From: "mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date: 2025-09-16T02:18:25+00:00
Subject: [ruby-core:123256] [Ruby Bug#21168] Prism doesn't require argument parentheses (in some cases) when a block is present but parse.y does

Issue #21168 has been updated by mame (Yusuke Endoh).


Discussed at the dev meeting.

Matz said that he wanted to permit passing a single command (a method call without parentheses) as an argument to a method call with parentheses.

So, parse.y should accept the following, unless it is technically difficult.


```ruby
foo(
  bar baz do
  end
)
```

And currently Prism accepts the following, but it must be rejected.

```ruby
foo(
    bar baz do
    end, 1, 2, 3
)
```

BTW, Matz confirmed that the two code fragments that @Earlopain showed should be both accepted. Currently both parsers accept them, so there is no problem.

```ruby
# A single command as an argument, which should be accepted
foo(
  bar baz {
  }
)

# This is not related to this topic because it is not an argument. This should be accepted
(
  bar baz do
  end
)

----------------------------------------
Bug #21168: Prism doesn't require argument parentheses (in some cases) when a block is present but parse.y does
https://bugs.ruby-lang.org/issues/21168#change-114620

* Author: Earlopain (Earlopain _)
* Status: Assigned
* Assignee: prism
* ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
It's a bit more than that but explaining it in full would be a bit much. Instead, see this:

```rb
foo(
  bar baz do
  end
)
```

```sh
$ ruby -c --parser=prism test.rb
Syntax OK
$ ruby -c --parser=parse.y test.rb
ruby: test.rb:2: syntax error, unexpected 'do' for block, expecting ')' (SyntaxError)
  bar baz do
          ^~
```

OTOH, this is consistently rejected:
```rb
[
  foo bar do
  end,
]
# And also
foo || bar baz do
end
```



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