Add `-Z borrowck=migrate` #52681

pnkfelix · 2018-07-24T23:47:24Z

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

rust-highfive · 2018-07-24T23:47:27Z

r? @eddyb

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pnkfelix · 2018-07-24T23:47:38Z

r? @nikomatsakis

nikomatsakis · 2018-07-25T14:39:36Z

r=me -- but @pnkfelix and I discussed on Zulip the idea of adding some tests to test the interaction of #![feature(nll)] and -Zborrowck=migrate. The expectation is roughly that #![feature(nll)] will give hard errors -- and also that --edition 2018 will switch to migrate mode.

nikomatsakis · 2018-07-25T14:39:58Z

Or we might do the --edition thing later

pnkfelix · 2018-07-25T23:13:31Z

@bors r=nikomatsakis

bors · 2018-07-25T23:13:32Z

📌 Commit 189b92d93d5ebdf64aec197cddc33dcc1541e75a has been approved by nikomatsakis

bors · 2018-07-25T23:13:33Z

🌲 The tree is currently closed for pull requests below priority 99, this pull request will be tested once the tree is reopened

…rrowck=migrate.

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`.)

pnkfelix · 2018-07-26T11:53:57Z

@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.

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.

…mode=...`

pnkfelix · 2018-07-26T13:01:12Z

r? @nikomatsakis to just double-check the commits I've added on, starting from "Bug fix: #![feature(nll)] takes precedence over -Z borrowck=migrate.

bors · 2018-07-27T06:08:23Z

⌛ Testing commit 9f05f29 with merge dfae368436e951c8583447ee673b3a912153fd6f...

bors · 2018-07-27T07:16:09Z

💔 Test failed - status-travis

rust-highfive · 2018-07-27T07:16:11Z

The job dist-i686-freebsd of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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travis_time:end:07812816:start=1532675755719172506,finish=1532675755726090284,duration=6917778
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:3986acd7
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:10bc68bf
travis_time:start:10bc68bf
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:087ed1e5
$ dmesg | grep -i kill

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 @TimNN. (Feature Requests)

kennytm · 2018-07-27T07:21:07Z

@bors retry travis-ci/travis-ci#9696

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

bors · 2018-07-27T09:10:14Z

⌛ Testing commit 9f05f29 with merge b18b9ed...

RalfJung · 2018-07-27T10:48:59Z

If your code is accepted by NLL, then we accept it.

Does that mean AST borrowck will not even run unless NLL borrowck fails?

bors · 2018-07-27T11:02:16Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing b18b9ed to master...

pnkfelix · 2018-07-27T11:21:03Z

@RalfJung asked:

Does that mean AST borrowck will not even run unless NLL borrowck fails?

That's right. Or at least, that's the intent.

…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)

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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pnkfelix added 7 commits July 26, 2018 13:17

Add flag indicating whether AST borrowck query signalled any error.

655894b

Add -Z borrowck=migrate flag, use it to link NLL up to AST-borrowck.

a23e8a7

Add migrate to list of values for -Z borrowck=...

ff2f9e0

Allow elaborate_drops to progress under errors that come up during bo…

3460115

…rrowck=migrate.

Test for -Z borrowck=migrate.

f808405

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.

Bug fix: #![feature(nll)] takes precedence over -Z borrowck=migrate.

1a59daf

(Includes test illustrating desired behavior; compare its diagnostic output to that of the file `borrowck-migreate-to-nll.rs`.)

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jul 26, 2018

pnkfelix added 2 commits July 26, 2018 14:51

compiletest: Add support for ignoring certain tests under `--compare-…

94a2972

…mode=...`

pnkfelix force-pushed the z-borrowck-migrate branch from 189b92d to 1c18be2 Compare July 26, 2018 12:51

Incorporate edition flag testing into tests of -Z borrowck=migrate.

9f05f29

pnkfelix force-pushed the z-borrowck-migrate branch from 1c18be2 to 9f05f29 Compare July 26, 2018 12:59

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bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jul 27, 2018

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bors merged commit 9f05f29 into rust-lang:master Jul 27, 2018

cramertj mentioned this pull request Jul 31, 2018

MIR generator compiler panic #52792

Closed

flip1995 mentioned this pull request Jul 31, 2018

Compiler Warnings 2018-07-30 rust-lang/rust-clippy#2982

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nikomatsakis mentioned this pull request Aug 3, 2018

non-lexical lifetimes (NLL) tracking issue #43234

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pnkfelix mentioned this pull request Oct 9, 2018

error: internal compiler error: Accessing (*_310) with the kind Write(Move) shouldn't be possible #54597

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pnkfelix mentioned this pull request May 13, 2019

NLL: turn off migration mode #58781

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jackh726 mentioned this pull request Jun 3, 2022

Remove migrate borrowck mode #95565

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Add `-Z borrowck=migrate` #52681

Add `-Z borrowck=migrate` #52681

pnkfelix commented Jul 24, 2018 •

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Add -Z borrowck=migrate #52681

Add -Z borrowck=migrate #52681

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Add `-Z borrowck=migrate` #52681

Add `-Z borrowck=migrate` #52681

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