[Definition] Print a helpful warning when a dependency is unused on any platform

2 files changed, 28 insertions, 3 deletions

diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index 12951cdf9c..9fbacf2cb4 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -808,8 +808,16 @@ module Bundler
       deps = []
       dependencies.each do |dep|
         dep = Dependency.new(dep, ">= 0") unless dep.respond_to?(:name)
-        next unless remote || dep.current_platform?
-        dep.gem_platforms(@platforms).each do |p|
+        next if !remote && !dep.current_platform?
+        platforms = dep.gem_platforms(@platforms)
+        if platforms.empty?
+          Bundler.ui.warn \
+            "The dependency #{dep} will be unused by any of the platforms Bundler is installing for. " \
+            "Bundler is installing for #{@platforms.join ", "} but the dependency " \
+            "is only for #{dep.platforms.map {|p| Dependency::PLATFORM_MAP[p] }.join ", "}. " \
+            "To add those platforms to the bundle, run `bundle lock --add-platform #{dep.platforms.join ", "}`."
+        end
+        platforms.each do |p|
           deps << DepProxy.new(dep, p) if remote || p == generic_local_platform
         end
       end
diff --git a/spec/install/gemfile/platform_spec.rb b/spec/install/gemfile/platform_spec.rb
index 58129bb313..f9ecdeb799 100644
--- a/spec/install/gemfile/platform_spec.rb
+++ b/spec/install/gemfile/platform_spec.rb
@@ -184,7 +184,7 @@ describe "bundle install with platform conditionals" do
 
     gemfile <<-G
       source "file://#{gem_repo1}"
-      gem "some_gem", platform: :rbx
+      gem "some_gem", :platform => :rbx
     G
 
     bundle "install --local"
@@ -204,6 +204,23 @@ describe "bundle install with platform conditionals" do
     bundle "install --local"
     expect(out).not_to match(/Could not find gem 'some_gem/)
   end
+
+  it "prints a helpful 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 => :jruby
+    G
+
+    bundle! "install"
+
+    expect(out).to include <<-O.strip
+The dependency 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 java. To add those platforms to the bundle, run `bundle lock --add-platform jruby`.
+    O
+  end
 end
 
 describe "when a gem has no architecture" do