[ASDAlexander77]

Under -mm=own, a callback stored into a class's field now keeps its family when other classes extend the class. Before, any derived class opened the field's family, so this.f(a[i]) in the base class's method reached any function. The new spec section is 57, and the limits in the user doc are updated.

Changes

Same key through the base's storage. A derived class's object holds its base's storage as its first field. A derived class reaches the base's field there, through a ts.PropertyRef of !ts.ref<!ts.class_storage<@Base>>, and the family used to see no such access. Now fieldFamilyKey gives that access the same key as one through an object of the base class: the class's constructor and -1 - the field's position. So a derived class's reads of the field (this.f(v)) and stores into it (this.f = drain) count toward the field's family. onlyCalledValue also treats a store into such a field as passing the parameter on.

When the family stays closed. Neither the class nor any class extending it may be built by another module, and no object of a class on that chain may become an interface, any, object, unknown or a union. A cast from a derived class to its base (Sub to Walker) keeps the family closed. The base-class check already in the file moved into a static helper, extendsClass, that both places now use.

Tests

• own_callback_extended: a derived class, and one two levels down, store into and call the base's field, with churn between steps. It runs under own, rc, gc and none, and own emits no counting. A repro of the same shape failed on main.
• own_err_callback_extended_drops: a derived class stores a callback that replaces a global array, and the walk reads an element of it after the call. It errors at :16:13. With a harmless callback swapped in, the same file compiles.
• Full ctest: 6047 of 6047 pass.
• DefaultLib under own: 163 passed and 11 skipped out of 174, in release and debug, compiled and under the JIT. That's unchanged. The 11 tests marked not own are refused by design: untyped Maps, an Array<T> of objects, and reduceRight returning an element.

Not in this PR

A class whose object, or a derived class's object, becomes an interface or any still keeps its fields' families open.

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