Improve some SAFETY comments following suggestions
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@ -315,12 +315,23 @@ mod lazy {
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// value (an aliasing violation). To avoid setting the "I'm running a
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// destructor" flag we just use `mem::replace` which should sequence the
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// operations a little differently and make this safe to call.
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//
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// `ptr` can be dereferenced safely since it was obtained from
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// `UnsafeCell::get`, which should not return a non-aligned or NUL pointer.
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// What's more a `LazyKeyInner` can only be created with `new`, which ensures
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// `inner` is correctly initialized and all calls to methods on `LazyKeyInner`
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// will leave `inner` initialized too.
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unsafe {
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let _ = mem::replace(&mut *ptr, Some(value));
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}
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// SAFETY: the *ptr operation is made safe by the `mem::replace`
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// call above that made sure a valid value is present behind it.
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// SAFETY: the `*ptr` operation is made safe by the `mem::replace`
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// call above combined with `ptr` being correct from the beginning
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// (see previous SAFETY: comment above).
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//
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// Plus, with the call to `mem::replace` it is guaranteed there is
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// a `Some` behind `ptr`, not a `None` so `unreachable_unchecked`
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// will never be reached.
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unsafe {
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// After storing `Some` we want to get a reference to the contents of
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// what we just stored. While we could use `unwrap` here and it should
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@ -337,8 +348,8 @@ mod lazy {
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#[allow(unused)]
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pub unsafe fn take(&mut self) -> Option<T> {
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// SAFETY: The other methods hand out references while taking &self.
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// As such, calling this method when such references are still alive
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// will fail because it takes a &mut self, conflicting with them.
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// As such, callers of this method must ensure no `&` and `&mut` are
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// available and used at the same time.
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unsafe { (*self.inner.get()).take() }
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}
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}
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@ -451,9 +462,9 @@ pub mod fast {
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// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
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#[inline(never)]
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unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
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// SAFETY: See comment above.
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// SAFETY: See comment above (this function doc).
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if !mem::needs_drop::<T>() || unsafe { self.try_register_dtor() } {
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// SAFETY: See comment above.
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// SAFETY: See comment above (his function doc).
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Some(unsafe { self.inner.initialize(init) })
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} else {
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None
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