Add -Z borrowck=migrate
#52681
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Add -Z borrowck=migrate
#52681
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r? @eddyb (rust_highfive has picked a reviewer for you, use r? to override) |
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r=me -- but @pnkfelix and I discussed on Zulip the idea of adding some tests to test the interaction of |
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Or we might do the |
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@bors r=nikomatsakis |
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📌 Commit 189b92d93d5ebdf64aec197cddc33dcc1541e75a has been approved by |
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🌲 The tree is currently closed for pull requests below priority 99, this pull request will be tested once the tree is reopened |
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Also convert an ICE that became reachable code under borrowck=migrate into a normally reported error (which is then downgraded to a warning). This actually has a nice side benefit of providing a somewhat more useful error message, at least in the particular case of the example from issue rust-lang#27282.
Note that this test is carefully crafted to *try* to not segfault during its run. Howver, it really is representing unsound code that should be rejected after we manage to remove the AST-borrowck entirely from the compiler.
(Includes test illustrating desired behavior; compare its diagnostic output to that of the file `borrowck-migreate-to-nll.rs`.)
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@bors r- Since the tree is closed anyway, I'll hold off on landing this until after I have the edition linkage ready to go. |
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As a driveby change, I made `#![feature(nll)]` *always* take precedence over `-Z borrowck`. The main effect this had is that it means tests with `#![feature(nll)]` will ignore uses of `-Z borrowck=compare`. This affected only one test as far as I can tell, and I think that test used `-Z borrowck=compare` only as a historical accident.
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r? @nikomatsakis to just double-check the commits I've added on, starting from "Bug fix: |
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⌛ Testing commit 9f05f29 with merge dfae368436e951c8583447ee673b3a912153fd6f... |
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💔 Test failed - status-travis |
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
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Add `-Z borrowck=migrate` This adds `-Z borrowck=migrate`, which represents the way we want to migrate to NLL under Rust versions to come. It also hooks this new mode into `--edition 2018`, which means we're officially turning NLL on in the 2018 edition. The basic idea of `-Z borrowck=migrate` that there are cases where NLL is fixing old soundness bugs in the borrow-checker, but in order to avoid just breaking code by immediately rejecting the programs that hit those soundness bugs, we instead use the following strategy: If your code is accepted by NLL, then we accept it. If your code is rejected by both NLL and the old AST-borrowck, then we reject it. If your code is rejected by NLL but accepted by the old AST-borrowck, then we emit the new NLL errors as **warnings**. These warnings will be turned into hard errors in the future, and they say so in these diagnostics. Fix #46908
Does that mean AST borrowck will not even run unless NLL borrowck fails? |
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☀️ Test successful - status-appveyor, status-travis |
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@RalfJung asked:
That's right. Or at least, that's the intent. |
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Jun 7, 2022
…matsakis Remove migrate borrowck mode Closes rust-lang#58781 Closes rust-lang#43234 # Stabilization proposal This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile. Tracking issue: rust-lang#43234 RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable). ## Motivation Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors. The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition. In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker. In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver. While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff. ## What is stabilized As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise. There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](rust-lang#95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl. As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions. ## What isn't stabilized This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck. ## Tests Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll` ## History * On 2017-07-14, [tracking issue opened](rust-lang#43234) * On 2017-07-20, [initial empty MIR pass added](rust-lang#43271) * On 2017-08-29, [RFC opened](rust-lang/rfcs#2094) * On 2017-11-16, [Integrate MIR type-checker with NLL](rust-lang#45825) * On 2017-12-20, [NLL feature complete](rust-lang#46862) * On 2018-07-07, [Don't run AST borrowck on mir mode](rust-lang#52083) * On 2018-07-27, [Add migrate mode](rust-lang#52681) * On 2019-04-22, [Enable migrate mode on 2015 edition](rust-lang#59114) * On 2019-08-26, [Don't downgrade errors on 2015 edition](rust-lang#64221) * On 2019-08-27, [Remove AST borrowck](rust-lang#64790)
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Jun 16, 2022
Remove migrate borrowck mode Closes #58781 Closes #43234 # Stabilization proposal This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile. Tracking issue: #43234 RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable). ## Motivation Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors. The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition. In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker. In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver. While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff. ## What is stabilized As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise. There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](rust-lang/rust#95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl. As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions. ## What isn't stabilized This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck. ## Tests Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll` ## History * On 2017-07-14, [tracking issue opened](rust-lang/rust#43234) * On 2017-07-20, [initial empty MIR pass added](rust-lang/rust#43271) * On 2017-08-29, [RFC opened](rust-lang/rfcs#2094) * On 2017-11-16, [Integrate MIR type-checker with NLL](rust-lang/rust#45825) * On 2017-12-20, [NLL feature complete](rust-lang/rust#46862) * On 2018-07-07, [Don't run AST borrowck on mir mode](rust-lang/rust#52083) * On 2018-07-27, [Add migrate mode](rust-lang/rust#52681) * On 2019-04-22, [Enable migrate mode on 2015 edition](rust-lang/rust#59114) * On 2019-08-26, [Don't downgrade errors on 2015 edition](rust-lang/rust#64221) * On 2019-08-27, [Remove AST borrowck](rust-lang/rust#64790)
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Sep 15, 2022
Remove migrate borrowck mode Closes #58781 Closes #43234 # Stabilization proposal This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile. Tracking issue: #43234 RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable). ## Motivation Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors. The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition. In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker. In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver. While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff. ## What is stabilized As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise. There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](rust-lang/rust#95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl. As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions. ## What isn't stabilized This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck. ## Tests Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll` ## History * On 2017-07-14, [tracking issue opened](rust-lang/rust#43234) * On 2017-07-20, [initial empty MIR pass added](rust-lang/rust#43271) * On 2017-08-29, [RFC opened](rust-lang/rfcs#2094) * On 2017-11-16, [Integrate MIR type-checker with NLL](rust-lang/rust#45825) * On 2017-12-20, [NLL feature complete](rust-lang/rust#46862) * On 2018-07-07, [Don't run AST borrowck on mir mode](rust-lang/rust#52083) * On 2018-07-27, [Add migrate mode](rust-lang/rust#52681) * On 2019-04-22, [Enable migrate mode on 2015 edition](rust-lang/rust#59114) * On 2019-08-26, [Don't downgrade errors on 2015 edition](rust-lang/rust#64221) * On 2019-08-27, [Remove AST borrowck](rust-lang/rust#64790)
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This adds
-Z borrowck=migrate, which represents the way we want to migrate to NLL under Rust versions to come. It also hooks this new mode into--edition 2018, which means we're officially turning NLL on in the 2018 edition.The basic idea of
-Z borrowck=migratethat there are cases where NLL is fixing old soundness bugs in the borrow-checker, but in order to avoid just breaking code by immediately rejecting the programs that hit those soundness bugs, we instead use the following strategy:If your code is accepted by NLL, then we accept it.
If your code is rejected by both NLL and the old AST-borrowck, then we reject it.
If your code is rejected by NLL but accepted by the old AST-borrowck, then we emit the new NLL errors as warnings.
These warnings will be turned into hard errors in the future, and they say so in these diagnostics.
Fix #46908