Deprecation in preparation for pg as an optional dependency, refs #640

lib/valkyrie/persistence/postgres.rb

@@ -1,8 +1,14 @@
 # frozen_string_literal: true
-#
 module Valkyrie::Persistence
   # Implements the DataMapper Pattern to store metadata into Postgres
   module Postgres
+    # Deprecation to allow us to make pg an optional dependency
+    path = Bundler.definition.gemfiles.first
+    matches = File.readlines(path).select { |l| l =~ /gem ['"]pg\b/ }
+    if matches.empty?
+      warn "[DEPRECATION] pg will not be included as a dependency in Valkyrie's gemspec as of the next major release. Please add the gem directly to your Gemfile if you use a postgres adapter."
+    end
+
     require 'valkyrie/persistence/postgres/metadata_adapter'
   end
 end

spec/valkyrie/persistence/postgres/persister_spec.rb

@@ -116,4 +116,31 @@ class CustomResource < Valkyrie::Resource
       end
     end
   end
+
+  describe "pg gem deprecation" do
+    let(:message) { /\[DEPRECATION\] pg will not be included/ }
+    let(:path) { Bundler.definition.gemfiles.first }
+
+    context "when the gemfile does not have an entry for pg" do
+      before do
+      end
+      it "gives a warning when the module loads" do
+        allow(File).to receive(:readlines).with(path).and_return(["gem \"rsolr\"\n"])
+        expect do
+          Valkyrie::Persistence.send(:remove_const, :Postgres)
+          load "lib/valkyrie/persistence/postgres.rb"
+        end.to output(message).to_stderr
+      end
+    end
+
+    context "when the gemfile does have an entry for pg" do
+      it "does not give a deprecation warning" do
+        allow(File).to receive(:readlines).with(path).and_return(["gem \"pg\", \"~> 1.0\"\n"])
+        expect do
+          Valkyrie::Persistence.send(:remove_const, :Postgres)
+          load "lib/valkyrie/persistence/postgres.rb"
+        end.not_to output(message).to_stderr
+      end
+    end
+  end
 end