Simplify SimulateSystem usage

Library/Homebrew/extend/on_system.rb

@@ -15,8 +15,7 @@ module OnSystem
   def arch_condition_met?(arch)
     raise ArgumentError, "Invalid arch condition: #{arch.inspect}" if ARCH_OPTIONS.exclude?(arch)
 
-    current_arch = Homebrew::SimulateSystem.arch || Hardware::CPU.type
-    arch == current_arch
+    arch == Homebrew::SimulateSystem.current_arch
   end
 
   sig { params(os_name: Symbol, or_condition: T.nilable(Symbol)).returns(T::Boolean) }
@@ -26,14 +25,7 @@ module OnSystem
       return true if [:macos, *MacOSVersions::SYMBOLS.keys].include?(os_name)
     end
 
-    if BASE_OS_OPTIONS.include?(os_name)
-      if Homebrew::SimulateSystem.none?
-        return OS.linux? if os_name == :linux
-        return OS.mac? if os_name == :macos
-      end
-
-      return Homebrew::SimulateSystem.send("#{os_name}?")
-    end
+    return Homebrew::SimulateSystem.send("treat_as_#{os_name}?") if BASE_OS_OPTIONS.include?(os_name)
 
     raise ArgumentError, "Invalid OS condition: #{os_name.inspect}" unless MacOSVersions::SYMBOLS.key?(os_name)
 
@@ -41,10 +33,10 @@ module OnSystem
       raise ArgumentError, "Invalid OS `or_*` condition: #{or_condition.inspect}"
     end
 
-    return false if Homebrew::SimulateSystem.linux? || (Homebrew::SimulateSystem.none? && OS.linux?)
+    return false if Homebrew::SimulateSystem.treat_as_linux?
 
     base_os = MacOS::Version.from_symbol(os_name)
-    current_os = MacOS::Version.from_symbol(Homebrew::SimulateSystem.os || MacOS.version.to_sym)
+    current_os = MacOS::Version.from_symbol(Homebrew::SimulateSystem.current_os)
 
     return current_os >= base_os if or_condition == :or_newer
     return current_os <= base_os if or_condition == :or_older

Library/Homebrew/simulate_system.rb

@@ -32,19 +32,31 @@ module Homebrew
       end
 
       sig { returns(T::Boolean) }
-      def none?
-        @os.nil? && @arch.nil?
-      end
+      def treat_as_macos?
+        return OS.mac? if @os.blank?
 
-      sig { returns(T::Boolean) }
-      def macos?
         [:macos, *MacOSVersions::SYMBOLS.keys].include?(@os)
       end
 
       sig { returns(T::Boolean) }
-      def linux?
+      def treat_as_linux?
+        return OS.linux? if @os.blank?
+
         @os == :linux
       end
+
+      sig { returns(Symbol) }
+      def current_arch
+        @arch || Hardware::CPU.type
+      end
+
+      sig { returns(Symbol) }
+      def current_os
+        return @os if @os.present?
+        return :linux if OS.linux?
+
+        MacOS.version.to_sym
+      end
     end
   end
 end

Library/Homebrew/test/simulate_system_spec.rb

@@ -0,0 +1,118 @@
+# typed: false
+# frozen_string_literal: true
+
+require "settings"
+
+describe Homebrew::SimulateSystem do
+  after do
+    described_class.clear
+  end
+
+  describe "::treat_as_macos?" do
+    it "returns true on macOS", :needs_macos do
+      described_class.clear
+      expect(described_class.treat_as_macos?).to be true
+    end
+
+    it "returns false on Linux", :needs_linux do
+      described_class.clear
+      expect(described_class.treat_as_macos?).to be false
+    end
+
+    it "returns false on macOS when simulating Linux", :needs_macos do
+      described_class.clear
+      described_class.os = :linux
+      expect(described_class.treat_as_macos?).to be false
+    end
+
+    it "returns true on Linux when simulating a generic macOS version", :needs_linux do
+      described_class.clear
+      described_class.os = :macos
+      expect(described_class.treat_as_macos?).to be true
+    end
+
+    it "returns true on Linux when simulating a specific macOS version", :needs_linux do
+      described_class.clear
+      described_class.os = :monterey
+      expect(described_class.treat_as_macos?).to be true
+    end
+  end
+
+  describe "::treat_as_linux?" do
+    it "returns true on Linux", :needs_linux do
+      described_class.clear
+      expect(described_class.treat_as_linux?).to be true
+    end
+
+    it "returns false on macOS", :needs_macos do
+      described_class.clear
+      expect(described_class.treat_as_linux?).to be false
+    end
+
+    it "returns true on macOS when simulating Linux", :needs_macos do
+      described_class.clear
+      described_class.os = :linux
+      expect(described_class.treat_as_linux?).to be true
+    end
+
+    it "returns false on Linux when simulating a generic macOS version", :needs_linux do
+      described_class.clear
+      described_class.os = :macos
+      expect(described_class.treat_as_linux?).to be false
+    end
+
+    it "returns false on Linux when simulating a specific macOS version", :needs_linux do
+      described_class.clear
+      described_class.os = :monterey
+      expect(described_class.treat_as_linux?).to be false
+    end
+  end
+
+  describe "::current_arch" do
+    it "returns the current architecture" do
+      described_class.clear
+      expect(described_class.current_arch).to eq Hardware::CPU.type
+    end
+
+    it "returns the simulated architecture" do
+      described_class.clear
+      simulated_arch = if Hardware::CPU.arm?
+        :intel
+      else
+        :arm
+      end
+      described_class.arch = simulated_arch
+      expect(described_class.current_arch).to eq simulated_arch
+    end
+  end
+
+  describe "::current_os" do
+    it "returns the current macOS version on macOS", :needs_macos do
+      described_class.clear
+      expect(described_class.current_os).to eq MacOS.version.to_sym
+    end
+
+    it "returns `:linux` on Linux", :needs_linux do
+      described_class.clear
+      expect(described_class.current_os).to eq :linux
+    end
+
+    it "returns `:linux` when simulating Linux on macOS", :needs_macos do
+      described_class.clear
+      described_class.os = :linux
+      expect(described_class.current_os).to eq :linux
+    end
+
+    it "returns `:macos` when simulating a generic macOS version on Linux", :needs_linux do
+      described_class.clear
+      described_class.os = :macos
+      expect(described_class.current_os).to eq :macos
+    end
+
+    it "returns `:macos` when simulating a specific macOS version on Linux", :needs_linux do
+      described_class.clear
+      described_class.os = :monterey
+      expect(described_class.current_os).to eq :monterey
+    end
+  end
+end