Provide additional context to errors involving const traits #144194
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Some changes occurred to constck cc @fee1-dead Some changes occurred to the CTFE machinery This PR modifies cc @jieyouxu |
| note: trait `PartialEq` is implemented but not `const` | ||
| --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL | ||
| note: trait `PartialEq` is implemented but not `const` | ||
| --> $SRC_DIR/core/src/ptr/mut_ptr.rs:LL:COL |
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Why is it pointing at the raw ptr impls?
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I think that they are incorrectly detected as CandidateSimilarity::Exact, which is incorrect. I can skip them explicitly on this PR by adding some other check, or look into it at another time.
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It's because of this:
rust/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
Lines 1689 to 1701 in 4ff3fa0
| trait_span.shrink_to_lo(), | ||
| format!("consider making trait `{trait_name}` const"), | ||
| format!("#[const_trait]\n{indentation}"), | ||
| Applicability::MachineApplicable, |
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This is not MachineApplicable, since it doesn't fix the bug completely.
| )); | ||
| note = false; | ||
| let def_kind = ccx.tcx.def_kind(callee); | ||
| if let DefKind::AssocTy | DefKind::AssocConst | DefKind::AssocFn = def_kind { |
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Callees are always AssocFns, why did you add DefKind::AssocTy | DefKind::AssocConst too?
| if let DefKind::AssocTy | DefKind::AssocConst | DefKind::AssocFn = def_kind { | ||
| let parent = ccx.tcx.parent(callee); | ||
| if let DefKind::Trait = ccx.tcx.def_kind(parent) |
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This whole check could be simplified if you looked at opt_associated_item and checked both the AssocKind and the AssocItemContainer, rather than using manual parenting logic.
| non_or_conditionally, | ||
| }); | ||
| let context_span = ccx.tcx.def_span(ccx.def_id()); | ||
| err.span_label(context_span, format!( |
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Why did you change this to a label only for this case, and keep it as a note for the rest? Having special logic changing it between a note and a label seems too special cased. I'd prefer if you reverted it.
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This line is pretty long for a label too.
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I wanted to point at the constant context in the output in some way, as it isn't always trivially obvious why a constant function was expected. As we already had a note talking about the const context I moved that same message over from the note to the label so we wouldn't need both.
It was
error[E0015]: cannot call non-const method `<T as Foo>::a` in constant functions
--> const-super-trait.rs:10:7
|
LL | const fn foo<T: ~const Bar>(x: &T) {
| ---------------------------------- calls in constant functions are limited to constant functions, tuple structs and tuple variants
LL | x.a();
| ^^^
vs
error[E0015]: cannot call non-const method `<T as Foo>::a` in constant functions
--> const-super-trait.rs:10:7
|
LL | x.a();
| ^^^
|
= note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
We could instead have
error[E0015]: cannot call non-const method `<T as Foo>::a` in constant functions
--> const-super-trait.rs:10:7
|
LL | const fn foo<T: ~const Bar>(x: &T) {
| ---------------------------------- required by this constant function
LL | x.a();
| ^^^
|
= note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
I was just trying to keep the verbosity increase to a minimum.
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I wanted to point at the constant context in the output in some way, as it isn't always trivially obvious why a constant function was expected.
I don't think the users need this to be a label. There's a tradeoff here with verbosity and I think this both complicates the implementation by having that note boolean and also splits the presentation of the diagnostic.
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Removed label in the last commit.
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☔ The latest upstream changes (presumably #144847) made this pull request unmergeable. Please resolve the merge conflicts. |
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Hi @oli-obk, it looks like Esteban has resolved all of the existing review feedback so this is ready for another round of review whenever you get a chance. Thanks! |
|
r? rust-lang/compiler |
compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
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When encountering an unmet `Ty: [const] Trait` bound, if `Trait` is `#[const_trait]` and there's an `impl Trait for Ty` point at it. If local, suggest `impl const Trait for Ty`, otherwise just point at it.
```
error[E0277]: the trait bound `NonConstAdd: [const] Add` is not satisfied
--> $DIR/assoc-type.rs:37:16
|
LL | type Bar = NonConstAdd;
| ^^^^^^^^^^^
|
note: required by a bound in `Foo::Bar`
--> $DIR/assoc-type.rs:33:15
|
LL | type Bar: [const] Add;
| ^^^^^^^^^^^ required by this bound in `Foo::Bar`
help: make the `impl` of trait `Add` `const`
|
LL | impl const Add for NonConstAdd {
| +++++
```
```
error[E0277]: the trait bound `T: [const] PartialEq` is not satisfied
--> tests/ui/traits/const-traits/call-generic-method-fail.rs:5:5
|
5 | *t == *t
| ^^^^^^^^
|
note: trait `PartialEq` is implemented but not `const`
--> /home/gh-estebank/rust/library/core/src/ptr/const_ptr.rs:1590:1
|
1590 | impl<T: PointeeSized> PartialEq for *const T {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: trait `PartialEq` is implemented but not `const`
--> /home/gh-estebank/rust/library/core/src/ptr/mut_ptr.rs:2011:1
|
2011 | impl<T: PointeeSized> PartialEq for *mut T {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
Point at trait and associated item when that associated item is used in a const context. Suggest making the trait `#[const_trait]`.
```
error[E0015]: cannot call non-const method `<() as Trait>::foo` in constant functions
--> $DIR/inline-incorrect-early-bound-in-ctfe.rs:26:8
|
LL | ().foo();
| ^^^^^
|
note: method `foo` is not const because trait `Trait` is not const
--> $DIR/inline-incorrect-early-bound-in-ctfe.rs:13:1
|
LL | trait Trait {
| ^^^^^^^^^^^ this trait is not const
LL | fn foo(self);
| ------------- this method is not const
= note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
help: consider making trait `Trait` const
|
LL + #[const_trait]
LL | trait Trait {
|
```
```
error[E0015]: cannot call non-const associated function `Foo::{constant#0}::Foo::<17>::value` in constants
--> $DIR/nested-type.rs:15:5
|
LL | struct Foo<const N: [u8; {
| __________________________-
LL | | struct Foo<const N: usize>;
LL | |
LL | | impl<const N: usize> Foo<N> {
... |
LL | | Foo::<17>::value()
| | ^^^^^^^^^^^^^^^^^^
LL | |
LL | | }]>;
| |_- calls in constants are limited to constant functions, tuple structs and tuple variants
```
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This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed. Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers. |
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When encountering an unmet
Ty: [const] Traitbound, ifTraitis#[const_trait]and there's animpl Trait for Typoint at it. If local, suggestimpl const Trait for Ty, otherwise just point at it.