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improve const infer error

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This commit is contained in:
Bastian Kauschke 2020-10-22 23:07:48 +02:00
parent a9cd294cf2
commit 40ab18d97d
2 changed files with 6 additions and 12 deletions
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16
compiler/rustc_middle/src/infer/unify_key.rs
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@ -176,17 +176,17 @@ impl<'tcx> UnifyValue for ConstVarValue<'tcx> {
type Error = (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>); type Error = (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>);
fn unify_values(value1: &Self, value2: &Self) -> Result<Self, Self::Error> { fn unify_values(value1: &Self, value2: &Self) -> Result<Self, Self::Error> {
let (val, span) = match (value1.val, value2.val) { let (val, origin) = match (value1.val, value2.val) {
(ConstVariableValue::Known { .. }, ConstVariableValue::Known { .. }) => { (ConstVariableValue::Known { .. }, ConstVariableValue::Known { .. }) => {
bug!("equating two const variables, both of which have known values") bug!("equating two const variables, both of which have known values")
} }
// If one side is known, prefer that one. // If one side is known, prefer that one.
(ConstVariableValue::Known { .. }, ConstVariableValue::Unknown { .. }) => { (ConstVariableValue::Known { .. }, ConstVariableValue::Unknown { .. }) => {
(value1.val, value1.origin.span) (value1.val, value1.origin)
} }
(ConstVariableValue::Unknown { .. }, ConstVariableValue::Known { .. }) => { (ConstVariableValue::Unknown { .. }, ConstVariableValue::Known { .. }) => {
(value2.val, value2.origin.span) (value2.val, value2.origin)
} }
// If both sides are *unknown*, it hardly matters, does it? // If both sides are *unknown*, it hardly matters, does it?
@ -200,17 +200,11 @@ impl<'tcx> UnifyValue for ConstVarValue<'tcx> {
// universe is the minimum of the two universes, because that is // universe is the minimum of the two universes, because that is
// the one which contains the fewest names in scope. // the one which contains the fewest names in scope.
let universe = cmp::min(universe1, universe2); let universe = cmp::min(universe1, universe2);
(ConstVariableValue::Unknown { universe }, value1.origin.span) (ConstVariableValue::Unknown { universe }, value1.origin)
} }
}; };
Ok(ConstVarValue { Ok(ConstVarValue { origin, val })
origin: ConstVariableOrigin {
kind: ConstVariableOriginKind::ConstInference,
span: span,
},
val,
})
} }
} }

2
src/test/ui/const-generics/infer/issue-77092.stderr
View file

@ -2,7 +2,7 @@ error[E0282]: type annotations needed
--> $DIR/issue-77092.rs:13:26 --> $DIR/issue-77092.rs:13:26
| |
LL | println!("{:?}", take_array_from_mut(&mut arr, i)); LL | println!("{:?}", take_array_from_mut(&mut arr, i));
| ^^^^^^^^^^^^^^^^^^^ cannot infer the value of the constant `{_: usize}` | ^^^^^^^^^^^^^^^^^^^ cannot infer the value of const parameter `N` declared on the function `take_array_from_mut`
error: aborting due to previous error error: aborting due to previous error