UsesOnSystem: Collect macOS requirements

When determining macOS requirements for a cask, we may need to
reference requirements from related on_system blocks (e.g.,
`on_monterey :or_older`, `on_ventura`, `on_sonoma :or_newer`) when
`depends_on macos` isn't adequate.

Sometimes casks specify different `depends_on macos` values in macOS
on_system blocks but that value is only set when the cask is loaded
in an environment that satisfies the on_system block's requirements.
There are other casks that contain macOS on_system blocks and use
`depends_on macos` outside of the on_system blocks but it may only
use the macOS version of the lowest on_system block (e.g.,
`>= :monterey`), which isn't sufficient if the cask's values vary
based on macOS version.

To be able to simulate macOS versions that meet the requirements of
all the on_system blocks in a cask, we need to collect the macOS
requirements in a way that doesn't require OS simulation. This is also
something that's easy to do in on_system methods, so this adds a
`macos_requirements` array to `UsesOnSystem`, containing
`MacOSRequirement` objects created from the cask's macOS on_system
block conditions.

Library/Homebrew/extend/on_system.rb

@@ -1,6 +1,7 @@
 # typed: strict
 # frozen_string_literal: true
 
+require "requirements/macos_requirement"
 require "simulate_system"
 
 module OnSystem
@@ -27,6 +28,7 @@ module OnSystem
     prop :intel, T::Boolean, default: false
     prop :linux, T::Boolean, default: false
     prop :macos, T::Boolean, default: false
+    prop :macos_requirements, T::Set[MacOSRequirement], default: Set[]
 
     alias arm? arm
     alias intel? intel
@@ -36,7 +38,7 @@ module OnSystem
     # Whether the object has only default values.
     sig { returns(T::Boolean) }
     def empty?
-      !@arm && !@intel && !@linux && !@macos
+      !@arm && !@intel && !@linux && !@macos && @macos_requirements.empty?
     end
 
     # Whether the object has any non-default values.
@@ -44,6 +46,20 @@ module OnSystem
     def present? = !empty?
   end
 
+  # Converts an `or_condition` value to a suitable `MacOSRequirements`
+  # `comparator` string, defaulting to `==` if the provided argument is `nil`.
+  sig { params(symbol: T.nilable(Symbol)).returns(String) }
+  def self.comparator_from_or_condition(symbol)
+    case symbol
+    when :or_newer
+      ">="
+    when :or_older
+      "<="
+    else
+      "=="
+    end
+  end
+
   sig { params(arch: Symbol).returns(T::Boolean) }
   def self.arch_condition_met?(arch)
     raise ArgumentError, "Invalid arch condition: #{arch.inspect}" if ARCH_OPTIONS.exclude?(arch)
@@ -142,6 +158,9 @@ module OnSystem
       else
         [macos.to_sym, nil]
       end
+
+      comparator = OnSystem.comparator_from_or_condition(or_condition)
+      @uses_on_system.macos_requirements << MacOSRequirement.new([os_version], comparator:)
       return if !OnSystem.os_condition_met?(os_version, or_condition) && !OnSystem.os_condition_met?(:linux)
 
       @called_in_on_system_block = true
@@ -172,6 +191,9 @@ module OnSystem
         @uses_on_system.macos = true
 
         os_condition = OnSystem.condition_from_method_name T.must(__method__)
+        comparator = OnSystem.comparator_from_or_condition(or_condition)
+        @uses_on_system.macos_requirements << MacOSRequirement.new([os_condition], comparator:)
+
         return unless OnSystem.os_condition_met? os_condition, or_condition
 
         @on_system_block_min_os = T.let(

Library/Homebrew/test/cask/dsl_spec.rb

@@ -855,6 +855,12 @@ RSpec.describe Cask::DSL, :cask do
       it "sets @uses_on_system.macos to true" do
         expect(cask.uses_on_system.macos?).to be true
       end
+
+      it "sets @uses_on_system.macos_requirements using macos argument" do
+        expect(cask.uses_on_system.macos_requirements).to eq(Set[
+          MacOSRequirement.new([:sequoia], comparator: ">="),
+        ])
+      end
     end
 
     context "when cask uses on_system_conditional" do
@@ -890,6 +896,14 @@ RSpec.describe Cask::DSL, :cask do
       it "sets @uses_on_system.macos to true" do
         expect(cask.uses_on_system.macos?).to be true
       end
+
+      it "sets @uses_on_system.macos_requirements using on_* macos version conditions" do
+        expect(cask.uses_on_system.macos_requirements).to eq(Set[
+          MacOSRequirement.new([:big_sur], comparator: "<="),
+          MacOSRequirement.new([:monterey], comparator: "=="),
+          MacOSRequirement.new([:ventura], comparator: ">="),
+        ])
+      end
     end
   end
 end

Library/Homebrew/test/extend/on_system_spec.rb

@@ -52,6 +52,24 @@ RSpec.describe OnSystem do
     end
   end
 
+  describe "::comparator_from_or_condition" do
+    it 'returns ">=" for `:or_newer` symbol' do
+      expect(described_class.comparator_from_or_condition(:or_newer)).to eq(">=")
+    end
+
+    it 'returns "<=" for `:or_older` symbol' do
+      expect(described_class.comparator_from_or_condition(:or_older)).to eq("<=")
+    end
+
+    it 'returns "==" for an unsupported symbol' do
+      expect(described_class.comparator_from_or_condition(:nonexistent)).to eq("==")
+    end
+
+    it 'returns "==" for `nil`' do
+      expect(described_class.comparator_from_or_condition(nil)).to eq("==")
+    end
+  end
+
   describe "::arch_condition_met?" do
     it "returns true if current arch equals provided arch" do
       Homebrew::SimulateSystem.with(arch: :arm) do

Library/Homebrew/test/formula_spec.rb

@@ -2073,6 +2073,12 @@ RSpec.describe Formula do
       it "sets @uses_on_system.macos to true" do
         expect(f_on_system.uses_on_system.macos?).to be true
       end
+
+      it "sets @uses_on_system.macos_requirements using macos argument" do
+        expect(f_on_system.uses_on_system.macos_requirements).to eq(Set[
+          MacOSRequirement.new([:sequoia], comparator: ">="),
+        ])
+      end
     end
 
     context "when formula uses on_system_conditional" do
@@ -2131,6 +2137,14 @@ RSpec.describe Formula do
       it "sets @uses_on_system.macos to true" do
         expect(f_on_macos_versions.uses_on_system.macos?).to be true
       end
+
+      it "sets @uses_on_system.macos_requirements using on_* macos version conditions" do
+        expect(f_on_macos_versions.uses_on_system.macos_requirements).to eq(Set[
+          MacOSRequirement.new([:big_sur], comparator: "<="),
+          MacOSRequirement.new([:monterey], comparator: "=="),
+          MacOSRequirement.new([:ventura], comparator: ">="),
+        ])
+      end
     end
   end