Add error message for private fn by JulianKnodt · Pull Request #79291 · rust-lang/rust

JulianKnodt · 2020-11-22T09:42:25Z

Attempts to add a more detailed error when a const_evaluatable fn from another scope is used inside of a scope which cannot access it.

r? @lcnr

petrochenkov · 2021-01-18T20:43:08Z

Could someone explain me what's happening here from the language point of view? (Or even better send a patch to https://github.com/rust-lang/rfcs/blob/master/text/2145-type-privacy.md)
I've just noticed that this PR touches type privacy which is a very sensitive piece of infrastructure.
Why aren't existing checks enough?

(Also, I don't think the diagnostic change is an improvement, the message is talking about the function type specifically, the function itself may even be marked with pub.)

petrochenkov · 2021-01-31T11:37:25Z

r=me with #79291 (comment) addressed and commits squashed, unless @lcnr has more comments.

Bless tests Update with changes from comments

petrochenkov · 2021-02-01T07:40:54Z

@bors r+

bors · 2021-02-01T07:40:55Z

📌 Commit 6a03f03 has been approved by petrochenkov

Add error message for private fn Attempts to add a more detailed error when a `const_evaluatable` fn from another scope is used inside of a scope which cannot access it. r? `@lcnr`

Add error message for private fn Attempts to add a more detailed error when a `const_evaluatable` fn from another scope is used inside of a scope which cannot access it. r? ``@lcnr``

…as-schievink Rollup of 12 pull requests Successful merges: - rust-lang#78641 (Let io::copy reuse BufWriter buffers) - rust-lang#79291 (Add error message for private fn) - rust-lang#81364 (Improve `rustc_mir_build::matches` docs) - rust-lang#81387 (Move some tests to more reasonable directories - 3) - rust-lang#81463 (Rename NLL* to Nll* accordingly to C-CASE) - rust-lang#81504 (Suggest accessing field when appropriate) - rust-lang#81529 (Fix invalid camel case suggestion involving unicode idents) - rust-lang#81536 (Indicate both start and end of pass RSS in time-passes output) - rust-lang#81592 (Rustdoc UI fixes) - rust-lang#81594 (Avoid building LLVM just for llvm-dwp) - rust-lang#81598 (Fix calling convention for CRT startup) - rust-lang#81618 (Sync rustc_codegen_cranelift) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

…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.

rust-highfive assigned lcnr Nov 22, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 22, 2020

JulianKnodt force-pushed the ce_priv branch 7 times, most recently from 912bf03 to e12acb8Compare December 2, 2020 21:35

JulianKnodt marked this pull request as ready for review December 2, 2020 21:36

JulianKnodt force-pushed the ce_priv branch 2 times, most recently from 3bb6317 to 387c1b9Compare December 2, 2020 21:52

lcnr reviewed Dec 3, 2020
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Comment threadsrc/test/ui/const-generics/eval-privacy.stderr Outdated

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petrochenkov added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 30, 2021

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Comment threadsrc/test/ui/privacy/associated-item-privacy-inherent.rs Outdated

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Add error message for private fn
6a03f03
Bless tests Update with changes from comments

JulianKnodt force-pushed the ce_priv branch from fd17ca0 to 6a03f03Compare January 31, 2021 20:45

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 1, 2021

JohnTitor mentioned this pull request Feb 1, 2021
Rollup of 8 pull requests #81620
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henryboisdequin mentioned this pull request Feb 1, 2021
Rollup of 7 pull requests #81621
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jonas-schievink mentioned this pull request Feb 1, 2021
Rollup of 13 pull requests #81622
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jonas-schievink mentioned this pull request Feb 1, 2021
Rollup of 12 pull requests #81625
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oli-obk mentioned this pull request Feb 1, 2021
const_evaluatable: consider sub-expressions to be evaluatable #81577
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bors merged commit 21d0e9b into rust-lang:masterFeb 1, 2021

rustbot added this to the 1.51.0 milestone Feb 1, 2021

JulianKnodt deleted the ce_priv branch February 1, 2021 19:48

lcnr added A-const-generics Area: const generics (parameters and arguments) F-generic_const_exprs `#![feature(generic_const_exprs)]` labels Aug 26, 2021

jswrenn mentioned this pull request Nov 4, 2021
Relax priv-in-pub lint on generic bounds and where clauses of trait impls. #90586
Merged

lcnr mentioned this pull request Dec 11, 2021
Tracking issue for const generics (RFC 2000) #44580
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Add error message for private fn - #79291

Add error message for private fn#79291
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