[rubygems/rubygems] Add checksum of gems hosted on private servers:

- ### Problem

  Running `bundle lock --add-checksums` doesn't add the checksum of
  gems hosted on server that don't implement the compact index API.

  This result in a lockfile which is unusable in production as
  some checksums will be missing and Bundler raising an error.
  Users can work around this problem by running:

  `BUNDLE_LOCKFILE_CHECKSUMS=true bundle install --force`

  But this means redownloading and installing all gems which isn't
  great and slow on large apps.

  ### Context

  Bundler uses the Compact Index API to get the checksum of gems,
  but most private gem servers don't implement the compact index API
  (such as cloudsmith or packagecloud). This results in a soft failure
  on bundler side, and bundler leaving out blank checksum for those
  gems.

  ### Solution

  For gems that are hosted on private servers that don't send back
  the checksum of the gem, I'd like to fallback to the
  `bundle install` mechanism, which don't rely on an external API but
  instead compute the checksum of the package installed on disk.

  This patch goes through the spec that didn't return a checksum,
  and compute one if the package exists on disk.
  This solution makes the  `bundle lock --add-checksums` command
  actually usable in real world scenarios while keeping the
  `bundle lock` command fast enough.

https://github.com/rubygems/rubygems/commit/8e9abb5472

lib/bundler/definition.rb

@@ -540,7 +540,18 @@ module Bundler
 
       setup_domain!(add_checksums: true)
 
-      specs # force materialization to real specifications, so that checksums are fetched
+      # force materialization to real specifications, so that checksums are fetched
+      specs.each do |spec|
+        next unless spec.source.is_a?(Bundler::Source::Rubygems)
+        # Checksum was fetched from the compact index API.
+        next if !spec.source.checksum_store.missing?(spec) && !spec.source.checksum_store.empty?(spec)
+        # The gem isn't installed, can't compute the checksum.
+        next unless spec.loaded_from
+
+        package = Gem::Package.new(spec.source.cached_built_in_gem(spec))
+        checksum = Checksum.from_gem_package(package)
+        spec.source.checksum_store.register(spec, checksum)
+      end
     end
 
     private

spec/bundler/commands/lock_spec.rb

@@ -2174,6 +2174,97 @@ RSpec.describe "bundle lock" do
     L
   end
 
+  it "add checksums for gems installed on disk" do
+    build_repo4 do
+      build_gem "warning", "18.0.0"
+    end
+
+    bundle "config lockfile_checksums false"
+
+    simulate_platform "x86_64-linux" do
+      install_gemfile(<<-G, artifice: "endpoint")
+        source "https://gem.repo4"
+
+        gem "warning"
+      G
+
+      bundle "config --delete lockfile_checksums"
+      bundle("lock --add-checksums", artifice: "endpoint")
+    end
+
+    checksums = checksums_section do |c|
+      c.checksum gem_repo4, "warning", "18.0.0"
+    end
+
+    expect(lockfile).to eq <<~L
+      GEM
+        remote: https://gem.repo4/
+        specs:
+          warning (18.0.0)
+
+      PLATFORMS
+        ruby
+        x86_64-linux
+
+      DEPENDENCIES
+        warning
+      #{checksums}
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+  end
+
+  it "doesn't add checksum for gems not installed on disk" do
+    lockfile(<<~L)
+      GEM
+        remote: https://gem.repo4/
+        specs:
+          warning (18.0.0)
+
+      PLATFORMS
+        #{local_platform}
+
+      DEPENDENCIES
+        warning
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+
+    gemfile(<<~G)
+      source "https://gem.repo4"
+
+      gem "warning"
+    G
+
+    build_repo4 do
+      build_gem "warning", "18.0.0"
+    end
+
+    FileUtils.rm_rf("#{gem_repo4}/gems")
+
+    bundle("lock --add-checksums", artifice: "endpoint")
+
+    expect(lockfile).to eq <<~L
+      GEM
+        remote: https://gem.repo4/
+        specs:
+          warning (18.0.0)
+
+      PLATFORMS
+        #{local_platform}
+
+      DEPENDENCIES
+        warning
+
+      CHECKSUMS
+        warning (18.0.0)
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+  end
+
   context "when re-resolving to include prereleases" do
     before do
       build_repo4 do