Include created_at in compact index /info endpoint

Pass the version's created_at timestamp to CompactIndex::GemVersion
so it is included in the /info response. The timestamp is formatted
as ISO 8601 UTC.

This enables Bundler clients to read publication dates from the
compact index directly, avoiding separate V1 API calls per gem when
implementing supply chain security features like min_age checks.

Depends on rubygems/compact_index adding created_at as an optional
8th field to the GemVersion struct.

Author: marcbest

app/models/gem_info.rb

@@ -108,8 +108,9 @@ def compute_compact_index_info
         end
       end
 
-      name, platform, checksum, info_checksum, ruby_version, rubygems_version, = r
-      CompactIndex::GemVersion.new(name, platform, Version._sha256_hex(checksum), info_checksum, deps, ruby_version, rubygems_version)
+      name, platform, checksum, info_checksum, ruby_version, rubygems_version, created_at, = r
+      CompactIndex::GemVersion.new(name, platform, Version._sha256_hex(checksum), info_checksum, deps, ruby_version, rubygems_version,
+        created_at&.utc&.iso8601)
     end
   end
 

test/models/gem_info_test.rb

@@ -16,9 +16,9 @@ class GemInfoTest < ActiveSupport::TestCase
   context "#compact_index_info" do
     setup do
       rubygem = create(:rubygem, name: "example")
-      version = create(:version, rubygem: rubygem, number: "1.0.0", info_checksum: "qw2dwe")
+      @version = create(:version, rubygem: rubygem, number: "1.0.0", info_checksum: "qw2dwe")
       dep = create(:rubygem, name: "exmaple_dep")
-      create(:dependency, rubygem: dep, version: version)
+      create(:dependency, rubygem: dep, version: @version)
 
       @expected_info = [CompactIndex::GemVersion.new(
         "1.0.0",
@@ -27,7 +27,8 @@ class GemInfoTest < ActiveSupport::TestCase
         "qw2dwe",
         [CompactIndex::Dependency.new("exmaple_dep", "= 1.0.0")],
         ">= 2.0.0",
-        ">= 2.6.3"
+        ">= 2.6.3",
+        @version.created_at.utc.iso8601
       )]
     end
 
@@ -37,6 +38,12 @@ class GemInfoTest < ActiveSupport::TestCase
       assert_equal @expected_info, info
     end
 
+    should "include created_at timestamp in gem version" do
+      info = GemInfo.new("example").compact_index_info
+
+      assert_equal @version.created_at.utc.iso8601, info.first.created_at
+    end
+
     should "write cache" do
       Rails.cache.expects(:write).with("info/example", @expected_info)