From: merch-redmine@...
Date: 2020-07-15T15:58:58+00:00
Subject: [ruby-core:99179] [Ruby master Bug#17017] Range#max & Range#minmax incorrectly use Float end as max

Issue #17017 has been updated by jeremyevans0 (Jeremy Evans).


marcandre (Marc-Andre Lafortune) wrote in #note-9:
> jeremyevans0 (Jeremy Evans) wrote in #note-7:
> > koic (Koichi ITO) wrote in #note-6:
> > > I encountered a breaking change in RuboCop repository when using ruby 2.8.0dev.
> > > https://github.com/rubocop-hq/rubocop/blob/v0.88.0/lib/rubocop/comment_config.rb#L110
> > > 
> > > So, I have a question. Is this an expected behaviour?
> > 
> > Yes, it is expected behavior, at least to me. I believe the Ruby 2.7 behavior is wrong, because a range that starts with an integer will never have a non-integer maximum value, since the increment is an integer. 
> 
> I should have been more clear when I commented to take care of Infinity, but I believe that previous behavior should remain. Since there is no `Integer::INFINITY`, returning `Float::INFINITY` is quite descriptive and useful. Raising a `RangeError` doesn't seem helpful. (I wrote `RangeError` since raising `FloatDomainError` as currently is definitely a mistake).

With current Ruby, you should use an endless range instead of range with an infinite end.

The previous behavior of returning `Float::INFINITY` seems wrong to me.  I suppose the current behavior of raising `FloatDomainError` may be unexpected, and `RangeError` could be returned instead.  Note that if you use the exclusive range (`42...Float::INFINITY`), you would get a `TypeError` in 2.7.1, so it's not like we exclusively used `RangeError` for issues like these.  Mathematically, `42..Float::INFINITY` and `42...Float::INFINITY` represent the same range, so you should get the same behavior for both.

All that said, I'm not completely opposed to special casing `Float::INFINITY` in this case.  I would like to hear opinions from other committers.


----------------------------------------
Bug #17017: Range#max & Range#minmax incorrectly use Float end as max
https://bugs.ruby-lang.org/issues/17017#change-86558

* Author: sambostock (Sam Bostock)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.8.0dev (2020-07-14T04:19:55Z master e60cd14d85) [x86_64-darwin17]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
While continuing to add edge cases to [`Range#minmax` specs](https://github.com/ruby/spec/pull/777), I discovered the following bug:

```ruby
(1..3.1).to_a        == [1, 2, 3] # As expected

(1..3.1).to_a.max    == 3         # As expected
(1..3.1).to_a.minmax == [1, 3]    # As expected

(1..3.1).max    == 3.1            # Should be 3, as above
(1..3.1).minmax == [1, 3.1]       # Should be [1, 3], as above
```

One way to detect this scenario might be to do (whatever the C equivalent is of)

```ruby
range_end.is_a?(Numeric)                      // Is this a numeric range?
  && (range_end - range_begin).modulo(1) == 0 // Can we reach the range_end using the standard step size (1)
```

As for how to handle it, a couple options come to mind:

- We could error out and do something similar to what we do for exclusive ranges

```ruby
raise TypeError, 'cannot exclude non Integer end value'
```

- We might be able to calculate the range end by doing something like

```ruby
num_steps = (range_end / range_beg).to_i - 1 # one fewer steps than would exceed the range_end
max = range_beg + num_steps                  # take that many steps all at once
```

- We could delegate to `super` and enumerate the range to find the max

```ruby
super
```

- We could update the documentation to define the max for this case as the `range_end`, similarly to how the documentation for `include?` says it behaves like `cover?` for numeric ranges.



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