Add config variable and check for platform warnings

lib/bundler/definition.rb

@@ -878,7 +878,7 @@ def expand_dependencies(dependencies, remote = false)
         dep = Dependency.new(dep, ">= 0") unless dep.respond_to?(:name)
         next if !remote && !dep.current_platform?
         platforms = dep.gem_platforms(sorted_platforms)
-        if platforms.empty?
+        if platforms.empty? && !Bundler.settings[:disable_platform_warnings]
           mapped_platforms = dep.platforms.map {|p| Dependency::PLATFORM_MAP[p] }
           Bundler.ui.warn \
             "The dependency #{dep} will be unused by any of the platforms Bundler is installing for. " \

lib/bundler/settings.rb

@@ -26,6 +26,7 @@ class Settings
       disable_exec_load
       disable_local_branch_check
       disable_multisource
+      disable_platform_warnings
       disable_shared_gems
       disable_version_check
       error_on_stderr

man/bundle-config.ronn

@@ -166,6 +166,8 @@ learn more about their operation in [bundle install(1)][bundle-install(1)].
    When set, Gemfiles containing multiple sources will produce errors
    instead of warnings.
    Use `bundle config --delete disable_multisource` to unset.
+* `disable_platform_warnings` (`BUNDLE_DISABLE_PLATFORM_WARNINGS`):
+   Whether Bundler should show platform warnings.
 * `disable_shared_gems` (`BUNDLE_DISABLE_SHARED_GEMS`):
    Stop Bundler from accessing gems installed to RubyGems' normal location.
 * `disable_version_check` (`BUNDLE_DISABLE_VERSION_CHECK`):

spec/install/gemfile/platform_spec.rb

@@ -246,6 +246,25 @@
 The dependency #{Gem::Dependency.new("rack", ">= 0")} will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
     O
   end
+
+  context "when disable_platform_warnings is true" do
+    before { bundle! "config disable_platform_warnings true" }
+
+    it "does not print the warning when a dependency is unused on any platform" do
+      simulate_platform "ruby"
+      simulate_ruby_engine "ruby"
+
+      gemfile <<-G
+        source "file://#{gem_repo1}"
+
+        gem "rack", :platform => [:mingw, :mswin, :x64_mingw, :jruby]
+      G
+
+      bundle! "install"
+
+      expect(out).not_to match(/The dependency (.*) will be unused/)
+    end
+  end
 end
 
 RSpec.describe "when a gem has no architecture" do