pr-pull: implement autosquash option

Library/Homebrew/dev-cmd/pr-pull.rb

@@ -31,6 +31,9 @@ module Homebrew
       switch "--keep-old",
              description: "If the formula specifies a rebuild version, " \
                           "attempt to preserve its value in the generated DSL."
+      switch "--autosquash",
+             description: "Automatically reformat and reword commits in the pull request to our "\
+                          "preferred format."
       switch "--branch-okay",
              description: "Do not warn if pulling to a branch besides master (useful for testing)."
       switch "--resolve",
@@ -39,6 +42,9 @@ module Homebrew
       switch "--warn-on-upload-failure",
              description: "Warn instead of raising an error if the bottle upload fails. "\
                           "Useful for repairing bottle uploads that previously failed."
+      flag   "--message=",
+             depends_on:  "--autosquash",
+             description: "Message to include when autosquashing revision bumps, deletions, and rebuilds."
       flag   "--workflow=",
              description: "Retrieve artifacts from the specified workflow (default: `tests.yml`)."
       flag   "--artifact=",
@@ -52,8 +58,8 @@ module Homebrew
       flag   "--bintray-mirror=",
              description: "Use the specified Bintray repository to automatically mirror stable URLs "\
                           "defined in the formulae (default: `mirror`)."
-
       min_named 1
+      conflicts "--clean", "--autosquash"
     end
   end
 
@@ -78,21 +84,29 @@ module Homebrew
     end
   end
 
-  def signoff!(pr, tap:, args:)
-    message = Utils.popen_read "git", "-C", tap.path, "log", "-1", "--pretty=%B"
+  # Separates a commit message into subject, body, and trailers.
+  def separate_commit_message(message)
     subject = message.lines.first.strip
 
     # Skip the subject and separate lines that look like trailers (e.g. "Co-authored-by")
     # from lines that look like regular body text.
     trailers, body = message.lines.drop(1).partition { |s| s.match?(/^[a-z-]+-by:/i) }
 
-    # Approving reviewers also sign-off on merge
-    trailers += GitHub.approved_reviews(tap.user, "homebrew-#{tap.repo}", pr).map do |r|
-      "Signed-off-by: #{r["name"]} <#{r["email"]}>\n"
-    end
     trailers = trailers.uniq.join.strip
     body = body.join.strip.gsub(/\n{3,}/, "\n\n")
 
+    [subject, body, trailers]
+  end
+
+  def signoff!(pr, tap:, args:)
+    message = Utils.popen_read "git", "-C", tap.path, "log", "-1", "--pretty=%B"
+    subject, body, trailers = separate_commit_message(message)
+
+    # Approving reviewers also sign-off on merge.
+    trailers += GitHub.approved_reviews(tap.user, "homebrew-#{tap.repo}", pr).map do |r|
+      "Signed-off-by: #{r["name"]} <#{r["email"]}>"
+    end.join("\n")
+
     close_message = "Closes ##{pr}."
     body += "\n\n#{close_message}" unless body.include? close_message
     new_message = [subject, body, trailers].join("\n\n").strip
@@ -104,6 +118,163 @@ module Homebrew
     end
   end
 
+  def determine_bump_subject(file, original_commit, path: ".", reason: nil)
+    full_path = Pathname.new(path)/file
+    formula_name = File.basename(file.chomp(".rb"))
+
+    new_formula = begin
+      Formulary::FormulaLoader.new(formula_name, full_path).get_formula(:stable)
+    rescue FormulaUnavailableError
+      return "#{formula_name}: delete #{reason}"
+    end
+
+    old_formula = begin
+      old_file = Utils.popen_read "git", "-C", path, "show", "#{original_commit}:#{file}"
+      Formulary.from_contents(formula_name, full_path, old_file, :stable)
+    rescue FormulaUnavailableError
+      return "#{formula_name} #{new_formula.stable.version} (new formula)"
+    end
+
+    if old_formula.stable.version != new_formula.stable.version
+      "#{formula_name} #{new_formula.stable.version}"
+    elsif old_formula.revision != new_formula.revision
+      "#{formula_name}: revision #{reason}"
+    else
+      "#{formula_name}: #{reason || "rebuild"}"
+    end
+  end
+
+  # Cherry picks a single commit that modifies a single file.
+  # Potentially rewords this commit using `determine_bump_subject`.
+  def reword_formula_commit(commit, file, args:, path: ".")
+    formula_name = File.basename(file.chomp(".rb"))
+    odebug "Cherry-picking #{file}: #{commit}"
+    Utils::Git.cherry_pick!(path, commit, verbose: args.verbose?, resolve: args.resolve?)
+
+    bump_subject = determine_bump_subject(file, "HEAD^", path: path, reason: args.message).strip
+    message = Utils.popen_read("git", "-C", path, "log", "-1", "--pretty=%B")
+    subject, body, trailers = separate_commit_message(message)
+
+    if subject != bump_subject && !subject.start_with?("#{formula_name}:")
+      safe_system("git", "-C", path, "commit", "--amend", "-q",
+                  "-m", bump_subject, "-m", subject, "-m", body, "-m", trailers)
+      ohai bump_subject
+    else
+      ohai subject
+    end
+  end
+
+  # Cherry picks multiple commits that each modify a single file.
+  # Words the commit according to `determine_bump_subject` with the body
+  # corresponding to all the original commit messages combined.
+  def squash_formula_commits(commits, file, args:, path: ".")
+    odebug "Squashing #{file}: #{commits.join " "}"
+
+    # Format commit messages into something similar to `git fmt-merge-message`.
+    # * subject 1
+    # * subject 2
+    #   optional body
+    # * subject 3
+    messages = []
+    trailers = []
+    commits.each do |commit|
+      original_message = Utils.safe_popen_read("git", "-C", path, "show", "--no-patch", "--pretty=%B", commit)
+      subject, body, trailer = separate_commit_message(original_message)
+      body = body.lines.map { |line| "  #{line.strip}" }.join("\n")
+      messages << "* #{subject}\n#{body}".strip
+      trailers << trailer
+    end
+
+    # Get the set of authors in this series.
+    authors = Utils.safe_popen_read("git", "-C", path, "show",
+                                    "--no-patch", "--pretty=%an <%ae>", *commits).lines.map(&:strip).uniq.compact
+
+    # Get the author and date of the first commit of this series, which we use for the squashed commit.
+    original_author = authors.shift
+    original_date = Utils.safe_popen_read "git", "-C", path, "show", "--no-patch", "--pretty=%ad", commits.first
+
+    # Generate trailers for coauthors and combine them with the existing trailers.
+    co_author_trailers = authors.map { |au| "Co-authored-by: #{au}" }
+    trailers = [trailers + co_author_trailers].flatten.uniq.compact
+
+    # Apply the patch series but don't commit anything yet.
+    Utils::Git.cherry_pick!(path, "--no-commit", *commits, verbose: args.verbose?, resolve: args.resolve?)
+
+    # Determine the bump subject by comparing the original state of the tree to its current state.
+    bump_subject = determine_bump_subject(file, "#{commits.first}^", path: path, reason: args.message).strip
+
+    # Commit with the new subject, body, and trailers.
+    safe_system("git", "-C", path, "commit", "--quiet",
+                "-m", bump_subject, "-m", messages.join("\n"), "-m", trailers.join("\n"),
+                "--author", original_author, "--date", original_date, "--", file)
+    ohai bump_subject
+  end
+
+  def autosquash!(original_commit, path: ".", args: nil)
+    # Autosquash assumes we've already modified the current state of the git repository,
+    # so just exit early if we're in a dry run.
+    return if args.dry_run?
+
+    original_head = Utils.safe_popen_read("git", "-C", path, "rev-parse", "HEAD").strip
+
+    commits = Utils.safe_popen_read("git", "-C", path, "rev-list",
+                                    "--reverse", "#{original_commit}..HEAD").lines.map(&:strip)
+
+    # Generate a bidirectional mapping of commits <=> formula files.
+    files_to_commits = {}
+    commits_to_files = commits.map do |commit|
+      files = Utils.safe_popen_read("git", "-C", path, "diff-tree", "--diff-filter=AMD",
+                                    "-r", "--name-only", "#{commit}^", commit).lines.map(&:strip)
+      files.each do |file|
+        files_to_commits[file] ||= []
+        files_to_commits[file] << commit
+        next if %r{^Formula/.*\.rb$}.match?(file)
+
+        odie <<~EOS
+          Autosquash can't squash commits that modify non-formula files.
+            File:   #{file}
+            Commit: #{commit}
+        EOS
+      end
+      [commit, files]
+    end.to_h
+
+    # Reset to state before cherry-picking.
+    safe_system "git", "-C", path, "reset", "--hard", original_commit
+
+    # Iterate over every commit in the pull request series, but if we have to squash
+    # multiple commits into one, ensure that we skip over commits we've already squashed.
+    processed_commits = []
+    commits.each do |commit|
+      next if processed_commits.include? commit
+
+      files = commits_to_files[commit]
+      if files.length == 1 && files_to_commits[files.first].length == 1
+        # If there's a 1:1 mapping of commits to files, just cherry pick and (maybe) reword.
+        reword_formula_commit(commit, files.first, path: path, args: args)
+        processed_commits << commit
+      elsif files.length == 1 && files_to_commits[files.first].length > 1
+        # If multiple commits modify a single file, squash them down into a single commit.
+        file = files.first
+        commits = files_to_commits[file]
+        squash_formula_commits(commits, file, path: path, args: args)
+        processed_commits += commits
+      else
+        # We can't split commits (yet) so just raise an error.
+        odie <<~EOS
+          Autosquash can't split commits that modify multiple files.
+            Commit: #{commit}
+            Files:  #{files.join " "}
+        EOS
+      end
+    end
+  rescue
+    opoo "Autosquash encountered an error; resetting to original cherry-picked state at #{original_head}"
+    system "git", "-C", path, "reset", "--hard", original_head
+    system "git", "-C", path, "cherry-pick", "--abort"
+    raise
+  end
+
   def cherry_pick_pr!(pr, args:, path: ".")
     if args.dry_run?
       puts <<~EOS
@@ -116,19 +287,9 @@ module Homebrew
       merge_base = Utils.popen_read("git", "-C", path, "merge-base", "HEAD", "FETCH_HEAD").strip
       commit_count = Utils.popen_read("git", "-C", path, "rev-list", "#{merge_base}..FETCH_HEAD").lines.count
 
-      # git cherry-pick unfortunately has no quiet option
-      ohai "Cherry-picking #{commit_count} commit#{"s" unless commit_count == 1} from ##{pr}"
-      cherry_pick_args = "git", "-C", path, "cherry-pick", "--ff", "--allow-empty", "#{merge_base}..FETCH_HEAD"
-      result = args.verbose? ? system(*cherry_pick_args) : quiet_system(*cherry_pick_args)
-
-      unless result
-        if args.resolve?
-          odie "Cherry-pick failed: try to resolve it."
-        else
-          system "git", "-C", path, "cherry-pick", "--abort"
-          odie "Cherry-pick failed!"
-        end
-      end
+      ohai "Using #{commit_count} commit#{"s" unless commit_count == 1} from ##{pr}"
+      Utils::Git.cherry_pick!(path, "--ff", "--allow-empty", "#{merge_base}..FETCH_HEAD",
+                              verbose: args.verbose?, resolve: args.resolve?)
     end
   end
 
@@ -231,6 +392,7 @@ module Homebrew
         cd dir do
           original_commit = Utils.popen_read("git", "-C", tap.path, "rev-parse", "HEAD").chomp
           cherry_pick_pr!(pr, path: tap.path, args: args)
+          autosquash!(original_commit, path: tap.path, args: args) if args.autosquash?
           signoff!(pr, tap: tap, args: args) unless args.clean?
 
           unless args.no_upload?

docs/Manpage.md

@@ -1096,12 +1096,16 @@ Requires write access to the repository.
   Do not amend the commits from pull requests.
 * `--keep-old`:
   If the formula specifies a rebuild version, attempt to preserve its value in the generated DSL.
+* `--autosquash`:
+  Automatically reformat and reword commits in the pull request to our preferred format.
 * `--branch-okay`:
   Do not warn if pulling to a branch besides master (useful for testing).
 * `--resolve`:
   When a patch fails to apply, leave in progress and allow user to resolve, instead of aborting.
 * `--warn-on-upload-failure`:
   Warn instead of raising an error if the bottle upload fails. Useful for repairing bottle uploads that previously failed.
+* `--message`:
+  Message to include when autosquashing revision bumps, deletions, and rebuilds.
 * `--workflow`:
   Retrieve artifacts from the specified workflow (default: `tests.yml`).
 * `--artifact`:

manpages/brew.1

@@ -1519,6 +1519,10 @@ Do not amend the commits from pull requests\.
 If the formula specifies a rebuild version, attempt to preserve its value in the generated DSL\.
 .
 .TP
+\fB\-\-autosquash\fR
+Automatically reformat and reword commits in the pull request to our preferred format\.
+.
+.TP
 \fB\-\-branch\-okay\fR
 Do not warn if pulling to a branch besides master (useful for testing)\.
 .
@@ -1531,6 +1535,10 @@ When a patch fails to apply, leave in progress and allow user to resolve, instea
 Warn instead of raising an error if the bottle upload fails\. Useful for repairing bottle uploads that previously failed\.
 .
 .TP
+\fB\-\-message\fR
+Message to include when autosquashing revision bumps, deletions, and rebuilds\.
+.
+.TP
 \fB\-\-workflow\fR
 Retrieve artifacts from the specified workflow (default: \fBtests\.yml\fR)\.
 .