Add an mswin? spec helper for the Windows skips

The forward-ported specs repeated RUBY_PLATFORM.include?("mswin") to gate
limitations specific to the nmake/MSVC build. Extract it into a
Spec::Platforms predicate so the make jobserver skip and the other Windows
skips share one definition.

Author: hsbt

spec/bundler/installer/parallel_installer_spec.rb

@@ -86,7 +86,7 @@
       # The make jobserver is a GNU make feature. On Windows extensions are built
       # with nmake, which has no `-j` jobserver, so the per-gem slot count never
       # appears in the build output.
-      skip "The make jobserver is not available on Windows (nmake)" if RUBY_PLATFORM.include?("mswin")
+      skip "The make jobserver is not available on Windows (nmake)" if mswin?
 
       # When run under a parent make that already passes `-j` (e.g. ruby/ruby's
       # `make test-bundler-parallel`), RubyGems' extension builder sees the

spec/commands/cache_spec.rb

@@ -208,7 +208,7 @@
     end
 
     it "prints a warn when using legacy windows rubies" do
-      skip "the legacy windows platform gem is not cached for the current mswin platform" if RUBY_PLATFORM.include?("mswin")
+      skip "the legacy windows platform gem is not cached for the current mswin platform" if mswin?
       gemfile <<-D
         source "https://gem.repo1"
         gem 'myrack', :platforms => [:ruby_20, :x64_mingw_20]

spec/commands/exec_spec.rb

@@ -72,7 +72,7 @@
   end
 
   it "works when exec'ing to rubygems" do
-    skip "https://github.com/ruby/rubygems/issues/3351" if RUBY_PLATFORM.include?("mswin")
+    skip "https://github.com/ruby/rubygems/issues/3351" if mswin?
     install_gemfile "source \"https://gem.repo1\"; gem \"myrack\""
     bundle "exec #{gem_cmd} --version"
     expect(out).to eq(Gem::VERSION)
@@ -205,7 +205,7 @@
       end
 
       it "uses version provided by ruby" do
-        skip "https://github.com/ruby/rubygems/issues/3351" if RUBY_PLATFORM.include?("mswin")
+        skip "https://github.com/ruby/rubygems/issues/3351" if mswin?
         bundle "exec erb --version"
 
         expect(stdboth).to eq(default_erb_version)
@@ -634,7 +634,7 @@
 
   describe "with gems bundled via :path with invalid gemspecs" do
     it "outputs the gemspec validation errors" do
-      skip "https://github.com/ruby/rubygems/issues/3351" if RUBY_PLATFORM.include?("mswin")
+      skip "https://github.com/ruby/rubygems/issues/3351" if mswin?
       build_lib "foo"
 
       gemspec = lib_path("foo-1.0").join("foo.gemspec").to_s
@@ -695,7 +695,7 @@ def bin_path(a,b,c)
     end
 
     it "works" do
-      skip "https://github.com/ruby/rubygems/issues/3351" if RUBY_PLATFORM.include?("mswin")
+      skip "https://github.com/ruby/rubygems/issues/3351" if mswin?
       bundle "exec #{gem_cmd} uninstall foo"
       expect(out).to eq("Successfully uninstalled foo-1.0")
     end
@@ -717,7 +717,7 @@ def bin_path(a,b,c)
     end
 
     it "does not load plugins outside of the bundle" do
-      skip "https://github.com/ruby/rubygems/issues/3351" if RUBY_PLATFORM.include?("mswin")
+      skip "https://github.com/ruby/rubygems/issues/3351" if mswin?
       bundle "exec #{gem_cmd} -v"
       expect(out).not_to include("FAIL")
     end

spec/commands/install_spec.rb

@@ -1352,7 +1352,7 @@ def run
       # The make jobserver is a GNU make feature. On Windows extensions are built
       # with nmake, which has no `-j` jobserver (and an inherited `-j` MAKEFLAGS
       # even breaks nmake), so the slot count these examples assert never appears.
-      skip "The make jobserver is not available on Windows (nmake)" if RUBY_PLATFORM.include?("mswin")
+      skip "The make jobserver is not available on Windows (nmake)" if mswin?
 
       @old_makeflags = ENV["MAKEFLAGS"]
       @gemspec = nil

spec/commands/pristine_spec.rb

@@ -232,7 +232,7 @@
     # This just verifies that the generated Makefile from the c_ext gem makes
     # use of the build_args from the bundle config
     it "applies the config when installing the gem" do
-      skip "the generated Makefile uses MSVC `-libpath:` syntax instead of `-L` on Windows" if RUBY_PLATFORM.include?("mswin")
+      skip "the generated Makefile uses MSVC `-libpath:` syntax instead of `-L` on Windows" if mswin?
       bundle "pristine"
 
       makefile_contents = File.read(c_ext_dir.join("Makefile").to_s)
@@ -250,7 +250,7 @@
     # This just verifies that the generated Makefile from the c_ext gem makes
     # use of the build_args from the bundle config
     it "applies the config when installing the gem" do
-      skip "the generated Makefile uses MSVC `-libpath:` syntax instead of `-L` on Windows" if RUBY_PLATFORM.include?("mswin")
+      skip "the generated Makefile uses MSVC `-libpath:` syntax instead of `-L` on Windows" if mswin?
       bundle "pristine"
 
       makefile_contents = File.read(c_ext_dir.join("Makefile").to_s)

spec/support/platforms.rb

@@ -28,6 +28,13 @@ def not_local_tag
       [:jruby, :windows, :ruby].find {|tag| tag != local_tag }
     end
 
+    # The mswin build uses nmake and MSVC, which differ from the mingw build in
+    # ways several specs need to skip (no make jobserver, MSVC Makefile syntax,
+    # extensionless executables, mswin-only fixtures).
+    def mswin?
+      RUBY_PLATFORM.include?("mswin")
+    end
+
     def local_ruby_engine
       RUBY_ENGINE
     end