cli_parser: Make Homebrew.args immutable once CLI arguments have been processed

Library/Homebrew/cli_parser.rb

@@ -126,6 +126,7 @@ module Homebrew
         remaining_args = @parser.parse(cmdline_args)
         check_constraint_violations
         Homebrew.args[:remaining] = remaining_args
+        Homebrew.args.freeze
         @parser
       end
 

Library/Homebrew/test/cli_parser_spec.rb

@@ -177,4 +177,18 @@ describe Homebrew::CLI::Parser do
       expect(Homebrew.args.switch_b?).to be true
     end
   end
+
+  describe "test immutability of args" do
+    subject(:parser) {
+      described_class.new do
+        switch "-a", "--switch-a"
+        switch "-b", "--switch-b"
+      end
+    }
+
+    it "raises exception upon Homebrew.args mutation" do
+      parser.parse(["--switch-a"])
+      expect { parser.parse(["--switch-b"]) }.to raise_error(RuntimeError, /can't modify frozen OpenStruct/)
+    end
+  end
 end