Small changes to the libgumbo build branch

- remove the `rebuild-libgumbo` target which is probably not needed
  once #3220 is merged
- avoid downloading googletest when just running `rake compile`
- update the Manifest check to ignore new gumbo-parser/ files
- simplify the 'host' variable in gumbo.rake, since we're only using
  it in development (and not cross-compiling)
- put back the libgumbo $libs, $LIBPATH, and include flags modifications

ext/nokogiri/extconf.rb

@@ -1058,6 +1058,10 @@ def configure
   libgumbo_recipe = process_recipe("libgumbo", "1.0.0-nokogiri", static_p, cross_build_p, false) do |recipe|
     recipe.source_directory = File.join(PACKAGE_ROOT_DIR, "gumbo-parser")
   end
+  append_cppflags("-I#{File.join(libgumbo_recipe.path, "include")}")
+  $libs = $libs + " " + File.join(libgumbo_recipe.path, "lib", "libgumbo.a")
+  $LIBPATH = $LIBPATH | [File.join(libgumbo_recipe.path, "lib")]
+  ensure_func("gumbo_parse_with_options", "nokogiri_gumbo.h")
 end
 
 have_func("xmlHasFeature") || abort("xmlHasFeature() is missing.") # introduced in libxml 2.6.21
@@ -1102,17 +1106,6 @@ def configure
       \t-$(Q)$(RUBY) $(srcdir)/extconf.rb --clean --#{static_p ? "enable" : "disable"}-static
     EOF
   end
-  File.open("Makefile", "at") do |mk|
-    mk.print(<<~EOF)
-
-      .PHONY: rebuild-libgumbo
-
-      $(TARGET_SO): rebuild-libgumbo
-      rebuild-libgumbo:
-      \t-$(Q)$(MAKE) -C tmp/#{libgumbo_recipe.host}/ports/libgumbo/1.0.0-nokogiri/libgumbo-1.0.0-nokogiri install
-    EOF
-  end
-
 end
 
 # rubocop:enable Style/GlobalVars

rakelib/check-manifest.rake

@@ -56,7 +56,12 @@ task :check_manifest, [:verbose] do |_, args|
     [0-9]*
     appveyor.yml
     **/compile_commands.json
+    gumbo-parser/Makefile.old
+    gumbo-parser/aclocal.m4
+    gumbo-parser/autom4te.cache/*
+    gumbo-parser/build-aux/*
     gumbo-parser/fuzzer/*
+    gumbo-parser/googletest/*
     gumbo-parser/test/*
     gumbo-parser/gperf-filter.sed
     lib/nokogiri/**/nokogiri.{jar,so}

rakelib/gumbo.rake

@@ -1,36 +1,34 @@
 # frozen_string_literal: true
 
+# We want to run the gumbo test suite using exactly the same compiled gumbo-parser
+# that Nokogiri uses.
+#
+# To that end, we first need to get the Rake ExtensionTask to run extconf.rb which will
+# run the gumbo-parser's configure script. We don't want to compile the extension
+# at this point, so we make `gumbo:test` depend on the Nokogiri Makefile.
 namespace "gumbo" do
-  # We want to run the gumbo test suite using exactly the same compiled gumbo-parser
-  # that Nokogiri uses.
-  #
-  # To that end, we first need to get the Rake ExtensionTask to run extconf.rb which will
-  # run the gumbo-parser's configure script. We don't want to compile the extension
-  # at this point, so we make `gumbo:test` depend on the Nokogiri Makefile.
-
-  gtest_pkg = "gumbo-parser/googletest"
-  host = RbConfig::CONFIG["host_alias"].empty? ? RbConfig::CONFIG["host"] : RbConfig::CONFIG["host_alias"]
-  host = host.gsub("i386", "i686")
+  host = RbConfig::CONFIG["host"]
   nokogiri_makefile = File.join("tmp/#{RUBY_PLATFORM}/nokogiri/#{RUBY_VERSION}/Makefile")
   gumbotest_builddir = "tmp/#{RUBY_PLATFORM}/nokogiri/#{RUBY_VERSION}/tmp/#{host}/ports/libgumbo/1.0.0-nokogiri/libgumbo-1.0.0-nokogiri"
   gumbotest_configure = File.absolute_path("gumbo-parser/configure")
 
+  gtest_pkg = "gumbo-parser/googletest"
   file gtest_pkg do
     sh(<<~EOF)
       curl -L https://github.com/google/googletest/archive/release-1.8.0.tar.gz | \
         tar zxf - --strip-components 1 -C gumbo-parser googletest-release-1.8.0/googletest
     EOF
   end
 
-  file gumbotest_configure => gtest_pkg do
-    sh("autoreconf", "-fiv", chdir: "gumbo-parser")
-  end
-
   desc "Run the gumbo parser test suite"
-  task "test" => nokogiri_makefile do
+  task "test" => [nokogiri_makefile, gtest_pkg] do
     sh("make", "-j2", "-C", gumbotest_builddir, "check")
   end
 
+  file gumbotest_configure do
+    sh("autoreconf", "-fiv", chdir: "gumbo-parser")
+  end
+
   # Make sure the libgumbo configure script is created before trying to compile the extension.
   file nokogiri_makefile => gumbotest_configure