Make PRs against the RFC branch do automatic renders (#5)

* Automatic nixpkgs formatting branch

* Exit on failure

* Make nixpkgs format run on all pull requests

---------

Co-authored-by: piegames <git@piegames.de>

.github/workflows/main.yml

@@ -0,0 +1,18 @@
+on: pull_request
+
+concurrency:
+  group: ${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  format_nixpkgs:
+    name: Format Nixpkgs
+    runs-on: ubuntu-latest
+    steps: 
+    - uses: actions/checkout@v3.5.2
+    - uses: cachix/install-nix-action@v20
+    - run: |
+        ./sync-pr.sh \
+          https://github.com/${{ github.repository }} \
+          ${{ github.event.pull_request.number }} \
+          https://${{ secrets.NIXPKGS_GITHUB_TOKEN }}@github.com/${{ github.repository_owner }}/nixpkgs \

sync-pr.sh

@@ -0,0 +1,241 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+tmp=$(mktemp -d)
+cd "$tmp"
+trap 'rm -rf "$tmp"' exit
+
+bodyForCommit() {
+  local index=$1
+  local commit=$2
+  if (( index == 0 )); then
+    subject=$(git -C nixfmt show -s --format=%s "$commit")
+    url="$nixfmtUrl"/commit/"$commit"
+    echo -e "base: $subject\n\nFormat using the base commit from nixfmt PR $nixfmtPrNumber: $url"
+  else
+    commit=$(git -C nixfmt show -s --pretty=%s "$commit")
+    subject=$(git -C nixfmt show -s --format=%s "$commit")
+    url="$nixfmtUrl"/pull/"$nixfmtPrNumber"/commits/"$commit"
+    echo -e "$index: $subject\n\nFormat using commit number $index from nixfmt PR $nixfmtPrNumber: $url"
+  fi
+}
+
+step() {
+  echo -e "\e[34m$1\e[0m"
+}
+
+isLinear() {
+  local repo=$1
+  local revs=$2
+  for mergeCommit in $(git 2>/dev/null -C "$repo" log --pretty=format:%H --min-parents=2 "$revs"); do
+    return 1
+  done
+}
+
+
+nixfmtUrl=$1
+nixfmtPrNumber=$2
+nixpkgsMirrorUrl=$3
+
+nixpkgsUpstreamUrl=https://github.com/NixOS/nixpkgs
+nixpkgsMirrorBranch=nixfmt-$nixfmtPrNumber
+
+step "Fetching nixfmt pull request and creating a branch for the head commit"
+git init nixfmt
+git -C nixfmt fetch "$nixfmtUrl" "refs/pull/$nixfmtPrNumber/merge"
+nixfmtBaseCommit=$(git -C nixfmt rev-parse FETCH_HEAD^1)
+nixfmtHeadCommit=$(git -C nixfmt rev-parse FETCH_HEAD^2)
+git -C nixfmt switch -c main "$nixfmtHeadCommit"
+
+step "Linearising nixfmt history after the base commit"
+# https://stackoverflow.com/a/17994534
+FILTER_BRANCH_SQUELCH_WARNING=1 git -C nixfmt filter-branch --parent-filter 'cut -f 2,3 -d " "' --msg-filter 'echo $GIT_COMMIT' "$nixfmtBaseCommit"..main
+
+nixfmtCommitCount=$(git -C nixfmt rev-list --count "$nixfmtBaseCommit"..main)
+if (( nixfmtCommitCount == 0 )); then
+  step "No commits, deleting the nixpkgs branch $nixpkgsPushBranch if it exists"
+  # git push requires a repository to work at all, _any_ repository
+  git init -q trash
+  git -C trash push "$nixpkgsPushRepository" :refs/heads/"$nixpkgsPushBranch"
+  rm -rf trash
+  exit 0
+else
+  echo "There are $nixfmtCommitCount linearised commits"
+fi
+
+commitsToMirror=("$nixfmtBaseCommit")
+readarray -t -O 1 commitsToMirror < <(git -C nixfmt rev-list --reverse "$nixfmtBaseCommit"..main)
+
+step "Fetching upstream Nixpkgs commit history"
+git init --bare nixpkgs.git
+
+git -C nixpkgs.git remote add upstream "$nixpkgsUpstreamUrl"
+git -C nixpkgs.git config remote.upstream.promisor true
+git -C nixpkgs.git config remote.upstream.partialclonefilter tree:0
+
+git -C nixpkgs.git fetch --no-tags upstream HEAD:master
+
+step "Finding the last Nixpkgs commit before the first commit on nixfmt's branch"
+nixfmtFirstCommit=${commitsToMirror[1]}
+# Commit date, not author date, not sure what's better
+nixfmtFirstCommitDateEpoch=$(git -C nixfmt log -1 --format=%ct "$nixfmtFirstCommit")
+nixfmtFirstCommitDateHuman=$(git -C nixfmt log -1 --format=%ci "$nixfmtFirstCommit")
+echo "The first nixfmt commit is $nixfmtFirstCommit on $nixfmtFirstCommitDateHuman"
+
+nixpkgsBaseCommit=$(git -C nixpkgs.git rev-list -1 master --before="$nixfmtFirstCommitDateEpoch")
+nixpkgsBaseCommitDateHuman=$(git -C nixpkgs.git log -1 --format=%ci "$nixpkgsBaseCommit")
+
+echo "The last Nixpkgs commit before then is $nixpkgsBaseCommit on $nixpkgsBaseCommitDateHuman, which will be used as the Nixpkgs base commit"
+
+step "Fetching mirror Nixpkgs commit history in branch $nixpkgsMirrorBranch if it exists"
+git -C nixpkgs.git remote add mirror "$nixpkgsMirrorUrl"
+git -C nixpkgs.git config remote.mirror.promisor true
+git -C nixpkgs.git config remote.mirror.partialclonefilter tree:0
+
+# After this:
+# - $startingCommit should be the nixpkgs commit that the branch should be reset to
+# - $extraCommits should be the number of commits already processed
+if ! git -C nixpkgs.git fetch --no-tags mirror "$nixpkgsMirrorBranch":mirrorBranch; then
+  echo "There is not"
+  startingCommit=$nixpkgsBaseCommit
+  extraCommits=0
+else
+  echo "There is, it points to $(git -C nixpkgs.git rev-parse mirrorBranch)"
+  step "Checking to which extent work from the existing branch can be reused"
+  if [[ -z "$(git -C nixpkgs.git branch --contains="$nixpkgsBaseCommit" mirrorBranch)" ]]; then
+    echo "It is not"
+    startingCommit=$nixpkgsBaseCommit
+    extraCommits=0
+  else
+    echo "It is!"
+    echo "Checking if the branch has a linear history"
+    if ! isLinear nixpkgs.git "$nixpkgsBaseCommit"..mirrorBranch; then
+      echo "It is not linear, resetting the branch"
+      startingCommit=$nixpkgsBaseCommit
+      extraCommits=0
+    else
+      echo "It is linear!"
+      nixpkgsCount=$(git -C nixpkgs.git rev-list --count "$nixpkgsBaseCommit"..mirrorBranch)
+      echo "There's $nixpkgsCount commits in the branch on top of the base commit"
+      extraCommits=0
+      # Check if there's at least 1 commits in nixpkgs and at least 0 commits in nixfmt
+      # Check if commit 1 in nixpkgs corresponds to commit 0 in nixfmt
+      # If true, increase extraCommits by one, otherwise break
+      # Check if there's at least 2 commits in nixpkgs and at least 1 commits in nixfmt
+      # If so, check if commit 2 in nixpkgs corresponds to commit 1 in nixfmt
+      # ...
+      while
+        if (( nixpkgsCount >= extraCommits + 1 && nixfmtCommitCount >= extraCommits)); then
+          echo "Checking whether commit with index $(( extraCommits + 1 )) in nixpkgs corresponds to commit with index $extraCommits in nixfmt"
+          nixpkgsCommit=$(git -C nixpkgs.git rev-parse "mirrorBranch~$((nixpkgsCount - (extraCommits + 1)))")
+          body=$(git -C nixpkgs.git log -1 "$nixpkgsCommit" --pretty=%B)
+          nixfmtCommit=${commitsToMirror[$extraCommits]}
+          expectedBody=$(bodyForCommit "$extraCommits" "$nixfmtCommit")
+          if [[ "$body" == "$expectedBody" ]]; then
+            echo "It does!"
+          else
+            echo "It does not, body of nixpkgs commit $nixpkgsCommit is"
+            echo "$body"
+            echo "But expected body is"
+            echo "$expectedBody"
+            false
+          fi
+        else
+          false
+        fi
+      do
+        extraCommits=$(( extraCommits + 1 ))
+      done
+
+      nixpkgsCommit=$(git -C nixpkgs.git rev-parse "mirrorBranch~$(( nixpkgsCount - extraCommits ))")
+      startingCommit="$nixpkgsCommit"
+    fi
+  fi
+fi
+
+echo "Starting commit is $startingCommit, extraCommits is $extraCommits"
+
+step "Fetching contents of Nixpkgs base commit $nixpkgsBaseCommit"
+git init nixpkgs
+git -C nixpkgs fetch --no-tags --depth 1 "$nixpkgsUpstreamUrl" "$nixpkgsBaseCommit":base
+
+step "Fetching contents of the starting commit and updating the mirror branch"
+if (( extraCommits == 0 )); then
+  git -C nixpkgs switch -c mirrorBranch "$startingCommit"
+else
+  git -C nixpkgs fetch --no-tags --depth 1 "$nixpkgsMirrorUrl" "$startingCommit":mirrorBranch
+  git -C nixpkgs switch mirrorBranch
+fi
+
+git -C nixpkgs push --force "$nixpkgsMirrorUrl" mirrorBranch:"$nixpkgsMirrorBranch"
+
+if (( extraCommits == 0 )); then
+  index=0
+else
+  index=$(( extraCommits - 1 ))
+fi
+
+if (( index == nixfmtCommitCount )); then
+  echo "Nothing to do"
+  exit 0
+fi
+
+git -C nixpkgs config user.name "GitHub Actions"
+git -C nixpkgs config user.email "actions@users.noreply.github.com"
+
+updateToIndex() {
+  nixfmtCommit=${commitsToMirror[$index]}
+
+  step "Checking out nixfmt at $nixfmtCommit"
+  git -C nixfmt checkout -q "$nixfmtCommit"
+
+  step "Building nixfmt"
+  nix build ./nixfmt
+}
+
+applyNixfmt() {
+  step "Checking out Nixpkgs at the base commit"
+  git -C nixpkgs checkout "$nixpkgsBaseCommit" -- .
+
+  step "Running nixfmt on nixpkgs"
+  if ! xargs -r -0 -P"$(nproc)" -n1 -a <(find nixpkgs -type f -name '*.nix' -print0) result/bin/nixfmt; then
+    echo -e "\e[31mFailed to run nixfmt on some files\e[0m"
+    exit 1
+  fi
+}
+
+commitResult() {
+  step "Committing the formatted result"
+  git -C nixpkgs add -A
+  git -C nixpkgs commit --allow-empty -m "$(bodyForCommit "$index" "$nixfmtCommit")"
+
+  step "Pushing result"
+  git -C nixpkgs push "$nixpkgsMirrorUrl" mirrorBranch:"$nixpkgsMirrorBranch"
+}
+
+
+updateToIndex
+
+appliedNixfmtPath=$(realpath result)
+
+if (( extraCommits == 0 )); then
+  applyNixfmt
+  commitResult
+fi
+
+while (( index != nixfmtCommitCount )); do
+  index=$(( index + 1 ))
+
+  updateToIndex
+
+  step "Formatting nixpkgs"
+  if [[ "$appliedNixfmtPath" != "$(realpath result)" ]]; then
+    applyNixfmt
+    commitResult
+    appliedNixfmtPath=$(realpath result)
+  else
+    echo "The nixfmt store path didn't change, saving ourselves a formatting"
+    commitResult
+  fi
+done