Bug #21114: Prism hangs up while parsing deeply nested `def`

• Status: Closed
• Assignee: prism
• Target version: -
• ruby -v: ruby 3.5.0dev (2025-02-05T08:15:30Z master 141f2924ee) +PRISM [x86_64-linux]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: DONE

[tompng (tomoya ishida)]

Prism.parse "def f\n" * 500 # Ruby 3.4
Prism.parse "def f\n" * 5000 # Ruby 3.5
Prism.parse "def initialize: ()->void\n" * 250 # Ruby 3.4
Prism.parse "def initialize: ()->void\n" * 2500 # Ruby 3.5
#=> hang up, Ctrl-C doesn't work

Expect to raise ParseError with @type=:nesting_too_deep like Prism.parse '(1+'*10000

Background

Runnning rdoc in ruby/rbs directory with Ruby 3.4, RDoc hangs up.
RDoc tries to parse the partial file content, and stops with stdlib/ripper/0/ripper.rbs (https://github.com/ruby/rbs/blob/a7178b12b041f5b304f4076aa01efed817ba8040/stdlib/ripper/0/ripper.rbs)

Parseable checking code in RDoc https://github.com/ruby/rdoc/blob/14a7631a3775e033791f13baa3be76c94b908e3d/lib/rdoc/markup/to_html.rb#L437

def parseable? text
  ...
  eval("BEGIN { throw :valid, true }\n#{text}")
  ...
end

However, RBS doesn't seem to use RDoc, so I think it's not a big problem.

[hsbt (Hiroshi SHIBATA)]

• Status changed from Open to Assigned

[kddnewton (Kevin Newton)]

https://github.com/ruby/prism/pull/3461

[kddnewton (Kevin Newton)]

• Status changed from Assigned to Closed

Applied in changeset git|b21e1aed2ed5b22b50efc658289a403eeed581df.

---

[ruby/prism] Fix infinite loop in error recovery

When recovering from a depth error that occurs at the end of the
file, we need to break out of parsing statements.

Fixes [Bug #21114]

https://github.com/ruby/prism/commit/a32e268787

[kddnewton (Kevin Newton)]

• Backport changed from 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: REQUIRED

[k0kubun (Takashi Kokubun)]

• Backport changed from 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: REQUIRED to 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: DONE

ruby_3_4 9a0984436888a59f4914c3035c53657baf62ce2b merged revision(s) b21e1aed2ed5b22b50efc658289a403eeed581df.