remove nokogumbo integration testing and version info libxml2_path (#…

…3042)

**What problem is this PR intended to solve?**

Nokogumbo has been EOL for two years, let's stop running the integration
testing, and remove the nokogumbo-specific VersionInfo key
`libxml/libxml2_path` (which has been superseded by `nokogiri/cppflags`
and `nokogiri/ldflags` values).


**Have you included adequate test coverage?**

Test coverage for nokogumbo integration scenarios was removed.


**Does this change affect the behavior of either the C or the Java
implementations?**

N/A

CHANGELOG.md

@@ -44,6 +44,7 @@ Documentation on what can be matched:
 * Removed `Nokogiri::HTML5.get` which was deprecated in v1.12.0. [#2278] (@flavorjones)
 * Removed the CSS-to-XPath utility modules `XPathVisitorAlwaysUseBuiltins` and `XPathVisitorOptimallyUseBuiltins`, which were deprecated in v1.13.0 in favor of `XPathVisitor` constructor args. [#2403] (@flavorjones)
 * Removed `XML::Reader#attribute_nodes` which was deprecated in v1.13.8 in favor of `#attribute_hash`. [#2598, #2599] (@flavorjones)
+* Removed the `libxml/libxml2_path` key from `VersionInfo`, used in the past for third-party library integration, in favor of the `nokogiri/cppflags` and `nokogiri/ldflags` keys. Please note that third-party library integration is not fully supported and may be deprecated soon, see #2746 for more context. [#2143] (@flavorjones)
 
 
 ## 1.15.5 / 2023-11-17

CONTRIBUTING.md

@@ -359,8 +359,6 @@ See [Making a release](#making-a-release) below for the checklist.
 
 `scripts/test-exported-symbols` checks the compiled `nokogiri.so` library for surprising exported symbols. This script likely only works on Linux, sorry.
 
-`scripts/test-nokogumbo-compatibility` is used by CI to ensure that Nokogumbo installs correctly against the currently-installed version of Nokogiri. Nokogumbo receives this extra care because it compiles against Nokogiri's and libxml2's header files, and makes assumptions about what symbols are exported by Nokogiri's extension library.
-
 `scripts/files-modified-by-open-prs` is a hack to see what files are being proposed to change in the set of open pull requests. This might be useful if you're thinking about radically changing a file, to be aware of what merge conflicts might result. This could probably be a rake task.
 
 There's a `Vagrantfile` in the project root which I've used once or twice to try to reproduce problems non-Linux systems (like OpenBSD). It's not well-maintained so YMMV.

ext/nokogiri/extconf.rb

@@ -651,8 +651,7 @@ def needs_darwin_linker_hack
 append_ldflags(ENV["LDFLAGS"].split) unless ENV["LDFLAGS"].nil?
 $LIBS = concat_flags($LIBS, ENV["LIBS"])
 
-# nokogumbo code uses C90/C99 features, let's make sure older compilers won't give
-# errors/warnings. see #2302
+# libgumbo uses C90/C99 features, see #2302
 append_cflags(["-std=c99", "-Wno-declaration-after-statement"])
 
 # gumbo html5 serialization is slower with O3, let's make sure we use O2

lib/nokogiri/version/info.rb

@@ -94,11 +94,14 @@ def to_hash
           nokogiri["version"] = Nokogiri::VERSION
 
           unless jruby?
-            #  enable gems like nokogumbo to build with the following in their extconf.rb:
+            #  enable gems to build against Nokogiri with the following in their extconf.rb:
             #
             #    append_cflags(Nokogiri::VERSION_INFO["nokogiri"]["cppflags"])
             #    append_ldflags(Nokogiri::VERSION_INFO["nokogiri"]["ldflags"])
             #
+            #  though, this won't work on all platform and versions of Ruby, and won't be supported
+            #  forever, see https://github.com/sparklemotion/nokogiri/discussions/2746 for context.
+            #
             cppflags = ["-I#{header_directory.shellescape}"]
             ldflags = []
 
@@ -108,7 +111,8 @@ def to_hash
             end
 
             if windows?
-              # on windows, nokogumbo needs to link against nokogiri.so to resolve symbols. see #2167
+              # on windows, third party libraries that wish to link against nokogiri
+              # should link against nokogiri.so to resolve symbols. see #2167
               lib_directory = File.expand_path(File.join(File.dirname(__FILE__), "../#{ruby_minor}"))
               unless File.exist?(lib_directory)
                 lib_directory = File.expand_path(File.join(File.dirname(__FILE__), ".."))
@@ -136,9 +140,6 @@ def to_hash
               libxml["source"] = "packaged"
               libxml["precompiled"] = libxml2_precompiled?
               libxml["patches"] = Nokogiri::LIBXML2_PATCHES
-
-              # this is for nokogumbo and shouldn't be forever
-              libxml["libxml2_path"] = header_directory
             else
               libxml["source"] = "system"
             end

scripts/test-gem-install

@@ -34,8 +34,3 @@ rm -rf lib ext # ensure we don't use the local files
 rake test
 
 ./scripts/test-gem-installation
-
-# delete the Gemfile because that's confusing to older versions of rubygems (e.g., bionic32)
-rm -f Gemfile Gemfile.lock
-./scripts/test-nokogumbo-compatibility 2.0.4
-./scripts/test-nokogumbo-compatibility 2.0.5

scripts/test-gem-installation

@@ -86,16 +86,7 @@ describe gemspec.full_name do
 
     describe "library" do
       describe "packaged" do
-        describe "for nokogumbo" do
-          # this is for nokogumbo and shouldn't be forever
-          it "declares where headers are installed" do
-            assert_equal(
-              nokogiri_ext_dir,
-              Nokogiri::VERSION_INFO["libxml"]["libxml2_path"],
-              "expected Nokogiri::VERSION_INFO to point to #{nokogiri_ext_dir}",
-            )
-          end
-
+        describe "for third-party library linking" do
           it "installs packaged libraries' headers" do
             packaged_library_header_files.each do |header|
               assert(