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Rollup merge of rust-lang#82112 - BoxyUwU:tumbleweed, r=varkor
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const_generics: Dont evaluate array length const when handling yet another error

Same ICE as rust-lang#82009 except triggered by a different error.
cc `@lcnr`
r? `@varkor`
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Dylan-DPC authored Feb 18, 2021
2 parents c53cc39 + 7e368e5 commit 5775894
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Showing 4 changed files with 49 additions and 23 deletions.
13 changes: 6 additions & 7 deletions compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
Original file line number Diff line number Diff line change
Expand Up @@ -72,17 +72,16 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
// We were unable to unify the abstract constant with
// a constant found in the caller bounds, there are
// now three possible cases here.
//
// - The substs are concrete enough that we can simply
// try and evaluate the given constant.
// - The abstract const still references an inference
// variable, in this case we return `TooGeneric`.
// - The abstract const references a generic parameter,
// this means that we emit an error here.
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
enum FailureKind {
/// The abstract const still references an inference
/// variable, in this case we return `TooGeneric`.
MentionsInfer,
/// The abstract const references a generic parameter,
/// this means that we emit an error here.
MentionsParam,
/// The substs are concrete enough that we can simply
/// try and evaluate the given constant.
Concrete,
}
let mut failure_kind = FailureKind::Concrete;
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -200,22 +200,15 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
if let Some(def) = aty.ty_adt_def() {
// We also want to be able to select the array's type's original
// signature with no type arguments resolved
flags.push((
sym::_Self,
Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
));
let tcx = self.tcx;
if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
flags.push((
sym::_Self,
Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
));
} else {
flags.push((
sym::_Self,
Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
));
}
let type_string = self.tcx.type_of(def.did).to_string();
flags.push((sym::_Self, Some(format!("[{}]", type_string))));

let len = len.val.try_to_value().and_then(|v| v.try_to_machine_usize(self.tcx));
let string = match len {
Some(n) => format!("[{}; {}]", type_string, n),
None => format!("[{}; _]", type_string),
};
flags.push((sym::_Self, Some(string)));
}
}
if let ty::Dynamic(traits, _) = self_ty.kind() {
Expand Down
22 changes: 22 additions & 0 deletions src/test/ui/const-generics/dont-evaluate-array-len-on-err-1.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
#![feature(const_generics, const_evaluatable_checked)]
#![allow(incomplete_features)]

// This tests that during error handling for the "trait not implemented" error
// we dont try to evaluate std::mem::size_of::<Self::Assoc> causing an ICE

struct Adt;

trait Foo {
type Assoc;
fn foo()
where
[Adt; std::mem::size_of::<Self::Assoc>()]: ,
{
<[Adt; std::mem::size_of::<Self::Assoc>()] as Foo>::bar()
//~^ Error: the trait bound
}

fn bar() {}
}

fn main() {}
12 changes: 12 additions & 0 deletions src/test/ui/const-generics/dont-evaluate-array-len-on-err-1.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
error[E0277]: the trait bound `[Adt; _]: Foo` is not satisfied
--> $DIR/dont-evaluate-array-len-on-err-1.rs:15:9
|
LL | <[Adt; std::mem::size_of::<Self::Assoc>()] as Foo>::bar()
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `[Adt; _]`
...
LL | fn bar() {}
| -------- required by `Foo::bar`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.

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