Preserve Windows paths in MAKE and rake environment variables

lib/rubygems/ext/builder.rb

@@ -32,7 +32,7 @@ def self.make(dest_path, results, make_dir = Dir.pwd, sitedir = nil, targets = [
     target_rbconfig["configure_args"] =~ /with-make-prog\=(\w+)/
     make_program_name = ENV["MAKE"] || ENV["make"] || $1
     make_program_name ||= RUBY_PLATFORM.include?("mswin") ? "nmake" : "make"
-    make_program = shellsplit(make_program_name)
+    make_program = shellsplit_command(make_program_name)
 
     is_nmake = /\bnmake/i.match?(make_program_name)
     # The installation of the bundled gems is failed when DESTDIR is empty in mswin platform.
@@ -102,6 +102,10 @@ def self.run(command, results, command_name = nil, dir = Dir.pwd, env = {})
       require "open3"
       # Set $SOURCE_DATE_EPOCH for the subprocess.
       build_env = { "SOURCE_DATE_EPOCH" => Gem.source_date_epoch_string }.merge(env)
+      # A single-element command would be parsed as a shell command line,
+      # splitting an unquoted command path containing spaces. Use the
+      # [cmdname, argv0] form to keep exec semantics.
+      command = [[command.first, command.first]] if command.size == 1
       output, status = begin
                          Open3.popen2e(build_env, *command, chdir: dir) do |stdin, stdouterr, wait_thread|
                            stdin.close
@@ -148,6 +152,21 @@ def self.shellsplit(command)
     Shellwords.split(command)
   end
 
+  ##
+  # Splits a command string such as ENV["MAKE"] into an argument list.
+  #
+  # On Windows, a value that names an existing file, such as
+  # <tt>C:\path\nmake.exe</tt>, is taken as a single word because POSIX
+  # shell splitting would consume the backslashes as escape characters.
+  # Any other value is split like a POSIX shell command line, where a
+  # path containing spaces must be quoted.
+
+  def self.shellsplit_command(command)
+    return [command] if Gem.win_platform? && File.file?(command)
+
+    shellsplit(command)
+  end
+
   def self.shelljoin(command)
     require "shellwords"
 

lib/rubygems/ext/rake_builder.rb

@@ -20,7 +20,7 @@ def self.build(extension, dest_path, results, args = [], lib_dir = nil, extensio
     rake = ENV["rake"]
 
     if rake
-      rake = shellsplit(rake)
+      rake = shellsplit_command(rake)
     else
       begin
         rake = ruby << "-rrubygems" << Gem.bin_path("rake", "rake")

test/rubygems/test_gem_ext_builder.rb

@@ -106,6 +106,78 @@ def test_custom_make_with_options
     assert_match(/install: OK/, results)
   end
 
+  def test_class_shellsplit_command_windows_path
+    win_platform = Gem.win_platform?
+
+    make = if win_platform
+      FileUtils.mkdir_p File.join(@tempdir, "make dir")
+      File.join(@tempdir, "make dir", "nmake.exe").tr("/", "\\")
+    else
+      # backslashes and spaces are plain filename characters on POSIX
+      File.join(@tempdir, 'C:\make dir\nmake.exe')
+    end
+    FileUtils.touch make
+
+    Gem.win_platform = true
+
+    assert_equal [make], Gem::Ext::Builder.shellsplit_command(make)
+  ensure
+    Gem.win_platform = win_platform
+  end
+
+  def test_class_shellsplit_command_quoted_path
+    assert_equal ['C:\make dir\nmake.exe'],
+                 Gem::Ext::Builder.shellsplit_command('"C:\make dir\nmake.exe"')
+  end
+
+  def test_class_shellsplit_command_with_arguments
+    win_platform = Gem.win_platform?
+
+    Gem.win_platform = true
+
+    assert_equal %w[make -j4], Gem::Ext::Builder.shellsplit_command("make -j4")
+
+    Gem.win_platform = false
+
+    assert_equal %w[make -j4], Gem::Ext::Builder.shellsplit_command("make -j4")
+  ensure
+    Gem.win_platform = win_platform
+  end
+
+  def test_class_shellsplit_command_existing_path_on_posix
+    win_platform = Gem.win_platform?
+
+    FileUtils.mkdir_p File.join(@tempdir, "make dir")
+    make = File.join(@tempdir, "make dir", "make")
+    FileUtils.touch make
+
+    Gem.win_platform = false
+
+    assert_equal make.split(" "), Gem::Ext::Builder.shellsplit_command(make)
+  ensure
+    Gem.win_platform = win_platform
+  end
+
+  def test_class_run_single_element_command_with_spaces
+    dir = File.join @tempdir, "cmd dir"
+    FileUtils.mkdir_p dir
+
+    if Gem.win_platform?
+      command = File.join dir, "say.cmd"
+      File.write command, "@echo spaces-ok\r\n"
+    else
+      command = File.join dir, "say"
+      File.write command, "#!/bin/sh\necho spaces-ok\n"
+      FileUtils.chmod 0o755, command
+    end
+
+    results = []
+
+    Gem::Ext::Builder.run([command], results)
+
+    assert_match(/spaces-ok/, results.join)
+  end
+
   def test_class_run_closes_stdin
     results = []
     check_stdin_script = <<~'RUBY'