Optimize symbol name length of InitClosure#153
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Currently, the `pin_init` library has an `Invariant` type alias, and it is instantiated using `PhantomData`. Generated code from `pin_data` on the other hand cannot access the crate-local type alias, so it generates `PhantomData<fn(T) -> T>` directly. This is all very inconsistent, despite the exact same use case of ensuring invariance. Add `PhantomInvariant` and `PhantomInvariantLifetime` and switch all users that need to express the concept of invariance to use these. They're polyfills of unstable types in the same names in the Rust standard library. Signed-off-by: Gary Guo <gary@garyguo.net>
The `__internal` module is for exposing internal items publicly to procedural macros (pin-init-internal). Types that are crate-local only can just have proper visibility and does not need to be in `__internal`. The type name of `InitClosure` can often shows up in symbol names, this reduces the length slightly. Signed-off-by: Gary Guo <gary@garyguo.net>
Move `E` from type to trait impl block. This greatly shortens the monomorphized type names. The `__pinned_init` function name is only slightly shortened as it still encodes the `E` as part of `PinInit<T, E>` in the symbol. `T` cannot be moved to trait impl block otherwise it will start to conflict with the `impl Init<T> for T` as Rust cannot deduce that there're no types that fulfill `T: FnOnce(*mut T)`. Signed-off-by: Gary Guo <gary@garyguo.net>
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By moving
InitClosureout from__internalit saves ~14 bytes from symbol name, and removeEsaves ~4 bytes. Not too significant, but the code is organized better anyway so this is an improvement regardless the saving.