From 0839e21425d203e9e636855c5074bc2086d472d0 Mon Sep 17 00:00:00 2001
From: Rylan Polster <rslpolster@gmail.com>
Date: Wed, 15 Nov 2023 18:38:53 +0000
Subject: [PATCH 1/6] Deprecate `MacOS` methods on Linux

---
 Library/Homebrew/os/linux.rb | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Library/Homebrew/os/linux.rb b/Library/Homebrew/os/linux.rb
index e813f1f13bee0..197c5ebda2c52 100644
--- a/Library/Homebrew/os/linux.rb
+++ b/Library/Homebrew/os/linux.rb
@@ -55,49 +55,60 @@ module Mac
     raise "Loaded OS::Linux on generic OS!" if ENV["HOMEBREW_TEST_GENERIC_OS"]
 
     def self.version
+      odeprecated "`MacOS.version` on Linux"
       MacOSVersion::NULL
     end
 
     def self.full_version
+      odeprecated "`MacOS.full_version` on Linux"
       MacOSVersion::NULL
     end
 
     def self.languages
+      odeprecated "`MacOS.languages` on Linux"
       @languages ||= Array(ENV["LANG"]&.slice(/[a-z]+/)).uniq
     end
 
     def self.language
+      odeprecated "`MacOS.language` on Linux"
       languages.first
     end
 
     def self.sdk_root_needed?
+      odeprecated "`MacOS.sdk_root_needed?` on Linux"
       false
     end
 
     def self.sdk_path_if_needed(_version = nil)
+      odeprecated "`MacOS.sdk_path_if_needed` on Linux"
       nil
     end
 
     def self.sdk_path(_version = nil)
+      odeprecated "`MacOS.sdk_path` on Linux"
       nil
     end
 
     module Xcode
       def self.version
+        odeprecated "`MacOS::Xcode.version` on Linux"
         ::Version::NULL
       end
 
       def self.installed?
+        odeprecated "`MacOS::Xcode.installed?` on Linux"
         false
       end
     end
 
     module CLT
       def self.version
+        odeprecated "`MacOS::CLT.version` on Linux"
         ::Version::NULL
       end
 
       def self.installed?
+        odeprecated "`MacOS::CLT.installed?` on Linux"
         false
       end
     end

From 8704e79cc0f4c6f5ae50bdbeb35cc2312f8788aa Mon Sep 17 00:00:00 2001
From: Rylan Polster <rslpolster@gmail.com>
Date: Wed, 15 Nov 2023 19:52:21 +0000
Subject: [PATCH 2/6] Separate `MacOS` references

---
 Library/Homebrew/cmd/gist-logs.rb             |  4 +---
 Library/Homebrew/extend/os/linkage_checker.rb |  6 ++++-
 Library/Homebrew/extend/os/mac/formula.rb     | 22 +++++++++++++++++++
 .../Homebrew/extend/os/mac/linkage_checker.rb | 13 +++++++++++
 Library/Homebrew/extend/os/mac/utils/curl.rb  | 15 +++++++++++++
 Library/Homebrew/extend/os/utils/curl.rb      |  4 ++++
 Library/Homebrew/formula.rb                   | 12 ++--------
 Library/Homebrew/linkage_checker.rb           |  8 +++++--
 Library/Homebrew/utils/curl.rb                | 14 +++++++-----
 9 files changed, 76 insertions(+), 22 deletions(-)
 create mode 100644 Library/Homebrew/extend/os/mac/linkage_checker.rb
 create mode 100644 Library/Homebrew/extend/os/mac/utils/curl.rb
 create mode 100644 Library/Homebrew/extend/os/utils/curl.rb

diff --git a/Library/Homebrew/cmd/gist-logs.rb b/Library/Homebrew/cmd/gist-logs.rb
index dba4217ee27fa..829cec0c4b410 100644
--- a/Library/Homebrew/cmd/gist-logs.rb
+++ b/Library/Homebrew/cmd/gist-logs.rb
@@ -73,9 +73,7 @@ def gistify_logs(formula, args:)
       EOS
     end
 
-    if args.new_issue?
-      url = GitHub.create_issue(formula.tap, "#{formula.name} failed to build on #{MacOS.full_version}", url)
-    end
+    url = GitHub.create_issue(formula.tap, "#{formula.name} failed to build on #{OS_VERSION}", url) if args.new_issue?
 
     puts url if url
   end
diff --git a/Library/Homebrew/extend/os/linkage_checker.rb b/Library/Homebrew/extend/os/linkage_checker.rb
index 3e8904e5eb0ef..175e201324b0e 100644
--- a/Library/Homebrew/extend/os/linkage_checker.rb
+++ b/Library/Homebrew/extend/os/linkage_checker.rb
@@ -1,4 +1,8 @@
 # typed: strict
 # frozen_string_literal: true
 
-require "extend/os/linux/linkage_checker" if OS.linux?
+if OS.mac?
+  require "extend/os/mac/linkage_checker"
+else
+  require "extend/os/linux/linkage_checker"
+end
diff --git a/Library/Homebrew/extend/os/mac/formula.rb b/Library/Homebrew/extend/os/mac/formula.rb
index 0d65ad84fee9c..a5dbd1684c62c 100644
--- a/Library/Homebrew/extend/os/mac/formula.rb
+++ b/Library/Homebrew/extend/os/mac/formula.rb
@@ -3,9 +3,31 @@
 
 class Formula
   undef valid_platform?
+  undef std_cmake_args
 
   sig { returns(T::Boolean) }
   def valid_platform?
     requirements.none?(LinuxRequirement)
   end
+
+  sig {
+    params(
+      install_prefix: T.any(String, Pathname),
+      install_libdir: T.any(String, Pathname),
+      find_framework: String,
+    ).returns(T::Array[String])
+  }
+  def std_cmake_args(install_prefix: prefix, install_libdir: "lib", find_framework: "LAST")
+    args = generic_std_cmake_args(install_prefix: install_prefix, install_libdir: install_libdir,
+                                  find_framework: find_framework)
+
+    # Avoid false positives for clock_gettime support on 10.11.
+    # CMake cache entries for other weak symbols may be added here as needed.
+    args << "-DHAVE_CLOCK_GETTIME:INTERNAL=0" if MacOS.version == "10.11" && MacOS::Xcode.version >= "8.0"
+
+    # Ensure CMake is using the same SDK we are using.
+    args << "-DCMAKE_OSX_SYSROOT=#{MacOS.sdk_for_formula(self).path}" if MacOS.sdk_root_needed?
+
+    args
+  end
 end
diff --git a/Library/Homebrew/extend/os/mac/linkage_checker.rb b/Library/Homebrew/extend/os/mac/linkage_checker.rb
new file mode 100644
index 0000000000000..9baba42a7d250
--- /dev/null
+++ b/Library/Homebrew/extend/os/mac/linkage_checker.rb
@@ -0,0 +1,13 @@
+# typed: true
+# frozen_string_literal: true
+
+class LinkageChecker
+  undef system_libraries_exist_in_cache?
+
+  private
+
+  def system_libraries_exist_in_cache?
+    # In macOS Big Sur and later, system libraries do not exist on-disk and instead exist in a cache.
+    MacOS.version >= :big_sur
+  end
+end
diff --git a/Library/Homebrew/extend/os/mac/utils/curl.rb b/Library/Homebrew/extend/os/mac/utils/curl.rb
new file mode 100644
index 0000000000000..56c7e56f51797
--- /dev/null
+++ b/Library/Homebrew/extend/os/mac/utils/curl.rb
@@ -0,0 +1,15 @@
+# typed: true
+# frozen_string_literal: true
+
+module Utils
+  module Curl
+    undef return_value_for_empty_http_status_code
+
+    def return_value_for_empty_http_status_code(url_type, url)
+      # Hack around https://github.com/Homebrew/brew/issues/3199
+      return if MacOS.version == :el_capitan
+
+      generic_return_value_for_empty_http_status_code url_type, url
+    end
+  end
+end
diff --git a/Library/Homebrew/extend/os/utils/curl.rb b/Library/Homebrew/extend/os/utils/curl.rb
new file mode 100644
index 0000000000000..fbd35e61e4d9f
--- /dev/null
+++ b/Library/Homebrew/extend/os/utils/curl.rb
@@ -0,0 +1,4 @@
+# typed: strict
+# frozen_string_literal: true
+
+require "extend/os/mac/utils/curl" if OS.mac?
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 1b04c8484d2f4..2ab55beccdccb 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -1646,7 +1646,7 @@ def std_cargo_args(root: prefix, path: ".")
     ).returns(T::Array[String])
   }
   def std_cmake_args(install_prefix: prefix, install_libdir: "lib", find_framework: "LAST")
-    args = %W[
+    %W[
       -DCMAKE_INSTALL_PREFIX=#{install_prefix}
       -DCMAKE_INSTALL_LIBDIR=#{install_libdir}
       -DCMAKE_BUILD_TYPE=Release
@@ -1655,16 +1655,8 @@ def std_cmake_args(install_prefix: prefix, install_libdir: "lib", find_framework
       -Wno-dev
       -DBUILD_TESTING=OFF
     ]
-
-    # Avoid false positives for clock_gettime support on 10.11.
-    # CMake cache entries for other weak symbols may be added here as needed.
-    args << "-DHAVE_CLOCK_GETTIME:INTERNAL=0" if MacOS.version == "10.11" && MacOS::Xcode.version >= "8.0"
-
-    # Ensure CMake is using the same SDK we are using.
-    args << "-DCMAKE_OSX_SYSROOT=#{MacOS.sdk_for_formula(self).path}" if MacOS.sdk_root_needed?
-
-    args
   end
+  alias generic_std_cmake_args std_cmake_args
 
   # Standard parameters for Go builds.
   sig {
diff --git a/Library/Homebrew/linkage_checker.rb b/Library/Homebrew/linkage_checker.rb
index b3b00bbeb36ed..d3befd6423ab7 100644
--- a/Library/Homebrew/linkage_checker.rb
+++ b/Library/Homebrew/linkage_checker.rb
@@ -196,9 +196,8 @@ def check_dylibs(rebuild_cache:)
 
           if (dep = dylib_to_dep(dylib))
             @broken_deps[dep] |= [dylib]
-          elsif MacOS.version >= :big_sur && dylib_found_via_dlopen(dylib)
+          elsif system_libraries_exist_in_cache? && dylib_found_via_dlopen(dylib)
             # If we cannot associate the dylib with a dependency, then it may be a system library.
-            # In macOS Big Sur and later, system libraries do not exist on-disk and instead exist in a cache.
             # If dlopen finds the dylib, then the linkage is not broken.
             @system_dylibs << dylib
           elsif !system_framework?(dylib)
@@ -227,6 +226,11 @@ def check_dylibs(rebuild_cache:)
   end
   alias generic_check_dylibs check_dylibs
 
+  def system_libraries_exist_in_cache?
+    false
+  end
+  alias generic_system_libraries_exist_in_cache? system_libraries_exist_in_cache?
+
   def dylib_found_via_dlopen(dylib)
     Fiddle.dlopen(dylib).close
     true
diff --git a/Library/Homebrew/utils/curl.rb b/Library/Homebrew/utils/curl.rb
index 5f594cc8df07a..a1b1c1b44b6a4 100644
--- a/Library/Homebrew/utils/curl.rb
+++ b/Library/Homebrew/utils/curl.rb
@@ -320,12 +320,7 @@ def curl_check_http_content(url, url_type, specs: {}, user_agents: [:default], r
         break if http_status_ok?(details[:status_code])
       end
 
-      unless details[:status_code]
-        # Hack around https://github.com/Homebrew/brew/issues/3199
-        return if MacOS.version == :el_capitan
-
-        return "The #{url_type} #{url} is not reachable"
-      end
+      return return_value_for_empty_http_status_code(url_type, url) unless details[:status_code]
 
       unless http_status_ok?(details[:status_code])
         return if details[:responses].any? do |response|
@@ -486,6 +481,11 @@ def http_status_ok?(status)
       (100..299).cover?(status.to_i)
     end
 
+    def return_value_for_empty_http_status_code(url_type, url)
+      "The #{url_type} #{url} is not reachable"
+    end
+    alias generic_return_value_for_empty_http_status_code return_value_for_empty_http_status_code
+
     # Separates the output text from `curl` into an array of HTTP responses and
     # the final response body (i.e. content). Response hashes contain the
     # `:status_code`, `:status_text`, and `:headers`.
@@ -619,3 +619,5 @@ def parse_curl_response(response_text)
     end
   end
 end
+
+require "extend/os/utils/curl"

From 529f7b7953d75657ef996059bfe50cff40f90d00 Mon Sep 17 00:00:00 2001
From: Rylan Polster <rslpolster@gmail.com>
Date: Thu, 16 Nov 2023 11:47:48 -0500
Subject: [PATCH 3/6] Remove El Capitan system curl workaround

---
 Library/Homebrew/extend/os/mac/utils/curl.rb | 15 ---------------
 Library/Homebrew/extend/os/utils/curl.rb     |  4 ----
 Library/Homebrew/utils/curl.rb               |  9 +--------
 3 files changed, 1 insertion(+), 27 deletions(-)
 delete mode 100644 Library/Homebrew/extend/os/mac/utils/curl.rb
 delete mode 100644 Library/Homebrew/extend/os/utils/curl.rb

diff --git a/Library/Homebrew/extend/os/mac/utils/curl.rb b/Library/Homebrew/extend/os/mac/utils/curl.rb
deleted file mode 100644
index 56c7e56f51797..0000000000000
--- a/Library/Homebrew/extend/os/mac/utils/curl.rb
+++ /dev/null
@@ -1,15 +0,0 @@
-# typed: true
-# frozen_string_literal: true
-
-module Utils
-  module Curl
-    undef return_value_for_empty_http_status_code
-
-    def return_value_for_empty_http_status_code(url_type, url)
-      # Hack around https://github.com/Homebrew/brew/issues/3199
-      return if MacOS.version == :el_capitan
-
-      generic_return_value_for_empty_http_status_code url_type, url
-    end
-  end
-end
diff --git a/Library/Homebrew/extend/os/utils/curl.rb b/Library/Homebrew/extend/os/utils/curl.rb
deleted file mode 100644
index fbd35e61e4d9f..0000000000000
--- a/Library/Homebrew/extend/os/utils/curl.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-# typed: strict
-# frozen_string_literal: true
-
-require "extend/os/mac/utils/curl" if OS.mac?
diff --git a/Library/Homebrew/utils/curl.rb b/Library/Homebrew/utils/curl.rb
index a1b1c1b44b6a4..8973d43d3c4f3 100644
--- a/Library/Homebrew/utils/curl.rb
+++ b/Library/Homebrew/utils/curl.rb
@@ -320,7 +320,7 @@ def curl_check_http_content(url, url_type, specs: {}, user_agents: [:default], r
         break if http_status_ok?(details[:status_code])
       end
 
-      return return_value_for_empty_http_status_code(url_type, url) unless details[:status_code]
+      return "The #{url_type} #{url} is not reachable" unless details[:status_code]
 
       unless http_status_ok?(details[:status_code])
         return if details[:responses].any? do |response|
@@ -481,11 +481,6 @@ def http_status_ok?(status)
       (100..299).cover?(status.to_i)
     end
 
-    def return_value_for_empty_http_status_code(url_type, url)
-      "The #{url_type} #{url} is not reachable"
-    end
-    alias generic_return_value_for_empty_http_status_code return_value_for_empty_http_status_code
-
     # Separates the output text from `curl` into an array of HTTP responses and
     # the final response body (i.e. content). Response hashes contain the
     # `:status_code`, `:status_text`, and `:headers`.
@@ -619,5 +614,3 @@ def parse_curl_response(response_text)
     end
   end
 end
-
-require "extend/os/utils/curl"

From f98b8f948ce20a57ae58ad5b9a0535ecee05d77b Mon Sep 17 00:00:00 2001
From: Rylan Polster <rslpolster@gmail.com>
Date: Wed, 22 Nov 2023 20:22:02 -0500
Subject: [PATCH 4/6] Add rubocop to remove `MacOS` references

---
 Library/Homebrew/rubocops/lines.rb            |  15 +++
 .../shared/on_system_conditionals_helper.rb   |  26 +++-
 .../test/rubocops/text/macos_on_linux_spec.rb | 127 ++++++++++++++++++
 3 files changed, 161 insertions(+), 7 deletions(-)
 create mode 100644 Library/Homebrew/test/rubocops/text/macos_on_linux_spec.rb

diff --git a/Library/Homebrew/rubocops/lines.rb b/Library/Homebrew/rubocops/lines.rb
index e44623e4595f4..fbb5c8208186a 100644
--- a/Library/Homebrew/rubocops/lines.rb
+++ b/Library/Homebrew/rubocops/lines.rb
@@ -441,6 +441,21 @@ def audit_formula(_node, _class_node, _parent_class_node, body_node)
         end
       end
 
+      # This cop makes sure the `MacOS` module is not used in Linux-facing formula code
+      #
+      # @api private
+      class MacOSOnLinux < FormulaCop
+        include OnSystemConditionalsHelper
+
+        ON_MACOS_BLOCKS = [:macos, *MACOS_VERSION_OPTIONS].map { |os| :"on_#{os}" }.freeze
+
+        def audit_formula(_node, _class_node, _parent_class_node, body_node)
+          audit_macos_references(body_node,
+                                 allowed_methods: OnSystemConditionals::NO_ON_SYSTEM_METHOD_NAMES,
+                                 allowed_blocks:  OnSystemConditionals::NO_ON_SYSTEM_BLOCK_NAMES + ON_MACOS_BLOCKS)
+        end
+      end
+
       # This cop makes sure that the `generate_completions_from_executable` DSL is used.
       #
       # @api private
diff --git a/Library/Homebrew/rubocops/shared/on_system_conditionals_helper.rb b/Library/Homebrew/rubocops/shared/on_system_conditionals_helper.rb
index c6e0142afb1d4..bee4847630a5a 100644
--- a/Library/Homebrew/rubocops/shared/on_system_conditionals_helper.rb
+++ b/Library/Homebrew/rubocops/shared/on_system_conditionals_helper.rb
@@ -17,6 +17,7 @@ module OnSystemConditionalsHelper
       BASE_OS_OPTIONS = [:macos, :linux].freeze
       MACOS_VERSION_OPTIONS = MacOSVersion::SYMBOLS.keys.freeze
       ON_SYSTEM_OPTIONS = [*ARCH_OPTIONS, *BASE_OS_OPTIONS, *MACOS_VERSION_OPTIONS, :system].freeze
+      MACOS_MODULE_NAMES = ["MacOS", "OS::Mac"].freeze
 
       MACOS_VERSION_CONDITIONALS = {
         "==" => nil,
@@ -82,7 +83,7 @@ def audit_arch_conditionals(body_node, allowed_methods: [], allowed_blocks: [])
         ARCH_OPTIONS.each do |arch_option|
           else_method = (arch_option == :arm) ? :on_intel : :on_arm
           if_arch_node_search(body_node, arch: :"#{arch_option}?") do |if_node, else_node|
-            next if if_node_is_allowed?(if_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
+            next if node_is_allowed?(if_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
 
             if_statement_problem(if_node, "if Hardware::CPU.#{arch_option}?", "on_#{arch_option}",
                                  else_method: else_method, else_node: else_node)
@@ -93,7 +94,7 @@ def audit_arch_conditionals(body_node, allowed_methods: [], allowed_blocks: [])
           hardware_cpu_search(body_node, method: method) do |method_node|
             # These should already be caught by `if_arch_node_search`
             next if method_node.parent.source.start_with? "if #{method_node.source}"
-            next if if_node_is_allowed?(method_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
+            next if node_is_allowed?(method_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
 
             offending_node(method_node)
             problem "Don't use `#{method_node.source}`, use `on_arm` and `on_intel` blocks instead."
@@ -109,7 +110,7 @@ def audit_base_os_conditionals(body_node, allowed_methods: [], allowed_blocks: [
             [:linux?, :on_macos]
           end
           if_base_os_node_search(body_node, base_os: os_method) do |if_node, else_node|
-            next if if_node_is_allowed?(if_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
+            next if node_is_allowed?(if_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
 
             if_statement_problem(if_node, "if OS.#{os_method}", "on_#{base_os_option}",
                                  else_method: else_method, else_node: else_node)
@@ -121,7 +122,7 @@ def audit_macos_version_conditionals(body_node, allowed_methods: [], allowed_blo
                                            recommend_on_system: true)
         MACOS_VERSION_OPTIONS.each do |macos_version_option|
           if_macos_version_node_search(body_node, os_version: macos_version_option) do |if_node, operator, else_node|
-            next if if_node_is_allowed?(if_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
+            next if node_is_allowed?(if_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
 
             autocorrect = else_node.blank? && MACOS_VERSION_CONDITIONALS.key?(operator.to_s)
             on_system_method_string = if recommend_on_system && operator == :<
@@ -141,7 +142,7 @@ def audit_macos_version_conditionals(body_node, allowed_methods: [], allowed_blo
           macos_version_comparison_search(body_node, os_version: macos_version_option) do |method_node|
             # These should already be caught by `if_macos_version_node_search`
             next if method_node.parent.source.start_with? "if #{method_node.source}"
-            next if if_node_is_allowed?(method_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
+            next if node_is_allowed?(method_node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
 
             offending_node(method_node)
             problem "Don't use `#{method_node.source}`, use `on_{macos_version}` blocks instead."
@@ -149,6 +150,17 @@ def audit_macos_version_conditionals(body_node, allowed_methods: [], allowed_blo
         end
       end
 
+      def audit_macos_references(body_node, allowed_methods: [], allowed_blocks: [])
+        MACOS_MODULE_NAMES.each do |macos_module_name|
+          find_const(body_node, macos_module_name) do |node|
+            next if node_is_allowed?(node, allowed_methods: allowed_methods, allowed_blocks: allowed_blocks)
+
+            offending_node(node)
+            problem "Don't use `#{macos_module_name}` where it could be called on Linux."
+          end
+        end
+      end
+
       private
 
       def if_statement_problem(if_node, if_statement_string, on_system_method_string,
@@ -170,10 +182,10 @@ def if_statement_problem(if_node, if_statement_string, on_system_method_string,
         end
       end
 
-      def if_node_is_allowed?(if_node, allowed_methods: [], allowed_blocks: [])
+      def node_is_allowed?(node, allowed_methods: [], allowed_blocks: [])
         # TODO: check to see if it's legal
         valid = T.let(false, T::Boolean)
-        if_node.each_ancestor do |ancestor|
+        node.each_ancestor do |ancestor|
           valid_method_names = case ancestor.type
           when :def
             allowed_methods
diff --git a/Library/Homebrew/test/rubocops/text/macos_on_linux_spec.rb b/Library/Homebrew/test/rubocops/text/macos_on_linux_spec.rb
new file mode 100644
index 0000000000000..c72c2395feed1
--- /dev/null
+++ b/Library/Homebrew/test/rubocops/text/macos_on_linux_spec.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require "rubocops/lines"
+
+describe RuboCop::Cop::FormulaAudit::MacOSOnLinux do
+  subject(:cop) { described_class.new }
+
+  it "reports an offense when `MacOS` is used in the `Formula` class" do
+    expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        if MacOS::Xcode.version >= "12.0"
+           ^^^^^ FormulaAudit/MacOSOnLinux: Don't use `MacOS` where it could be called on Linux.
+          url 'https://brew.sh/linux-1.0.tgz'
+        end
+      end
+    RUBY
+  end
+
+  it "reports an offense when `MacOS` is used in a `resource` block" do
+    expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        url 'https://brew.sh/linux-1.0.tgz'
+
+        resource "foo" do
+          url "https://brew.sh/linux-1.0.tgz" if MacOS::full_version >= "12.0"
+                                                 ^^^^^ FormulaAudit/MacOSOnLinux: Don't use `MacOS` where it could be called on Linux.
+        end
+      end
+    RUBY
+  end
+
+  it "reports an offense when `MacOS` is used in an `on_linux` block" do
+    expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        on_linux do
+          if MacOS::Xcode.version >= "12.0"
+             ^^^^^ FormulaAudit/MacOSOnLinux: Don't use `MacOS` where it could be called on Linux.
+            url 'https://brew.sh/linux-1.0.tgz'
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports an offense when `MacOS` is used in an `on_arm` block" do
+    expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        on_arm do
+          if MacOS::Xcode.version >= "12.0"
+             ^^^^^ FormulaAudit/MacOSOnLinux: Don't use `MacOS` where it could be called on Linux.
+            url 'https://brew.sh/linux-1.0.tgz'
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports an offense when `MacOS` is used in an `on_intel` block" do
+    expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        on_intel do
+          if MacOS::Xcode.version >= "12.0"
+             ^^^^^ FormulaAudit/MacOSOnLinux: Don't use `MacOS` where it could be called on Linux.
+            url 'https://brew.sh/linux-1.0.tgz'
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offenses when `MacOS` is used in an `on_macos` block" do
+    expect_no_offenses(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        on_macos do
+          if MacOS::Xcode.version >= "12.0"
+            url 'https://brew.sh/linux-1.0.tgz'
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offenses when `MacOS` is used in an `on_ventura` block" do
+    expect_no_offenses(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        on_ventura :or_older do
+          if MacOS::Xcode.version >= "12.0"
+            url 'https://brew.sh/linux-1.0.tgz'
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offenses when `MacOS` is used in the `install` method" do
+    expect_no_offenses(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        url 'https://brew.sh/linux-1.0.tgz'
+
+        def install
+          MacOS.version
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offenses when `MacOS` is used in the `test` block" do
+    expect_no_offenses(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+      class Foo < Formula
+        desc "foo"
+        url 'https://brew.sh/linux-1.0.tgz'
+
+        test do
+          MacOS.version
+        end
+      end
+    RUBY
+  end
+end

From 4efd7cdb2837858a13f24f2ca49d511320eff3da Mon Sep 17 00:00:00 2001
From: Rylan Polster <rslpolster@gmail.com>
Date: Wed, 22 Nov 2023 21:21:29 -0500
Subject: [PATCH 5/6] Comment out `MacOS` on Linux deprecations

---
 Library/Homebrew/os/linux.rb | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/Library/Homebrew/os/linux.rb b/Library/Homebrew/os/linux.rb
index 197c5ebda2c52..877255268def7 100644
--- a/Library/Homebrew/os/linux.rb
+++ b/Library/Homebrew/os/linux.rb
@@ -55,60 +55,60 @@ module Mac
     raise "Loaded OS::Linux on generic OS!" if ENV["HOMEBREW_TEST_GENERIC_OS"]
 
     def self.version
-      odeprecated "`MacOS.version` on Linux"
+      # odeprecated "`MacOS.version` on Linux"
       MacOSVersion::NULL
     end
 
     def self.full_version
-      odeprecated "`MacOS.full_version` on Linux"
+      # odeprecated "`MacOS.full_version` on Linux"
       MacOSVersion::NULL
     end
 
     def self.languages
-      odeprecated "`MacOS.languages` on Linux"
+      # odeprecated "`MacOS.languages` on Linux"
       @languages ||= Array(ENV["LANG"]&.slice(/[a-z]+/)).uniq
     end
 
     def self.language
-      odeprecated "`MacOS.language` on Linux"
+      # odeprecated "`MacOS.language` on Linux"
       languages.first
     end
 
     def self.sdk_root_needed?
-      odeprecated "`MacOS.sdk_root_needed?` on Linux"
+      # odeprecated "`MacOS.sdk_root_needed?` on Linux"
       false
     end
 
     def self.sdk_path_if_needed(_version = nil)
-      odeprecated "`MacOS.sdk_path_if_needed` on Linux"
+      # odeprecated "`MacOS.sdk_path_if_needed` on Linux"
       nil
     end
 
     def self.sdk_path(_version = nil)
-      odeprecated "`MacOS.sdk_path` on Linux"
+      # odeprecated "`MacOS.sdk_path` on Linux"
       nil
     end
 
     module Xcode
       def self.version
-        odeprecated "`MacOS::Xcode.version` on Linux"
+        # odeprecated "`MacOS::Xcode.version` on Linux"
         ::Version::NULL
       end
 
       def self.installed?
-        odeprecated "`MacOS::Xcode.installed?` on Linux"
+        # odeprecated "`MacOS::Xcode.installed?` on Linux"
         false
       end
     end
 
     module CLT
       def self.version
-        odeprecated "`MacOS::CLT.version` on Linux"
+        # odeprecated "`MacOS::CLT.version` on Linux"
         ::Version::NULL
       end
 
       def self.installed?
-        odeprecated "`MacOS::CLT.installed?` on Linux"
+        # odeprecated "`MacOS::CLT.installed?` on Linux"
         false
       end
     end

From b7532a86e14c7879f2815ae4c0a85e3daf7aa2ac Mon Sep 17 00:00:00 2001
From: Rylan Polster <rslpolster@gmail.com>
Date: Wed, 22 Nov 2023 21:22:00 -0500
Subject: [PATCH 6/6] Add commented out deprecations for `MacOS` when
 simulating Linux

---
 Library/Homebrew/os/mac.rb       | 10 ++++++++++
 Library/Homebrew/os/mac/xcode.rb |  4 ++++
 Library/Homebrew/readall.rb      |  8 +++++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/Library/Homebrew/os/mac.rb b/Library/Homebrew/os/mac.rb
index 84a1775947eb3..ed9a875e04627 100644
--- a/Library/Homebrew/os/mac.rb
+++ b/Library/Homebrew/os/mac.rb
@@ -7,6 +7,9 @@
 require "os/mac/sdk"
 require "os/mac/keg"
 
+# TODO: remove this once the `MacOS` module is undefined on Linux
+require "simulate_system"
+
 module OS
   # Helper module for querying system information on macOS.
   module Mac
@@ -21,6 +24,7 @@ module Mac
     # using the standard Ruby Comparable methods.
     sig { returns(MacOSVersion) }
     def self.version
+      # odeprecated "`MacOS.version` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       @version ||= full_version.strip_patch
     end
 
@@ -28,6 +32,7 @@ def self.version
     # using the standard Ruby Comparable methods.
     sig { returns(MacOSVersion) }
     def self.full_version
+      # odeprecated "`MacOS.full_version` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       @full_version ||= if ENV["HOMEBREW_FAKE_EL_CAPITAN"] # for Portable Ruby building
         MacOSVersion.new("10.11.6")
       else
@@ -60,6 +65,7 @@ def self.preferred_perl_version
     end
 
     def self.languages
+      # odeprecated "`MacOS.languages` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       return @languages if @languages
 
       os_langs = Utils.popen_read("defaults", "read", "-g", "AppleLanguages")
@@ -73,6 +79,7 @@ def self.languages
     end
 
     def self.language
+      # odeprecated "`MacOS.language` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       languages.first
     end
 
@@ -83,6 +90,7 @@ def self.active_developer_dir
 
     sig { returns(T::Boolean) }
     def self.sdk_root_needed?
+      # odeprecated "`MacOS.sdk_root_needed?` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       if MacOS::CLT.installed?
         # If there's no CLT SDK, return false
         return false unless MacOS::CLT.provides_sdk?
@@ -131,11 +139,13 @@ def self.sdk_for_formula(formula, version = nil, check_only_runtime_requirements
 
     # Returns the path to an SDK or nil, following the rules set by {sdk}.
     def self.sdk_path(version = nil)
+      # odeprecated "`MacOS.sdk_path` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       s = sdk(version)
       s&.path
     end
 
     def self.sdk_path_if_needed(version = nil)
+      # odeprecated "`MacOS.sdk_path_if_needed` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
       # Prefer CLT SDK when both Xcode and the CLT are installed.
       # Expected results:
       # 1. On Xcode-only systems, return the Xcode SDK.
diff --git a/Library/Homebrew/os/mac/xcode.rb b/Library/Homebrew/os/mac/xcode.rb
index 9402bf5d6e11d..e589d2d670c8e 100755
--- a/Library/Homebrew/os/mac/xcode.rb
+++ b/Library/Homebrew/os/mac/xcode.rb
@@ -126,6 +126,7 @@ def self.bundle_path
 
       sig { returns(T::Boolean) }
       def self.installed?
+        # odeprecated "`MacOS::Xcode.installed?` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
         !prefix.nil?
       end
 
@@ -174,6 +175,7 @@ def self.update_instructions
 
       sig { returns(::Version) }
       def self.version
+        # odeprecated "`MacOS::Xcode.version` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
         # may return a version string
         # that is guessed based on the compiler, so do not
         # use it in order to check if Xcode is installed.
@@ -264,6 +266,7 @@ module CLT
       # Returns true even if outdated tools are installed.
       sig { returns(T::Boolean) }
       def self.installed?
+        # odeprecated "`MacOS::CLT.installed?` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
         !version.null?
       end
 
@@ -397,6 +400,7 @@ def self.detect_version_from_clang_version
       # version numbers.
       sig { returns(::Version) }
       def self.version
+        # odeprecated "`MacOS::CLT.version` on Linux" if Homebrew::SimulateSystem.simulating_or_running_on_linux?
         if @version ||= detect_version
           ::Version.new @version
         else
diff --git a/Library/Homebrew/readall.rb b/Library/Homebrew/readall.rb
index bfe714e02d9f6..8faa67554a6fa 100644
--- a/Library/Homebrew/readall.rb
+++ b/Library/Homebrew/readall.rb
@@ -11,6 +11,10 @@ module Readall
   class << self
     include Cachable
 
+    # TODO: remove this once the `MacOS` module is undefined on Linux
+    MACOS_MODULE_REGEX = /\b(MacOS|OS::Mac)(\.|::)\b/.freeze
+    private_constant :MACOS_MODULE_REGEX
+
     private :cache
 
     def valid_ruby_syntax?(ruby_files)
@@ -59,7 +63,9 @@ def valid_formulae?(tap, bottle_tag: nil)
                                                        flags: [], ignore_errors: false)
         readall_formula = readall_formula_class.new(formula_name, file, :stable, tap: tap)
         readall_formula.to_hash
-        cache[:valid_formulae][file] = if readall_formula.on_system_blocks_exist?
+        # TODO: Remove check for MACOS_MODULE_REGEX once the `MacOS` module is undefined on Linux
+        cache[:valid_formulae][file] = if readall_formula.on_system_blocks_exist? ||
+                                          formula_contents.match?(MACOS_MODULE_REGEX)
           [bottle_tag, *cache[:valid_formulae][file]]
         else
           true