feat: introduce activate(mkmf: true) with support for pkg-config

which will set $LDFLAGS and $CFLAGS according to the pkg-config file

This should allow gems with C extensions that use mini_portile to pass
in the pkg-config and everything should just work.

.gitignore

@@ -3,3 +3,4 @@ Gemfile.lock
 pkg
 ports
 tmp
+mkmf.log

examples/Rakefile

@@ -3,8 +3,6 @@ require 'rbconfig'
 $: << File.expand_path(File.join(File.dirname(__FILE__), "../lib"))
 require "mini_portile2"
 
-require "mkmf"
-
 recipes = []
 recipe_hooks = {}
 
@@ -132,8 +130,7 @@ yaml.files = [{
               }]
 recipes.push(yaml)
 recipe_hooks["yaml"] = lambda do |recipe|
-  conf = pkg_config(File.join(recipe.path, "lib", "pkgconfig", "yaml-0.1.pc"))
-  puts "pkg_config: #{conf.inspect}"
+  recipe.activate_mkmf(pkgconf: File.join(recipe.path, "lib", "pkgconfig", "yaml-0.1.pc"))
 
   expected = "-L" + MiniPortile.native_path(File.join(recipe.path, "lib"))
   $LDFLAGS.split.include?(expected) or raise(<<~MSG)
@@ -158,9 +155,10 @@ namespace :ports do
     desc "Install port #{recipe.name} #{recipe.version}"
     task recipe.name => ["ports"] do |t|
       recipe.cook
-      recipe.activate
       if hook = recipe_hooks[recipe.name]
         hook.call(recipe)
+      else
+        recipe.activate
       end
     end
 

lib/mini_portile2/mini_portile.rb

@@ -236,7 +236,21 @@ def cook
     return true
   end
 
-  def activate
+  def activate(mkmf: false, pkgconf: nil)
+    if mkmf
+      activate_mkmf(pkgconf:)
+    else
+      activate_classic(pkgconf:)
+    end
+  end
+
+  def activate_classic(pkgconf: nil)
+    if pkgconf
+      # because I don't know if anybody has this use case,
+      # I just haven't bothered to implement this yet.
+      raise NotImplementedError, "MiniPortile#activate classic does not yet support a pkgconf. If you want this functionality, please open an issue! ♥ ♥ ♥"
+    end
+
     lib_path = File.join(port_path, "lib")
     vars = {
       'PATH'          => File.join(port_path, 'bin'),
@@ -268,6 +282,33 @@ def activate
     end
   end
 
+  def activate_mkmf(pkgconf: nil)
+    if !pkgconf
+      raise NotImplementedError, "MiniPortile#activate for mkmf does not yet work without a pkgconf. If you want this functionality, please open an issue! ♥ ♥ ♥"
+    end
+
+    unless File.exist?(pkgconf)
+      raise RuntimeError, "pkg-config file '#{pkgconf}' does not exist"
+    end
+
+    output "Activating #{@name} #{@version} using #{pkgconf} ..."
+
+    require_relative "mkmf_patches"
+
+    # on macos, pkg-config will not return --cflags without this
+    ENV["PKG_CONFIG_ALLOW_SYSTEM_CFLAGS"] = "t"
+
+    cflags = MakeMakefile.pkg_config(pkgconf, "cflags")
+    ldflags = MakeMakefile.pkg_config(pkgconf, "libs", "static")
+
+    MakeMakefile.append_cflags(cflags)
+    MakeMakefile.append_ldflags(ldflags)
+
+    # make sure future calls to activate_mkmf are able to find this pkg-config
+    # e.g., in nokogiri, the libxslt pc file references libxml2
+    ENV["PKG_CONFIG_PATH"] = "#{native_path(File.dirname(pkgconf))}#{File::PATH_SEPARATOR}#{ENV["PKG_CONFIG_PATH"]}"
+  end
+
   def path
     File.expand_path(port_path)
   end
@@ -656,4 +697,8 @@ def with_tempfile(filename, full_path)
     FileUtils.mkdir_p File.dirname(full_path)
     FileUtils.mv temp_file.path, full_path, :force => true
   end
+
+  def abort_pkg_config(id)
+    abort("\nCould not configure the build properly (#{id}). Please install either the `pkg-config` utility or the `pkg-config` rubygem.\n\n")
+  end
 end

test/test_activate.rb

@@ -3,14 +3,17 @@
 class TestActivate < TestCase
   attr_reader :recipe
 
+  LIBXML_PC = File.join(__dir__, "assets", "pkgconf", "libxml2", "libxml-2.0.pc")
+  LIBXSLT_PC = File.join(__dir__, "assets", "pkgconf", "libxslt", "libxslt.pc")
+
   def setup
     super
 
     @save_env = %w[PATH CPATH LIBRARY_PATH LDFLAGS].inject({}) do |env, var|
       env.update(var => ENV[var])
     end
-    $LDFLAGS = nil
-    $CPPFLAGS = nil
+    $LDFLAGS = ""
+    $CFLAGS = ""
 
     FileUtils.rm_rf(["tmp", "ports"]) # remove any previous test files
 
@@ -22,8 +25,8 @@ def setup
   def teardown
     FileUtils.rm_rf(["tmp", "ports"]) # remove any previous test files
 
-    $LDFLAGS = nil
-    $CPPFLAGS = nil
+    $LDFLAGS = ""
+    $CFLAGS = ""
     @save_env.each do |var, val|
       ENV[var] = val
     end
@@ -119,6 +122,55 @@ def test_LDFLAGS_env_var_when_cross_compiling
     assert_equal(flag_elements('LDFLAGS').first, "-L#{lib_path}")
   end
 
+  def test_activate_classic_with_pkgconf_raises_an_exception
+    assert_raises(NotImplementedError) do
+      recipe.activate(pkgconf: "fake/path/to/foo.pc")
+    end
+
+    assert_raises(NotImplementedError) do
+      recipe.activate_classic(pkgconf: "fake/path/to/foo.pc")
+    end
+  end
+
+  def test_activate_mkmf_without_pkgconf_raises_an_exception
+    assert_raises(NotImplementedError) do
+      recipe.activate(mkmf: true)
+    end
+
+    assert_raises(NotImplementedError) do
+      recipe.activate_mkmf
+    end
+  end
+
+  def test_activate_mkmf_pkgconf_does_not_exist
+    assert_raises(RuntimeError) do
+      recipe.activate(mkmf: true, pkgconf: "nonexistent/foo.pc")
+    end
+  end
+
+  def test_activate_mkmf_LDFLAGS_global
+    recipe.activate(mkmf: true, pkgconf: LIBXML_PC)
+
+    assert_includes($LDFLAGS.split, "-lxml2")
+    assert_includes($LDFLAGS.split, "-L#{MiniPortile.native_path("/foo/libxml2/2.11.5/lib")}")
+  end
+
+  def test_activate_mkmf_CFLAGS_global
+    recipe.activate(mkmf: true, pkgconf: LIBXML_PC)
+
+    assert_includes($CFLAGS.split, "-I#{MiniPortile.native_path("/foo/libxml2/2.11.5/include/libxml2")}")
+  end
+
+  def test_activate_mkmf_chains_pkgconf_path
+    recipe.activate(mkmf: true, pkgconf: LIBXML_PC)
+    recipe.activate(mkmf: true, pkgconf: LIBXSLT_PC)
+
+    xmlflags = $LDFLAGS.split.select { |v| v == "-L#{MiniPortile.native_path("/foo/libxml2/2.11.5/lib")}" }
+
+    # the -L from both libxml and libxslt should be present
+    assert_equal(2, xmlflags.size)
+  end
+
   private
 
   def path_elements(varname)