Bug #15285: lambda return behavior regression from #14639

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN

[nmueller (Nate Mueller)]

The change in ea15ceddbef2cc4c459c1ad5796e43ae9fa2cbf1 to use rb_yield_force_blockarg changes the behavior of returns called inside a passed lambda function. In 2.5.1 and below, including before the enum.c change, the attached script would print true. In 2.5.3 it prints false.

[shyouhei (Shyouhei Urabe)]

• Related to Bug #14639: Array#map and lambda arity regression added

[shyouhei (Shyouhei Urabe)]

ea15ceddbef2cc4c459c1ad5796e43ae9fa2cbf1 is r64996, which is a backport of r63030, which fixes #14639.

@nobu (Nobuyoshi Nakada) any idea?

[jhawthorn (John Hawthorn)]

• File test.rb test.rb added

I also ran into this problem in ruby 2.5.3.

This is a little confusing because there are two things being changed here:

1. How arguments are handled in a passed &lambda, which was asked for in #14639
2. How return is handled in a passed &lambda

I attached a test script to help demonstrate

In ruby 2.3, the passed lambda will always splat the arguments (the lambda treats arguments like a block), but return only returns from the lambda

2.3.7
Array#map
  args    ✅
  return  ✅ lambda return semantics
Enumerable#map
  args    ✅
  return  ✅ lambda return semantics
Array#each
  args    ✅
  return  ✅ lambda return semantics
Array#map!
  args    ✅
  return  ✅ lambda return semantics

In ruby 2.4, the passed lambda now treats arguments like a normal lambda (it won't splat them). I think this is a good change (but that could be a debate). This is the complaint in #14639

2.4.4
Array#map
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics
Enumerable#map
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics
Array#each
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics
Array#map!
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics

In ruby 2.5.3 and in 2.6.0-preview3, Array#map was changed to always treat the passed lambda as a block. This changed both how it treats arguments (the desired change) and how it treats return (this bug).

In addition, it only made this change to Array#map aka Array#collect, which now doesn't match similar methods like Enumerable#map or Array#each or Array#map!. It's also a weird behaviour to have since it would be hard to write a custom MyClass#map in ruby which behaved the same way.

2.6.0
Array#map
  args    ✅
  return  ❌ block return semantics
Enumerable#map
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics
Array#each
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics
Array#map!
  args    💣 wrong number of arguments (given 1, expected 2)
  return  ✅ lambda return semantics

I think both r64996 (for 2.5.x) and r63030 should be reverted.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset trunk|r65923.

---

Revert r63030

• array.c (rb_ary_collect): no longer splat sole array for lambda.
  [ruby-core:89734] [Bug #15285]