cleaner: rewrite pkg-config file Cellar paths and keg-only

Library/Homebrew/cleaner.rb

@@ -59,6 +59,8 @@
       observe_file_removal info_dir_file
     end
 
+    # TODO: rewrite_config_scripts
+    rewrite_pkgconfig
     rewrite_shebangs
     clean_python_metadata
 
@@ -153,6 +155,42 @@
     end
   end
 
+  sig { void }
+  def rewrite_pkgconfig
+    basepath = @formula.prefix.realpath
+    pc_files = %w[lib share].flat_map do |subdir|
+      next [] unless (pc_dir = basepath/subdir/"pkgconfig").exist?
+      next [] if @formula.skip_clean?(basepath/subdir) || @formula.skip_clean?(pc_dir)
+
+      pc_dir.glob("*.pc").reject { |pc_file| @formula.skip_clean?(pc_file) }
+    end
+    return if pc_files.empty?
+
+    keg_only_pc_files = @formula.deps
+                                .reject { |d| d.build? || d.test? }
+                                .map(&:to_formula)
+                                .select(&:keg_only?)
+                                .flat_map { |f| f.prefix.glob("{lib,share}/pkgconfig/*.pc") }
+                                .to_h { |pc_file| [pc_file.basename(".pc").to_s, pc_file.to_s] }
+    keg_only_modules_pattern = keg_only_pc_files.keys.map { |mod| Regexp.escape(mod) }.join("|")
+
+    pc_files.each do |pc_file|
+      any_modification = T.let(false, T::Boolean)
+      lines = pc_file.each_line.map do |line|
+        any_modification ||= line.gsub!(@formula.prefix.realpath.to_s, @formula.opt_prefix.to_s).present?
+        next line if keg_only_pc_files.empty? || !line.start_with?(/Requires(?:\.private)?:/)
+
+        line.gsub(/(?<=[:,\s])(#{keg_only_modules_pattern})(?=[<=>!,\s])/) do |match|
+          any_modification ||= keg_only_pc_files.include?(match)
+          keg_only_pc_files[match] || match
+        end
+      end
+      next unless any_modification
+
+      pc_file.atomic_write(lines.join)
+    end
+  end
+
   sig { void }
   def rewrite_shebangs
     require "language/node"