ENV/shared: specify which Perl version we want to use

Library/Homebrew/extend/ENV/shared.rb

@@ -50,6 +50,7 @@ module SharedEnvExtension
     reset
   end
   private :setup_build_environment
+  alias generic_shared_setup_build_environment setup_build_environment
 
   sig { void }
   def reset

Library/Homebrew/extend/os/mac/extend/ENV/shared.rb

@@ -4,6 +4,16 @@
 module SharedEnvExtension
   extend T::Sig
 
+  def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_arch: nil, testing_formula: false)
+    generic_shared_setup_build_environment(
+      formula: formula, cc: cc, build_bottle: build_bottle,
+      bottle_arch: bottle_arch, testing_formula: testing_formula
+    )
+
+    # Normalise the system Perl version used, where multiple may be available
+    self["VERSIONER_PERL_VERSION"] = MacOS.preferred_perl_version
+  end
+
   sig { returns(T::Boolean) }
   def no_weak_imports_support?
     return false unless compiler == :clang

Library/Homebrew/os/mac.rb

@@ -60,6 +60,17 @@ module OS
       version >= "12"
     end
 
+    sig { returns(String) }
+    def preferred_perl_version
+      if version >= :big_sur
+        "5.30"
+      elsif version == :catalina
+        "5.28"
+      else
+        "5.18"
+      end
+    end
+
     def languages
       return @languages if @languages