Add Formatter::enumeration.

Library/Homebrew/test/formatter_spec.rb

@@ -76,4 +76,22 @@ describe Formatter do
       expect(described_class.pluralize(2, "new formula")).to eq("2 new formulae")
     end
   end
+
+  describe "::enumeration" do
+    it "returns nil if given no arguments" do
+      expect(described_class.enumeration).to be nil
+    end
+
+    it "returns the input as string if there is only one argument" do
+      expect(described_class.enumeration(1)).to eq("1")
+    end
+
+    it "concatenates two items with “and”" do
+      expect(described_class.enumeration(1, 2)).to eq("1 and 2")
+    end
+
+    it "concatenates all items with a comma and appends the last with “and”" do
+      expect(described_class.enumeration(1, 2, 3)).to eq("1, 2 and 3")
+    end
+  end
 end

Library/Homebrew/utils/formatter.rb

@@ -108,4 +108,11 @@ module Formatter
 
     show_count ? "#{count} #{words}" : words
   end
+
+  def enumeration(*items)
+    *items, last = items.map(&:to_s)
+    return last if items.empty?
+
+    "#{items.join(", ")} and #{last}"
+  end
 end