[@vue/reactivity] effect() and computed() should not react to changes in a Map's values() when only keys() was ever accessed

[nmsmith]

Version

3.0.0-alpha.9

Reproduction link

https://jsfiddle.net/kxy9bued/1/

Steps to reproduce

See code sample. To summarise:

• Create a reactive() Map.
• Create an effect() wherein (only) the keys() of the Map are accessed.
• Use set() to update an existing entry in the Map. The effect() is re-invoked, even though the keys() haven't changed.

Note that this makes the behaviour of a Map different to that of a Set, even if the Map is merely used as a Set.

What is expected?

The behaviour of a Map should match that of a Set. Specifically, when a Map key is UPDATED, rather than newly added, effect() should not react as if the list of keys() has changed.

What is actually happening?

The effect() is re-invoked, as if the list of keys() has changed. In the code sample, this causes an extra line of output to be printed.