Implement Pathname.mktmpdir in builtin Pathname

Move mktmpdir from lib/pathname.rb (which delegated to Dir.mktmpdir)
into pathname_builtin.rb with a pure Ruby implementation that resolves
temporary directories from environment variables and Etc.systmpdir
without requiring the tmpdir library.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

lib/pathname.rb

@@ -9,46 +9,3 @@
 #
 # For documentation, see class Pathname.
 #
-
-class Pathname    # * tmpdir *
-  # call-seq:
-  #   Pathname.mktmpdir -> new_pathname
-  #   Pathname.mktmpdir {|pathname| ... } -> object
-  #
-  # Creates:
-  #
-  # - A temporary directory via Dir.mktmpdir.
-  # - A \Pathname object that contains the path to that directory.
-  #
-  # With no block given, returns the created pathname;
-  # the caller should delete the created directory when it is no longer needed
-  # (FileUtils.rm_r is a convenient method for the deletion):
-  #
-  #   pathname = Pathname.mktmpdir
-  #   dirpath = pathname.to_s
-  #   Dir.exist?(dirpath) # => true
-  #   # Do something with the directory.
-  #   require 'fileutils'
-  #   FileUtils.rm_r(dirpath)
-  #
-  # With a block given, calls the block with the created pathname;
-  # on block exit, automatically deletes the created directory and all its contents;
-  # returns the block's exit value:
-  #
-  #   pathname = Pathname.mktmpdir do |p|
-  #     # Do something with the directory.
-  #     p
-  #   end
-  #   Dir.exist?(pathname.to_s) # => false
-  def self.mktmpdir
-    require 'tmpdir' unless defined?(Dir.mktmpdir)
-    if block_given?
-      Dir.mktmpdir do |dir|
-        dir = self.new(dir)
-        yield dir
-      end
-    else
-      self.new(Dir.mktmpdir)
-    end
-  end
-end

pathname_builtin.rb

@@ -1400,6 +1400,43 @@ def rmtree
     self
   end
 
+  # call-seq:
+  #   Pathname.mktmpdir -> new_pathname
+  #   Pathname.mktmpdir {|pathname| ... } -> object
+  #
+  # Creates a temporary directory and returns a Pathname for it.
+  #
+  # The previous implementation delegated to Dir.mktmpdir and required
+  # the tmpdir library. This builtin implementation removes that dependency.
+  #
+  # With no block given, returns the created pathname;
+  # the caller should delete the created directory when it is no longer needed:
+  #
+  #   pathname = Pathname.mktmpdir
+  #   Dir.exist?(pathname.to_s) # => true
+  #
+  # With a block given, calls the block with the created pathname;
+  # on block exit, automatically deletes the created directory and all its contents;
+  # returns the block's exit value:
+  #
+  #   Pathname.mktmpdir do |dir|
+  #     # Do something with dir.
+  #   end
+  #
+  def self.mktmpdir
+    tmpdir = self.new(resolve_tmpdir)
+    path = tmpdir.__send__(:make_tmpdir)
+    if block_given?
+      begin
+        yield path
+      ensure
+        path.rmtree if path.exist?
+      end
+    else
+      path
+    end
+  end
+
   private
 
   def remove_entry(path)
@@ -1413,6 +1450,40 @@ def remove_entry(path)
       File.unlink(path)
     end
   end
+
+  def self.resolve_tmpdir
+    ['TMPDIR', 'TMP', 'TEMP'].each do |name|
+      dir = ENV[name] rescue next
+      next if dir.nil? || dir.empty?
+      dir = File.expand_path(dir)
+      stat = File.stat(dir) rescue next
+      next unless stat.directory?
+      next unless File.writable?(dir)
+      next if stat.world_writable? && !stat.sticky?
+      return dir
+    end
+    systmpdir = (defined?(Etc.systmpdir) ? Etc.systmpdir : '/tmp')
+    return systmpdir if File.directory?(systmpdir) && File.writable?(systmpdir)
+    '/tmp'
+  end
+
+  def make_tmpdir
+    t = Time.now.strftime("%Y%m%d")
+    n = nil
+    begin
+      name = "d#{t}-#{$$}-#{random_name}#{n ? "-#{n}" : ''}"
+      path = File.join(@path, name)
+      Dir.mkdir(path, 0700)
+    rescue Errno::EEXIST
+      n = (n || 0) + 1
+      retry
+    end
+    self.class.new(path)
+  end
+
+  def random_name
+    Random.urandom(4).unpack1("L").%(36**6).to_s(36)
+  end
 end
 
 class Pathname