Remove the C extension, using a Rakefile also works

ext/mimemagic/extconf.rb → ext/mimemagic/Rakefile

-require "mkmf"
+require "rubygems"
+require "rake/clean"
 
 def locate_mime_database
   # User provided path.
@@ -16,7 +17,14 @@ def locate_mime_database
   raise "No database of MIME types could be found. Ensure you have either installed the shared-mime-types package for your distribution, or obtain a version of freedesktop.org.xml, and set FREEDESKTOP_MIME_TYPES_PATH to the location of that file."
 end
 
-mime_database_path = locate_mime_database
-$defs.push("-DMIMEDB_PATH=\\\"#{mime_database_path}\\\"")
-create_header
-create_makefile("mimemagic/mimemagic")
\ No newline at end of file
+desc "Build a file pointing at the database"
+task :default do
+  mime_database_path = locate_mime_database
+  open("../../lib/mimemagic/path.rb", "w") do |f|
+    f.print(%Q{
+      module MimeMagic
+        DATABASE_PATH="#{mime_database_path}"
+      end
+    })
+  end
+end
\ No newline at end of file

ext/mimemagic/mimemagic.c

-#include <ruby.h>
-#include "extconf.h"
-
-void Init_mimemagic(void) {
-    VALUE cMimeMagic;
-
-    cMimeMagic = rb_const_get(rb_cObject, rb_intern("MimeMagic"));
-
-    rb_define_const(cMimeMagic, "DATABASE_PATH", rb_str_new(MIMEDB_PATH, strlen(MIMEDB_PATH)));
-}

lib/mimemagic/tables.rb

@@ -2,6 +2,7 @@
 # frozen_string_literal: true
 # Generated from script/freedesktop.org.xml
 require 'nokogiri'
+require 'mimemagic/path'
 
 class MimeMagic
   EXTENSIONS = {}
@@ -55,7 +56,6 @@ class MimeMagic
   end
 
   def self.open_mime_database
-    require "mimemagic/mimemagic"
     path = MimeMagic::DATABASE_PATH
     File.open(path)
   end

mimemagic.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |s|
 
   s.files         = `git ls-files`.split("\n").reject { |f| f.match(%r{^(test|script)/}) }
   s.require_paths = %w(lib)
-  s.extensions = %w(ext/mimemagic/extconf.rb)
+  s.extensions = %w(ext/mimemagic/Rakefile)
 
   s.summary = 'Fast mime detection by extension or content'
   s.description = 'Fast mime detection by extension or content in pure ruby (Uses freedesktop.org.xml shared-mime-info database)'