Bug #21661: Endless method definition as a default value of block parameter is wrongly accepted in Prism

• Status: Open
• Assignee: prism
• Target version: -
• 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

[tompng (tomoya ishida)]

These are syntax error in parse.y but not in Prism.

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.