cli_parser: Output help text on invalid option passed

Library/Homebrew/cli_parser.rb

@@ -123,7 +123,12 @@ module Homebrew
       end
 
       def parse(cmdline_args = ARGV)
-        remaining_args = @parser.parse(cmdline_args)
+        begin
+          remaining_args = @parser.parse(cmdline_args)
+        rescue OptionParser::InvalidOption => e
+          puts generate_help_text
+          raise e
+        end
         check_constraint_violations
         Homebrew.args[:remaining] = remaining_args
         Homebrew.args.freeze

Library/Homebrew/test/cli_parser_spec.rb

@@ -42,6 +42,10 @@ describe Homebrew::CLI::Parser do
       expect { parser.parse(["--random"]) }.to raise_error(OptionParser::InvalidOption, /--random/)
     end
 
+    it "outputs help text on failure" do
+      expect { parser.parse(["--random"]) }.to raise_error(OptionParser::InvalidOption, /Usage: brew/)
+    end
+
     it "maps environment var to an option" do
       parser.parse([])
       expect(Homebrew.args.pry?).to be true