From: "sferik (Erik Berlin) via ruby-core" <ruby-core@...>
Date: 2026-10-13T02:09:42+00:00
Subject: [ruby-core:127084] [Ruby Bug#22432] Range#include? returns true for the end of an empty range of single-character Strings

Issue #22432 has been reported by sferik (Erik Berlin).

----------------------------------------
Bug #22432: Range#include? returns true for the end of an empty range of single-character Strings
https://bugs.ruby-lang.org/issues/22432

* Author: sferik (Erik Berlin)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
A Range whose ends are both single ASCII characters reports that it includes its end even when the range is empty.

```ruby
r = "z".."a"
r.to_a          #=> []
r.include?("a") #=> true
r.member?("a")  #=> true
r.cover?("a")   #=> false
r === "a"       #=> false
```

I expect `include?` and `member?` to return false here, as `cover?` does and as iterating the range implies. The same happens with digits, for example `("1".."0").include?("0")`.

Only the end is affected. Other values are correctly reported as not included:

```ruby
("z".."a").include?("z") #=> false
("z".."a").include?("m") #=> false
```

`Range#include?` has a shortcut for ranges of single-character Strings, which compares the characters instead of iterating. It is in `rb_str_include_range_p` in string.c:

```c
if (ISASCII(b) && ISASCII(e) && ISASCII(v)) {
    if (b <= v && v < e) return Qtrue;
    return RBOOL(!RTEST(exclusive) && v == e);
}
```

The last line returns true whenever the value equals the end, without checking that the begin is not after the end.



-- 
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