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Use correct location for type tests in promoted constants #102187

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Oct 12, 2022
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9 changes: 9 additions & 0 deletions compiler/rustc_borrowck/src/type_check/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -587,6 +587,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
// modify their locations.
let all_facts = &mut None;
let mut constraints = Default::default();
let mut type_tests = Default::default();
let mut closure_bounds = Default::default();
let mut liveness_constraints =
LivenessValues::new(Rc::new(RegionValueElements::new(&promoted_body)));
Expand All @@ -598,6 +599,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
&mut this.cx.borrowck_context.constraints.outlives_constraints,
&mut constraints,
);
mem::swap(&mut this.cx.borrowck_context.constraints.type_tests, &mut type_tests);
mem::swap(
&mut this.cx.borrowck_context.constraints.closure_bounds_mapping,
&mut closure_bounds,
Expand All @@ -622,6 +624,13 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
swap_constraints(self);

let locations = location.to_locations();

// Use location of promoted const in collected constraints
for type_test in type_tests.iter() {
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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?

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@b-naber b-naber Sep 26, 2022

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Or are the type tests shared with something else and the in place modification would break something else, or something like that?

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.

let mut type_test = type_test.clone();
type_test.locations = locations;
self.cx.borrowck_context.constraints.type_tests.push(type_test)
}
for constraint in constraints.outlives().iter() {
let mut constraint = constraint.clone();
constraint.locations = locations;
Expand Down
30 changes: 30 additions & 0 deletions src/test/ui/consts/issue-102117.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
#![feature(inline_const, const_type_id)]

use std::alloc::Layout;
use std::any::TypeId;
use std::mem::transmute;
use std::ptr::drop_in_place;

pub struct VTable {
layout: Layout,
type_id: TypeId,
drop_in_place: unsafe fn(*mut ()),
}

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>)
},
}
}
}
}

fn main() {}
37 changes: 37 additions & 0 deletions src/test/ui/consts/issue-102117.stderr
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 {
| +++++++++

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 {
| +++++++++

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0310`.