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Use correct location for type tests in promoted constants #102187
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,30 @@ | ||
#![feature(inline_const, const_type_id)] | ||
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use std::alloc::Layout; | ||
use std::any::TypeId; | ||
use std::mem::transmute; | ||
use std::ptr::drop_in_place; | ||
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pub struct VTable { | ||
layout: Layout, | ||
type_id: TypeId, | ||
drop_in_place: unsafe fn(*mut ()), | ||
} | ||
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impl VTable { | ||
pub fn new<T>() -> &'static Self { | ||
const { | ||
//~^ ERROR the parameter type `T` may not live long enough | ||
//~| ERROR the parameter type `T` may not live long enough | ||
&VTable { | ||
layout: Layout::new::<T>(), | ||
type_id: TypeId::of::<T>(), | ||
drop_in_place: unsafe { | ||
transmute::<unsafe fn(*mut T), unsafe fn(*mut ())>(drop_in_place::<T>) | ||
}, | ||
} | ||
} | ||
} | ||
} | ||
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fn main() {} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,37 @@ | ||
error[E0310]: the parameter type `T` may not live long enough | ||
--> $DIR/issue-102117.rs:16:9 | ||
| | ||
LL | / const { | ||
LL | | | ||
LL | | | ||
LL | | &VTable { | ||
... | | ||
LL | | } | ||
LL | | } | ||
| |_________^ ...so that the type `T` will meet its required lifetime bounds | ||
| | ||
help: consider adding an explicit lifetime bound... | ||
| | ||
LL | pub fn new<T: 'static>() -> &'static Self { | ||
| +++++++++ | ||
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error[E0310]: the parameter type `T` may not live long enough | ||
--> $DIR/issue-102117.rs:16:9 | ||
| | ||
LL | / const { | ||
LL | | | ||
LL | | | ||
LL | | &VTable { | ||
... | | ||
LL | | } | ||
LL | | } | ||
| |_________^ ...so that the type `T` will meet its required lifetime bounds | ||
| | ||
help: consider adding an explicit lifetime bound... | ||
| | ||
LL | pub fn new<T: 'static>() -> &'static Self { | ||
| +++++++++ | ||
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error: aborting due to 2 previous errors | ||
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For more information about this error, try `rustc --explain E0310`. |
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Is it possible to do this by iterating over
self.cx.borrowck_context.constraints.type_tests
directly and modifying in place? Or are the type tests shared with something else and the in place modification would break something else, or something like that?There was a problem hiding this comment.
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Yes the type tests are shared with those of the body that contains the promoted constant, so we need some way to only collect the type tests of the promoted constant body when we type check that.
swap_constraints
is currently used for this. I'm not sure what the problem is with spawning an entirely new borrow checking context when type checking promoteds. Presumably this would cause slight performance problems when we only really care about the constraints being different? Not sure.