move leak-check to during coherence, candidate eval #72493

nikomatsakis · 2020-05-23T09:53:31Z

Implementation of MCP rust-lang/compiler-team#295.

I'd like to do a crater run on this.

Note to @rust-lang/lang: This PR is a breaking change (bugfix). It causes tests like the following to go from a future-compatibility warning #56105 to a hard error:

trait Trait {}
impl Trait for for<'a, 'b> fn(&'a u32, &'b u32) {}
impl Trait for for<'c> fn(&'c u32, &'c u32) {} // now rejected, used to warn

I am not aware of any instances of this code in the wild, but that is why we are doing a crater run. The reason for this change is that those two types are, in fact, the same type, and hence the two impls are overlapping.

There will still be impls that trigger #56105 after this lands, however -- I hope that we will eventually just accept those impls without warning, for the most part. One example of such an impl is this pattern, which is used by wasm-bindgen and other crates as well:

trait Trait {}
impl<T> Trait for fn(&T) { }
impl<T> Trait for fn(T) { } // still accepted, but warns

rust-highfive · 2020-05-23T09:53:35Z

r? @varkor

(rust_highfive has picked a reviewer for you, use r? to override)

nikomatsakis · 2020-05-23T09:53:48Z

r? @matthewjasper

nikomatsakis · 2020-05-23T09:54:20Z

@bors try

bors · 2020-05-23T09:54:32Z

⌛ Trying commit 097b7686a20f091e5da71e83a28642237bc6c537 with merge e2aab98dd8975a0990f9fbb79b3ea4b40559a184...

nikomatsakis · 2020-05-23T13:10:28Z

Whoops, I just noticed that I forgot to remove those first 2 commits from the history. I'll leave it as is for now so as not to disturb the try run, but we should clean that up before landing.

Aaron1011 · 2020-05-24T22:02:10Z

@nikomatsakis: What would it mean to accept the impl

trait Trait {}
impl<T> Trait for fn(&T) { }
impl<T> Trait for fn(T) { } // still accepted, but warns

without warnings? Would the impl<T> Trait for fn(&T) { } essentialy be ignored, or would it implicitly 'specialize' impl<T> Trait for fn(T) { } without actually using #![feature(specialization)])?

nikomatsakis · 2020-05-25T15:03:33Z

@Aaron1011

Neither, they would be considered distinct types. In particular, the first type fn(T) cannot ever be equal to the second type for<'a> fn(&'a U) because there is no value of T that can name 'a.

The reason for the warning, however, is that we cannot yet distinguish that type from those where implied bounds lets us figure out that 'a is equal to some other region that T could name (I give some examples in the MCP, I think).

nikomatsakis · 2020-05-25T15:04:03Z

I can't tell if the try build succeeded or failed :) or maybe it's still pending?

Aaron1011 · 2020-05-25T17:19:19Z

Neither, they would be considered distinct types. In particular, the first type fn(T) cannot ever be equal to the second type for<'a> fn(&'a U) because there is no value of T that can name 'a.

I see. Does that mean that it's impossible to write a blanket impl (or collection of blanket impls) that apply to all potential fn(T)s? For example, neither impl<T> Trait for fn(&T) { } or impl<T> Trait for fn(T) { } would apply to fn((&u8, &u8))

nikomatsakis · 2020-05-26T14:16:41Z

@Aaron1011

Does that mean that it's impossible to write a blanket impl (or collection of blanket impls) that apply to all potential fn(T)s?

Yes, that is presently impossible. You might be interested though in this proto-proposal, which addresses some related use cases. (I've been wanting to try and move that forward, I was sort of waiting until we establish the new lang team process, though it's probably not necessary, I'd love to see someone experiment with it...)

Mark-Simulacrum · 2020-05-26T21:56:30Z

@craterbot run mode=check-only start=master#7f940ef5d91b53e889f111f27e00849f2f5ae4a2 end=try#e2aab98dd8975a0990f9fbb79b3ea4b40559a184

craterbot · 2020-05-26T21:56:33Z

👌 Experiment pr-72493 created and queued.
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

bors · 2020-05-28T03:58:53Z

☔ The latest upstream changes (presumably #72494) made this pull request unmergeable. Please resolve the merge conflicts.

craterbot · 2020-05-28T20:33:46Z

🚧 Experiment pr-72493 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

lqf96 · 2020-05-30T19:25:34Z

@Aaron1011 In the long term I think this can be solved by introducing variadic lifetimes. For example, you would write something like impl<'...a, T> Trait for fn(T<'...a>) so that your implementation can apply to any type that takes zero or more lifetime parameters. The '...a lifetime parameter pack would capture all the lifetime parameters and their constraints of the T type.

craterbot · 2020-05-30T23:58:00Z

🎉 Experiment pr-72493 is completed!
📊 1 regressed and 2 fixed (106133 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

matthewjasper · 2020-05-31T00:03:12Z

Regressions/fixes all look spurious.

Motivation: - we want to use leak-check sparingly, first off - these calls were essentially the same as doing the check during subtyping

The bug was revealed by the behavior of the old-lub-glb-hr-noteq1.rs test. The old-lub-glb-hr-noteq2 test shows the current 'order dependent' behavior of coercions around higher-ranked functions, at least when running with `-Zborrowck=mir`. Also, run compare-mode=nll.

nikomatsakis · 2020-06-22T21:00:41Z

@bors r=matthewjasper

bors · 2020-06-22T21:00:42Z

📌 Commit d57689f has been approved by matthewjasper

@ghost

…arth Rollup of 9 pull requests Successful merges: - rust-lang#72271 (Improve compiler error message for wrong generic parameter order) - rust-lang#72493 ( move leak-check to during coherence, candidate eval) - rust-lang#73398 (A way forward for pointer equality in const eval) - rust-lang#73472 (Clean up E0689 explanation) - rust-lang#73496 (Account for multiple impl/dyn Trait in return type when suggesting `'_`) - rust-lang#73515 (Add second message for LiveDrop errors) - rust-lang#73567 (Clarify --extern documentation.) - rust-lang#73572 (Fix typos in doc comments) - rust-lang#73590 (bootstrap: no `config.toml` exists regression) Failed merges: r? @ghost

according to various people on tech-pkg@, there are no problems with the Firefox build Version 1.46.0 (2020-08-27) ========================== Language -------- - [`if`, `match`, and `loop` expressions can now be used in const functions.][72437] - [Additionally you are now also able to coerce and cast to slices (`&[T]`) in const functions.][73862] - [The `#[track_caller]` attribute can now be added to functions to use the function's caller's location information for panic messages.][72445] - [Recursively indexing into tuples no longer needs parentheses.][71322] E.g. `x.0.0` over `(x.0).0`. - [`mem::transmute` can now be used in static and constants.][72920] **Note** You currently can't use `mem::transmute` in constant functions. Compiler -------- - [You can now use the `cdylib` target on Apple iOS and tvOS platforms.][73516] - [Enabled static "Position Independent Executables" by default for `x86_64-unknown-linux-musl`.][70740] Libraries --------- - [`mem::forget` is now a `const fn`.][73887] - [`String` now implements `From<char>`.][73466] - [The `leading_ones`, and `trailing_ones` methods have been stabilised for all integer types.][73032] - [`vec::IntoIter<T>` now implements `AsRef<[T]>`.][72583] - [All non-zero integer types (`NonZeroU8`) now implement `TryFrom` for their zero-able equivalent (e.g. `TryFrom<u8>`).][72717] - [`&[T]` and `&mut [T]` now implement `PartialEq<Vec<T>>`.][71660] - [`(String, u16)` now implements `ToSocketAddrs`.][73007] - [`vec::Drain<'_, T>` now implements `AsRef<[T]>`.][72584] Stabilized APIs --------------- - [`Option::zip`] - [`vec::Drain::as_slice`] Cargo ----- Added a number of new environment variables that are now available when compiling your crate. - [`CARGO_BIN_NAME` and `CARGO_CRATE_NAME`][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate. - [`CARGO_PKG_LICENSE`][cargo/8325] The license from the manifest of the package. - [`CARGO_PKG_LICENSE_FILE`][cargo/8387] The path to the license file. Compatibility Notes ------------------- - [The target configuration option `abi_blacklist` has been renamed to `unsupported_abis`.][74150] The old name will still continue to work. - [Rustc will now warn if you cast a C-like enum that implements `Drop`.][72331] This was previously accepted but will become a hard error in a future release. - [Rustc will fail to compile if you have a struct with `#[repr(i128)]` or `#[repr(u128)]`.][74109] This representation is currently only allowed on `enum`s. - [Tokens passed to `macro_rules!` are now always captured.][73293] This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information. - [The InnoSetup installer for Windows is no longer available.][72569] This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built. - [`{f32, f64}::asinh` now returns the correct values for negative numbers.][72486] - [Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.][72493] - [Rustc now correctly relates the lifetime of an existential associated type.][71896] This fixes some edge cases where `rustc` would erroneously allow you to pass a shorter lifetime than expected. - [Rustc now dynamically links to `libz` (also called `zlib`) on Linux.][74420] The library will need to be installed for `rustc` to work, even though we expect it to be already available on most systems. - [Tests annotated with `#[should_panic]` are broken on ARMv7 while running under QEMU.][74820] - [Pretty printing of some tokens in procedural macros changed.][75453] The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system. [75453]: rust-lang/rust#75453 [74820]: rust-lang/rust#74820 [74420]: rust-lang/rust#74420 [74109]: rust-lang/rust#74109 [74150]: rust-lang/rust#74150 [73862]: rust-lang/rust#73862 [73887]: rust-lang/rust#73887 [73466]: rust-lang/rust#73466 [73516]: rust-lang/rust#73516 [73293]: rust-lang/rust#73293 [73007]: rust-lang/rust#73007 [73032]: rust-lang/rust#73032 [72920]: rust-lang/rust#72920 [72569]: rust-lang/rust#72569 [72583]: rust-lang/rust#72583 [72584]: rust-lang/rust#72584 [72717]: rust-lang/rust#72717 [72437]: rust-lang/rust#72437 [72445]: rust-lang/rust#72445 [72486]: rust-lang/rust#72486 [72493]: rust-lang/rust#72493 [72331]: rust-lang/rust#72331 [71896]: rust-lang/rust#71896 [71660]: rust-lang/rust#71660 [71322]: rust-lang/rust#71322 [70740]: rust-lang/rust#70740 [cargo/8270]: rust-lang/cargo#8270 [cargo/8325]: rust-lang/cargo#8325 [cargo/8387]: rust-lang/cargo#8387 [`Option::zip`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.zip [`vec::Drain::as_slice`]: https://doc.rust-lang.org/stable/std/vec/struct.Drain.html#method.as_slice

Pkgsrc changes: * Portability patches for Illumos have been intregrated upstream, so are no longer needed in pkgsrc. * Adjust one other patch, and update vendor/libc cargo checksum. Upstream changes: Version 1.46.0 (2020-08-27) ========================== Language -------- - [`if`, `match`, and `loop` expressions can now be used in const functions.] [72437] - [Additionally you are now also able to coerce and cast to slices (`&[T]`) in const functions.][73862] - [The `#[track_caller]` attribute can now be added to functions to use the function's caller's location information for panic messages.][72445] - [Recursively indexing into tuples no longer needs parentheses.][71322] E.g. `x.0.0` over `(x.0).0`. - [`mem::transmute` can now be used in static and constants.][72920] **Note** You currently can't use `mem::transmute` in constant functions. Compiler -------- - [You can now use the `cdylib` target on Apple iOS and tvOS platforms.][73516] - [Enabled static "Position Independent Executables" by default for `x86_64-unknown-linux-musl`.][70740] Libraries --------- - [`mem::forget` is now a `const fn`.][73887] - [`String` now implements `From<char>`.][73466] - [The `leading_ones`, and `trailing_ones` methods have been stabilised for all integer types.][73032] - [`vec::IntoIter<T>` now implements `AsRef<[T]>`.][72583] - [All non-zero integer types (`NonZeroU8`) now implement `TryFrom` for their zero-able equivalent (e.g. `TryFrom<u8>`).][72717] - [`&[T]` and `&mut [T]` now implement `PartialEq<Vec<T>>`.][71660] - [`(String, u16)` now implements `ToSocketAddrs`.][73007] - [`vec::Drain<'_, T>` now implements `AsRef<[T]>`.][72584] Stabilized APIs --------------- - [`Option::zip`] - [`vec::Drain::as_slice`] Cargo ----- Added a number of new environment variables that are now available when compiling your crate. - [`CARGO_BIN_NAME` and `CARGO_CRATE_NAME`][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate. - [`CARGO_PKG_LICENSE`][cargo/8325] The license from the manifest of the package. - [`CARGO_PKG_LICENSE_FILE`][cargo/8387] The path to the license file. Compatibility Notes ------------------- - [The target configuration option `abi_blacklist` has been renamed to `unsupported_abis`.][74150] The old name will still continue to work. - [Rustc will now warn if you have a C-like enum that implements `Drop`.][72331] This was previously accepted but will become a hard error in a future release. - [Rustc will fail to compile if you have a struct with `#[repr(i128)]` or `#[repr(u128)]`.][74109] This representation is currently only allowed on `enum`s. - [Tokens passed to `macro_rules!` are now always captured.][73293] This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information. - [The InnoSetup installer for Windows is no longer available.][72569] This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built. - [`{f32, f64}::asinh` now returns the correct values for negative numbers.] [72486] - [Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.][72493] - [Rustc now correctly relates the lifetime of an existential associated type.][71896] This fixes some edge cases where `rustc` would erroneously allow you to pass a shorter lifetime than expected. - [Rustc now dynamically links to `libz` (also called `zlib`) on Linux.][74420] The library will need to be installed for `rustc` to work, even though we expect it to be already available on most systems. - [Tests annotated with `#[should_panic]` are broken on ARMv7 while running under QEMU.][74820] - [Pretty printing of some tokens in procedural macros changed.][75453] The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system. [75453]: rust-lang/rust#75453 [74820]: rust-lang/rust#74820 [74420]: rust-lang/rust#74420 [74109]: rust-lang/rust#74109 [74150]: rust-lang/rust#74150 [73862]: rust-lang/rust#73862 [73887]: rust-lang/rust#73887 [73466]: rust-lang/rust#73466 [73516]: rust-lang/rust#73516 [73293]: rust-lang/rust#73293 [73007]: rust-lang/rust#73007 [73032]: rust-lang/rust#73032 [72920]: rust-lang/rust#72920 [72569]: rust-lang/rust#72569 [72583]: rust-lang/rust#72583 [72584]: rust-lang/rust#72584 [72717]: rust-lang/rust#72717 [72437]: rust-lang/rust#72437 [72445]: rust-lang/rust#72445 [72486]: rust-lang/rust#72486 [72493]: rust-lang/rust#72493 [72331]: rust-lang/rust#72331 [71896]: rust-lang/rust#71896 [71660]: rust-lang/rust#71660 [71322]: rust-lang/rust#71322 [70740]: rust-lang/rust#70740 [cargo/8270]: rust-lang/cargo#8270 [cargo/8325]: rust-lang/cargo#8325 [cargo/8387]: rust-lang/cargo#8387 [`Option::zip`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.zip [`vec::Drain::as_slice`]: https://doc.rust-lang.org/stable/std/vec/struct.Drain.html#method.as_slice

See rust-lang/rust#72493

QuineDot · 2022-05-30T01:32:00Z

The lint should be updated to reflect the current direction of the language. Namely, this:

trait Trait {}
impl<T> Trait for fn(&T) { }
impl<T> Trait for fn(T) { }

Says

  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!

But as I understand it, the goal is to support that indefinitely.

rust-highfive assigned varkor May 23, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 23, 2020

rust-highfive assigned matthewjasper and unassigned varkor May 23, 2020

nikomatsakis force-pushed the move-leak-check branch from 097b768 to 912428a Compare May 23, 2020 12:02

nikomatsakis mentioned this pull request May 23, 2020

tracking issue for "universe transition" #56105

Open

nikomatsakis added the relnotes Marks issues that should be documented in the release notes of the next release. label May 23, 2020

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 26, 2020

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels May 30, 2020

nikomatsakis force-pushed the move-leak-check branch from 912428a to 88fa452 Compare June 2, 2020 13:11

nikomatsakis added 8 commits June 22, 2020 18:51

remove snapshot calls from "match" operations during select

70cf33f

Motivation: - we want to use leak-check sparingly, first off - these calls were essentially the same as doing the check during subtyping

remove leak-check from project

6873a76

remove leak_check from the outlives predicate evaluations

3a68d56

add new tests from MCP and the tracking issue

be0d10f

add new coherence tests and update the documentation

93e2982

WIP bless test and compare-mode=nll

c88a76e

cite issue 73154

d57689f

nikomatsakis force-pushed the move-leak-check branch from 6075cde to d57689f Compare June 22, 2020 18:51

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 Jun 22, 2020

Manishearth mentioned this pull request Jun 23, 2020

Rollup of 9 pull requests #73643

Merged

bors merged commit 903823c into rust-lang:master Jun 23, 2020

alecmocatta mentioned this pull request Jun 25, 2020

Fix on latest nightly alecmocatta/serde_traitobject#28

Merged

JohnTitor mentioned this pull request Jul 20, 2020

Type mismatch in function arguments E0631, E0271 are falsely recognized as E0308 mismatched types #74400

Closed

nikomatsakis mentioned this pull request Aug 27, 2020

diagnostics: "one type is more general" for two identical types? #75791

Closed

nikomatsakis mentioned this pull request Nov 5, 2020

revert #75443, update mir validator #78410

Merged

Xanewok added a commit to Xanewok/rust-semverver that referenced this pull request Nov 18, 2020

Fix test failure due to rust-lang/rust#72493

10813ea

See rust-lang/rust#72493

Xanewok added a commit to Xanewok/rust-semverver that referenced this pull request Nov 19, 2020

Fix test failure due to rust-lang/rust#72493

735056e

See rust-lang/rust#72493

Xanewok added a commit to Xanewok/rust-semverver that referenced this pull request Nov 19, 2020

Fix test failure due to rust-lang/rust#72493

0d52c24

See rust-lang/rust#72493

spastorino mentioned this pull request Aug 6, 2021

Consolidate HKTBs, leak-check and universes information around with what we have in the guide rust-lang/rustc-dev-guide#1184

Open

QuineDot mentioned this pull request Aug 11, 2021

iter::Fuse is unsound with how specialization currently behaves around HRTB fn pointers #85863

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QuineDot mentioned this pull request May 30, 2022

anonymous constants are overly restrictive wrt variance #90629

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QuineDot mentioned this pull request Apr 19, 2023

broken MIR in DefId(...) (NoSolution) #110534

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move leak-check to during coherence, candidate eval #72493

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move leak-check to during coherence, candidate eval #72493

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