Problem: building RPMs with mock is quite slow

Especially when there is a lot of dependencies.

Solution: ensure we order them correctly

This way, mock doesn't have to dynamically re-retry when it is missing
dependencies.

Author: yrashk

exe/pgpm

@@ -111,9 +111,7 @@ module Pgpm
           os.with_scope do
             arch.with_scope do
               selected_pgdist.with_scope do
-                pkgs = pkgs.flat_map do |pkg|
-                  [pkg, *pkg.all_requirements]
-                end.reject(&:contrib?)
+                pkgs = pkgs.flat_map(&:topologically_ordered_with_dependencies).uniq.reject(&:contrib?)
 
                 b = pkgs.reduce(nil) do |c, p|
                   if p.broken?

lib/pgpm/package/dependencies.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "tsort"
+
 module Pgpm
   class Package
     module Dependencies
@@ -21,6 +23,33 @@ def all_requirements
         requires.flat_map { |r| [r, *r.all_requirements] }.uniq
       end
 
+      def topologically_ordered_with_dependencies
+        TopologicalPackageSorter.new([self, *all_requirements]).sorted_packages
+      end
+
+      class TopologicalPackageSorter
+        include TSort
+
+        def initialize(packages)
+          @packages = packages.each_with_object({}) do |pkg, hash|
+            hash[pkg.name] = pkg
+          end
+        end
+
+        def tsort_each_node(&block)
+          @packages.each_key(&block)
+        end
+
+        def tsort_each_child(node, &block)
+          package = @packages[node]
+          package.requires.each { |req| block.call(req) if @packages.key?(req) }
+        end
+
+        def sorted_packages
+          tsort.map { |name| @packages[name] }.reverse
+        end
+      end
+
       def c_files_present?
         Dir.glob("*.c", base: source).any?
       end