Ad-hoc fix for platform regression

We should be able to remove this once we have proper bundler version
switching.

bundler/lib/bundler.rb

@@ -212,6 +212,15 @@ def locked_gems
         end
     end
 
+    def locked_bundler_version
+      return nil unless defined?(@definition) && @definition
+
+      locked_gems = definition.locked_gems
+      return nil unless locked_gems
+
+      locked_gems.bundler_version
+    end
+
     def ruby_scope
       "#{Bundler.rubygems.ruby_engine}/#{RbConfig::CONFIG["ruby_version"]}"
     end

bundler/lib/bundler/lazy_specification.rb

@@ -82,7 +82,13 @@ def __materialize__
         search_object = if source.is_a?(Source::Path)
           Dependency.new(name, version)
         else
-          self
+          locked_bundler_version = Bundler.locked_bundler_version
+
+          if locked_bundler_version && Gem::Version.new(locked_bundler_version) < Gem::Version.new("2.2.0")
+            Dependency.new(name, version)
+          else
+            self
+          end
         end
         platform_object = Gem::Platform.new(platform)
         candidates = source.specs.search(search_object)

bundler/spec/install/gemfile/specific_platform_spec.rb

@@ -21,6 +21,35 @@
       ])
     end
 
+    it "understands that a non-plaform specific gem in a old lockfile doesn't necessarily mean installing the non-specific variant" do
+      setup_multiplatform_gem
+
+      install_gemfile(google_protobuf)
+
+      # simulate lockfile created with old bundler, which only locks for ruby platform
+      lockfile <<-L
+        GEM
+          remote: #{file_uri_for(gem_repo2)}/
+          specs:
+            google-protobuf (3.0.0.alpha.5.0.5.1)
+
+        PLATFORMS
+          ruby
+
+        DEPENDENCIES
+          google-protobuf
+
+        BUNDLED WITH
+           2.1.4
+      L
+
+      # force strict usage of the lock file by setting frozen mode
+      bundle "config set --local frozen true"
+
+      # make sure the platform that got actually installed with the old bundler is used
+      expect(the_bundle).to include_gem("google-protobuf 3.0.0.alpha.5.0.5.1 universal-darwin")
+    end
+
     it "caches both the universal-darwin and ruby gems when --all-platforms is passed and properly picks them up on further bundler invocations" do
       setup_multiplatform_gem
       gemfile(google_protobuf)