feat: introduce MiniPortile.mkmf_config

which will set $LDFLAGS and $CFLAGS for the recipe, including a new
feature to support pkg-config files for the library.

This should allow gems with C extensions that use mini_portile to more
easily configure compiler and linker flags.

.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 = {}
 
@@ -130,17 +128,20 @@ yaml.files = [{
                 url: "https://github.com/yaml/libyaml/releases/download/0.2.5/yaml-0.2.5.tar.gz",
                 sha256: "c642ae9b75fee120b2d96c712538bd2cf283228d2337df2cf2988e3c02678ef4",
               }]
-recipes.push(yaml)
+recipes.unshift(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.mkmf_config(pkg: "yaml-0.1")
 
-  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}
     should have included '#{expected}'
   MSG
+
+  unless have_library("yaml", "yaml_get_version", "yaml.h")
+    raise("could not find libyaml development environment")
+  end
 end
 
 namespace :ports do
@@ -158,9 +159,10 @@ 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
 
@@ -173,7 +175,9 @@ namespace :ports do
       puts "Artifacts of '#{recipe.name}' in '#{recipe.path}'"
     end
     puts "LIBRARY_PATH: #{ENV['LIBRARY_PATH'].inspect}"
-    puts "LDFLAGS: #{ENV['LDFLAGS'].inspect}, #{$LDFLAGS.inspect}"
+    puts "LDFLAGS: #{ENV['LDFLAGS'].inspect}"
+    puts "$LDFLAGS: #{$LDFLAGS.inspect}"
+    puts "$CFLAGS: #{$CFLAGS.inspect}"
   end
 end
 

lib/mini_portile2/mini_portile.rb

@@ -268,6 +268,43 @@ def activate
     end
   end
 
+  def mkmf_config(pkg: nil, dir: nil)
+    require "mkmf"
+
+    if pkg
+      dir ||= File.join(path, "lib", "pkgconfig")
+      pcfile = File.join(dir, "#{pkg}.pc")
+      unless File.exist?(pcfile)
+        raise ArgumentError, "pkg-config file '#{pcfile}' does not exist"
+      end
+
+      output "Configuring MakeMakefile for #{File.basename(pcfile)} (in #{File.dirname(pcfile)})\n"
+
+      # on macos, pkg-config will not return --cflags without this
+      ENV["PKG_CONFIG_ALLOW_SYSTEM_CFLAGS"] = "t"
+
+      # append to PKG_CONFIG_PATH as we go, so later pkg-config files can depend on earlier ones
+      ENV["PKG_CONFIG_PATH"] = [ENV["PKG_CONFIG_PATH"], dir].compact.join(File::PATH_SEPARATOR)
+
+      cflags = minimal_pkg_config(pcfile, "cflags")
+      ldflags = minimal_pkg_config(pcfile, "libs", "static")
+    else
+      output "Configuring MakeMakefile for #{@name} #{@version} (from #{path})\n"
+
+      include_path = File.join(path, "include")
+      lib_path = File.join(path, "lib")
+
+      lib_name = name.sub(/\Alib/, "") # TODO: use delete_prefix when we no longer support ruby 2.4
+
+      cflags = "-I#{include_path}" if Dir.exist?(include_path)
+      ldflags = "-L#{lib_path} -l#{lib_name}" if Dir.exist?(lib_path)
+    end
+
+    $CFLAGS << " " << cflags if cflags
+    $CXXFLAGS << " " << cflags if cflags
+    $LDFLAGS << " " << ldflags if ldflags
+  end
+
   def path
     File.expand_path(port_path)
   end
@@ -656,4 +693,29 @@ def with_tempfile(filename, full_path)
     FileUtils.mkdir_p File.dirname(full_path)
     FileUtils.mv temp_file.path, full_path, :force => true
   end
+
+  #
+  #  this minimal version of pkg_config is based on ruby 29dc9378 (2023-01-09)
+  #
+  #  specifically with the fix from b90e56e6 to support multiple pkg-config options, and removing
+  #  code paths that aren't helpful for mini-portile's use case of parsing pc files.
+  #
+  def minimal_pkg_config(pkg, *pcoptions)
+    if pcoptions.empty?
+      raise ArgumentError, "no pkg-config options are given"
+    end
+
+    if ($PKGCONFIG ||=
+        (pkgconfig = MakeMakefile.with_config("pkg-config") {MakeMakefile.config_string("PKG_CONFIG") || "pkg-config"}) &&
+        MakeMakefile.find_executable0(pkgconfig) && pkgconfig)
+      pkgconfig = $PKGCONFIG
+    else
+      raise RuntimeError, "pkg-config is not found"
+    end
+
+    pcoptions = Array(pcoptions).map { |o| "--#{o}" }
+    response = IO.popen([pkgconfig, *pcoptions, pkg], err:[:child, :out], &:read)
+    raise RuntimeError, response unless $?.success?
+    response.strip
+  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/libexslt.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: libexslt
+Version: 0.8.21
+Description: EXSLT Extension library
+Requires: libxml-2.0, libxslt
+Cflags: -I${includedir}
+Libs: -L${libdir} -lexslt
+Libs.private: -lm 

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_mkmf_config.rb

@@ -0,0 +1,133 @@
+require File.expand_path('../helper', __FILE__)
+
+class TestMkmfConfig < TestCase
+  attr_reader :recipe, :include_path, :lib_path
+
+  LIBXML_PCP = File.join(__dir__, "assets", "pkgconf", "libxml2")
+  LIBXSLT_PCP = File.join(__dir__, "assets", "pkgconf", "libxslt")
+
+  def setup
+    super
+
+    @save_env = %w[PATH CPATH LIBRARY_PATH LDFLAGS PKG_CONFIG_PATH].inject({}) do |env, var|
+      env.update(var => ENV[var])
+    end
+    $LDFLAGS = ""
+    $CFLAGS = ""
+
+    FileUtils.rm_rf(["tmp", "ports"]) # remove any previous test files
+
+    @recipe = MiniPortile.new("libfoo", "1.0.0").tap do |recipe|
+      recipe.logger = StringIO.new
+    end
+    @include_path = File.join(@recipe.path, "include")
+    @lib_path = File.join(@recipe.path, "lib")
+  end
+
+  def teardown
+    FileUtils.rm_rf(["tmp", "ports"]) # remove any previous test files
+
+    $LDFLAGS = ""
+    $CFLAGS = ""
+    @save_env.each do |var, val|
+      ENV[var] = val
+    end
+
+    super
+  end
+
+  def test_mkmf_config_recipe_LDFLAGS_global_lib_dir_does_not_exist
+    recipe.mkmf_config
+
+    refute_includes($LDFLAGS.split, "-L#{lib_path}")
+    refute_includes($LDFLAGS.split, "-lfoo")
+  end
+
+  def test_mkmf_config_recipe_LDFLAGS_global
+    FileUtils.mkdir_p(lib_path)
+
+    recipe.mkmf_config
+
+    assert_includes($LDFLAGS.split, "-L#{lib_path}")
+    assert_includes($LDFLAGS.split, "-lfoo") # note the recipe name is "libfoo"
+  end
+
+  def test_mkmf_config_recipe_CFLAGS_global_include_dir_does_not_exist
+    recipe.mkmf_config
+
+    refute_includes($CFLAGS.split, "-I#{include_path}")
+  end
+
+  def test_mkmf_config_recipe_CFLAGS_global
+    FileUtils.mkdir_p(include_path)
+
+    recipe.mkmf_config
+
+    assert_includes($CFLAGS.split, "-I#{include_path}")
+  end
+
+  def test_mkmf_config_pkgconf_does_not_exist
+    assert_raises(ArgumentError) do
+      recipe.mkmf_config(pkg: "foo")
+    end
+  end
+
+  def test_mkmf_config_pkgconf_LDFLAGS_global
+    # can't get the pkgconf utility to install on windows with ruby 2.3 in CI
+    skip if MiniPortile.windows? && RUBY_VERSION < "2.4"
+
+    recipe.mkmf_config(pkg: "libxml-2.0", dir: LIBXML_PCP)
+
+    assert_includes($LDFLAGS.split, "-L/foo/libxml2/2.11.5/lib")
+    assert_includes($LDFLAGS.split, "-lxml2")
+  end
+
+  def test_mkmf_config_pkgconf_CFLAGS_global
+    # can't get the pkgconf utility to install on windows with ruby 2.3 in CI
+    skip if MiniPortile.windows? && RUBY_VERSION < "2.4"
+
+    recipe.mkmf_config(pkg: "libxml-2.0", dir: LIBXML_PCP)
+
+    assert_includes($CFLAGS.split, "-I/foo/libxml2/2.11.5/include/libxml2")
+  end
+
+  def test_mkmf_config_pkgconf_path_accumulation
+    # can't get the pkgconf utility to install on windows with ruby 2.3 in CI
+    skip if MiniPortile.windows? && RUBY_VERSION < "2.4"
+
+    (ENV["PKG_CONFIG_PATH"] || "").split(File::PATH_SEPARATOR).tap do |pcpaths|
+      refute_includes(pcpaths, LIBXML_PCP)
+      refute_includes(pcpaths, LIBXSLT_PCP)
+    end
+
+    recipe.mkmf_config(pkg: "libxml-2.0", dir: LIBXML_PCP)
+
+    ENV["PKG_CONFIG_PATH"].split(File::PATH_SEPARATOR).tap do |pcpaths|
+      assert_includes(pcpaths, LIBXML_PCP)
+      refute_includes(pcpaths, LIBXSLT_PCP)
+    end
+
+    recipe.mkmf_config(pkg: "libxslt", dir: LIBXSLT_PCP)
+
+    ENV["PKG_CONFIG_PATH"].split(File::PATH_SEPARATOR).tap do |pcpaths|
+      assert_includes(pcpaths, LIBXML_PCP)
+      assert_includes(pcpaths, LIBXSLT_PCP)
+    end
+
+    recipe.mkmf_config(pkg: "libexslt", dir: LIBXSLT_PCP)
+
+    $CFLAGS.split.tap do |cflags|
+      assert_includes(cflags, "-I/foo/libxml2/2.11.5/include/libxml2")
+      assert_includes(cflags, "-I/foo/libxslt/1.1.38/include")
+    end
+    $LDFLAGS.split.tap do |ldflags|
+      assert_includes(ldflags, "-L/foo/libxml2/2.11.5/lib")
+      assert_includes(ldflags, "-lxml2")
+      assert_includes(ldflags, "-L/foo/libxslt/1.1.38/lib")
+      assert_includes(ldflags, "-lxslt")
+      assert_includes(ldflags, "-lexslt")
+      assert_includes(ldflags, "-L/foo/zlib/1.3/lib") # from `--static`
+      assert_includes(ldflags, "-lz") # from `--static`
+    end
+  end
+end