Use #flat_map on Ruby 2.0 +

lib/molinillo.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'molinillo/compatibility'
 require 'molinillo/gem_metadata'
 require 'molinillo/errors'
 require 'molinillo/resolver'

lib/molinillo/compatibility.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Molinillo
+  # Hacks needed for old Ruby versions.
+  module Compatibility
+    module_function
+
+    if [].respond_to?(:flat_map)
+      # Flat map
+      # @param [Enumerable] enum an enumerable object
+      # @block the block to flat-map with
+      # @return The enum, flat-mapped
+      def flat_map(enum, &blk)
+        enum.flat_map(&blk)
+      end
+    else
+      # Flat map
+      # @param [Enumerable] enum an enumerable object
+      # @block the block to flat-map with
+      # @return The enum, flat-mapped
+      def flat_map(enum, &blk)
+        enum.map(&blk).flatten(1)
+      end
+    end
+  end
+end

lib/molinillo/dependency_graph/vertex.rb

@@ -54,7 +54,7 @@ def predecessors
       #   {#descendent?}
       def recursive_predecessors
         vertices = predecessors
-        vertices += vertices.map(&:recursive_predecessors).flatten(1)
+        vertices += Compatibility.flat_map(vertices, &:recursive_predecessors)
         vertices.uniq!
         vertices
       end
@@ -69,7 +69,7 @@ def successors
       #   {#ancestor?}
       def recursive_successors
         vertices = successors
-        vertices += vertices.map(&:recursive_successors).flatten(1)
+        vertices += Compatibility.flat_map(vertices, &:recursive_successors)
         vertices.uniq!
         vertices
       end

lib/molinillo/errors.rb

@@ -65,7 +65,7 @@ class VersionConflict < ResolverError
     # @param [SpecificationProvider] specification_provider see {#specification_provider}
     def initialize(conflicts, specification_provider)
       pairs = []
-      conflicts.values.flatten.map(&:requirements).flatten.each do |conflicting|
+      Compatibility.flat_map(conflicts.values.flatten, &:requirements).each do |conflicting|
         conflicting.each do |source, conflict_requirements|
           conflict_requirements.each do |c|
             pairs << [c, source]