From: naruse@...
Date: 2020-03-15T12:04:09+00:00
Subject: [ruby-core:97505] [Ruby master Bug#16519] pp [Hash.ruby2_keywords_hash({})] shows `[nil]`

Issue #16519 has been updated by naruse (Yui NARUSE).


```
  1) Failure:
PPTestModule::PPCycleTest#test_hash [/Users/naruse/work/ruby_2_7/test/test_pp.rb:133]:
<"{0=>{...}}\n"> expected but was
<"{[0, {...}]=>{}}\n">.

  2) Failure:
PPTestModule::PPSingleLineTest#test_hash [/Users/naruse/work/ruby_2_7/test/test_pp.rb:176]:
<"{1=>1}"> expected but was
<"{[1, 1]=>{}}">.
```

----------------------------------------
Bug #16519: pp [Hash.ruby2_keywords_hash({})] shows `[nil]`
https://bugs.ruby-lang.org/issues/16519#change-84654

* Author: Eregon (Benoit Daloze)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 2.8.0dev (2020-01-21T13:45:10Z master 5798d35ff6) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: REQUIRED
----------------------------------------
This happens on `master`:

```
$ ruby -ve 'ruby2_keywords def flag(*a); a.last; end; pp [flag(**{})]'
ruby 2.8.0dev (2020-01-21T13:45:10Z master 5798d35ff6) [x86_64-linux]
[nil]
```

Of course it should be `[{}]`, as it is for `pp [{}]`.

On 2.7.0 it warns (should be fixed, it's valid to `pp` a flagged Hash):
```
$ ruby -ve 'ruby2_keywords def flag(*a); a.last; end; pp [flag(**{})]'
ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux]
[/home/eregon/.rubies/ruby-2.7.0/lib/ruby/2.7.0/pp.rb:226: warning: Passing the keyword argument as the last hash parameter is deprecated
/home/eregon/.rubies/ruby-2.7.0/lib/ruby/2.7.0/pp.rb:334: warning: The called method is defined here
{}]
```

The warning being in the middle of the output is a fun fact here.
Lines it refers to (still the same on current master):
https://github.com/ruby/ruby/blob/v2_7_0/lib/pp.rb#L226
https://github.com/ruby/ruby/blob/v2_7_0/lib/pp.rb#L334

This is very confusing as it can happen during `test-all` and then show output such as:
```
<[{:a=>1}]> expected but was
<[{:a=>1}, nil]>.
```
when the reality is (can be verified with `p` before the `assert_equal`):
```
<[{:a=>1}]> expected but was
<[{:a=>1}, {}]>.
```



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