[ASDAlexander77]

Summary

Under -mm=own a generator's state captured its parameters as borrows (spec §19). The result of a lazy helper like iter.map(f) was therefore bounded by its arguments: it could not be stored, returned or handed to another generator. @keeps on a generator now names the parameters its state takes over:

• Callers move the named arguments in, and the state's release frees them.
• A @keeps generator is not bounded by its arguments.
• A captured parameter left out of @keeps is an error ("names 'iter', but its body keeps 'iter', 'f'").
• Using an argument after the call is the usual use-after-move error.
• A generator without @keeps still borrows, as before.

Implementation:

• paramsCapturedIntoState (OwnershipSignatureGenerators) finds the heap-owning parameter cells a generator's state captures. localOwnedParams counts them as kept when the maker says @keeps.
• findBorrowingStates marks such a state owns. Its captured box is not a borrowing field, so the release routine frees it, and the result is not marked bounded.
• decideEscaping no longer reports a kept parameter's cell as "its value is the caller's".
• isFresh accepts an extension call to a defined function, and holdsNoBlock accepts a function reference cast.

Spec §38 and docs/own-memory-model.md are updated.

DefaultLib uses this for take/filter/map/drop in ASDAlexander77/TypeScriptCompilerDefaultLib (PR to follow).

Tests

• New tests:
  • own_generator_keeps: a class argument, an iterator argument, an iterator plus a callback, a @keeps generator nested in another, a generator returned from a function or stored in a global, and one given up after one step. It churns between steps and runs under own, rc, gc and none.
  • Three error tests: @keeps missing a parameter, an argument used after the move, and a generator without @keeps that is stored.
• Full ctest -C Release: 5872 passed, 0 failed.
• DefaultLib suites with the companion change:
  • rc, gc and none pass every test.
  • own goes from 137 to 139/170 (iterator_map, iterator_filter), with no new failures.

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