feat: introduce activate_mkmf 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 = {}
 
@@ -132,10 +130,9 @@ 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"))
+  expected = "-L" + File.join(recipe.path, "lib")
   $LDFLAGS.split.include?(expected) or raise(<<~MSG)
     assertion failed: LDFLAGS not updated correctly:
     #{$LDFLAGS}
@@ -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

@@ -94,6 +94,44 @@ def self.posix_path(path)
     end
   end
 
+  #
+  #  this minimal version of pkg_config is based on ruby 29dc9378 (2023-01-09)
+  #
+  #  specifically with the fix from b90e56e6 to support multiple pkg-config options
+  #
+  def self.pkg_config(pkg, *options)
+    if options.empty?
+      raise ArgumentError, "no pkg-config options are given"
+    end
+
+    fmt = "not found"
+    def fmt.%(x)
+      x ? x.inspect : self
+    end
+
+    MakeMakefile.checking_for "mini_portile pkg-config for #{pkg}", fmt do
+      if ($PKGCONFIG ||=
+          (pkgconfig = MakeMakefile.with_config("pkg-config") {MakeMakefile.config_string("PKG_CONFIG") || "pkg-config"}) &&
+          MakeMakefile.find_executable0(pkgconfig) && pkgconfig)
+        # default to pkg-config command
+        pkgconfig = $PKGCONFIG
+        args = [pkg]
+      elsif MakeMakefile.find_executable0(pkgconfig = "#{pkg}-config")
+      # default to package specific config command, as a last resort.
+      else
+        raise RuntimeError, "pkg-config is not found"
+      end
+
+      opts = Array(options).map { |o| "--#{o}" }
+
+      output = MakeMakefile.xpopen([pkgconfig, *opts, *args], err:[:child, :out], &:read)
+      MakeMakefile::Logging.open {puts output.each_line.map{|s|"=> #{s.inspect}"}}
+      raise RuntimeError, output unless $?.success?
+
+      output.strip
+    end
+  end
+
   def initialize(name, version, **kwargs)
     @name = name
     @version = version
@@ -236,7 +274,21 @@ def cook
     return true
   end
 
-  def activate
+  def activate(mkmf: false, pkgconf: nil)
+    if mkmf
+      activate_mkmf(pkgconf: pkgconf)
+    else
+      activate_classic(pkgconf: 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 +320,33 @@ 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 "mkmf"
+
+    # on macos, pkg-config will not return --cflags without this
+    ENV["PKG_CONFIG_ALLOW_SYSTEM_CFLAGS"] = "t"
+
+    cflags = MiniPortile.pkg_config(pkgconf, "cflags")
+    ldflags = MiniPortile.pkg_config(pkgconf, "libs", "static")
+
+    $CFLAGS << " " << cflags
+    $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 +735,8 @@ 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/assets/pkgconf/libxml2/libxml-2.0.pc

@@ -0,0 +1,13 @@
+prefix=/foo/libxml2/2.11.5
+exec_prefix=${prefix}
+libdir=/foo/libxml2/2.11.5/lib
+includedir=${prefix}/include
+modules=1
+
+Name: libXML
+Version: 2.11.5
+Description: libXML library version2.
+Requires:
+Libs: -L${libdir} -lxml2
+Libs.private: -L/foo/zlib/1.3/lib -lz     -lm  
+Cflags: -I${includedir}/libxml2 

test/assets/pkgconf/libxslt/libxslt.pc

@@ -0,0 +1,13 @@
+prefix=/foo/libxslt/1.1.38
+exec_prefix=${prefix}
+libdir=/foo/libxslt/1.1.38/lib
+includedir=${prefix}/include
+
+
+Name: libxslt
+Version: 1.1.38
+Description: XSLT library version 2.
+Requires: libxml-2.0
+Cflags: -I${includedir}
+Libs: -L${libdir} -lxslt
+Libs.private: -lm

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|
+    @save_env = %w[PATH CPATH LIBRARY_PATH LDFLAGS PKG_CONFIG_PATH].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 +122,64 @@ 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
+    # can't get pkgconf to install on windows with ruby 2.3
+    skip if MiniPortile.windows? && RUBY_VERSION < "2.4"
+
+    recipe.activate(mkmf: true, pkgconf: LIBXML_PC)
+
+    assert_includes($LDFLAGS.split, "-lxml2")
+    assert_includes($LDFLAGS.split, "-L/foo/libxml2/2.11.5/lib")
+  end
+
+  def test_activate_mkmf_CFLAGS_global
+    # can't get pkgconf to install on windows with ruby 2.3
+    skip if MiniPortile.windows? && RUBY_VERSION < "2.4"
+
+    recipe.activate(mkmf: true, pkgconf: LIBXML_PC)
+
+    assert_includes($CFLAGS.split, "-I/foo/libxml2/2.11.5/include/libxml2")
+  end
+
+  def test_activate_mkmf_chains_pkgconf_path
+    # can't get pkgconf to install on windows with ruby 2.3
+    skip if MiniPortile.windows? && RUBY_VERSION < "2.4"
+
+    recipe.activate(mkmf: true, pkgconf: LIBXML_PC)
+    recipe.activate(mkmf: true, pkgconf: LIBXSLT_PC)
+
+    xmlflags = $CFLAGS.split.select { |v| v == "-I/foo/libxml2/2.11.5/include/libxml2" }
+
+    # the -I from libxml should be present twice -- once from libxml2 and once from libxslt (transitively)
+    assert_equal(2, xmlflags.size, $CFLAGS)
+  end
+
   private
 
   def path_elements(varname)