formula_installer: handle unexpected .brew presence/absence

Library/Homebrew/formula_cellar_checks.rb

@@ -285,13 +285,15 @@ def check_service_command(formula)
   end
 
   def check_cpuid_instruction(formula)
-    return unless formula.prefix.directory?
-    # TODO: add methods to `utils/ast` to allow checking for method use
-    return unless (formula.prefix/".brew/#{formula.name}.rb").read.include? "ENV.runtime_cpu_detection"
     # Checking for `cpuid` only makes sense on Intel:
     # https://en.wikipedia.org/wiki/CPUID
     return unless Hardware::CPU.intel?
 
+    dot_brew_formula = formula.prefix/".brew/#{formula.name}.rb"
+    return unless dot_brew_formula.exist?
+    # TODO: add methods to `utils/ast` to allow checking for method use
+    return unless dot_brew_formula.read.include? "ENV.runtime_cpu_detection"
+
     # macOS `objdump` is a bit slow, so we prioritise llvm's `llvm-objdump` (~5.7x faster)
     # or binutils' `objdump` (~1.8x faster) if they are installed.
     objdump   = Formula["llvm"].opt_bin/"llvm-objdump" if Formula["llvm"].any_version_installed?

Library/Homebrew/formula_installer.rb

@@ -460,7 +460,7 @@ def install
       end
       s = formula_contents.gsub(/  bottle do.+?end\n\n?/m, "")
       brew_prefix = formula.prefix/".brew"
-      brew_prefix.mkdir
+      brew_prefix.mkpath
       Pathname(brew_prefix/"#{formula.name}.rb").atomic_write(s)
 
       keg = Keg.new(formula.prefix)