Deprecate ENV.libxml2

- Use `pkg-config` or explicit include paths instead.
- Stop injecting libxml2 paths into the macOS Superenv.

Author: MikeMcQuaid

Library/Homebrew/extend/ENV/std.rb

@@ -70,6 +70,11 @@ def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_a
     append_path "PATH", gcc_formula.opt_bin.to_s
   end
 
+  sig { void }
+  def libxml2
+    odeprecated "ENV.libxml2", "`pkg-config` or explicit include paths"
+  end
+
   sig { returns(T.nilable(PATH)) }
   def determine_pkg_config_libdir
     PATH.new(

Library/Homebrew/extend/os/linux/diagnostic.rb

@@ -203,14 +203,16 @@ def check_linux_sandbox
 
           ::Homebrew::Diagnostic::Finding.new(
             ::Sandbox.failure_reason || "The Linux sandbox is not available.",
-            remediation: if state == :missing_fiddle
-                           "Run Homebrew with its vendored Ruby, which includes Fiddle."
-                         else
-                           <<~EOS.chomp
-                             Homebrew's Linux sandbox requires a kernel with Landlock enabled.
-                             Upgrade to a Linux kernel with Landlock enabled.
-                           EOS
-            end,
+            remediation: (
+              if state == :missing_fiddle
+                "Run Homebrew with its vendored Ruby, which includes Fiddle."
+              else
+                <<~EOS.chomp
+                  Homebrew's Linux sandbox requires a kernel with Landlock enabled.
+                  Upgrade to a Linux kernel with Landlock enabled.
+                EOS
+              end
+            ),
           )
         end
 

Library/Homebrew/extend/os/linux/extend/ENV/std.rb

@@ -35,6 +35,7 @@ def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_a
 
       sig { void }
       def libxml2
+        super
         append "CPPFLAGS", "-I#{::Formula["libxml2"].include/"libxml2"}"
       rescue FormulaUnavailableError
         nil

Library/Homebrew/extend/os/mac/extend/ENV/std.rb

@@ -108,6 +108,7 @@ def macosxsdk(version = nil, formula: nil, testing_formula: false)
       # This is a no-op with all supported macOS SDKs.
       sig { void }
       def libxml2
+        super
         sdk = self["SDKROOT"] || MacOS.sdk_path
         # Use the includes from the sdk
         append "CPPFLAGS", "-I#{sdk}/usr/include/libxml2" unless Pathname("#{sdk}/usr/include/libxml").directory?

Library/Homebrew/extend/os/mac/extend/ENV/super.rb

@@ -33,18 +33,9 @@ def homebrew_extra_pkg_config_paths
         ].map { |p| ::Pathname.new(p) }
       end
 
-      sig { returns(T::Boolean) }
-      def libxml2_include_needed?
-        return false if deps.any? { |d| d.name == "libxml2" }
-        return false if ::Pathname.new("#{self["HOMEBREW_SDKROOT"]}/usr/include/libxml").directory?
-
-        true
-      end
-
       sig { returns(T::Array[::Pathname]) }
       def homebrew_extra_isystem_paths
         paths = []
-        paths << "#{self["HOMEBREW_SDKROOT"]}/usr/include/libxml2" if libxml2_include_needed?
         paths << "#{self["HOMEBREW_SDKROOT"]}/usr/include/apache2" if MacOS::Xcode.without_clt?
         paths << "#{self["HOMEBREW_SDKROOT"]}/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers"
         paths.map { |p| ::Pathname.new(p) }
@@ -64,7 +55,6 @@ def homebrew_extra_library_paths
       sig { returns(T::Array[::Pathname]) }
       def homebrew_extra_cmake_include_paths
         paths = []
-        paths << "#{self["HOMEBREW_SDKROOT"]}/usr/include/libxml2" if libxml2_include_needed?
         paths << "#{self["HOMEBREW_SDKROOT"]}/usr/include/apache2" if MacOS::Xcode.without_clt?
         paths << "#{self["HOMEBREW_SDKROOT"]}/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers"
         paths.map { |p| ::Pathname.new(p) }

Library/Homebrew/test/ENV_spec.rb

@@ -243,6 +243,15 @@
 
   describe Stdenv do
     include_examples EnvActivation
+
+    describe "#libxml2" do
+      it "is deprecated" do
+        expect(env).to receive(:odeprecated)
+          .with("ENV.libxml2", "`pkg-config` or explicit include paths")
+
+        env.libxml2
+      end
+    end
   end
 
   describe Superenv do