Hide niches under UnsafeCell #68491
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Hide niches under UnsafeCell #68491
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r? @zackmdavis (rust_highfive has picked a reviewer for you, use r? to override) |
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pnkfelix
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Jan 23, 2020
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Was the choice of |
We did discuss it at the relevant lang team meeting. I think it is fair to say that no one there was a strong champion of the I nonetheless went with it. It is more readily adaptable if we discover other cases that should be treated like this. It is also more flexible: for example, if we decide that we want #[lang = "unsafe_cell"]
#[repr(transparent)]
struct UnsafeCellWithExposedNiche<T: ?Sized> {
value: T,
}
#[repr(transparent)]
#[repr(no_niche)]
pub struct UnsafeCell<T: ?Sized> {
value: UnsafeCellWithExposedNiche<T>,
}
#[repr(transparent)]
pub struct Cell<T: ?Sized> {
value: UnsafeCellWithExposedNiche<T>,
} |
oli-obk
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Jan 25, 2020
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I didn't give a super detailed review, but this looks good to me. I think that having |
eddyb
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Jan 27, 2020
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@bors r+ |
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📌 Commit c29be616278e583b76d8aa2d486585ae8112c1c2 has been approved by |
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
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@bors r- |
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(I lost the race with PR #68122; I'll rebase atop current master and update the test to remove |
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@bors r=oli |
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📌 Commit 56491287a37cbd684c341c8c0d982ac215ff9dfc has been approved by |
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
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👉 "who's got two thumbs and thought 'surely nothing bad could happen if I just change the issue number in the feature meta-data to point at this PR rather than the issue, and move the meta-data record to a more appropriate spot in the list!' ...? This guy!" 👈 |
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@pnkfelix I think I would prefer to have a true tracking issue, myself, versus pointing to this PR. It'd be great to link to (e.g.) the write-up that I did, the original issue, and to give some context about how this mechanism is rustc-internal and not expected to be stabilized. |
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
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@nikomatsakis The standard approach to internal feature gates is to put them in the "internal feature gates" section without a tracking issue: rust/src/librustc_feature/active.rs Lines 96 to 98 in b181835 |
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⌛ Testing commit ea11b244d9793c9c7a2bcf61e95ea0f7e9aed6ec with merge 483c481cc8cd6bad32fedc84cd407fbf72f60149... |
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💥 Test timed out |
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☔ The latest upstream changes (presumably #68933) made this pull request unmergeable. Please resolve the merge conflicts. |
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This repr-hint makes a struct/enum hide any niche within from its surrounding type-construction context. It is meant (at least initially) as an implementation detail for resolving issue 68303. We will not stabilize the repr-hint unless someone finds motivation for doing so. (So, declaration of `no_niche` feature lives in section of file where other internal implementation details are grouped, and deliberately leaves out the tracking issue number.) incorporated review feedback, and fixed post-rebase.
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@bors r=oli |
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📌 Commit 1b12232 has been approved by |
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@bors p=1 |
This was referenced Feb 11, 2020
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☀️ Test successful - checks-azure |
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Hide any niche of T from type-construction context of
UnsafeCell<T>.Fix #68303
Fix #68206