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Rollup merge of rust-lang#90586 - jswrenn:relax-privacy-lints, r=petr…
…ochenkov Relax priv-in-pub lint on generic bounds and where clauses of trait impls. The priv-in-pub lint is a legacy mechanism of the compiler, supplanted by a reachability-based [type privacy](https://github.com/rust-lang/rfcs/blob/master/text/2145-type-privacy.md) analysis. This PR does **not** relax type privacy; it only relaxes the lint (as proposed by the type privacy RFC) in the case of trait impls. ## Current Behavior On public trait impls, it's currently an **error** to have a `where` bound constraining a private type with a trait: ```rust pub trait Trait {} pub struct Type {} struct Priv {} impl Trait for Priv {} impl Trait for Type where Priv: Trait // ERROR {} ``` ...and it's a **warning** to have have a public type constrained by a private trait: ```rust pub trait Trait {} pub struct Type {} pub struct Pub {} trait Priv {} impl Priv for Pub {} impl Trait for Type where Pub: Priv // WARNING {} ``` This lint applies to `where` clauses in other contexts, too; e.g. on free functions: ```rust struct Priv<T>(T); pub trait Pub {} impl<T: Pub> Pub for Priv<T> {} pub fn function<T>() where Priv<T>: Pub // WARNING {} ``` **These constraints could be relaxed without issue.** ## New Behavior This lint is relaxed for `where` clauses on trait impls, such that it's okay to have a `where` bound constraining a private type with a trait: ```rust pub trait Trait {} pub struct Type {} struct Priv {} impl Trait for Priv {} impl Trait for Type where Priv: Trait // OK {} ``` ...and it's okay to have a public type constrained by a private trait: ```rust pub trait Trait {} pub struct Type {} pub struct Pub {} trait Priv {} impl Priv for Pub {} impl Trait for Type where Pub: Priv // OK {} ``` ## Rationale While the priv-in-pub lint is not essential for soundness, it *can* help programmers avoid pitfalls that would make their libraries difficult to use by others. For instance, such a lint *is* useful for free functions; e.g. if a downstream crate tries to call the `function` in the previous snippet in a generic context: ```rust fn callsite<T>() where Priv<T>: Pub // ERROR: omitting this bound is a compile error, but including it is too { function::<T>() } ``` ...it cannot do so without repeating `function`'s `where` bound, which we cannot do because `Priv` is out-of-scope. A lint for this case is arguably helpful. However, this same reasoning **doesn't** hold for trait impls. To call an unconstrained method on a public trait impl with private bounds, you don't need to forward those private bounds, you can forward the public trait: ```rust mod upstream { pub trait Trait { fn method(&self) {} } pub struct Type<T>(T); pub struct Pub<T>(T); trait Priv {} impl<T: Priv> Priv for Pub<T> {} impl<T> Trait for Type<T> where Pub<T>: Priv // WARNING {} } mod downstream { use super::upstream::*; fn function<T>(value: Type<T>) where Type<T>: Trait // <- no private deets! { value.method(); } } ``` **This PR only eliminates the lint on trait impls.** It leaves it intact for all other contexts, including trait definitions, inherent impls, and function definitions. It doesn't need to exist in those cases either, but I figured I'd first target a case where it's mostly pointless. ## Other Notes - See discussion [on zulip](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/relax.20priv-in-pub.20lint.20for.20trait.20impl.20.60where.60.20bounds/near/222458397). - This PR effectively reverts rust-lang#79291.
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35 changes: 2 additions & 33 deletions
35
src/test/ui/const-generics/generic_const_exprs/eval-privacy.stderr
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,43 +1,12 @@ | ||
| warning: private type `fn(u8) -> u8 {my_const_fn}` in public interface (error E0446) | ||
| --> $DIR/eval-privacy.rs:12:1 | ||
| | | ||
| LL | / impl<const U: u8> Trait for Const<U> | ||
| LL | | | ||
| LL | | | ||
| LL | | | ||
| ... | | ||
| LL | | } | ||
| LL | | } | ||
| | |_^ | ||
| | | ||
| = note: `#[warn(private_in_public)]` on by default | ||
| = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! | ||
| = note: for more information, see issue #34537 <https://github.com/rust-lang/rust/issues/34537> | ||
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| warning: private type `fn(u8) -> u8 {my_const_fn}` in public interface (error E0446) | ||
| --> $DIR/eval-privacy.rs:12:1 | ||
| | | ||
| LL | / impl<const U: u8> Trait for Const<U> | ||
| LL | | | ||
| LL | | | ||
| LL | | | ||
| ... | | ||
| LL | | } | ||
| LL | | } | ||
| | |_^ | ||
| | | ||
| = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! | ||
| = note: for more information, see issue #34537 <https://github.com/rust-lang/rust/issues/34537> | ||
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| error[E0446]: private type `fn(u8) -> u8 {my_const_fn}` in public interface | ||
| --> $DIR/eval-privacy.rs:21:5 | ||
| --> $DIR/eval-privacy.rs:16:5 | ||
| | | ||
| LL | type AssocTy = Const<{ my_const_fn(U) }>; | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type | ||
| ... | ||
| LL | const fn my_const_fn(val: u8) -> u8 { | ||
| | ----------------------------------- `fn(u8) -> u8 {my_const_fn}` declared as private | ||
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| error: aborting due to previous error; 2 warnings emitted | ||
| error: aborting due to previous error | ||
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| For more information about this error, try `rustc --explain E0446`. |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| // priv-in-pub lint tests where the private type appears in the | ||
| // `where` clause of a public item | ||
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| #![crate_type = "lib"] | ||
| #![feature(generic_const_exprs)] | ||
| #![allow(incomplete_features)] | ||
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| struct PrivTy; | ||
| trait PrivTr {} | ||
| pub struct PubTy; | ||
| pub struct PubTyGeneric<T>(T); | ||
| pub trait PubTr {} | ||
| impl PubTr for PrivTy {} | ||
| pub trait PubTrWithAssocTy { type AssocTy; } | ||
| impl PubTrWithAssocTy for PrivTy { type AssocTy = PrivTy; } | ||
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| pub struct S | ||
| //~^ WARNING private type `PrivTy` in public interface | ||
| //~| WARNING hard error | ||
| where | ||
| PrivTy: | ||
| {} | ||
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| pub enum E | ||
| //~^ WARNING private type `PrivTy` in public interface | ||
| //~| WARNING hard error | ||
| where | ||
| PrivTy: | ||
| {} | ||
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| pub fn f() | ||
| //~^ WARNING private type `PrivTy` in public interface | ||
| //~| WARNING hard error | ||
| where | ||
| PrivTy: | ||
| {} | ||
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| impl S | ||
| //~^ ERROR private type `PrivTy` in public interface | ||
| where | ||
| PrivTy: | ||
| { | ||
| pub fn f() | ||
| //~^ WARNING private type `PrivTy` in public interface | ||
| //~| WARNING hard error | ||
| where | ||
| PrivTy: | ||
| {} | ||
| } | ||
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| impl PubTr for PubTy | ||
| where | ||
| PrivTy: | ||
| {} | ||
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| impl<T> PubTr for PubTyGeneric<T> | ||
| where | ||
| T: PubTrWithAssocTy<AssocTy=PrivTy> | ||
| {} | ||
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| pub struct Const<const U: u8>; | ||
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| pub trait Trait { | ||
| type AssocTy; | ||
| fn assoc_fn() -> Self::AssocTy; | ||
| } | ||
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| impl<const U: u8> Trait for Const<U> | ||
| where | ||
| Const<{ my_const_fn(U) }>: , | ||
| { | ||
| type AssocTy = Const<{ my_const_fn(U) }>; | ||
| //~^ ERROR private type | ||
| fn assoc_fn() -> Self::AssocTy { | ||
| Const | ||
| } | ||
| } | ||
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| const fn my_const_fn(val: u8) -> u8 { | ||
| // body of this function doesn't matter | ||
| val | ||
| } |
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