Runtime error in Lint/DefEndAlignment auto-correct

[gotrevor]

Using this file (crash.rb) as input:

# encoding: utf-8
def func
  foo
rescue
  baz
  end

With this option enabled:

Lint/DefEndAlignment:
  AutoCorrect: true

I get the following crash:

[~/repos/rubocop] $ bin/rubocop crash.rb -a -d
...
An error occurred while Lint/DefEndAlignment cop was inspecting /Users/gotrevor/repos/rubocop/crash.rb.
undefined method `expression' for nil:NilClass
/Users/gotrevor/repos/rubocop/lib/rubocop/cop/mixin/end_keyword_alignment.rb:49:in `align'
/Users/gotrevor/repos/rubocop/lib/rubocop/cop/lint/def_end_alignment.rb:52:in `autocorrect'
...

I've tracked the problem down to the method investigate here:
https://github.com/bbatsov/rubocop/blob/v0.32.1/lib/rubocop/cop/variable_force.rb#L71-L79
processed_source enters with

processed_source.ast.ancestors.first == nil

it exists with

processed_source.ast.ancestors.first != nil 
&& processed_source.ast.ancestors.first.loc == nil

This causes the crash here:
https://github.com/bbatsov/rubocop/blob/v0.32.1/lib/rubocop/cop/mixin/end_keyword_alignment.rb#L49
Which assumes that a non-nil node will have a loc. Is that a valid assumption?

I suspect that VariableForce#investigate shouldn't be mutating processed_source.ast.
Am I right about that?

[jonas054]

Thanks, @gotrevor for the analysis. I'm working on this problem already, but hadn't gotten down to VariableForce#investigate yet. I'll take your views in to consideration, and will make a PR soon.

[jonas054]

To answer your question, I think it is reasonable for EndKeywordAlignment#align to expect that nodes given to it as the base for alignment have a loc attribute. When the node turns out to be a "fake" begin node, then it's the caller that's in error.