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Chris Tate
70697b45c3
Generic arrow and function-expression bindings compile to shared
instances, and their declarations emit no store. Code that can run before
the declaration then diverged from Node.
- Inside a function, a nested function lowered before the declaration
reads the binding through a TDZ box that nothing initialized. That
covers closures above the declaration and hoisted function
declarations. Such a read threw a ReferenceError even after the
declaration ran. The declaration now stores the instance its declared
signature pins into that box.
- At module scope, calls and pinned value reads went straight to the
instances even when a hoisted function or an earlier closure ran them
before the declaration. A binding with such a use now has a flag that
its declaration sets.
- Uses that can run first check the flag.
- A let or const throws Node's ReferenceError before the arguments
run.
- A var runs the arguments and then throws "is not a function".
- Uses that follow the declaration stay direct calls: later statements,
closures created after it, its own initializer, and function
declarations that only such code calls.
A var binding inside a function that is called from a place that can run
before its declaration would need a per-call flag shared with its
closures. That shape now fails with SC1090 instead of calling the
instance.