[ruby-core:112906] [Ruby master Bug#19531] ObjectSpace::WeakMap: replaced values still clear the key they were assigned to

Issue #19531 has been reported by byroot (Jean Boussier). ---------------------------------------- Bug #19531: ObjectSpace::WeakMap: replaced values still clear the key they were assigned to https://bugs.ruby-lang.org/issues/19531 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal * Backport: 2.7: WONTFIX, 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED ---------------------------------------- ### Reproduction script ```ruby wmap = ObjectSpace::WeakMap.new a = "A" b = "B" wmap[1] = a wmap[1] = b # the table entry with 1 is still in the list of entries to clear when `a` is GCed a = nil GC.start p wmap[1] # Should be `"B"`, but is `nil` ``` ### Explanation What happens is that when we set `wmap[1] = "A"`, WeakMap internally keeps a list of keys to clear when `"A"` is GCed, e.g. pseudo code: ```ruby class WeakMap def []=(key, value) @hash[key] = value @reverse[value] << key end end ``` But it doesn't clear previously kept mapping when a key is overwritten. I'll work on a fix. ### References https://github.com/protocolbuffers/protobuf/pull/12216 -- https://bugs.ruby-lang.org/