Issue #16008 has been updated by jeremyevans0 (Jeremy Evans).

File ripper-hash-pattern-on_label-16008.patch added

I believe this issue comes from `new_unique_key_hash`, which expects the `kw_args` member of the `hshptn` node to be in a certain format (see https://github.com/ruby/ruby/blob/master/parse.y#L811).  If you modify the size of the array, it can't recognize the results to determine if the hash is unique, and treats it as an error, which results in a `nil` value being used.

You can currently work around this by including your metadata as an extra member of the location array:

```ruby
  def on_label(token)
    super.tap{|a| a.last.push(:metadata=>nil)}
  end 
```

It may be better to return the array as-is in case the format doesn't match what is expected, and only treat actual duplicate keys as errors.  The attached patch implements that approach.

----------------------------------------
Bug #16008: Ripper hshptn node drops information
https://bugs.ruby-lang.org/issues/16008#change-81958

* Author: kddeisz (Kevin Deisz)
* Status: Open
* Priority: Normal
* Assignee: nobu (Nobuyoshi Nakada)
* Target version: 
* ruby -v: 2.7.0-preview1
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
Hi - I'm the author of the prettier plugin for ruby. I'm trying to get it to support 2.7 pattern matching. It works well for everything to do with the array pattern. However, for hash patterns, it drops certain information if you touch the `on_label` method (which I do to add metadata about the location of the token). For example,


``` ruby
require 'ripper'

class Parser < Ripper::SexpBuilder
  private

  def on_label(token)
    [:@label, token]
  end
end

content = <<~EORUBY
  case foo
  in { a: 1 }
    bar
  else
    baz
  end
EORUBY

pp Ripper::SexpBuilder.new(content).parse
pp Parser.new(content).parse
```

This script results in:

```ruby
[:program,
 [:stmts_add,
  [:stmts_new],
  [:case,
   [:vcall, [:@ident, "foo", [1, 5]]],
   [:in,
    [:hshptn, nil, [[[:@label, "a:", [2, 5]], [:@int, "1", [2, 8]]]], nil],
    [:stmts_add, [:stmts_new], [:vcall, [:@ident, "bar", [3, 2]]]],
    [:else, [:stmts_add, [:stmts_new], [:vcall, [:@ident, "baz", [5, 2]]]]]]]]]
[:program,
 [:stmts_add,
  [:stmts_new],
  [:case,
   [:vcall, [:@ident, "foo", [1, 5]]],
   [:in,
    [:hshptn, nil, nil, nil],
    [:stmts_add, [:stmts_new], [:vcall, [:@ident, "bar", [3, 2]]]],
    [:else, [:stmts_add, [:stmts_new], [:vcall, [:@ident, "baz", [5, 2]]]]]]]]]
```

As you can see, in the second example the `hashptn` node has no label on it. I'm not entirely sure what's going on there. Any insight would be appreciated.


---Files--------------------------------
ripper-hash-pattern-on_label-16008.patch (1.87 KB)


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