Use SimulateSystem for ignore_missing_libraries

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

@@ -23,17 +23,4 @@ class Formula
 
   sig { params(targets: T.nilable(T.any(Pathname, String))).void }
   def deuniversalize_machos(*targets); end
-
-  class << self
-    undef ignore_missing_libraries
-
-    def ignore_missing_libraries(*libs)
-      libraries = libs.flatten
-      if libraries.any? { |x| !x.is_a?(String) && !x.is_a?(Regexp) }
-        raise FormulaSpecificationError, "#{__method__} can handle Strings and Regular Expressions only"
-      end
-
-      allowed_missing_libraries.merge(libraries)
-    end
-  end
 end

Library/Homebrew/formula.rb

@@ -3214,10 +3214,17 @@ class Formula
     end
 
     # Permit links to certain libraries that don't exist. Available on Linux only.
-    def ignore_missing_libraries(*)
-      return if Homebrew::SimulateSystem.linux?
+    def ignore_missing_libraries(*libs)
+      unless Homebrew::SimulateSystem.treat_as_linux?
+        raise FormulaSpecificationError, "#{__method__} is available on Linux only"
+      end
 
-      raise FormulaSpecificationError, "#{__method__} is available on Linux only"
+      libraries = libs.flatten
+      if libraries.any? { |x| !x.is_a?(String) && !x.is_a?(Regexp) }
+        raise FormulaSpecificationError, "#{__method__} can handle Strings and Regular Expressions only"
+      end
+
+      allowed_missing_libraries.merge(libraries)
     end
 
     # @private

Library/Homebrew/test/formula_spec.rb

@@ -1845,4 +1845,52 @@ describe Formula do
       expect(f.test).to eq(2)
     end
   end
+
+  describe "#ignore_missing_libraries" do
+    after do
+      Homebrew::SimulateSystem.clear
+    end
+
+    it "adds library to allowed_missing_libraries on Linux", :needs_linux do
+      Homebrew::SimulateSystem.clear
+      f = formula do
+        url "foo-1.0"
+
+        ignore_missing_libraries "bar.so"
+      end
+      expect(f.class.allowed_missing_libraries.to_a).to eq(["bar.so"])
+    end
+
+    it "adds library to allowed_missing_libraries on macOS when simulating Linux", :needs_macos do
+      Homebrew::SimulateSystem.os = :linux
+      f = formula do
+        url "foo-1.0"
+
+        ignore_missing_libraries "bar.so"
+      end
+      expect(f.class.allowed_missing_libraries.to_a).to eq(["bar.so"])
+    end
+
+    it "raises an error on macOS", :needs_macos do
+      Homebrew::SimulateSystem.clear
+      expect {
+        formula do
+          url "foo-1.0"
+
+          ignore_missing_libraries "bar.so"
+        end
+      }.to raise_error("ignore_missing_libraries is available on Linux only")
+    end
+
+    it "raises an error on Linux when simulating macOS", :needs_linux do
+      Homebrew::SimulateSystem.os = :macos
+      expect {
+        formula do
+          url "foo-1.0"
+
+          ignore_missing_libraries "bar.so"
+        end
+      }.to raise_error("ignore_missing_libraries is available on Linux only")
+    end
+  end
 end