[ruby-core:88391] [Ruby trunk Bug#14974] "if" statement executes wrong branch

Issue #14974 has been updated by shevegen (Robert A. Heiler).


> occurs only when a nonsense assignment like foo = foo is used.

Could happen because of a typo or the brain-associated with the
fingers in some thought process. I made very strange mistakes
myself; most common one I still make is "=" rather than "=="
simply because I somehow forget to type == (hit = twice). Happens
perhaps 1 in 1000 times only when I am very alert but when I
am quite sleepy it may be 1 in 100 times.

What I mean to say is that we can expect the unexpected as a 
result of humans working with computers in general. :)

----------------------------------------
Bug #14974: "if" statement executes wrong branch
https://bugs.ruby-lang.org/issues/14974#change-73444

* Author: kratob (Tobias Kraze)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
I've stumbled over a rather weird bug where Ruby 2.5+ executes an `else` branch of a condition when it should not. The best minimal example I could come up with is this:

~~~
def broken
  foo = 1
  if is_true or is_false
    foo = foo
  else
    raise "FAIL"
  end
  puts "PASS"
end

def is_true
  true
end

def is_false
  false
end

broken()
~~~

For me this script raises "FAIL" instead of printing "PASS".

Note that this is actually pretty much minimal; any of the following will "fix" the issue:
* inlining `is_true` or `is_false`
* removing the `foo = foo` or adding any other code to the `if` branch
* replacing `raise "FAIL"` with  `puts "FAIL"`
* removing the `puts "PASS"`



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