[ruby-core:120397] [Ruby master Bug#20980] Range#size new TypeError vs semi-open ranges

Issue #20980 has been reported by zverok (Victor Shepelev).

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Bug #20980: Range#size new TypeError vs semi-open ranges
https://bugs.ruby-lang.org/issues/20980

* Author: zverok (Victor Shepelev)
* Status: Open
* ruby -v: ruby 3.4.0dev (2024-12-24T14:40:12Z master 07e89bde46) +PRISM [x86_64-linux]
* Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED
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Since #18984, `Range#size` throws `TypeError` if the `begin` is not iterable (doesn't respond to `#succ`). It produces one small inconvenience compared to 3.3:

```ruby
('a'..).size #=> nil
(..'a').size 
# 3.3: nil
# 3.4: can't iterate from NilClass (TypeError) -- well, probably makes sense

# BUT:
(3..).size #=> Infinity -- cool!
(..3).size 
# 3.3: Infinity -- reasonable?
# 3.4: can't iterate from NilClass (TypeError) -- worse?
```

I believe that while 3.4's behavior is explainable, 3.3's one has better DX.

(Obviously too late to change before the release, but maybe might be considered for some patch version or Ruby 3.5?..)



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