From 75be0ca4d08de6d00b1fe17ae1aee20f80c25ade Mon Sep 17 00:00:00 2001
From: Jonathan Chang <me@jonathanchang.org>
Date: Fri, 27 Nov 2020 18:40:08 +1100
Subject: [PATCH 1/5] git_repository: add type signatures and comments

---
 Library/Homebrew/extend/git_repository.rb  | 22 +++++++++++++++++++++-
 Library/Homebrew/extend/git_repository.rbi |  8 ++++++++
 Library/Homebrew/utils/git.rb              |  1 +
 3 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 Library/Homebrew/extend/git_repository.rbi

diff --git a/Library/Homebrew/extend/git_repository.rb b/Library/Homebrew/extend/git_repository.rb
index 56a8ced860..067f518bbf 100644
--- a/Library/Homebrew/extend/git_repository.rb
+++ b/Library/Homebrew/extend/git_repository.rb
@@ -1,50 +1,70 @@
-# typed: false
+# typed: strict
 # frozen_string_literal: true
 
 require "utils/git"
 require "utils/popen"
 
+# Extensions to {Pathname} for querying Git repository information.
+# @see Utils::Git
+# @api private
 module GitRepositoryExtension
+  extend T::Sig
+
+  sig { returns(T::Boolean) }
   def git?
     join(".git").exist?
   end
 
+  # Gets the URL of the Git origin remote.
+  sig { returns(T.nilable(String)) }
   def git_origin
     return unless git? && Utils::Git.available?
 
     Utils.popen_read("git", "config", "--get", "remote.origin.url", chdir: self).chomp.presence
   end
 
+  # Sets the URL of the Git origin remote.
+  sig { params(origin: String).returns(T.nilable(T::Boolean)) }
   def git_origin=(origin)
     return unless git? && Utils::Git.available?
 
     safe_system "git", "remote", "set-url", "origin", origin, chdir: self
   end
 
+  # Gets the full commit hash of the HEAD commit.
+  sig { returns(T.nilable(String)) }
   def git_head
     return unless git? && Utils::Git.available?
 
     Utils.popen_read("git", "rev-parse", "--verify", "-q", "HEAD", chdir: self).chomp.presence
   end
 
+  # Gets a short commit hash of the HEAD commit.
+  sig { returns(T.nilable(String)) }
   def git_short_head
     return unless git? && Utils::Git.available?
 
     Utils.popen_read("git", "rev-parse", "--short=4", "--verify", "-q", "HEAD", chdir: self).chomp.presence
   end
 
+  # Gets the relative date of the last commit, e.g. "1 hour ago"
+  sig { returns(T.nilable(String)) }
   def git_last_commit
     return unless git? && Utils::Git.available?
 
     Utils.popen_read("git", "show", "-s", "--format=%cr", "HEAD", chdir: self).chomp.presence
   end
 
+  # Gets the name of the currently checked-out branch, or HEAD if the repository is in a detached HEAD state.
+  sig { returns(T.nilable(String)) }
   def git_branch
     return unless git? && Utils::Git.available?
 
     Utils.popen_read("git", "rev-parse", "--abbrev-ref", "HEAD", chdir: self).chomp.presence
   end
 
+  # Returns the date of the last commit, in YYYY-MM-DD format.
+  sig { returns(T.nilable(String)) }
   def git_last_commit_date
     return unless git? && Utils::Git.available?
 
diff --git a/Library/Homebrew/extend/git_repository.rbi b/Library/Homebrew/extend/git_repository.rbi
new file mode 100644
index 0000000000..534b936b96
--- /dev/null
+++ b/Library/Homebrew/extend/git_repository.rbi
@@ -0,0 +1,8 @@
+# typed: strict
+
+module GitRepositoryExtension
+  include Kernel
+
+  sig { params(args: T.any(String, Pathname)).returns(Pathname) }
+  def join(*args); end
+end
diff --git a/Library/Homebrew/utils/git.rb b/Library/Homebrew/utils/git.rb
index 59025a3064..0b9039dfcf 100644
--- a/Library/Homebrew/utils/git.rb
+++ b/Library/Homebrew/utils/git.rb
@@ -4,6 +4,7 @@
 module Utils
   # Helper functions for querying Git information.
   #
+  # @see GitRepositoryExtension
   # @api private
   module Git
     module_function

From 5bda84b59471bd4b48093c9aafe66b3df4af2a93 Mon Sep 17 00:00:00 2001
From: Jonathan Chang <me@jonathanchang.org>
Date: Fri, 27 Nov 2020 18:41:40 +1100
Subject: [PATCH 2/5] dev-cmd/pr-pull: use git_extensions

---
 Library/Homebrew/dev-cmd/pr-pull.rb           | 5 +++--
 Library/Homebrew/test/dev-cmd/pr-pull_spec.rb | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/Library/Homebrew/dev-cmd/pr-pull.rb b/Library/Homebrew/dev-cmd/pr-pull.rb
index 4c3317e52c..02e498baec 100644
--- a/Library/Homebrew/dev-cmd/pr-pull.rb
+++ b/Library/Homebrew/dev-cmd/pr-pull.rb
@@ -216,7 +216,8 @@ module Homebrew
   end
 
   def autosquash!(original_commit, path: ".", reason: "", verbose: false, resolve: false)
-    original_head = Utils.safe_popen_read("git", "-C", path, "rev-parse", "HEAD").strip
+    path = Pathname(path).extend(GitRepositoryExtension)
+    original_head = path.git_head
 
     commits = Utils.safe_popen_read("git", "-C", path, "rev-list",
                                     "--reverse", "#{original_commit}..HEAD").lines.map(&:strip)
@@ -394,7 +395,7 @@ module Homebrew
       ohai "Fetching #{tap} pull request ##{pr}"
       Dir.mktmpdir pr do |dir|
         cd dir do
-          original_commit = Utils.popen_read("git", "-C", tap.path, "rev-parse", "HEAD").chomp
+          original_commit = tap.path.git_head
           cherry_pick_pr!(user, repo, pr, path: tap.path, args: args)
           if args.autosquash? && !args.dry_run?
             autosquash!(original_commit, path: tap.path,
diff --git a/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb b/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb
index 848323c00f..98a95c4ae6 100644
--- a/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb
+++ b/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb
@@ -58,7 +58,7 @@ describe Homebrew do
         safe_system Utils::Git.git, "commit", formula_file, "-m", "revision"
         File.open(formula_file, "w") { |f| f.write(formula_version) }
         safe_system Utils::Git.git, "commit", formula_file, "-m", "version", "--author=#{secondary_author}"
-        described_class.autosquash!(original_hash, path: ".")
+        described_class.autosquash!(original_hash, path: path)
         expect(Utils::Git.commit_message(path)).to include("foo 2.0")
         expect(Utils::Git.commit_message(path)).to include("Co-authored-by: #{secondary_author}")
       end

From d802b3755a6df6a9c1081061017d1d995c34771a Mon Sep 17 00:00:00 2001
From: Jonathan Chang <me@jonathanchang.org>
Date: Fri, 27 Nov 2020 18:45:59 +1100
Subject: [PATCH 3/5] utils/git: remove redundant current_branch

---
 Library/Homebrew/dev-cmd/pr-pull.rb | 2 +-
 Library/Homebrew/utils/git.rb       | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Library/Homebrew/dev-cmd/pr-pull.rb b/Library/Homebrew/dev-cmd/pr-pull.rb
index 02e498baec..8a0e93f946 100644
--- a/Library/Homebrew/dev-cmd/pr-pull.rb
+++ b/Library/Homebrew/dev-cmd/pr-pull.rb
@@ -385,7 +385,7 @@ module Homebrew
       _, user, repo, pr = *url_match
       odie "Not a GitHub pull request: #{arg}" unless pr
 
-      current_branch = Utils::Git.current_branch(tap.path)
+      current_branch = tap.path.git_branch
       origin_branch = Utils::Git.origin_branch(tap.path).split("/").last
 
       if current_branch != origin_branch || args.branch_okay? || args.clean?
diff --git a/Library/Homebrew/utils/git.rb b/Library/Homebrew/utils/git.rb
index 0b9039dfcf..bb8deabe55 100644
--- a/Library/Homebrew/utils/git.rb
+++ b/Library/Homebrew/utils/git.rb
@@ -140,7 +140,8 @@ module Utils
     end
 
     def current_branch(repo)
-      Utils.popen_read("git", "-C", repo, "symbolic-ref", "--short", "HEAD").chomp.presence
+      odeprecated "Utils::Git.current_branch(repo)", "Pathname(repo).git_branch"
+      Pathname(repo).extend(GitRepositoryExtension).git_branch
     end
 
     # Special case of `git cherry-pick` that permits non-verbose output and

From 92d3eda91425db1b5bf41a7ac02cc2d500106d8f Mon Sep 17 00:00:00 2001
From: Jonathan Chang <me@jonathanchang.org>
Date: Fri, 27 Nov 2020 18:45:13 +1100
Subject: [PATCH 4/5] git_extensions: move origin_branch from utils/git

---
 Library/Homebrew/dev-cmd/bump-cask-pr.rb    |  6 +-
 Library/Homebrew/dev-cmd/bump-formula-pr.rb | 69 ++++++++++-----------
 Library/Homebrew/dev-cmd/pr-pull.rb         |  7 +--
 Library/Homebrew/diagnostic.rb              | 11 +---
 Library/Homebrew/extend/git_repository.rb   | 15 +++++
 Library/Homebrew/utils/git.rb               |  4 +-
 Library/Homebrew/utils/github.rb            | 12 ++--
 7 files changed, 62 insertions(+), 62 deletions(-)

diff --git a/Library/Homebrew/dev-cmd/bump-cask-pr.rb b/Library/Homebrew/dev-cmd/bump-cask-pr.rb
index 1a70fed47f..7a4b74e6bb 100644
--- a/Library/Homebrew/dev-cmd/bump-cask-pr.rb
+++ b/Library/Homebrew/dev-cmd/bump-cask-pr.rb
@@ -77,8 +77,8 @@ module Homebrew
     old_hash = cask.sha256.to_s
 
     tap_full_name = cask.tap&.full_name
-    origin_branch = Utils::Git.origin_branch(cask.tap.path) if cask.tap
-    origin_branch ||= "origin/master"
+    default_remote_branch = cask.tap.path.git_origin_branch if cask.tap
+    default_remote_branch ||= "master"
     previous_branch = "-"
 
     check_open_pull_requests(cask, tap_full_name, args: args)
@@ -200,7 +200,7 @@ module Homebrew
     pr_info = {
       sourcefile_path: cask.sourcefile_path,
       old_contents:    old_contents,
-      origin_branch:   origin_branch,
+      remote_branch:   default_remote_branch,
       branch_name:     "bump-#{cask.token}-#{new_version.tr(",:", "-")}",
       commit_message:  "Update #{cask.token} from #{old_version} to #{new_version}",
       previous_branch: previous_branch,
diff --git a/Library/Homebrew/dev-cmd/bump-formula-pr.rb b/Library/Homebrew/dev-cmd/bump-formula-pr.rb
index dffc4dcdf3..19e28f8f32 100644
--- a/Library/Homebrew/dev-cmd/bump-formula-pr.rb
+++ b/Library/Homebrew/dev-cmd/bump-formula-pr.rb
@@ -84,44 +84,38 @@ module Homebrew
   end
 
   def use_correct_linux_tap(formula, args:)
-    if OS.linux? && formula.tap.core_tap?
-      tap_full_name = formula.tap.full_name.gsub("linuxbrew", "homebrew")
-      homebrew_core_url = "https://github.com/#{tap_full_name}"
-      homebrew_core_remote = "homebrew"
-      homebrew_core_branch = "master"
-      origin_branch = "#{homebrew_core_remote}/#{homebrew_core_branch}"
-      previous_branch = Utils.popen_read("git -C \"#{formula.tap.path}\" symbolic-ref -q --short HEAD").chomp
-      previous_branch = "master" if previous_branch.empty?
-      formula_path = formula.path.to_s[%r{(Formula/.*)}, 1]
+    default_origin_branch = formula.tap.path.git_origin_branch if formula.tap
 
-      if args.dry_run? || args.write?
-        ohai "git remote add #{homebrew_core_remote} #{homebrew_core_url}"
-        ohai "git fetch #{homebrew_core_remote} #{homebrew_core_branch}"
-        ohai "git cat-file -e #{origin_branch}:#{formula_path}"
-        ohai "git checkout #{origin_branch}"
-        return tap_full_name, origin_branch, previous_branch
-      else
-        formula.path.parent.cd do
-          unless Utils.popen_read("git remote -v").match?(%r{^homebrew.*Homebrew/homebrew-core.*$})
-            ohai "Adding #{homebrew_core_remote} remote"
-            safe_system "git", "remote", "add", homebrew_core_remote, homebrew_core_url
-          end
-          ohai "Fetching #{origin_branch}"
-          safe_system "git", "fetch", homebrew_core_remote, homebrew_core_branch
-          if quiet_system "git", "cat-file", "-e", "#{origin_branch}:#{formula_path}"
-            ohai "#{formula.full_name} exists in #{origin_branch}"
-            safe_system "git", "checkout", origin_branch
-            return tap_full_name, origin_branch, previous_branch
-          end
-        end
+    return formula.tap&.full_name, "origin", default_origin_branch, "-" if !OS.linux? || !formula.tap.core_tap?
+
+    tap_full_name = formula.tap.full_name.gsub("linuxbrew", "homebrew")
+    homebrew_core_url = "https://github.com/#{tap_full_name}"
+    homebrew_core_remote = "homebrew"
+    previous_branch = formula.tap.path.git_branch || "master"
+    formula_path = formula.path.relative_path_from(formula.tap.path)
+    full_origin_branch = "#{homebrew_core_remote}/#{default_origin_branch}"
+
+    if args.dry_run? || args.write?
+      ohai "git remote add #{homebrew_core_remote} #{homebrew_core_url}"
+      ohai "git fetch #{homebrew_core_remote} HEAD #{default_origin_branch}"
+      ohai "git cat-file -e #{full_origin_branch}:#{formula_path}"
+      ohai "git checkout #{full_origin_branch}"
+      return tap_full_name, homebrew_core_remote, default_origin_branch, previous_branch
+    end
+
+    formula.tap.path.cd do
+      unless Utils.popen_read("git remote -v").match?(%r{^homebrew.*Homebrew/homebrew-core.*$})
+        ohai "Adding #{homebrew_core_remote} remote"
+        safe_system "git", "remote", "add", homebrew_core_remote, homebrew_core_url
+      end
+      ohai "Fetching remote #{homebrew_core_remote}"
+      safe_system "git", "fetch", homebrew_core_remote, "HEAD", default_origin_branch
+      if quiet_system "git", "cat-file", "-e", "#{full_origin_branch}:#{formula_path}"
+        ohai "#{formula.full_name} exists in #{full_origin_branch}"
+        safe_system "git", "checkout", full_origin_branch
+        return tap_full_name, homebrew_core_remote, default_origin_branch, previous_branch
       end
     end
-    if formula.tap
-      origin_branch = Utils.popen_read("git", "-C", formula.tap.path.to_s, "symbolic-ref", "-q", "--short",
-                                       "refs/remotes/origin/HEAD").chomp.presence
-    end
-    origin_branch ||= "origin/master"
-    [formula.tap&.full_name, origin_branch, "-"]
   end
 
   def bump_formula_pr
@@ -142,7 +136,7 @@ module Homebrew
 
     odie "This formula is disabled!" if formula.disabled?
 
-    tap_full_name, origin_branch, previous_branch = use_correct_linux_tap(formula, args: args)
+    tap_full_name, remote, remote_branch, previous_branch = use_correct_linux_tap(formula, args: args)
     check_open_pull_requests(formula, tap_full_name, args: args)
 
     new_version = args.version
@@ -355,7 +349,8 @@ module Homebrew
       sourcefile_path:  formula.path,
       old_contents:     old_contents,
       additional_files: alias_rename,
-      origin_branch:    origin_branch,
+      remote:           remote,
+      remote_branch:    remote_branch,
       branch_name:      "bump-#{formula.name}-#{new_formula_version}",
       commit_message:   "#{formula.name} #{new_formula_version}",
       previous_branch:  previous_branch,
diff --git a/Library/Homebrew/dev-cmd/pr-pull.rb b/Library/Homebrew/dev-cmd/pr-pull.rb
index 8a0e93f946..f866da3b9d 100644
--- a/Library/Homebrew/dev-cmd/pr-pull.rb
+++ b/Library/Homebrew/dev-cmd/pr-pull.rb
@@ -385,11 +385,8 @@ module Homebrew
       _, user, repo, pr = *url_match
       odie "Not a GitHub pull request: #{arg}" unless pr
 
-      current_branch = tap.path.git_branch
-      origin_branch = Utils::Git.origin_branch(tap.path).split("/").last
-
-      if current_branch != origin_branch || args.branch_okay? || args.clean?
-        opoo "Current branch is #{current_branch}: do you need to pull inside #{origin_branch}?"
+      if !tap.path.git_default_origin_branch? || args.branch_okay? || args.clean?
+        opoo "Current branch is #{tap.path.git_branch}: do you need to pull inside #{tap.path.git_origin_branch}?"
       end
 
       ohai "Fetching #{tap} pull request ##{pr}"
diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index 74c9aca8cd..3199df2ac5 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -572,16 +572,9 @@ module Homebrew
         return unless Utils::Git.available?
 
         commands = Tap.map do |tap|
-          next unless tap.path.git?
-          next if tap.path.git_origin.blank?
+          next if tap.path.git_default_origin_branch?
 
-          branch = tap.path.git_branch
-          next if branch.blank?
-
-          origin_branch = Utils::Git.origin_branch(tap.path)&.split("/")&.last
-          next if origin_branch == branch
-
-          "git -C $(brew --repo #{tap.name}) checkout #{origin_branch}"
+          "git -C $(brew --repo #{tap.name}) checkout #{tap.path.git_origin_branch}"
         end.compact
 
         return if commands.blank?
diff --git a/Library/Homebrew/extend/git_repository.rb b/Library/Homebrew/extend/git_repository.rb
index 067f518bbf..09c18ae1f2 100644
--- a/Library/Homebrew/extend/git_repository.rb
+++ b/Library/Homebrew/extend/git_repository.rb
@@ -63,6 +63,21 @@ module GitRepositoryExtension
     Utils.popen_read("git", "rev-parse", "--abbrev-ref", "HEAD", chdir: self).chomp.presence
   end
 
+  # Gets the name of the default origin HEAD branch.
+  sig { returns(T.nilable(String)) }
+  def git_origin_branch
+    return unless git? && Utils::Git.available?
+
+    Utils.popen_read("git", "symbolic-ref", "-q", "--short", "refs/remotes/origin/HEAD", chdir: self)
+         .chomp.presence&.split("/")&.last
+  end
+
+  # Returns true if the repository's current branch matches the default origin branch.
+  sig { returns(T.nilable(T::Boolean)) }
+  def git_default_origin_branch?
+    git_origin_branch == git_branch
+  end
+
   # Returns the date of the last commit, in YYYY-MM-DD format.
   sig { returns(T.nilable(String)) }
   def git_last_commit_date
diff --git a/Library/Homebrew/utils/git.rb b/Library/Homebrew/utils/git.rb
index bb8deabe55..875bfea354 100644
--- a/Library/Homebrew/utils/git.rb
+++ b/Library/Homebrew/utils/git.rb
@@ -135,8 +135,8 @@ module Utils
     end
 
     def origin_branch(repo)
-      Utils.popen_read(git, "-C", repo, "symbolic-ref", "-q", "--short",
-                       "refs/remotes/origin/HEAD").chomp.presence
+      odeprecated "Utils::Git.origin_branch(repo)", "Pathname(repo).git_origin_branch"
+      Pathname(repo).extend(GitRepositoryExtension).git_origin_branch
     end
 
     def current_branch(repo)
diff --git a/Library/Homebrew/utils/github.rb b/Library/Homebrew/utils/github.rb
index 8aeb60a21a..c589748168 100644
--- a/Library/Homebrew/utils/github.rb
+++ b/Library/Homebrew/utils/github.rb
@@ -679,7 +679,8 @@ module GitHub
     sourcefile_path = info[:sourcefile_path]
     old_contents = info[:old_contents]
     additional_files = info[:additional_files] || []
-    origin_branch = info[:origin_branch]
+    remote = info[:remote] || "origin"
+    remote_branch = info[:remote_branch]
     branch = info[:branch_name]
     commit_message = info[:commit_message]
     previous_branch = info[:previous_branch]
@@ -688,7 +689,6 @@ module GitHub
     pr_message = info[:pr_message]
 
     sourcefile_path.parent.cd do
-      _, base_branch = origin_branch.split("/")
       git_dir = Utils.popen_read("git rev-parse --git-dir").chomp
       shallow = !git_dir.empty? && File.exist?("#{git_dir}/shallow")
       changed_files = [sourcefile_path]
@@ -698,12 +698,12 @@ module GitHub
         ohai "try to fork repository with GitHub API" unless args.no_fork?
         ohai "git fetch --unshallow origin" if shallow
         ohai "git add #{changed_files.join(" ")}"
-        ohai "git checkout --no-track -b #{branch} #{origin_branch}"
+        ohai "git checkout --no-track -b #{branch} #{remote}/#{remote_branch}"
         ohai "git commit --no-edit --verbose --message='#{commit_message}'" \
              " -- #{changed_files.join(" ")}"
         ohai "git push --set-upstream $HUB_REMOTE #{branch}:#{branch}"
         ohai "git checkout --quiet #{previous_branch}"
-        ohai "create pull request with GitHub API (base branch: #{base_branch})"
+        ohai "create pull request with GitHub API (base branch: #{remote_branch})"
       else
 
         unless args.commit?
@@ -723,7 +723,7 @@ module GitHub
         end
 
         safe_system "git", "add", *changed_files
-        safe_system "git", "checkout", "--no-track", "-b", branch, origin_branch unless args.commit?
+        safe_system "git", "checkout", "--no-track", "-b", branch, "#{remote}/#{remote_branch}" unless args.commit?
         safe_system "git", "commit", "--no-edit", "--verbose",
                     "--message=#{commit_message}",
                     "--", *changed_files
@@ -746,7 +746,7 @@ module GitHub
 
         begin
           url = GitHub.create_pull_request(tap_full_name, commit_message,
-                                           "#{username}:#{branch}", base_branch, pr_message)["html_url"]
+                                           "#{username}:#{branch}", remote_branch, pr_message)["html_url"]
           if args.no_browse?
             puts url
           else

From 8b206dfa335d55f3fa59f9bfd4c5701e246f851c Mon Sep 17 00:00:00 2001
From: Jonathan Chang <me@jonathanchang.org>
Date: Sat, 28 Nov 2020 22:56:43 +1100
Subject: [PATCH 5/5] git_extensions: move commit_message from utils/git

---
 Library/Homebrew/dev-cmd/pr-pull.rb           |  6 +++---
 Library/Homebrew/extend/git_repository.rb     |  8 ++++++++
 Library/Homebrew/test/dev-cmd/pr-pull_spec.rb |  8 ++++----
 Library/Homebrew/test/utils/git_spec.rb       | 13 -------------
 Library/Homebrew/utils/git.rb                 |  3 ++-
 5 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/Library/Homebrew/dev-cmd/pr-pull.rb b/Library/Homebrew/dev-cmd/pr-pull.rb
index f866da3b9d..daa2bcaf2f 100644
--- a/Library/Homebrew/dev-cmd/pr-pull.rb
+++ b/Library/Homebrew/dev-cmd/pr-pull.rb
@@ -89,7 +89,7 @@ module Homebrew
   end
 
   def signoff!(path, pr: nil, dry_run: false)
-    subject, body, trailers = separate_commit_message(Utils::Git.commit_message(path))
+    subject, body, trailers = separate_commit_message(path.git_commit_message)
 
     if pr
       # This is a tap pull request and approving reviewers should also sign-off.
@@ -156,7 +156,7 @@ module Homebrew
     new_formula = Utils::Git.file_at_commit(path, file, "HEAD")
 
     bump_subject = determine_bump_subject(old_formula, new_formula, formula_file, reason: reason).strip
-    subject, body, trailers = separate_commit_message(Utils::Git.commit_message(path))
+    subject, body, trailers = separate_commit_message(path.git_commit_message)
 
     if subject != bump_subject && !subject.start_with?("#{formula_name}:")
       safe_system("git", "-C", path, "commit", "--amend", "-q",
@@ -181,7 +181,7 @@ module Homebrew
     messages = []
     trailers = []
     commits.each do |commit|
-      subject, body, trailer = separate_commit_message(Utils::Git.commit_message(path, commit))
+      subject, body, trailer = separate_commit_message(path.git_commit_message(commit))
       body = body.lines.map { |line| "  #{line.strip}" }.join("\n")
       messages << "* #{subject}\n#{body}".strip
       trailers << trailer
diff --git a/Library/Homebrew/extend/git_repository.rb b/Library/Homebrew/extend/git_repository.rb
index 09c18ae1f2..e69e6a1a29 100644
--- a/Library/Homebrew/extend/git_repository.rb
+++ b/Library/Homebrew/extend/git_repository.rb
@@ -85,4 +85,12 @@ module GitRepositoryExtension
 
     Utils.popen_read("git", "show", "-s", "--format=%cd", "--date=short", "HEAD", chdir: self).chomp.presence
   end
+
+  # Gets the full commit message of the specified commit, or of the HEAD commit if unspecified.
+  sig { params(commit: String).returns(T.nilable(String)) }
+  def git_commit_message(commit = "HEAD")
+    return unless git? && Utils::Git.available?
+
+    Utils.popen_read("git", "log", "-1", "--pretty=%B", commit, "--", chdir: self, err: :out).strip.presence
+  end
 end
diff --git a/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb b/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb
index 98a95c4ae6..47a494a016 100644
--- a/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb
+++ b/Library/Homebrew/test/dev-cmd/pr-pull_spec.rb
@@ -38,7 +38,7 @@ describe Homebrew do
     EOS
   end
   let(:formula_file) { path/"Formula/foo.rb" }
-  let(:path) { Tap::TAP_DIRECTORY/"homebrew/homebrew-foo" }
+  let(:path) { (Tap::TAP_DIRECTORY/"homebrew/homebrew-foo").extend(GitRepositoryExtension) }
 
   describe "Homebrew.pr_pull_args" do
     it_behaves_like "parseable arguments"
@@ -59,8 +59,8 @@ describe Homebrew do
         File.open(formula_file, "w") { |f| f.write(formula_version) }
         safe_system Utils::Git.git, "commit", formula_file, "-m", "version", "--author=#{secondary_author}"
         described_class.autosquash!(original_hash, path: path)
-        expect(Utils::Git.commit_message(path)).to include("foo 2.0")
-        expect(Utils::Git.commit_message(path)).to include("Co-authored-by: #{secondary_author}")
+        expect(path.git_commit_message).to include("foo 2.0")
+        expect(path.git_commit_message).to include("Co-authored-by: #{secondary_author}")
       end
     end
   end
@@ -75,7 +75,7 @@ describe Homebrew do
         safe_system Utils::Git.git, "commit", "-m", "foo 1.0 (new formula)"
       end
       described_class.signoff!(path)
-      expect(Utils::Git.commit_message(path)).to include("Signed-off-by:")
+      expect(path.git_commit_message).to include("Signed-off-by:")
     end
   end
 
diff --git a/Library/Homebrew/test/utils/git_spec.rb b/Library/Homebrew/test/utils/git_spec.rb
index 0ec9310910..5bc2585a31 100644
--- a/Library/Homebrew/test/utils/git_spec.rb
+++ b/Library/Homebrew/test/utils/git_spec.rb
@@ -52,19 +52,6 @@ describe Utils::Git do
   let(:files_hash2) { [@h2[0..6], ["README.md"]] }
   let(:cherry_pick_commit) { @cherry_pick_commit[0..6] }
 
-  describe "#commit_message" do
-    it "returns the commit message" do
-      expect(described_class.commit_message(HOMEBREW_CACHE, file_hash1)).to eq("File added")
-      expect(described_class.commit_message(HOMEBREW_CACHE, file_hash2)).to eq("written to File")
-    end
-
-    it "errors when commit doesn't exist" do
-      expect {
-        described_class.commit_message(HOMEBREW_CACHE, "bad_refspec")
-      }.to raise_error(ErrorDuringExecution, /bad revision/)
-    end
-  end
-
   describe "#cherry_pick!" do
     it "can cherry pick a commit" do
       expect(described_class.cherry_pick!(HOMEBREW_CACHE, cherry_pick_commit)).to be_truthy
diff --git a/Library/Homebrew/utils/git.rb b/Library/Homebrew/utils/git.rb
index 875bfea354..39f0932309 100644
--- a/Library/Homebrew/utils/git.rb
+++ b/Library/Homebrew/utils/git.rb
@@ -89,8 +89,9 @@ module Utils
     end
 
     def commit_message(repo, commit = nil)
+      odeprecated "Utils::Git.commit_message(repo)", "Pathname(repo).git_commit_message"
       commit ||= "HEAD"
-      Utils.safe_popen_read(git, "-C", repo, "log", "-1", "--pretty=%B", commit, "--", err: :out).strip
+      Pathname(repo).extend(GitRepositoryExtension).git_commit_message(commit)
     end
 
     def ensure_installed!