os/linux/ld: add functions for querying dynamic linker

Library/Homebrew/os/linux/ld.rb

@@ -0,0 +1,74 @@
+# typed: strict
+# frozen_string_literal: true
+
+module OS
+  module Linux
+    # Helper functions for querying `ld` information.
+    #
+    # @api private
+    module Ld
+      sig { returns(String) }
+      def self.brewed_ld_so_diagnostics
+        brewed_ld_so = HOMEBREW_PREFIX/"lib/ld.so"
+        return "" unless brewed_ld_so.exist?
+
+        ld_so_output = Utils.popen_read(brewed_ld_so, "--list-diagnostics")
+        return "" unless $CHILD_STATUS.success?
+
+        ld_so_output
+      end
+
+      sig { returns(String) }
+      def self.sysconfdir
+        fallback_sysconfdir = "/etc"
+
+        match = brewed_ld_so_diagnostics.match(/path.sysconfdir="(.+)"/)
+        return fallback_sysconfdir unless match
+
+        match.captures.compact.first || fallback_sysconfdir
+      end
+
+      sig { returns(T::Array[String]) }
+      def self.system_dirs
+        dirs = []
+
+        brewed_ld_so_diagnostics.split("\n").each do |line|
+          match = line.match(/path.system_dirs\[0x.*\]="(.*)"/)
+          next unless match
+
+          dirs << match.captures.compact.first
+        end
+
+        dirs
+      end
+
+      sig { params(conf_path: T.any(Pathname, String)).returns(T::Array[String]) }
+      def self.library_paths(conf_path = Pathname(sysconfdir)/"ld.so.conf")
+        conf_file = Pathname(conf_path)
+        paths = Set.new
+        directory = conf_file.realpath.dirname
+
+        conf_file.readlines.each do |line|
+          # Remove comments and leading/trailing whitespace
+          line.strip!
+          line.sub!(/\s*#.*$/, "")
+
+          if line.start_with?(/\s*include\s+/)
+            include_path = Pathname(line.sub(/^\s*include\s+/, "")).expand_path
+            wildcard = include_path.absolute? ? include_path : directory/include_path
+
+            Dir.glob(wildcard.to_s).each do |include_file|
+              paths += library_paths(include_file)
+            end
+          elsif line.empty?
+            next
+          else
+            paths << line
+          end
+        end
+
+        paths.to_a
+      end
+    end
+  end
+end

Library/Homebrew/test/os/linux/ld_spec.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "os/linux/ld"
+require "tmpdir"
+
+RSpec.describe OS::Linux::Ld do
+  describe "::library_paths" do
+    ld_etc = Pathname("")
+    before do
+      ld_etc = Pathname(Dir.mktmpdir("homebrew-tests-ld-etc-", Dir.tmpdir))
+      FileUtils.mkdir [ld_etc/"subdir1", ld_etc/"subdir2"]
+      (ld_etc/"ld.so.conf").write <<~EOS
+        # This line is a comment
+
+        include #{ld_etc}/subdir1/*.conf # This is an end-of-line comment, should be ignored
+
+        # subdir2 is an empty directory
+        include #{ld_etc}/subdir2/*.conf
+
+        /a/b/c
+          /d/e/f # Indentation on this line should be ignored
+        /a/b/c # Duplicate entry should be ignored
+      EOS
+
+      (ld_etc/"subdir1/1-1.conf").write <<~EOS
+        /foo/bar
+        /baz/qux
+      EOS
+
+      (ld_etc/"subdir1/1-2.conf").write <<~EOS
+        /g/h/i
+      EOS
+
+      # Empty files (or files containing only whitespace) should be ignored
+      (ld_etc/"subdir1/1-3.conf").write "\n\t\n\t\n"
+      (ld_etc/"subdir1/1-4.conf").write ""
+    end
+
+    after do
+      FileUtils.rm_rf ld_etc
+    end
+
+    it "parses library paths successfully" do
+      expect(described_class.library_paths(ld_etc/"ld.so.conf")).to eq(%w[/foo/bar /baz/qux /g/h/i /a/b/c /d/e/f])
+    end
+  end
+end