error messages on unsupported platforms or when bundler platforms aren't correct

.github/workflows/gem-install.yml

@@ -5,7 +5,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        platform: ["x64-mingw32", "x86_64-darwin", "x86_64-linux"]
+        platform: ["ruby", "x64-mingw32", "x86_64-darwin", "x86_64-linux"]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -21,6 +21,20 @@ jobs:
           path: pkg
           retention-days: 1
 
+  vanilla-install:
+    needs: ["package"]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "3.0"
+      - uses: actions/download-artifact@v2
+        with:
+          name: gem-ruby
+          path: pkg
+      - run: "gem install pkg/tailwindcss-rails-*.gem"
+      - run: "tailwindcss 2>&1 | fgrep 'ERROR: Cannot find the tailwindcss executable'"
+
   linux-install:
     needs: ["package"]
     runs-on: ubuntu-latest

exe/tailwindcss

@@ -2,17 +2,37 @@
 # because rubygems shims assume a gem's executables are Ruby
 
 require "shellwords"
+require "tailwindcss/upstream"
 
-platform_dir = Dir.glob(File.join(__dir__, "*")).select do |f|
-  File.directory?(f) && Gem::Platform.match(File.basename(f))
-end.first
-if platform_dir.nil?
-  raise "Cannot find the tailwindcss executable in #{__dir__} (1)"
+supported_platforms = Tailwindcss::Upstream::NATIVE_PLATFORMS.keys
+
+if supported_platforms.none? { |supported_platform| Gem::Platform.match(supported_platform) }
+  STDERR.puts(<<~ERRMSG)
+    ERROR: tailwindcss-rails does not support the #{::Gem::Platform.local} platform
+    Please install tailwindcss following instructions at https://tailwindcss.com/docs/installation
+  ERRMSG
+  exit 1
+end
+
+exe_path = Dir.glob(File.join(__dir__, "*", "tailwindcss")).find do |f|
+  Gem::Platform.match(File.basename(File.dirname(f)))
 end
+if exe_path.nil?
+  STDERR.puts(<<~ERRMSG)
+    ERROR: Cannot find the tailwindcss executable for #{::Gem::Platform.local} in #{__dir__}
+    If you're using bundler, please make sure you're on the latest bundler version:
+
+      gem install bundler
+      bundle update --bundler
+
+    Then make sure your lock file includes this platform by running:
+
+      bundle lock --add-platform #{::Gem::Platform.local}
+      bundle install
 
-exe_path = File.join(platform_dir, "tailwindcss")
-if !File.exist?(exe_path)
-  raise "Cannot find the tailwindcss executable in #{__dir__} (2)"
+    See `bundle lock --help` output for details.
+  ERRMSG
+  exit 1
 end
 
 command = Shellwords.join([exe_path, ARGV].flatten)

lib/tailwindcss-rails.rb

@@ -1,5 +1,6 @@
 module Tailwindcss
 end
 
+require "tailwindcss/upstream"
 require "tailwindcss/version"
 require "tailwindcss/engine"

lib/tailwindcss/upstream.rb

@@ -0,0 +1,14 @@
+module Tailwindcss
+  # constants describing the upstream tailwindcss project
+  module Upstream
+    VERSION = "v3.0.5"
+
+    # rubygems platform name => upstream release filename
+    NATIVE_PLATFORMS = {
+      "arm64-darwin" => "tailwindcss-macos-arm64",
+      "x64-mingw32" => "tailwindcss-windows-x64.exe",
+      "x86_64-darwin" => "tailwindcss-macos-x64",
+      "x86_64-linux" => "tailwindcss-linux-x64",
+    }
+  end
+end

rakelib/package.rake

@@ -4,8 +4,8 @@
 #
 #  TL;DR: run "rake package"
 #
-#  The native platform gems (defined by TAILWINDCSS_NATIVE_PLATFORMS below) will each contain two
-#  files in addition to what the vanilla ruby gem contains:
+#  The native platform gems (defined by Tailwindcss::Upstream::NATIVE_PLATFORMS) will each contain
+#  two files in addition to what the vanilla ruby gem contains:
 #
 #     exe/
 #     ├── tailwindcss                             #  generic ruby script to find and run the binary
@@ -56,19 +56,10 @@
 #
 require "rubygems/package_task"
 require "open-uri"
-
-TAILWINDCSS_VERSION = "v3.0.5" # string used to generate the download URL
-
-# rubygems platform name => upstream release filename
-TAILWINDCSS_NATIVE_PLATFORMS = {
-  "arm64-darwin" => "tailwindcss-macos-arm64",
-  "x64-mingw32" => "tailwindcss-windows-x64.exe",
-  "x86_64-darwin" => "tailwindcss-macos-x64",
-  "x86_64-linux" => "tailwindcss-linux-x64",
-}
+require_relative "../lib/tailwindcss/upstream"
 
 def tailwindcss_download_url(filename)
-  "https://github.com/tailwindlabs/tailwindcss/releases/download/#{TAILWINDCSS_VERSION}/#{filename}"
+  "https://github.com/tailwindlabs/tailwindcss/releases/download/#{Tailwindcss::Upstream::VERSION}/#{filename}"
 end
 
 TAILWINDCSS_RAILS_GEMSPEC = Bundler.load_gemspec("tailwindcss-rails.gemspec")
@@ -78,15 +69,14 @@ desc "Build the ruby gem"
 task "gem:ruby" => [gem_path]
 
 exepaths = []
-TAILWINDCSS_NATIVE_PLATFORMS.each do |platform, filename|
+Tailwindcss::Upstream::NATIVE_PLATFORMS.each do |platform, filename|
   TAILWINDCSS_RAILS_GEMSPEC.dup.tap do |gemspec|
     exedir = File.join(gemspec.bindir, platform) # "exe/x86_64-linux"
     exepath = File.join(exedir, "tailwindcss") # "exe/x86_64-linux/tailwindcss"
     exepaths << exepath
 
     # modify a copy of the gemspec to include the native executable
     gemspec.platform = platform
-    gemspec.executables << "tailwindcss"
     gemspec.files += [exepath, "LICENSE-DEPENDENCIES"]
 
     # create a package task

tailwindcss-rails.gemspec

@@ -16,6 +16,7 @@ Gem::Specification.new do |spec|
 
   spec.files = Dir["{app,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
   spec.bindir = "exe"
+  spec.executables << "tailwindcss"
 
   spec.add_dependency "railties", ">= 6.0.0"
 end