unpack_strategy/directory: use FileUtils.mv

This should allow automatically deal with file systems though it may not
allow for GNU `cp -a` preservation of hardlinks.

Library/Homebrew/test/unpack_strategy/directory_spec.rb

@@ -27,8 +27,9 @@
     expect(unpack_dir/"folderSymlink").to be_a_symlink
   end
 
-  it "preserves hardlinks" do
-    strategy.extract(to: unpack_dir)
+  it "preserves hardlinks with move enabled" do
+    strategy_with_move = described_class.new(path, move: true)
+    strategy_with_move.extract(to: unpack_dir)
     expect((unpack_dir/"file").stat.ino).to eq (unpack_dir/"hardlink").stat.ino
   end
 

Library/Homebrew/unpack_strategy.rb

@@ -183,7 +183,7 @@ def extract_nestedly(to: nil, basename: nil, verbose: false, prioritize_extensio
         FileUtils.chmod "u+w", path, verbose:
       end
 
-      Directory.new(tmp_unpack_dir).extract(to:, verbose:)
+      Directory.new(tmp_unpack_dir, move: true).extract(to:, verbose:)
     end
   end
 

Library/Homebrew/unpack_strategy/directory.rb

@@ -16,33 +16,55 @@ def self.can_extract?(path)
       path.directory?
     end
 
+    sig {
+      params(
+        path:         T.any(String, Pathname),
+        ref_type:     T.nilable(Symbol),
+        ref:          T.nilable(String),
+        merge_xattrs: T::Boolean,
+        move:         T::Boolean,
+      ).void
+    }
+    def initialize(path, ref_type: nil, ref: nil, merge_xattrs: false, move: false)
+      super(path, ref_type:, ref:, merge_xattrs:)
+      @move = move
+    end
+
     private
 
     sig { override.params(unpack_dir: Pathname, basename: Pathname, verbose: T::Boolean).void }
     def extract_to_dir(unpack_dir, basename:, verbose:)
-      path_children = path.children
-      return if path_children.empty?
-
-      existing = unpack_dir.children
-
-      # We run a few cp attempts in the following order:
-      #
-      # 1. Start with `-al` to create hardlinks rather than copying files if the source and
-      #    target are on the same filesystem. On macOS, this is the only cp option that can
-      #    preserve hardlinks but it is only available since macOS 12.3 (file_cmds-353.100.22).
-      # 2. Try `-a` as GNU `cp -a` preserves hardlinks. macOS `cp -a` is identical to `cp -pR`.
-      # 3. Fall back on `-pR` to handle the case where GNU `cp -a` failed. This may happen if
-      #    installing into a filesystem that doesn't support hardlinks like an exFAT USB drive.
-      cp_arg_attempts = ["-a", "-pR"]
-      cp_arg_attempts.unshift("-al") if path.stat.dev == unpack_dir.stat.dev
-
-      cp_arg_attempts.each do |arg|
-        args = [arg, *path_children, unpack_dir]
-        must_succeed = print_stderr = (arg == cp_arg_attempts.last)
-        result = system_command("cp", args:, verbose:, must_succeed:, print_stderr:)
-        break if result.success?
-
-        FileUtils.rm_r(unpack_dir.children - existing)
+      if @move
+        path.find(ignore_error: false) do |src|
+          next if src == path
+
+          dst = unpack_dir/src.relative_path_from(path)
+
+          if dst.exist?
+            dst_real_dir = dst.directory? && !dst.symlink?
+            src_real_dir = src.directory? && !src.symlink?
+            # Avoid trying to move a non-directory over an existing directory or vice versa.
+            # This is similar to `cp` which fails with 'cp: <dst>: Not a directory'.
+            # However, unlike `cp`, this will fail early rather than at the end.
+            raise "Cannot extract when only one of #{src} and #{dst} is a directory" if dst_real_dir ^ src_real_dir
+
+            # Remove non-directory and just let `mv` handle to simplify handling
+            dst.unlink unless dst_real_dir
+          end
+
+          # Defer writing over existing directories to let `cp` handle preserving information
+          unless dst.directory?
+            FileUtils.mv(src, dst)
+            Find.prune
+          end
+        end
+      end
+
+      path.each_child do |child|
+        system_command! "cp",
+                        args:    ["-pR", (child.directory? && !child.symlink?) ? "#{child}/." : child,
+                                  unpack_dir/child.basename],
+                        verbose:
       end
     end
   end