Add --gemfile option not to rely on BUNDLE_GEMFILE environment variable

The env var `BUNDLE_GEMFILE` was used to specify the Gemfile path by
bundler. However, bundler somehow discards the env var when nested
`bundle exec`. This commit adds `--gemfile` option to specify the
Gemfile path explicitly without relying on the env var propagation.

Author: kateinoigakukun

lib/ruby_wasm/cli.rb

@@ -54,6 +54,7 @@ def build(args)
         profile: "full",
         stdlib: true,
         disable_gems: false,
+        gemfile: nil,
         patches: [],
       }
       OptionParser
@@ -115,6 +116,10 @@ def build(args)
             options[:format] = format
           end
 
+          opts.on("--gemfile GEMFILE", "Gemfile") do |gemfile|
+            options[:gemfile] = gemfile
+          end
+
           opts.on("--print-ruby-cache-key", "Print Ruby cache key") do
             options[:print_ruby_cache_key] = true
           end
@@ -279,7 +284,10 @@ def self.bundled_patches_path
     def derive_packager(options)
       __skip__ =
         if defined?(Bundler) && !options[:disable_gems]
-          definition = Bundler.definition
+          if options[:gemfile]
+            Bundler::SharedHelpers.set_env "BUNDLE_GEMFILE", options[:gemfile]
+          end
+          definition = Bundler.definition(true) # unlock=true to re-evaluate "BUNDLE_GEMFILE"
         end
       RubyWasm::Packager.new(root, build_config(options), definition)
     end

rakelib/packaging.rake

@@ -52,7 +52,7 @@ namespace :npm do
           "RUBY_WASM_ROOT" => base_dir
         }
         if gemfile_path = pkg[:gemfile]
-          env["BUNDLE_GEMFILE"] = File.join(base_dir, gemfile_path)
+          build_command.push "--gemfile", gemfile_path
         else
           # Explicitly disable rubygems integration since Bundler finds
           # Gemfile in the repo root directory.

sig/ruby_wasm/cli.rbs

@@ -15,6 +15,7 @@ module RubyWasm
       profile: String,
       stdlib: bool,
       disable_gems: bool,
+      gemfile: String?,
       patches: Array[String],
       format: String,
     }