formula API: expose uses_from_macos list

Library/Homebrew/extend/os/mac/software_spec.rb

@@ -4,12 +4,18 @@ class SoftwareSpec
   undef uses_from_macos
 
   def uses_from_macos(deps, **args)
+    @uses_from_macos_elements ||= []
+
     if deps.is_a?(Hash)
       args = deps
       deps = Hash[*args.shift]
     end
 
-    depends_on(deps) if add_mac_dependency?(args)
+    if add_mac_dependency?(args)
+      depends_on(deps)
+    else
+      @uses_from_macos_elements << deps
+    end
   end
 
   private

Library/Homebrew/formula.rb

@@ -428,6 +428,9 @@ class Formula
   # The {Dependency}s for the currently active {SoftwareSpec}.
   delegate deps: :active_spec
 
+  # Dependencies provided by macOS for the currently active {SoftwareSpec}.
+  delegate uses_from_macos_elements: :active_spec
+
   # The {Requirement}s for the currently active {SoftwareSpec}.
   delegate requirements: :active_spec
 
@@ -1589,6 +1592,7 @@ class Formula
   # @private
   def to_hash
     dependencies = deps
+    uses_from_macos = uses_from_macos_elements || []
 
     hsh = {
       "name"                     => name,
@@ -1624,6 +1628,7 @@ class Formula
       "optional_dependencies"    => dependencies.select(&:optional?)
                                                 .map(&:name)
                                                 .uniq,
+      "uses_from_macos"          => uses_from_macos.uniq,
       "requirements"             => [],
       "conflicts_with"           => conflicts.map(&:name),
       "caveats"                  => caveats&.gsub(HOMEBREW_PREFIX, "$(brew --prefix)"),

Library/Homebrew/software_spec.rb

@@ -26,6 +26,7 @@ class SoftwareSpec
   attr_reader :dependency_collector
   attr_reader :bottle_specification
   attr_reader :compiler_failures
+  attr_reader :uses_from_macos_elements
 
   def_delegators :@resource, :stage, :fetch, :verify_download_integrity, :source_modified_time
   def_delegators :@resource, :download_name, :cached_download, :clear_cache