Hash#rehash removes @first elements from hash

[BlobCodes]

Bug Report

The following code should explain the issue:

hash = {"a" => 2, "b" => 3, "c" => 1}
hash.delete("a")

puts hash # => {"b" => 3, "c" => 1}
hash.rehash
puts hash # => {"c" => 1}
hash.rehash
puts hash # => {}

# ---

hash = {"a" => 2, "b" => 3, "c" => 1, "d" => 0, "e" => 6}
hash.delete("a")
hash.delete("b")

puts hash # => {"c" => 1, "d" => 0, "e" => 6}
hash.rehash
puts hash # => {"e" => 6}
hash.rehash
puts hash # => {}

The hash deletes @first elements at the beginning of of hash.

The state of the Hash seems to be invalid after the rehash as it's also possible to get segfaults:

hash = {"a" => 2, "b" => 3}
hash.delete("a")
hash.rehash
hash.first_key[0] # => Invalid memory access (signal 11) at address 0x4

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$ crystal -v
Crystal 1.12.1 [4cea10199] (2024-04-11)

LLVM: 15.0.7
Default target: x86_64-unknown-linux-gnu