Make Linux cask requirements explicit

- stop surfacing casks on Linux unless `supports_linux?`
  says they are safe to advertise, so `search` and
  `bundle` stay conservative about unknown support
- move cask platform output into a `Requirements`
  section so `brew info` explains macOS-only casks the
  same way on macOS and Linux
- reuse `requires macOS` in `brew bundle` for both
  `brew` and `cask` entries so platform warnings use the
  same language across commands
- cover the shared policy with regressions around
  `search`, `cask/info`, `bundle/skipper`, and
  `Cask#supports_linux?`

Library/Homebrew/cask/info.rb

@@ -28,6 +28,8 @@ module Cask
       output << desc_info(cask)
       deps = deps_info(cask)
       output << deps if deps
+      requirements = requirements_info(cask)
+      output << requirements if requirements
       language = language_info(cask)
       output << language if language
       output << "#{artifact_info(cask)}\n"
@@ -131,6 +133,47 @@ module Cask
       installed ? pretty_installed(dep) : pretty_uninstalled(dep)
     end
 
+    sig { params(cask: Cask).returns(T.nilable(String)) }
+    def self.requirements_info(cask)
+      require "cask_dependent"
+
+      requirements = CaskDependent.new(cask).requirements.grep_v(CaskDependent::Requirement)
+      return if requirements.empty?
+
+      supports_linux = cask.supports_linux?
+      oldest_allowed = MacOSVersion.new(HOMEBREW_MACOS_OLDEST_ALLOWED)
+      output = "#{ohai_title("Requirements")}\n"
+      %w[build required recommended optional].each do |type|
+        reqs = case type
+        when "build"
+          requirements.select(&:build?)
+        when "required"
+          requirements.select(&:required?)
+        when "recommended"
+          requirements.select(&:recommended?)
+        when "optional"
+          requirements.select(&:optional?)
+        else
+          []
+        end
+        next if reqs.empty?
+
+        output << "#{type.capitalize}: #{reqs.map do |requirement|
+          requires_macos = requirement.is_a?(MacOSRequirement) && !supports_linux
+          requirement_s = if requires_macos && requirement.comparator == ">=" && requirement.version == oldest_allowed
+            "macOS"
+          elsif requires_macos
+            requirement.display_s.delete_suffix(" (or Linux)")
+          else
+            requirement.display_s
+          end
+          installed = requirement.satisfied?
+          installed ? pretty_installed(requirement_s) : pretty_uninstalled(requirement_s)
+        end.join(", ")}\n"
+      end
+      output
+    end
+
     sig { params(cask: Cask).returns(T.nilable(String)) }
     def self.language_info(cask)
       return if cask.languages.empty?

Library/Homebrew/extend/os/linux/bundle/skipper.rb

@@ -2,42 +2,31 @@
 # frozen_string_literal: true
 
 require "cask/cask_loader"
-require "cask/installer"
-
 module OS
   module Linux
     module Bundle
       module Skipper
         module ClassMethods
           sig { params(entry: Homebrew::Bundle::Dsl::Entry).returns(T::Boolean) }
-          def macos_only_entry?(entry)
-            entry.type == :mas
-          end
-
-          sig { params(entry: Homebrew::Bundle::Dsl::Entry).returns(T::Boolean) }
-          def macos_only_cask?(entry)
-            return false if entry.type != :cask
-
-            cask = ::Cask::CaskLoader.load(entry.name)
-            installer = ::Cask::Installer.new(cask)
-            installer.check_stanza_os_requirements
-
-            false
+          def requires_macos?(entry)
+            case entry.type
+            when :mas
+              true
+            when :cask
+              !::Cask::CaskLoader.load(entry.name).supports_linux?
+            else
+              false
+            end
           rescue ::Cask::CaskError
             true
           end
 
           sig { params(entry: Homebrew::Bundle::Dsl::Entry, silent: T::Boolean).returns(T::Boolean) }
           def skip?(entry, silent: false)
-            if macos_only_entry?(entry) || macos_only_cask?(entry)
-              unless silent
-                $stdout.puts Formatter.warning "Skipping #{entry.type} #{entry.name} (unsupported on Linux)"
-              end
+            return super unless requires_macos?(entry)
 
-              true
-            else
-              super(entry)
-            end
+            $stdout.puts Formatter.warning("Skipping #{entry.type} #{entry.name} (requires macOS)") unless silent
+            true
           end
         end
       end

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

@@ -0,0 +1,17 @@
+# typed: strict
+# frozen_string_literal: true
+
+module OS
+  module Linux
+    module Search
+      module ClassMethods
+        sig { params(cask: ::Cask::Cask).returns(T::Boolean) }
+        def ignore_cask?(cask)
+          !cask.supports_linux?
+        end
+      end
+    end
+  end
+end
+
+Homebrew::Search.singleton_class.prepend(OS::Linux::Search::ClassMethods)

Library/Homebrew/extend/os/search.rb

@@ -0,0 +1,4 @@
+# typed: strict
+# frozen_string_literal: true
+
+require "extend/os/linux/search" if OS.linux?

Library/Homebrew/search.rb

@@ -46,6 +46,9 @@ module Homebrew
       raise "#{query} is not a valid regex."
     end
 
+    sig { params(_cask: Cask::Cask).returns(T::Boolean) }
+    def self.ignore_cask?(_cask) = false
+
     T::Sig::WithoutRuntime.sig {
       params(
         string_or_regex: T.any(Regexp, String),
@@ -148,7 +151,8 @@ module Homebrew
     def self.search_casks(string_or_regex)
       if string_or_regex.is_a?(String) && string_or_regex.match?(HOMEBREW_TAP_CASK_REGEX)
         return begin
-          [Cask::CaskLoader.load(string_or_regex).token]
+          matched_cask = Cask::CaskLoader.load(string_or_regex)
+          ignore_cask?(matched_cask) ? [] : [matched_cask.token]
         rescue Cask::CaskUnavailableError
           []
         end
@@ -169,8 +173,10 @@ module Homebrew
                                            .correct(string_or_regex)
       end
 
-      results.sort.map do |name|
+      results.sort.filter_map do |name|
         cask = Cask::CaskLoader.load(name)
+        next if ignore_cask?(cask)
+
         display_name = if cask.installed?
           pretty_installed(cask.full_name)
         else
@@ -245,3 +251,5 @@ module Homebrew
     end
   end
 end
+
+require "extend/os/search"

Library/Homebrew/test/bundle/skipper_spec.rb

@@ -70,6 +70,20 @@ RSpec.describe Homebrew::Bundle::Skipper do
       end
     end
 
+    context "with a cask that requires macOS", :needs_linux do
+      let(:entry) { Homebrew::Bundle::Dsl::Entry.new(:cask, "testball") }
+
+      it "skips on Linux with warning" do
+        allow(Cask::CaskLoader).to receive(:load).with("testball").and_return(
+          instance_double(Cask::Cask, supports_linux?: false),
+        )
+        expect($stdout).to receive(:puts).with(
+          Formatter.warning("Skipping cask testball (requires macOS)"),
+        )
+        expect(skipper.skip?(entry)).to be true
+      end
+    end
+
     context "with a listed formula in a failed tap" do
       let(:entry) { Homebrew::Bundle::Dsl::Entry.new(:brew, "org/repo/formula") }
 

Library/Homebrew/test/cask/cask_spec.rb

@@ -392,6 +392,12 @@ RSpec.describe Cask::Cask, :cask do
     end
   end
 
+  describe "#supports_linux?" do
+    it "returns false when Linux support is not explicitly declared" do
+      expect(Cask::CaskLoader.load("with-non-executable-binary").supports_linux?).to be false
+    end
+  end
+
   describe "#to_h" do
     let(:expected_json) { (TEST_FIXTURE_DIR/"cask/everything.json").read.strip }
 

Library/Homebrew/test/cask/info_spec.rb

@@ -17,6 +17,13 @@ RSpec.describe Cask::Info, :cask do
     "#{Tty.bold}#{string} #{Formatter.success("✔")}#{Tty.reset}"
   end
 
+  def requirements_section(string)
+    <<~EOS.chomp
+      #{ohai_title "Requirements"}
+      Required: #{string}
+    EOS
+  end
+
   def mock_cask_installed(cask_name)
     cask = Cask::CaskLoader.load(cask_name)
     allow(cask).to receive(:installed?).and_return(true)
@@ -44,6 +51,7 @@ RSpec.describe Cask::Info, :cask do
       Transmission
       ==> Description
       BitTorrent client
+      #{requirements_section("macOS")}
       ==> Artifacts
       Transmission.app (App)
     EOS
@@ -65,6 +73,7 @@ RSpec.describe Cask::Info, :cask do
       #{Formatter.error("None")}
       #{ohai_title "Dependencies"}
       #{uninstalled("local-caffeine (cask)")}, #{installed("local-transmission-zip (cask)")}
+      #{requirements_section(installed("macOS"))}
       #{ohai_title "Artifacts"}
       Caffeine.app (App)
     EOS
@@ -72,6 +81,12 @@ RSpec.describe Cask::Info, :cask do
 
   it "prints cask and formulas dependencies if the Cask has both" do
     allow_any_instance_of(StringIO).to receive(:tty?).and_return(true)
+    arch_requirements = if Hardware::CPU.arm?
+      "#{uninstalled("x86_64 architecture")}, #{installed("arm64 architecture")}"
+    else
+      "#{installed("x86_64 architecture")}, #{uninstalled("arm64 architecture")}"
+    end
+
     expect do
       described_class.info(Cask::CaskLoader.load("with-depends-on-everything"), args:)
     end.to output(<<~EOS).to_stdout
@@ -85,6 +100,7 @@ RSpec.describe Cask::Info, :cask do
       #{Formatter.error("None")}
       #{ohai_title "Dependencies"}
       #{uninstalled("unar")}, #{uninstalled("local-caffeine (cask)")}, #{uninstalled("with-depends-on-cask (cask)")}
+      #{requirements_section("#{arch_requirements}, #{installed("macOS")}")}
       #{ohai_title "Artifacts"}
       Caffeine.app (App)
     EOS
@@ -102,6 +118,7 @@ RSpec.describe Cask::Info, :cask do
       AutoUpdates
       ==> Description
       None
+      #{requirements_section("macOS")}
       ==> Artifacts
       AutoUpdates.app (App)
     EOS
@@ -119,6 +136,7 @@ RSpec.describe Cask::Info, :cask do
       None
       ==> Description
       None
+      #{requirements_section("macOS")}
       ==> Artifacts
       Caffeine.app (App)
       ==> Caveats
@@ -146,6 +164,7 @@ RSpec.describe Cask::Info, :cask do
       None
       ==> Description
       None
+      #{requirements_section("macOS")}
       ==> Artifacts
       Caffeine.app (App)
     EOS
@@ -163,6 +182,7 @@ RSpec.describe Cask::Info, :cask do
       None
       ==> Description
       None
+      #{requirements_section("macOS")}
       ==> Languages
       zh, en-US
       ==> Artifacts
@@ -182,6 +202,7 @@ RSpec.describe Cask::Info, :cask do
       None
       ==> Description
       None
+      #{requirements_section("macOS")}
       ==> Artifacts
       Caffeine.app (App)
     EOS
@@ -213,6 +234,7 @@ RSpec.describe Cask::Info, :cask do
         Transmission
         ==> Description
         BitTorrent client
+        #{requirements_section(installed("macOS"))}
         ==> Artifacts
         Transmission.app (App)
       EOS
@@ -250,9 +272,28 @@ RSpec.describe Cask::Info, :cask do
         Transmission
         ==> Description
         BitTorrent client
+        #{requirements_section(installed("macOS"))}
         ==> Artifacts
         Transmission.app (App)
       EOS
     end
   end
+
+  it "shows requirements" do
+    expect do
+      described_class.info(Cask::CaskLoader.load("with-non-executable-binary"), args:)
+    end.to output(<<~EOS).to_stdout
+      ==> with-non-executable-binary: 1.2.3
+      https://brew.sh/with-binary
+      Not installed
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/w/with-non-executable-binary.rb
+      ==> Name
+      None
+      ==> Description
+      None
+      #{requirements_section("macOS")}
+      ==> Artifacts
+      naked_non_executable (Binary)
+    EOS
+  end
 end

Library/Homebrew/test/search_spec.rb

@@ -95,7 +95,14 @@ RSpec.describe Homebrew::Search do
 
   describe "#search_casks" do
     let(:cask) do
-      instance_double(Cask::Cask, full_name: "testball", installed?: false, deprecated?: false, disabled?: false)
+      instance_double(
+        Cask::Cask,
+        full_name:       "testball",
+        installed?:      false,
+        deprecated?:     false,
+        disabled?:       false,
+        supports_linux?: true,
+      )
     end
 
     before do
@@ -117,6 +124,12 @@ RSpec.describe Homebrew::Search do
     it "does not annotate normal casks", :needs_macos do
       expect(described_class.search_casks(/testball/)).to eq(["testball"])
     end
+
+    it "hides macOS-only casks on Linux", :needs_linux do
+      allow(cask).to receive(:supports_linux?).and_return(false)
+
+      expect(described_class.search_casks(/testball/)).to eq([])
+    end
   end
 
   describe "#search_descriptions" do