[rubygems/rubygems] Print a better debug message when lockfile does not include the current platform

https://github.com/rubygems/rubygems/commit/afb7a6d754

lib/bundler/definition.rb

@@ -137,7 +137,7 @@ module Bundler
       end
       @unlocking ||= @unlock[:ruby] ||= (!@locked_ruby_version ^ !@ruby_version)
 
-      add_current_platform unless Bundler.frozen_bundle?
+      @current_platform_missing = add_current_platform unless Bundler.frozen_bundle?
 
       converge_path_sources_to_gemspec_sources
       @path_changes = converge_paths
@@ -484,6 +484,7 @@ module Bundler
 
       !@source_changes &&
         !@dependency_changes &&
+        !@current_platform_missing &&
         @new_platforms.empty? &&
         !@path_changes &&
         !@local_changes &&
@@ -676,7 +677,8 @@ module Bundler
       @most_specific_non_local_locked_ruby_platform = find_most_specific_locked_ruby_platform
       return if @most_specific_non_local_locked_ruby_platform
 
-      add_platform(local_platform)
+      @platforms << local_platform
+      true
     end
 
     def find_most_specific_locked_ruby_platform
@@ -704,6 +706,7 @@ module Bundler
       [
         [@source_changes, "the list of sources changed"],
         [@dependency_changes, "the dependencies in your gemfile changed"],
+        [@current_platform_missing, "your lockfile does not include the current platform"],
         [@new_platforms.any?, "you added a new platform to your gemfile"],
         [@path_changes, "the gemspecs for path gems changed"],
         [@local_changes, "the gemspecs for git local gems changed"],

spec/bundler/commands/install_spec.rb

@@ -1136,12 +1136,16 @@ RSpec.describe "bundle install with gem sources" do
     end
   end
 
-  context "in a frozen bundle" do
+  context "when current platform not included in the lockfile" do
-    before do
+    around do |example|
       build_repo4 do
         build_gem "libv8", "8.4.255.0" do |s|
           s.platform = "x86_64-darwin-19"
         end
+
+        build_gem "libv8", "8.4.255.0" do |s|
+          s.platform = "x86_64-linux"
+        end
       end
 
       gemfile <<-G
@@ -1166,11 +1170,36 @@ RSpec.describe "bundle install with gem sources" do
            #{Bundler::VERSION}
       L
 
-      bundle "config set --local deployment true"
+      simulate_platform("x86_64-linux", &example)
     end
 
-    it "should fail loudly if the lockfile platforms don't include the current platform" do
+    it "adds the current platform to the lockfile" do
-      simulate_platform("x86_64-linux") { bundle "install", raise_on_error: false }
+      bundle "install --verbose"
+
+      expect(out).to include("re-resolving dependencies because your lockfile does not include the current platform")
+
+      expect(lockfile).to eq <<~L
+        GEM
+          remote: https://gem.repo4/
+          specs:
+            libv8 (8.4.255.0-x86_64-darwin-19)
+            libv8 (8.4.255.0-x86_64-linux)
+
+        PLATFORMS
+          x86_64-darwin-19
+          x86_64-linux
+
+        DEPENDENCIES
+          libv8
+
+        BUNDLED WITH
+           #{Bundler::VERSION}
+      L
+    end
+
+    it "fails loudly if frozen mode set" do
+      bundle "config set --local deployment true"
+      bundle "install", raise_on_error: false
 
       expect(err).to eq(
         "Your bundle only supports platforms [\"x86_64-darwin-19\"] but your local platform is x86_64-linux. " \