[ruby-core:123648] [Ruby Bug#21661] Endless method definition as a default value of block parameter is wrongly accepted in Prism
From:
"tompng (tomoya ishida) via ruby-core" <ruby-core@...>
Date:
2025-11-02 14:51:00 UTC
List:
ruby-core #123648
Issue #21661 has been updated by tompng (tomoya ishida).
Inside `| |` style block parameter, binary operators (example: `1+2`, `1|2`) are rejected because we need to reject ambiguous `|`.
On the right hand side of assignment and endless def, binary operators are allowed, unless we introduce a special state or something.
So `def foo(a = b = 1+2); end`, `def foo(a = def f = 1+2); end`, `->(a = b = 1+2){}`, `->(a = def f = 1+2) {}` are all consistently accepted, and consistently rejected when surrounded by `{| |}`.
Assignment in default value of method definition is already used. https://github.com/ruby/ruby/blob/11583f53b172ead33355330c1445964d5af47f46/array.rb#L129C3-L129C35
~~~ruby
class Array
def first n = unspecified = true
end
~~~
Also need to fix default value of keyword parameter `proc { |a: def f = 1, **| }`
----------------------------------------
Bug #21661: Endless method definition as a default value of block parameter is wrongly accepted in Prism
https://bugs.ruby-lang.org/issues/21661#change-115031
* Author: tompng (tomoya ishida)
* Status: Open
* Assignee: prism
* ruby -v: ruby 3.5.0dev (2025-11-01T00:18:01Z master 17a7b4e031) +PRISM [x86_64-linux]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
These are syntax error in parse.y but not in Prism.
~~~ruby
p do |a = def f = 1; b| end
p do |a = def f = 1| 2; b|c end # `|` inside block parameter
~~~
Normal assignment as a default value `p do |a = b = 1| end` is already syntax error.
--
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