Old method incorrectly called after redefining it

[nalimilan]

I've experienced a weird bug when working on #16401. When debugging the hash(::AbstractArray, ::UInt) method, I repeatedly pasted it in the REPL and called hash(::AbstractArray). It turns out that under some circumstances, the redefinition has no effect: the old method is still used.

I've been able to reproduce the problem with relatively simple steps:

1. start REPL in the Julia source directory and call import Base: hash, hash_range, TypeRangeStep, RangeStepRegular, hashaa_seed, hashr_seed, hashrle_seed
2. copy these lines to the REPL after adding a statement like println(1) at the top of the function
3. call hash([1]) and check that it prints 1
4. run using Test; include("test/hashing.jl")
5. copy the lines from step 2 after increasing the value in the println call
6. call hash([1]) and observe that it still prints 1

If you skip step 4, the call in the last step prints 2 as expected.

[StefanKarpinski]

cc @vtjnash

[timholy]

I've seen something like this before too but never tracked down a reproducer. Awesome work, @nalimilan.

[nalimilan]

Yeah, when I started to have serious doubts about the fact that I wasn't just mad, but that something weird was going on, I thought it was probably worth reporting, since it's not that common to be able to reproduce this kind of thing. The fact that I identified the problem is an indication of the hard time I had getting the hashing algorithm to work (and of my lazy trial-and-error approach :-p).

[KristofferC]

This doesn't repro anymore and a lot of things have changed since the issue opened. Please reopen if this can be reproduced some other way.