Move migrations into UpdateMigrator module.

Library/Homebrew/brew.rb

@@ -14,6 +14,8 @@ end
 
 require_relative "global"
 
+require "update_migrator"
+
 begin
   trap("INT", std_trap) # restore default CTRL-C handler
 
@@ -76,7 +78,7 @@ begin
   end
 
   # Migrate LinkedKegs/PinnedKegs if update didn't already do so
-  migrate_legacy_keg_symlinks_if_necessary
+  UpdateMigrator.migrate_legacy_keg_symlinks_if_necessary
 
   # Uninstall old brew-cask if it's still around; we just use the tap now.
   if cmd == "cask" && (HOMEBREW_CELLAR/"brew-cask").exist?

Library/Homebrew/cmd/update-report.rb

@@ -7,7 +7,7 @@ require "migrator"
 require "formulary"
 require "descriptions"
 require "cleanup"
-require "hbc/download"
+require "update_migrator"
 
 module Homebrew
   module_function
@@ -111,10 +111,10 @@ module Homebrew
       updated = true
     end
 
-    migrate_legacy_cache_if_necessary
+    UpdateMigrator.migrate_legacy_cache_if_necessary
-    migrate_cache_entries_to_double_dashes(initial_version)
+    UpdateMigrator.migrate_cache_entries_to_double_dashes(initial_version)
-    migrate_cache_entries_to_symlinks(initial_version)
+    UpdateMigrator.migrate_cache_entries_to_symlinks(initial_version)
-    migrate_legacy_keg_symlinks_if_necessary
+    UpdateMigrator.migrate_legacy_keg_symlinks_if_necessary
 
     if !updated
       if !ARGV.include?("--preinstall") && !ENV["HOMEBREW_UPDATE_FAILED"]
@@ -140,7 +140,7 @@ module Homebrew
     # This should always be the last thing to run (but skip on auto-update).
     if !ARGV.include?("--preinstall") ||
        ENV["HOMEBREW_ENABLE_AUTO_UPDATE_MIGRATION"]
-      migrate_legacy_repository_if_necessary
+      UpdateMigrator.migrate_legacy_repository_if_necessary
     end
   end
 
@@ -158,323 +158,6 @@ module Homebrew
     ENV["HOMEBREW_UPDATE_AFTER_HOMEBREW_HOMEBREW_CORE"] = revision
   end
 
-  def migrate_legacy_cache_if_necessary
-    legacy_cache = Pathname.new "/Library/Caches/Homebrew"
-    return if HOMEBREW_CACHE.to_s == legacy_cache.to_s
-    return unless legacy_cache.directory?
-    return unless legacy_cache.readable_real?
-
-    migration_attempted_file = legacy_cache/".migration_attempted"
-    return if migration_attempted_file.exist?
-
-    return unless legacy_cache.writable_real?
-    FileUtils.touch migration_attempted_file
-
-    # This directory could have been compromised if it's world-writable/
-    # a symlink/owned by another user so don't copy files in those cases.
-    world_writable = legacy_cache.stat.mode & 0777 == 0777
-    return if world_writable
-    return if legacy_cache.symlink?
-    return if !legacy_cache.owned? && legacy_cache.lstat.uid.nonzero?
-
-    ohai "Migrating #{legacy_cache} to #{HOMEBREW_CACHE}..."
-    HOMEBREW_CACHE.mkpath
-    legacy_cache.cd do
-      legacy_cache.entries.each do |f|
-        next if [".", "..", ".migration_attempted"].include? f.to_s
-        begin
-          FileUtils.cp_r f, HOMEBREW_CACHE
-        rescue
-          @migration_failed ||= true
-        end
-      end
-    end
-
-    if @migration_failed
-      opoo <<~EOS
-        Failed to migrate #{legacy_cache} to
-        #{HOMEBREW_CACHE}. Please do so manually.
-      EOS
-    else
-      ohai "Deleting #{legacy_cache}..."
-      FileUtils.rm_rf legacy_cache
-      if legacy_cache.exist?
-        FileUtils.touch migration_attempted_file
-        opoo <<~EOS
-          Failed to delete #{legacy_cache}.
-          Please do so manually.
-        EOS
-      end
-    end
-  end
-
-  def formula_resources(formula)
-    specs = [formula.stable, formula.devel, formula.head].compact
-
-    [*formula.bottle&.resource] + specs.flat_map do |spec|
-      [
-        spec,
-        *spec.resources.values,
-        *spec.patches.select(&:external?).map(&:resource),
-      ]
-    end
-  end
-
-  def parse_extname(url)
-    uri_path = if URI::DEFAULT_PARSER.make_regexp =~ url
-      uri = URI(url)
-      uri.query ? "#{uri.path}?#{uri.query}" : uri.path
-    else
-      url
-    end
-
-    # Given a URL like https://example.com/download.php?file=foo-1.0.tar.gz
-    # the extension we want is ".tar.gz", not ".php".
-    Pathname.new(uri_path).ascend do |path|
-      ext = path.extname[/[^?&]+/]
-      return ext if ext
-    end
-
-    nil
-  end
-
-  def migrate_cache_entries_to_double_dashes(initial_version)
-    return if initial_version && initial_version > "1.7.1"
-
-    return if ENV.key?("HOMEBREW_DISABLE_LOAD_FORMULA")
-
-    ohai "Migrating cache entries..."
-
-    Formula.each do |formula|
-      formula_resources(formula).each do |resource|
-        downloader = resource.downloader
-
-        url = downloader.url
-        name = resource.download_name
-        version = resource.version
-
-        extname = parse_extname(url)
-        old_location = downloader.cache/"#{name}-#{version}#{extname}"
-        new_location = downloader.cache/"#{name}--#{version}#{extname}"
-
-        next unless old_location.file?
-
-        if new_location.exist?
-          begin
-            FileUtils.rm_rf old_location
-          rescue Errno::EACCES
-            opoo "Could not remove #{old_location}, please do so manually."
-          end
-        else
-          begin
-            FileUtils.mv old_location, new_location
-          rescue Errno::EACCES
-            opoo "Could not move #{old_location} to #{new_location}, please do so manually."
-          end
-        end
-      end
-    end
-  end
-
-  def migrate_cache_entries_to_symlinks(initial_version)
-    return if initial_version && initial_version > "1.7.2"
-
-    return if ENV.key?("HOMEBREW_DISABLE_LOAD_FORMULA")
-
-    ohai "Migrating cache entries..."
-
-    load_formula = lambda do |formula|
-      begin
-        Formula[formula]
-      rescue FormulaUnavailableError
-        nil
-      end
-    end
-
-    load_cask = lambda do |cask|
-      begin
-        Hbc::CaskLoader.load(cask)
-      rescue Hbc::CaskUnavailableError
-        nil
-      end
-    end
-
-    formula_downloaders = if HOMEBREW_CACHE.directory?
-      HOMEBREW_CACHE.children
-                    .select(&:file?)
-                    .map { |child| child.basename.to_s.sub(/\-\-.*/, "") }
-                    .uniq
-                    .map(&load_formula)
-                    .compact
-                    .flat_map { |formula| formula_resources(formula) }
-                    .map { |resource| [resource.downloader, resource.download_name, resource.version] }
-    else
-      []
-    end
-
-    cask_downloaders = if (HOMEBREW_CACHE/"Cask").directory?
-      (HOMEBREW_CACHE/"Cask").children
-                             .map { |child| child.basename.to_s.sub(/\-\-.*/, "") }
-                             .uniq
-                             .map(&load_cask)
-                             .compact
-                             .map { |cask| [Hbc::Download.new(cask).downloader, cask.token, cask.version] }
-    else
-      []
-    end
-
-    downloaders = formula_downloaders + cask_downloaders
-
-    downloaders.each do |downloader, name, version|
-      next unless downloader.respond_to?(:symlink_location)
-
-      url = downloader.url
-      extname = parse_extname(url)
-      old_location = downloader.cache/"#{name}--#{version}#{extname}"
-      next unless old_location.file?
-
-      new_symlink_location = downloader.symlink_location
-      new_location = downloader.cached_location
-
-      if new_location.exist? && new_symlink_location.symlink?
-        begin
-          FileUtils.rm_rf old_location unless old_location == new_symlink_location
-        rescue Errno::EACCES
-          opoo "Could not remove #{old_location}, please do so manually."
-        end
-      else
-        begin
-          new_location.dirname.mkpath
-          FileUtils.mv old_location, new_location unless new_location.exist?
-          symlink_target = new_location.relative_path_from(new_symlink_location.dirname)
-          new_symlink_location.dirname.mkpath
-          FileUtils.ln_s symlink_target, new_symlink_location, force: true
-        rescue Errno::EACCES
-          opoo "Could not move #{old_location} to #{new_location}, please do so manually."
-        end
-      end
-    end
-  end
-
-  def migrate_legacy_repository_if_necessary
-    return unless HOMEBREW_PREFIX.to_s == "/usr/local"
-    return unless HOMEBREW_REPOSITORY.to_s == "/usr/local"
-
-    ohai "Migrating HOMEBREW_REPOSITORY (please wait)..."
-
-    unless HOMEBREW_PREFIX.writable_real?
-      ofail <<~EOS
-        #{HOMEBREW_PREFIX} is not writable.
-
-        You should change the ownership and permissions of #{HOMEBREW_PREFIX}
-        temporarily back to your user account so we can complete the Homebrew
-        repository migration:
-          sudo chown -R $(whoami) #{HOMEBREW_PREFIX}
-      EOS
-      return
-    end
-
-    new_homebrew_repository = Pathname.new "/usr/local/Homebrew"
-    new_homebrew_repository.rmdir_if_possible
-    if new_homebrew_repository.exist?
-      ofail <<~EOS
-        #{new_homebrew_repository} already exists.
-        Please remove it manually or uninstall and reinstall Homebrew into a new
-        location as the migration cannot be done automatically.
-      EOS
-      return
-    end
-    new_homebrew_repository.mkpath
-
-    repo_files = HOMEBREW_REPOSITORY.cd do
-      Utils.popen_read("git ls-files").lines.map(&:chomp)
-    end
-
-    unless Utils.popen_read("git status --untracked-files=all --porcelain").empty?
-      HOMEBREW_REPOSITORY.cd do
-        quiet_system "git", "merge", "--abort"
-        quiet_system "git", "rebase", "--abort"
-        quiet_system "git", "reset", "--mixed"
-        safe_system "git", "-c", "user.email=brew-update@localhost",
-                           "-c", "user.name=brew update",
-                           "stash", "save", "--include-untracked"
-      end
-      stashed = true
-    end
-
-    FileUtils.cp_r "#{HOMEBREW_REPOSITORY}/.git", "#{new_homebrew_repository}/.git"
-    new_homebrew_repository.cd do
-      safe_system "git", "checkout", "--force", "."
-      safe_system "git", "stash", "pop" if stashed
-    end
-
-    if (HOMEBREW_REPOSITORY/"Library/Locks").exist?
-      FileUtils.cp_r "#{HOMEBREW_REPOSITORY}/Library/Locks", "#{new_homebrew_repository}/Library/Locks"
-    end
-
-    if (HOMEBREW_REPOSITORY/"Library/Taps").exist?
-      FileUtils.cp_r "#{HOMEBREW_REPOSITORY}/Library/Taps", "#{new_homebrew_repository}/Library/Taps"
-    end
-
-    unremovable_paths = []
-    extra_remove_paths = [".git", "Library/Locks", "Library/Taps",
-                          "Library/Homebrew/cask", "Library/Homebrew/test"]
-    (repo_files + extra_remove_paths).each do |file|
-      path = Pathname.new "#{HOMEBREW_REPOSITORY}/#{file}"
-      begin
-        FileUtils.rm_rf path
-      rescue Errno::EACCES
-        unremovable_paths << path
-      end
-      quiet_system "rmdir", "-p", path.parent if path.parent.exist?
-    end
-
-    unless unremovable_paths.empty?
-      ofail <<~EOS
-        Could not remove old HOMEBREW_REPOSITORY paths!
-        Please do this manually with:
-          sudo rm -rf #{unremovable_paths.join " "}
-      EOS
-    end
-
-    (Keg::ALL_TOP_LEVEL_DIRECTORIES + ["Cellar"]).each do |dir|
-      FileUtils.mkdir_p "#{HOMEBREW_PREFIX}/#{dir}"
-    end
-
-    src = Pathname.new("#{new_homebrew_repository}/bin/brew")
-    dst = Pathname.new("#{HOMEBREW_PREFIX}/bin/brew")
-    begin
-      FileUtils.ln_s(src.relative_path_from(dst.parent), dst)
-    rescue Errno::EACCES, Errno::ENOENT
-      ofail <<~EOS
-        Could not create symlink at #{dst}!
-        Please do this manually with:
-          sudo ln -sf #{src} #{dst}
-          sudo chown $(whoami) #{dst}
-      EOS
-    end
-
-    link_completions_manpages_and_docs(new_homebrew_repository)
-
-    ohai "Migrated HOMEBREW_REPOSITORY to #{new_homebrew_repository}!"
-    puts <<~EOS
-      Homebrew no longer needs to have ownership of /usr/local. If you wish you can
-      return /usr/local to its default ownership with:
-        sudo chown root:wheel #{HOMEBREW_PREFIX}
-    EOS
-  rescue => e
-    ofail <<~EOS
-      #{Tty.bold}Failed to migrate HOMEBREW_REPOSITORY to #{new_homebrew_repository}!#{Tty.reset}
-      The error was:
-        #{e}
-      Please try to resolve this error yourself and then run `brew update` again to
-      complete the migration. If you need help please +1 an existing error or comment
-      with your new error in issue:
-        #{Formatter.url("https://github.com/Homebrew/brew/issues/987")}
-    EOS
-    $stderr.puts e.backtrace
-  end
-
   def link_completions_manpages_and_docs(repository = HOMEBREW_REPOSITORY)
     command = "brew update"
     Utils::Link.link_completions(repository, command)

Library/Homebrew/test/update_migrator_spec.rb

@@ -1,6 +1,6 @@
-require "cmd/update-report"
+require "update_migrator"
 
-describe "brew update-report" do
+describe UpdateMigrator do
   describe "::migrate_cache_entries_to_double_dashes" do
     let(:formula_name) { "foo" }
     let(:f) {
@@ -18,7 +18,7 @@ describe "brew update-report" do
     end
 
     it "moves old files to use double dashes when upgrading from <= 1.7.1" do
-      Homebrew.migrate_cache_entries_to_double_dashes(Version.new("1.7.1"))
+      described_class.migrate_cache_entries_to_double_dashes(Version.new("1.7.1"))
 
       expect(old_cache_file).not_to exist
       expect(new_cache_file).to exist
@@ -28,8 +28,8 @@ describe "brew update-report" do
       let(:formula_name) { "foo-bar" }
 
       it "does not introduce extra double dashes when called multiple times" do
-        Homebrew.migrate_cache_entries_to_double_dashes(Version.new("1.7.1"))
+        described_class.migrate_cache_entries_to_double_dashes(Version.new("1.7.1"))
-        Homebrew.migrate_cache_entries_to_double_dashes(Version.new("1.7.1"))
+        described_class.migrate_cache_entries_to_double_dashes(Version.new("1.7.1"))
 
         expect(old_cache_file).not_to exist
         expect(new_cache_file).to exist
@@ -37,7 +37,7 @@ describe "brew update-report" do
     end
 
     it "does not move files if upgrading from > 1.7.1" do
-      Homebrew.migrate_cache_entries_to_double_dashes(Version.new("1.7.2"))
+      described_class.migrate_cache_entries_to_double_dashes(Version.new("1.7.2"))
 
       expect(old_cache_file).to exist
       expect(new_cache_file).not_to exist
@@ -63,7 +63,7 @@ describe "brew update-report" do
     end
 
     it "moves old files to use symlinks when upgrading from <= 1.7.2" do
-      Homebrew.migrate_cache_entries_to_symlinks(Version.new("1.7.2"))
+      described_class.migrate_cache_entries_to_symlinks(Version.new("1.7.2"))
 
       expect(old_cache_file).to eq(new_cache_symlink)
       expect(new_cache_symlink).to be_a_symlink
@@ -74,7 +74,7 @@ describe "brew update-report" do
     end
 
     it "does not move files if upgrading from > 1.7.2" do
-      Homebrew.migrate_cache_entries_to_symlinks(Version.new("1.7.3"))
+      described_class.migrate_cache_entries_to_symlinks(Version.new("1.7.3"))
 
       expect(old_cache_file).to exist
       expect(new_cache_file).not_to exist

Library/Homebrew/update_migrator.rb

@@ -0,0 +1,39 @@
+require "update_migrator/cache_entries_to_double_dashes"
+require "update_migrator/cache_entries_to_symlinks"
+require "update_migrator/legacy_cache"
+require "update_migrator/legacy_keg_symlinks"
+require "update_migrator/legacy_repository"
+
+module UpdateMigrator
+  module_function
+
+  def formula_resources(formula)
+    specs = [formula.stable, formula.devel, formula.head].compact
+
+    [*formula.bottle&.resource] + specs.flat_map do |spec|
+      [
+        spec,
+        *spec.resources.values,
+        *spec.patches.select(&:external?).map(&:resource),
+      ]
+    end
+  end
+
+  def parse_extname(url)
+    uri_path = if URI::DEFAULT_PARSER.make_regexp =~ url
+      uri = URI(url)
+      uri.query ? "#{uri.path}?#{uri.query}" : uri.path
+    else
+      url
+    end
+
+    # Given a URL like https://example.com/download.php?file=foo-1.0.tar.gz
+    # the extension we want is ".tar.gz", not ".php".
+    Pathname.new(uri_path).ascend do |path|
+      ext = path.extname[/[^?&]+/]
+      return ext if ext
+    end
+
+    nil
+  end
+end

Library/Homebrew/update_migrator/cache_entries_to_double_dashes.rb

@@ -0,0 +1,41 @@
+module UpdateMigrator
+  module_function
+
+  def migrate_cache_entries_to_double_dashes(initial_version)
+    return if initial_version && initial_version > "1.7.1"
+
+    return if ENV.key?("HOMEBREW_DISABLE_LOAD_FORMULA")
+
+    ohai "Migrating cache entries..."
+
+    Formula.each do |formula|
+      formula_resources(formula).each do |resource|
+        downloader = resource.downloader
+
+        url = downloader.url
+        name = resource.download_name
+        version = resource.version
+
+        extname = parse_extname(url)
+        old_location = downloader.cache/"#{name}-#{version}#{extname}"
+        new_location = downloader.cache/"#{name}--#{version}#{extname}"
+
+        next unless old_location.file?
+
+        if new_location.exist?
+          begin
+            FileUtils.rm_rf old_location
+          rescue Errno::EACCES
+            opoo "Could not remove #{old_location}, please do so manually."
+          end
+        else
+          begin
+            FileUtils.mv old_location, new_location
+          rescue Errno::EACCES
+            opoo "Could not move #{old_location} to #{new_location}, please do so manually."
+          end
+        end
+      end
+    end
+  end
+end

Library/Homebrew/update_migrator/cache_entries_to_symlinks.rb

@@ -0,0 +1,90 @@
+require "hbc/cask_loader"
+require "hbc/download"
+
+module UpdateMigrator
+  module_function
+
+  def migrate_cache_entries_to_symlinks(initial_version)
+    return if initial_version && initial_version > "1.7.2"
+
+    return if ENV.key?("HOMEBREW_DISABLE_LOAD_FORMULA")
+
+    ohai "Migrating cache entries..."
+
+    load_formula = lambda do |formula|
+      begin
+        Formula[formula]
+      rescue FormulaUnavailableError
+        nil
+      end
+    end
+
+    load_cask = lambda do |cask|
+      begin
+        Hbc::CaskLoader.load(cask)
+      rescue Hbc::CaskUnavailableError
+        nil
+      end
+    end
+
+    formula_downloaders = if HOMEBREW_CACHE.directory?
+      HOMEBREW_CACHE.children
+                    .select(&:file?)
+                    .map { |child| child.basename.to_s.sub(/\-\-.*/, "") }
+                    .uniq
+                    .map(&load_formula)
+                    .compact
+                    .flat_map { |formula| formula_resources(formula) }
+                    .map { |resource| [resource.downloader, resource.download_name, resource.version] }
+    else
+      []
+    end
+
+    cask_downloaders = if (HOMEBREW_CACHE/"Cask").directory?
+      (HOMEBREW_CACHE/"Cask").children
+                             .map { |child| child.basename.to_s.sub(/\-\-.*/, "") }
+                             .uniq
+                             .map(&load_cask)
+                             .compact
+                             .map { |cask| [Hbc::Download.new(cask).downloader, cask.token, cask.version] }
+    else
+      []
+    end
+
+    downloaders = formula_downloaders + cask_downloaders
+
+    downloaders.each do |downloader, name, version|
+      next unless downloader.respond_to?(:symlink_location)
+
+      url = downloader.url
+      extname = parse_extname(url)
+      old_location = downloader.cache/"#{name}--#{version}#{extname}"
+      next unless old_location.file?
+
+      new_symlink_location = downloader.symlink_location
+      new_location = downloader.cached_location
+
+      if new_location.exist? && new_symlink_location.symlink?
+        begin
+          FileUtils.rm_rf old_location unless old_location == new_symlink_location
+        rescue Errno::EACCES
+          opoo "Could not remove #{old_location}, please do so manually."
+        end
+      else
+        begin
+          new_location.dirname.mkpath
+          if new_location.exist?
+            FileUtils.rm_rf old_location
+          else
+            FileUtils.mv old_location, new_location
+          end
+          symlink_target = new_location.relative_path_from(new_symlink_location.dirname)
+          new_symlink_location.dirname.mkpath
+          FileUtils.ln_s symlink_target, new_symlink_location, force: true
+        rescue Errno::EACCES
+          opoo "Could not move #{old_location} to #{new_location}, please do so manually."
+        end
+      end
+    end
+  end
+end

Library/Homebrew/update_migrator/legacy_cache.rb

@@ -0,0 +1,53 @@
+module UpdateMigrator
+  module_function
+
+  def migrate_legacy_cache_if_necessary
+    legacy_cache = Pathname.new "/Library/Caches/Homebrew"
+    return if HOMEBREW_CACHE.to_s == legacy_cache.to_s
+    return unless legacy_cache.directory?
+    return unless legacy_cache.readable_real?
+
+    migration_attempted_file = legacy_cache/".migration_attempted"
+    return if migration_attempted_file.exist?
+
+    return unless legacy_cache.writable_real?
+    FileUtils.touch migration_attempted_file
+
+    # This directory could have been compromised if it's world-writable/
+    # a symlink/owned by another user so don't copy files in those cases.
+    world_writable = legacy_cache.stat.mode & 0777 == 0777
+    return if world_writable
+    return if legacy_cache.symlink?
+    return if !legacy_cache.owned? && legacy_cache.lstat.uid.nonzero?
+
+    ohai "Migrating #{legacy_cache} to #{HOMEBREW_CACHE}..."
+    HOMEBREW_CACHE.mkpath
+    legacy_cache.cd do
+      legacy_cache.entries.each do |f|
+        next if [".", "..", ".migration_attempted"].include? f.to_s
+        begin
+          FileUtils.cp_r f, HOMEBREW_CACHE
+        rescue
+          @migration_failed ||= true
+        end
+      end
+    end
+
+    if @migration_failed
+      opoo <<~EOS
+        Failed to migrate #{legacy_cache} to
+        #{HOMEBREW_CACHE}. Please do so manually.
+      EOS
+    else
+      ohai "Deleting #{legacy_cache}..."
+      FileUtils.rm_rf legacy_cache
+      if legacy_cache.exist?
+        FileUtils.touch migration_attempted_file
+        opoo <<~EOS
+          Failed to delete #{legacy_cache}.
+          Please do so manually.
+        EOS
+      end
+    end
+  end
+end

Library/Homebrew/update_migrator/legacy_keg_symlinks.rb

@@ -0,0 +1,42 @@
+module UpdateMigrator
+  module_function
+
+  def migrate_legacy_keg_symlinks_if_necessary
+    legacy_linked_kegs = HOMEBREW_LIBRARY/"LinkedKegs"
+    return unless legacy_linked_kegs.directory?
+
+    HOMEBREW_LINKED_KEGS.mkpath unless legacy_linked_kegs.children.empty?
+    legacy_linked_kegs.children.each do |link|
+      name = link.basename.to_s
+      src = begin
+        link.realpath
+      rescue Errno::ENOENT
+        begin
+          (HOMEBREW_PREFIX/"opt/#{name}").realpath
+        rescue Errno::ENOENT
+          begin
+            Formulary.factory(name).installed_prefix
+          rescue
+            next
+          end
+        end
+      end
+      dst = HOMEBREW_LINKED_KEGS/name
+      dst.unlink if dst.exist?
+      FileUtils.ln_sf(src.relative_path_from(dst.parent), dst)
+    end
+    FileUtils.rm_rf legacy_linked_kegs
+
+    legacy_pinned_kegs = HOMEBREW_LIBRARY/"PinnedKegs"
+    return unless legacy_pinned_kegs.directory?
+
+    HOMEBREW_PINNED_KEGS.mkpath unless legacy_pinned_kegs.children.empty?
+    legacy_pinned_kegs.children.each do |link|
+      name = link.basename.to_s
+      src = link.realpath
+      dst = HOMEBREW_PINNED_KEGS/name
+      FileUtils.ln_sf(src.relative_path_from(dst.parent), dst)
+    end
+    FileUtils.rm_rf legacy_pinned_kegs
+  end
+end

Library/Homebrew/update_migrator/legacy_repository.rb

@@ -0,0 +1,122 @@
+module UpdateMigrator
+  module_function
+
+  def migrate_legacy_repository_if_necessary
+    return unless HOMEBREW_PREFIX.to_s == "/usr/local"
+    return unless HOMEBREW_REPOSITORY.to_s == "/usr/local"
+
+    ohai "Migrating HOMEBREW_REPOSITORY (please wait)..."
+
+    unless HOMEBREW_PREFIX.writable_real?
+      ofail <<~EOS
+        #{HOMEBREW_PREFIX} is not writable.
+
+        You should change the ownership and permissions of #{HOMEBREW_PREFIX}
+        temporarily back to your user account so we can complete the Homebrew
+        repository migration:
+          sudo chown -R $(whoami) #{HOMEBREW_PREFIX}
+      EOS
+      return
+    end
+
+    new_homebrew_repository = Pathname.new "/usr/local/Homebrew"
+    new_homebrew_repository.rmdir_if_possible
+    if new_homebrew_repository.exist?
+      ofail <<~EOS
+        #{new_homebrew_repository} already exists.
+        Please remove it manually or uninstall and reinstall Homebrew into a new
+        location as the migration cannot be done automatically.
+      EOS
+      return
+    end
+    new_homebrew_repository.mkpath
+
+    repo_files = HOMEBREW_REPOSITORY.cd do
+      Utils.popen_read("git ls-files").lines.map(&:chomp)
+    end
+
+    unless Utils.popen_read("git status --untracked-files=all --porcelain").empty?
+      HOMEBREW_REPOSITORY.cd do
+        quiet_system "git", "merge", "--abort"
+        quiet_system "git", "rebase", "--abort"
+        quiet_system "git", "reset", "--mixed"
+        safe_system "git", "-c", "user.email=brew-update@localhost",
+                           "-c", "user.name=brew update",
+                           "stash", "save", "--include-untracked"
+      end
+      stashed = true
+    end
+
+    FileUtils.cp_r "#{HOMEBREW_REPOSITORY}/.git", "#{new_homebrew_repository}/.git"
+    new_homebrew_repository.cd do
+      safe_system "git", "checkout", "--force", "."
+      safe_system "git", "stash", "pop" if stashed
+    end
+
+    if (HOMEBREW_REPOSITORY/"Library/Locks").exist?
+      FileUtils.cp_r "#{HOMEBREW_REPOSITORY}/Library/Locks", "#{new_homebrew_repository}/Library/Locks"
+    end
+
+    if (HOMEBREW_REPOSITORY/"Library/Taps").exist?
+      FileUtils.cp_r "#{HOMEBREW_REPOSITORY}/Library/Taps", "#{new_homebrew_repository}/Library/Taps"
+    end
+
+    unremovable_paths = []
+    extra_remove_paths = [".git", "Library/Locks", "Library/Taps",
+                          "Library/Homebrew/cask", "Library/Homebrew/test"]
+    (repo_files + extra_remove_paths).each do |file|
+      path = Pathname.new "#{HOMEBREW_REPOSITORY}/#{file}"
+      begin
+        FileUtils.rm_rf path
+      rescue Errno::EACCES
+        unremovable_paths << path
+      end
+      quiet_system "rmdir", "-p", path.parent if path.parent.exist?
+    end
+
+    unless unremovable_paths.empty?
+      ofail <<~EOS
+        Could not remove old HOMEBREW_REPOSITORY paths!
+        Please do this manually with:
+          sudo rm -rf #{unremovable_paths.join " "}
+      EOS
+    end
+
+    (Keg::ALL_TOP_LEVEL_DIRECTORIES + ["Cellar"]).each do |dir|
+      FileUtils.mkdir_p "#{HOMEBREW_PREFIX}/#{dir}"
+    end
+
+    src = Pathname.new("#{new_homebrew_repository}/bin/brew")
+    dst = Pathname.new("#{HOMEBREW_PREFIX}/bin/brew")
+    begin
+      FileUtils.ln_s(src.relative_path_from(dst.parent), dst)
+    rescue Errno::EACCES, Errno::ENOENT
+      ofail <<~EOS
+        Could not create symlink at #{dst}!
+        Please do this manually with:
+          sudo ln -sf #{src} #{dst}
+          sudo chown $(whoami) #{dst}
+      EOS
+    end
+
+    link_completions_manpages_and_docs(new_homebrew_repository)
+
+    ohai "Migrated HOMEBREW_REPOSITORY to #{new_homebrew_repository}!"
+    puts <<~EOS
+      Homebrew no longer needs to have ownership of /usr/local. If you wish you can
+      return /usr/local to its default ownership with:
+        sudo chown root:wheel #{HOMEBREW_PREFIX}
+    EOS
+  rescue => e
+    ofail <<~EOS
+      #{Tty.bold}Failed to migrate HOMEBREW_REPOSITORY to #{new_homebrew_repository}!#{Tty.reset}
+      The error was:
+        #{e}
+      Please try to resolve this error yourself and then run `brew update` again to
+      complete the migration. If you need help please +1 an existing error or comment
+      with your new error in issue:
+        #{Formatter.url("https://github.com/Homebrew/brew/issues/987")}
+    EOS
+    $stderr.puts e.backtrace
+  end
+end

Library/Homebrew/utils.rb

@@ -498,45 +498,6 @@ def truncate_text_to_approximate_size(s, max_bytes, options = {})
   out
 end
 
-def migrate_legacy_keg_symlinks_if_necessary
-  legacy_linked_kegs = HOMEBREW_LIBRARY/"LinkedKegs"
-  return unless legacy_linked_kegs.directory?
-
-  HOMEBREW_LINKED_KEGS.mkpath unless legacy_linked_kegs.children.empty?
-  legacy_linked_kegs.children.each do |link|
-    name = link.basename.to_s
-    src = begin
-      link.realpath
-    rescue Errno::ENOENT
-      begin
-        (HOMEBREW_PREFIX/"opt/#{name}").realpath
-      rescue Errno::ENOENT
-        begin
-          Formulary.factory(name).installed_prefix
-        rescue
-          next
-        end
-      end
-    end
-    dst = HOMEBREW_LINKED_KEGS/name
-    dst.unlink if dst.exist?
-    FileUtils.ln_sf(src.relative_path_from(dst.parent), dst)
-  end
-  FileUtils.rm_rf legacy_linked_kegs
-
-  legacy_pinned_kegs = HOMEBREW_LIBRARY/"PinnedKegs"
-  return unless legacy_pinned_kegs.directory?
-
-  HOMEBREW_PINNED_KEGS.mkpath unless legacy_pinned_kegs.children.empty?
-  legacy_pinned_kegs.children.each do |link|
-    name = link.basename.to_s
-    src = link.realpath
-    dst = HOMEBREW_PINNED_KEGS/name
-    FileUtils.ln_sf(src.relative_path_from(dst.parent), dst)
-  end
-  FileUtils.rm_rf legacy_pinned_kegs
-end
-
 # Calls the given block with the passed environment variables
 # added to ENV, then restores ENV afterwards.
 # Example: