will not do anything.
          await run('git', 'config', 'unset', 'remote.origin.promisor')
          await run('git', 'config', 'unset', 'remote.origin.partialclonefilter')

          // Getting the pinned SHA via API allows us to do one single fetch call for all commits.
          // Otherwise we would have to fetch merged/target first, read pinned, fetch again.
          // A single fetch call comes with a lot less overhead. The fetch takes essentially the
          // same time no matter whether its 1, 2 or 3 commits at once.
          async function getPinnedSha(ref) {
            if (!ref) return undefined
            const { content, encoding } = (await github.rest.repos.getContent({
              ...context.repo,
              path: 'ci/pinned.json',
              ref,
            })).data
            const pinned = JSON.parse(Buffer.from(content, encoding).toString())
            return pinned.pins.nixpkgs.revision
          }

          // Getting the pin-bump diff via the API avoids issues with `git fetch`
          // thin-packs not having enough base objects to be applied locally.
          // Returns a unified diff suitable for `git apply`.
          async function getPinBumpDiff(ref) {
            const { data } = await github.rest.repos.getCommit({
              mediaType: { format: 'diff' },
              ...context.repo,
              ref,
            })
            return data
          }

          const pin_bump_sha = process.env.PIN_BUMP_SHA

          const commits = [
            {
              sha: process.env.MERGED_SHA,
              path: 'untrusted',
            },
            {
              sha: await getPinnedSha(pin_bump_sha || process.env.MERGED_SHA),
              path: 'untrusted-pinned'
            },
            {
              sha: process.env.TARGET_SHA,
              path: 'trusted',
            },
            {
              sha: await getPinnedSha(process.env.TARGET_SHA),
              path: 'trusted-pinned'
            }
          ].filter(({ sha }) => Boolean(sha))

          console.log('Checking out the following commits:', commits)

          // Fetching all commits at once is much faster than doing multiple checkouts.
          // This would fail without --refetch, because the we had a partial clone before, but changed it above.
          await run('git', 'fetch', '--depth=1', '--refetch', 'origin', ...(commits.map(({ sha }) => sha)))

          // On Linux, checking out onto tmpfs takes 1s and is faster by at least 10x.
          // Currently, on Darwin we can only allocate 3.5GB, which isn't enough.
          // See https://github.com/NixOS/nixpkgs/pull/506437
          await run('mkdir', 'nixpkgs')
          if (process.env.RUNNER_OS === 'Linux') {
            await run('sudo', 'mount', '-t', 'tmpfs', 'tmpfs', 'nixpkgs')
          }

          // Git worktree setup can race when multiple worktrees are created and
          // initialized at the same time against one repository. See #511286.
          // Keep the setup sequential so shared repo config updates cannot contend.
          for (const { sha, path } of commits) {
            await run('git', 'worktree', 'add', join('nixpkgs', path), sha, '--no-checkout')
            await run('git', '-C', join('nixpkgs', path), 'sparse-checkout', 'disable')
            await run('git', '-C', join('nixpkgs', path), 'checkout', '--progress')
          }

          // Apply pin bump to untrusted worktree
          if (pin_bump_sha) {
            console.log('Fetching ci/pinned.json bump commit:', pin_bump_sha)
            await writeFile('pin-bump.patch', await getPinBumpDiff(pin_bump_sha))

            console.log('Applying untrusted ci/pinned.json bump to ./nixpkgs/untrusted')
            try {
              await run('git', '-C', join('nixpkgs', 'untrusted'), 'apply', '--3way', join('..', '..', 'pin-bump.patch'))
            } catch {
              core.setFailed([
                `Failed to apply ci/pinned.json bump commit ${pin_bump_sha}.`,
                `This commit does not apply cleanly onto the untrusted base ${process.env.MERGED_SHA}.`,
                `Please rebase the PR or ensure the pin bump is standalone.`
              ].join(' '))
              return
            } finally {
              await rm('pin-bump.patch')
            }
          }

          console.log('final disk usage:')
          await run('df', '-h')