[rubygems/rubygems] Improve log message about adding a new platform

This message is printed when running `bundle lock --add-platform`. This
command affects the lockfile, not the gemfile, and I think it's better
to use "You are adding" rather than "You added", because the addition is
happening during the current invocation (as opposed to other log
messages that talk about a change made to the Gemfile prior to running
the command).

ruby/rubygems@aba1e55f5b

Author: deivid-rodriguez

lib/bundler/definition.rb

@@ -623,7 +623,7 @@ def resolution_packages
       @resolution_packages ||= begin
         last_resolve = converge_locked_specs
         remove_invalid_platforms!
-        new_resolution_platforms = @current_platform_missing ? @new_platforms.append(local_platform) : @new_platforms
+        new_resolution_platforms = @current_platform_missing ? @new_platforms + [local_platform] : @new_platforms
         packages = Resolver::Base.new(source_requirements, expanded_dependencies, last_resolve, @platforms, locked_specs: @originally_locked_specs, unlock: @unlocking_all || @gems_to_unlock, prerelease: gem_version_promoter.pre?, prefer_local: @prefer_local, new_platforms: new_resolution_platforms)
         packages = additional_base_requirements_to_prevent_downgrades(packages)
         packages = additional_base_requirements_to_force_updates(packages)
@@ -797,7 +797,7 @@ def change_reason
         [@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"],
+        [@new_platforms.any?, "you are adding a new platform to your lockfile"],
         [@path_changes, "the gemspecs for path gems changed"],
         [@local_changes, "the gemspecs for git local gems changed"],
         [@missing_lockfile_dep, "your lock file is missing \"#{@missing_lockfile_dep}\""],

spec/bundler/commands/install_spec.rb

@@ -1369,7 +1369,7 @@ def run
       bundle "install --verbose"
 
       expect(out).to include("re-resolving dependencies because your lockfile does not include the current platform")
-      expect(out).not_to include("you added a new platform to your gemfile")
+      expect(out).not_to include("you are adding a new platform to your lockfile")
 
       expect(lockfile).to eq <<~L
         GEM

spec/bundler/commands/lock_spec.rb

@@ -761,8 +761,18 @@
     expect(lockfile).to end_with("BUNDLED WITH\n   99\n")
   end
 
-  it "supports adding new platforms" do
-    bundle "lock --add-platform java x86-mingw32"
+  it "supports adding new platforms when there's no previous lockfile" do
+    bundle "lock --add-platform java x86-mingw32 --verbose"
+    expect(out).to include("Resolving dependencies because there's no lockfile")
+
+    allow(Bundler::SharedHelpers).to receive(:find_gemfile).and_return(bundled_app_gemfile)
+    expect(the_bundle.locked_platforms).to match_array(default_platform_list("java", "x86-mingw32"))
+  end
+
+  it "supports adding new platforms when a previous lockfile exists" do
+    bundle "lock"
+    bundle "lock --add-platform java x86-mingw32 --verbose"
+    expect(out).to include("Found changes from the lockfile, re-resolving dependencies because you are adding a new platform to your lockfile")
 
     allow(Bundler::SharedHelpers).to receive(:find_gemfile).and_return(bundled_app_gemfile)
     expect(the_bundle.locked_platforms).to match_array(default_platform_list("java", "x86-mingw32"))