Spike adding dead_end to Ruby

[schneems]

This commit adds the dead_end syntax error display tool to Ruby through the same mechanism as error_highlight and did_you_mean.

What is dead_end?

When a syntax error is raised by requiring a file, dead_end will use a combination of indentation and lexing to identify the problem.

Demo

Generate a file with a syntax error:

$ echo "require_relative 'syntax_error'" > test.rb
$ cat > syntax_error.rb <<EOF
class Dog < Animal
  def sit
    super
  end

  def bark
    puts "woof"

  def happy
    tail.wag
  end
end
EOF

Build and run ruby:

$ make
$ make runruby
generating vm_call_iseq_optimized.inc
vm_call_iseq_optimized.inc unchanged
RUBY_ON_BUG='gdb -x ./.gdbinit -p' ./miniruby -I./lib -I. -I.ext/common  ./tool/runruby.rb --extout=.ext  -- --disable-gems  ./test.rb
Run `$ dead_end /Users/rschneeman/Documents/projects/ruby/syntax_error.rb` for more options

DeadEnd: Missing `end` detected

This code has a missing `end`. Ensure that all
syntax keywords (`def`, `do`, etc.) have a matching `end`.

file: /Users/rschneeman/Documents/projects/ruby/syntax_error.rb
simplified:

       1  class Dog < Animal
    ❯  6    def bark
    ❯  9    def happy
    ❯ 11    end
      12  end



/Users/rschneeman/Documents/projects/ruby/lib/dead_end/auto.rb:30:in `require': /Users/rschneeman/Documents/projects/ruby/syntax_error.rb:12: syntax error, unexpected end-of-input, expecting `end' (SyntaxError)

Status

This commit is a proof of concept spike (https://en.wikipedia.org/wiki/Spike_(software_development)). If core likes this approach, then I can refine and improve it.

Known issues

• This implementation did not wire up any code that updates the vendored gem version from the source. It would be not difficult to add https://github.com/ruby/ruby/blob/41867532ac07515543e4d7e75094edeff09de743/tool/sync_default_gems.rb
• This implementation does not add dead_end as a feature to be enabled yet:

  ruby/ruby.c

  Line 97 in cb4e2cb

  X(error_highlight) \

  .
• DeadEnd's approach of showing syntax errors only works through integration with require, load, autoload, and require_relative (since it monkeypatches them to detect syntax errors). It does not work with direct Ruby file invocations Doesn't work direct from Ruby CLI syntax_suggest#31.
  • We could extend or modify the Ruby API to hook into a better place with guidance and approval.
• The current release of dead_end also annotates no method errors. I will turn this off in favor of error_highlight gem.

[schneems]

I've opened a non-spike PR #5859