Inherit from the new versioned migration class

e.g. `ActiveRecord::Migration[5.1]`

Fixes #949

Following the example of the devise gem, use erb. In addition, add
the `.erb` file extension to fix syntax highlighting in editor.

Deletes create_versions_spec.rb because the file is no longer valid
ruby so those tests will have to be re-written. We can either
generate a valid ruby file and continue to use similar assertions,
or we can convert those features to use erb, which will have the
benefit of cleaner generated files.

CHANGELOG.md

@@ -15,7 +15,8 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
 
 ### Fixed
 
-- None
+- [#949](https://github.com/airblade/paper_trail/issues/949) - Inherit from the
+  new versioned migration class, e.g. `ActiveRecord::Migration[5.1]`
 
 ## 7.0.0 (2017-04-01)
 

lib/generators/paper_trail/install_generator.rb

@@ -50,7 +50,18 @@ module PaperTrail
       if self.class.migration_exists?(migration_dir, template)
         ::Kernel.warn "Migration already exists: #{template}"
       else
-        migration_template "#{template}.rb", "db/migrate/#{template}.rb"
+        migration_template(
+          "#{template}.rb.erb",
+          "db/migrate/#{template}.rb",
+          migration_version: migration_version
+        )
+      end
+    end
+
+    def migration_version
+      major = ActiveRecord::VERSION::MAJOR
+      if major >= 5
+        "[#{major}.#{ActiveRecord::VERSION::MINOR}]"
       end
     end
   end

lib/generators/paper_trail/templates/create_versions.rb.erb

@@ -1,6 +1,6 @@
 # This migration creates the `versions` table, the only schema PT requires.
 # All other migrations PT provides are optional.
-class CreateVersions < ActiveRecord::Migration
+class CreateVersions < ActiveRecord::Migration<%= migration_version %>
   # Class names of MySQL adapters.
   # - `MysqlAdapter` - Used by gems: `mysql`, `activerecord-jdbcmysql-adapter`.
   # - `Mysql2Adapter` - Used by `mysql2` gem.

spec/generators/install_generator_spec.rb

@@ -15,12 +15,21 @@ RSpec.describe PaperTrail::InstallGenerator, type: :generator do
     end
 
     it "generates a migration for creating the 'versions' table" do
+      expected_parent_class = lambda {
+        old_school = "ActiveRecord::Migration"
+        ar_version = ActiveRecord::VERSION
+        if ar_version::MAJOR >= 5
+          format("%s[%d.%d]", old_school, ar_version::MAJOR, ar_version::MINOR)
+        else
+          old_school
+        end
+      }.call
       expect(destination_root).to(
         have_structure {
           directory("db") {
             directory("migrate") {
               migration("create_versions") {
-                contains "class CreateVersions"
+                contains("class CreateVersions < " + expected_parent_class)
                 contains "def change"
                 contains "create_table :versions"
               }

spec/generators/paper_trail/templates/create_versions_spec.rb

@@ -1,51 +0,0 @@
-require "rails_helper"
-require "generators/paper_trail/templates/create_versions"
-
-RSpec.describe CreateVersions do
-  describe "#change", verify_stubs: false do
-    let(:migration) { described_class.new }
-
-    before do
-      allow(migration).to receive(:add_index)
-      allow(migration).to receive(:create_table)
-    end
-
-    it "creates the versions table" do
-      migration.change
-      expect(migration).to have_received(:create_table) do |arg1|
-        expect(arg1).to eq(:versions)
-      end
-    end
-
-    case ENV["DB"]
-    when "mysql"
-      it "uses InnoDB engine" do
-        migration.change
-        expect(migration).to have_received(:create_table) do |_, arg2|
-          expect(arg2[:options]).to match(/ENGINE=InnoDB/)
-        end
-      end
-
-      it "uses utf8mb4 character set" do
-        migration.change
-        expect(migration).to have_received(:create_table) do |_, arg2|
-          expect(arg2[:options]).to match(/DEFAULT CHARSET=utf8mb4/)
-        end
-      end
-
-      it "uses utf8mb4_col collation" do
-        migration.change
-        expect(migration).to have_received(:create_table) do |_, arg2|
-          expect(arg2[:options]).to match(/COLLATE=utf8mb4_general_ci/)
-        end
-      end
-    else
-      it "passes an empty options hash to create_table" do
-        migration.change
-        expect(migration).to have_received(:create_table) do |_, arg2|
-          expect(arg2).to eq({})
-        end
-      end
-    end
-  end
-end