core: more heuristics for determining Cygwin

lib/vagrant/util/platform.rb

@@ -10,10 +10,17 @@ module Vagrant
     class Platform
       class << self
         def cygwin?
+          # Installer detects Cygwin
           return true if ENV["VAGRANT_DETECTED_OS"] &&
             ENV["VAGRANT_DETECTED_OS"].downcase.include?("cygwin")
 
-          platform.include?("cygwin")
+          # Ruby running in Cygwin
+          return true if platform.include?("cygwin")
+
+          # Heuristic. If the path contains Cygwin, we just assume we're
+          # in Cygwin. It is generally a safe bet.
+          path = ENV["PATH"] || ""
+          return path.include?("cygwin")
         end
 
         [:darwin, :bsd, :freebsd, :linux, :solaris].each do |type|

test/unit/support/shared/base_context.rb

@@ -107,6 +107,7 @@ shared_context "unit" do
     # can replace them back in later.
     old_env = {}
     environment.each do |key, value|
+      key          = key.to_s
       old_env[key] = ENV[key]
       ENV[key]     = value
     end

test/unit/vagrant/util/platform_test.rb

@@ -3,8 +3,43 @@ require File.expand_path("../../../base", __FILE__)
 require "vagrant/util/platform"
 
 describe Vagrant::Util::Platform do
+  include_context "unit"
+
   subject { described_class }
 
+  describe "#cygwin?" do
+    before do
+      allow(subject).to receive(:platform).and_return("test")
+    end
+
+    around do |example|
+      with_temp_env(VAGRANT_DETECTED_OS: "nope", PATH: "") do
+        example.run
+      end
+    end
+
+    it "returns true if VAGRANT_DETECTED_OS includes cygwin" do
+      with_temp_env(VAGRANT_DETECTED_OS: "cygwin") do
+        expect(subject).to be_cygwin
+      end
+    end
+
+    it "returns true if platform has cygwin" do
+      allow(subject).to receive(:platform).and_return("cygwin")
+      expect(subject).to be_cygwin
+    end
+
+    it "returns true if the PATH contains cygwin" do
+      with_temp_env(PATH: "C:/cygwin") do
+        expect(subject).to be_cygwin
+      end
+    end
+
+    it "returns false if nothing is available" do
+      expect(subject).to_not be_cygwin
+    end
+  end
+
   describe "#fs_real_path" do
     it "fixes drive letters on Windows", :windows do
       expect(described_class.fs_real_path("c:/foo").to_s).to eql("C:/foo")