Bug #19759: Surprising automatic splat with ruby2_keywords_hash

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [arm64-darwin22]
• Backport: 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: DONE

[alanwu (Alan Wu)]

On Ruby 3 and newer the following prints [:aa, :bb, :k]:

def yielder(splat)
  yield([:a, :b], *splat)
end

yielder([[:aa, :bb], Hash.ruby2_keywords_hash({k: :k})]) do |a, b, k:|
  p [a, b, k]
end

It expanded the second array involved and [:a, :b] vanished.
This is surprising because automatic array expansion for blocks
used to only happen when passing one array in total.

The script prints [[:a, :b], [:aa, :bb], :k] with 2.7.3.

---

I found this while puzzling over this line in the autosplat logic:

if (given_argc == (NIL_P(keyword_hash) ? 1 : 2) &&

It might be tempting to fix it by reversing part of beae6cbf0fd and make it if (given_argc == 1).
However that's incorrect due to inducing a behavior change for cases like
yield(*[[:a, :b], keywords_hash]).

[jeremyevans0 (Jeremy Evans)]

I submitted a pull request to fix this: https://github.com/ruby/ruby/pull/8039

• Status changed from Open to Closed

Applied in changeset git|3874381c4483ba7794ac2abf157e265546f9bfa7.

---

Fix autosplat conditions to handle ruby2_keywords case

Autosplat should not occur if there are two arguments but second
argument is an array containing a ruby2_keywords splat. Only
autosplat if a single argument to be yielded to the block, and there
is no splatted flagged keyword hash passed.

Fixes [Bug #19759]

[jeremyevans0 (Jeremy Evans)]

• Backport changed from 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN to 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: REQUIRED to 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: DONE

ruby_3_2 3354aacb73c65420a10cb41c0696e62dd1ba279b merged revision(s) 3874381c4483ba7794ac2abf157e265546f9bfa7.