Bug #22452: `rb_equal` returns true for `NaN == NaN`

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[byroot (Jean Boussier)]

I noticed this while trying to cleanup and simplify rb_equal.

>> Float::NAN == Float::NAN
=> false
>> [Float::NAN].index(Float::NAN)
=> 0

I would expect it to return nil.

Array#index is just an example, any core method, and even C extension relying on rb_equal is similarly impacted.

This bug is present on all Ruby versions, except for versions between 2.1 and 2.4.

The bug seem to have been re-introduced in 2.5 by 6e0e067de31511cebec01d176f628442371db879

JRuby seem to have the same behavior, but TruffleRuby correctly returnsnil.

[byroot (Jean Boussier)]

• Description updated (diff)

[byroot (Jean Boussier)]

• Related to Bug #1720: [NaN] == [NaN] が true になる added

[byroot (Jean Boussier)]

Possibly a duplicate of [Bug #1720] where it was established that Float::NaN == Float::NaN is "undefined" therefore OK.

It seems that the motivation was to not prevent optimization of rb_equal.