feat: fall back to locally-installed tailwindcss executables

Closes #224

Author: flavorjones

lib/tailwindcss/commands.rb

@@ -15,21 +15,23 @@ def platform
         [:cpu, :os].map { |m| Gem::Platform.local.send(m) }.join("-")
       end
 
-      def executable(
-        exe_path: File.expand_path(File.join(__dir__, "..", "..", "exe"))
-      )
-        if Tailwindcss::Upstream::NATIVE_PLATFORMS.keys.none? { |p| Gem::Platform.match(Gem::Platform.new(p)) }
-          raise UnsupportedPlatformException, <<~MESSAGE
-            tailwindcss-rails does not support the #{platform} platform
-            Please install tailwindcss following instructions at https://tailwindcss.com/docs/installation
-          MESSAGE
-        end
-
+      def executable(exe_path: File.expand_path(File.join(__dir__, "..", "..", "exe")))
         exe_path = Dir.glob(File.expand_path(File.join(exe_path, "*", "tailwindcss"))).find do |f|
           Gem::Platform.match(Gem::Platform.new(File.basename(File.dirname(f))))
         end
 
         if exe_path.nil?
+          exe_path = find_executable_in_path("tailwindcss")
+        end
+
+        if exe_path.nil?
+          if Tailwindcss::Upstream::NATIVE_PLATFORMS.keys.none? { |p| Gem::Platform.match(Gem::Platform.new(p)) }
+            raise UnsupportedPlatformException, <<~MESSAGE
+              tailwindcss-rails does not support the #{platform} platform
+              Please install tailwindcss following instructions at https://tailwindcss.com/docs/installation
+            MESSAGE
+          end
+
           raise ExecutableNotFoundException, <<~MESSAGE
             Cannot find the tailwindcss executable for #{platform} in #{exe_path}
 
@@ -72,6 +74,33 @@ def watch_command(poll: false, **kwargs)
           command << "-p" if poll
         end
       end
+
+      private
+
+      def find_executable_in_path(bin)
+        # based on MakeMakefile.find_executable0
+        executable_file = proc do |name|
+          begin
+            stat = File.stat(name)
+          rescue SystemCallError
+          else
+            next name if stat.file? and stat.executable?
+          end
+        end
+
+        if path ||= ENV['PATH']
+          path = path.split(File::PATH_SEPARATOR)
+        else
+          path = %w[/usr/local/bin /usr/ucb /usr/bin /bin]
+        end
+
+        file = nil
+        path.each do |dir|
+          dir.sub!(/\A"(.*)"\z/m, '\1') if /mswin|mingw/ =~ RUBY_PLATFORM
+          return file if executable_file.call(file = File.join(dir, bin))
+        end
+        nil
+      end
     end
   end
 end

test/lib/tailwindcss/commands_test.rb

@@ -2,9 +2,13 @@
 require "minitest/mock"
 
 class Tailwindcss::CommandsTest < ActiveSupport::TestCase
-  test ".platform is a string containing just the cpu and os (not the version)" do
-    expected = "#{Gem::Platform.local.cpu}-#{Gem::Platform.local.os}"
-    assert_equal(expected, Tailwindcss::Commands.platform)
+  setup do
+    @orig_path = ENV["PATH"]
+    ENV["PATH"] = ""
+  end
+
+  teardown do
+    ENV["PATH"] = @orig_path
   end
 
   def mock_exe_directory(platform)
@@ -18,6 +22,23 @@ def mock_exe_directory(platform)
     end
   end
 
+  def mock_path_binary
+    Dir.mktmpdir do |dir|
+      orig_path = ENV["PATH"]
+      ENV["PATH"] = [dir, ENV["PATH"]].join(File::PATH_SEPARATOR)
+      FileUtils.touch(File.join(dir, "tailwindcss"))
+      FileUtils.chmod("ugo+x", File.join(dir, "tailwindcss"))
+      yield(dir)
+    ensure
+      ENV["PATH"] = orig_path
+    end
+  end
+
+  test ".platform is a string containing just the cpu and os (not the version)" do
+    expected = "#{Gem::Platform.local.cpu}-#{Gem::Platform.local.os}"
+    assert_equal(expected, Tailwindcss::Commands.platform)
+  end
+
   test ".executable returns the absolute path to the binary" do
     mock_exe_directory("sparc-solaris2.8") do |dir, executable|
       expected = File.expand_path(File.join(dir, "sparc-solaris2.8", "tailwindcss"))
@@ -26,6 +47,23 @@ def mock_exe_directory(platform)
     end
   end
 
+  test "when a packaged exe is not found, .executable returns the absolute path to `tailwindcss` that is in PATH" do
+    mock_path_binary do |installed|
+      expected = File.join(installed, "tailwindcss")
+      assert_equal(expected, Tailwindcss::Commands.executable(exe_path: "/blurgh"))
+    end
+  end
+
+  test "when a packaged exe is found, .executable ignores what's in PATH" do
+    mock_exe_directory("sparc-solaris2.8") do |dir, executable|
+      mock_path_binary do |installed|
+        expected = File.expand_path(File.join(dir, "sparc-solaris2.8", "tailwindcss"))
+        assert_equal(expected, executable, "assert on setup")
+        assert_equal(expected, Tailwindcss::Commands.executable(exe_path: dir))
+      end
+    end
+  end
+
   test ".executable raises UnsupportedPlatformException when we're not on a supported platform" do
     Gem::Platform.stub(:match, false) do # nothing is supported
       assert_raises(Tailwindcss::Commands::UnsupportedPlatformException) do