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2022-07-19Rollup merge of #99401 - TaKO8Ki:avoid-symbol-to-&str-conversions, r=nnethercoteMatthias Krüger-1/+1
Avoid `Symbol` to `&str` conversions `Symbol::as_str` is a slowish operation, so this patch removes some usages of it.
2022-07-18Rollup merge of #98998 - ↵Dylan DPC-0/+7
workingjubilee:naked-means-no-clothes-enforcement-technology, r=Amanieu Remove branch target prologues from `#[naked] fn` This patch hacks around rust-lang/rust#98768 for now via injecting appropriate attributes into the LLVMIR we emit for naked functions. I intend to pursue this upstream so that these attributes can be removed in general, but it's slow going wading through C++ for me.
2022-07-18avoid `Symbol` to `&str` conversionsTakayuki Maeda-1/+1
2022-07-16Stabilize `let_chains`Caio-1/+1
2022-07-16Auto merge of #95685 - oxidecomputer:restore-static-dwarf, r=pnkfelixbors-18/+8
Revert "Work around invalid DWARF bugs for fat LTO" Since September, the toolchain has not been generating reliable DWARF information for static variables when LTO is on. This has affected projects in the embedded space where the use of LTO is typical. In our case, it has kept us from bumping past the 2021-09-22 nightly toolchain lest our debugger break. This has been a pretty dramatic regression for people using debuggers and static variables. See #90357 for more info and a repro case. This commit is a mechanical revert of d5de680e20def848751cb3c11e1182408112b1d3 from PR #89041, which caused the issue. (Note on that PR that the commit's author has requested it be reverted.) I have locally verified that this fixes #90357 by restoring the functionality of both the repro case I posted on that bug, and debugger behavior on real programs. There do not appear to be test cases for this in the toolchain; if I've missed them, point me at 'em and I'll update them.
2022-07-14fix dwarf debuginfo being used in addition to CodeView on windowsRémy Rakic-17/+20
Fixes the debuginfo size increase regression introduced by the DWARF5 support.
2022-07-13Rename `debugging_opts` to `unstable_opts`Joshua Nelson-32/+32
This is no longer used only for debugging options (e.g. `-Zoutput-width`, `-Zallow-features`). Rename it to be more clear.
2022-07-13Rollup merge of #99155 - Amanieu:unstable-target-features, r=davidtwcoDylan DPC-20/+23
Keep unstable target features for asm feature checking Inline assembly uses the target features to determine which registers are available on the current target. However it needs to be able to access unstable target features for this. Fixes #99071
2022-07-11Keep unstable target features for asm feature checkingAmanieu d'Antras-20/+23
Inline assembly uses the target features to determine which registers are available on the current target. However it needs to be able to access unstable target features for this. Fixes #99071
2022-07-09don't allow ZST in ScalarIntRalf Jung-5/+4
There are several indications that we should not ZST as a ScalarInt: - We had two ways to have ZST valtrees, either an empty `Branch` or a `Leaf` with a ZST in it. `ValTree::zst()` used the former, but the latter could possibly arise as well. - Likewise, the interpreter had `Immediate::Uninit` and `Immediate::Scalar(Scalar::ZST)`. - LLVM codegen already had to special-case ZST ScalarInt. So instead add new ZST variants to those types that did not have other variants which could be used for this purpose.
2022-07-08Implement support for DWARF version 5.Patrick Walton-8/+8
DWARF version 5 brings a number of improvements over version 4. Quoting from the announcement [1]: > Version 5 incorporates improvements in many areas: better data compression, > separation of debugging data from executable files, improved description of > macros and source files, faster searching for symbols, improved debugging > optimized code, as well as numerous improvements in functionality and > performance. On platforms where DWARF version 5 is supported (Linux, primarily), this commit adds support for it behind a new `-Z dwarf-version=5` flag. [1]: https://dwarfstd.org/Public_Review.php
2022-07-08Auto merge of #98638 - bjorn3:less_string_interning, r=tmiaskobors-19/+23
Use less string interning This removes string interning in a couple of places where doing so won't result in perf improvements. I also switched one place to use pre-interned symbols.
2022-07-06Also stop emitting BTI prologues for naked functionsJubilee Young-0/+2
Same idea but for AArch64.
2022-07-06Stop emitting CET prologues for naked functionsJubilee Young-0/+5
We can apply nocf_check as a hack for now.
2022-07-06Allow to create definitions inside the query system.Camille GILLOT-2/+3
2022-07-06Update TypeVisitor pathsAlan Egerton-4/+4
2022-07-05Auto merge of #96862 - oli-obk:enum_cast_mir, r=RalfJungbors-4/+4
Change enum->int casts to not go through MIR casts. follow-up to https://github.com/rust-lang/rust/pull/96814 this simplifies all backends and even gives LLVM more information about the return value of `Rvalue::Discriminant`, enabling optimizations in more cases.
2022-07-05Prefer trace level instrumentation for the new noisy instrument attributesOli Scherer-1/+1
2022-06-30llvm-wrapper: adapt for LLVMConstExtractValue removalKrasimir Georgiev-7/+2
2022-06-29Some tracing cleanupsOli Scherer-4/+4
2022-06-28Avoid unnecessary string interning for const_strbjorn3-19/+23
2022-06-27Update `smallvec` to 1.8.1.Nicholas Nethercote-1/+1
This pulls in https://github.com/servo/rust-smallvec/pull/282, which gives some small wins for rustc.
2022-06-26Rollup merge of #98385 - m-ou-se:llvm-12-memory-order, r=petrochenkovYuki Okushi-1/+15
Work around llvm 12's memory ordering restrictions. Older llvm has the pre-C++17 restriction on success and failure memory ordering, requiring the former to be at least as strong as the latter. So, for llvm 12, this upgrades the success ordering to a stronger one if necessary. See https://github.com/rust-lang/rust/issues/68464
2022-06-24Rollup merge of #98214 - petrochenkov:islike, r=compiler-errorsYuki Okushi-2/+2
rustc_target: Remove some redundant target properties `is_like_emscripten` is equivalent to `os == "emscripten"`, so it's removed. `is_like_fuchsia` is equivalent to `os == "fuchsia"`, so it's removed. `is_like_osx` also falls into the same category and is equivalent to `vendor == "apple"`, but it's commonly used so I kept it as is for now. `is_like_(solaris,windows,wasm)` are combinations of different operating systems or architectures (see compiler/rustc_target/src/spec/tests/tests_impl.rs) so they are also kept as is. I think `is_like_wasm` (and maybe `is_like_osx`) are sufficiently closed sets, so we can remove these fields as well and replace them with methods like `fn is_like_wasm() { arch == "wasm32" || arch == "wasm64" }`. On other hand, `is_like_solaris` and `is_like_windows` are sufficiently open and I can imagine custom targets introducing other values for `os`. This is kind of a gray area.
2022-06-22Work around llvm 12's memory ordering restrictions.Mara Bos-1/+15
Older llvm has the pre-C++17 restriction on success and failure memory ordering, requiring the former to be at least as strong as the latter. So, for llvm 12, this upgrades the success ordering to a stronger one if necessary.
2022-06-21Auto merge of #98098 - bjorn3:archive_refactor, r=michaelwoeristerbors-95/+25
Remove the source archive functionality of ArchiveWriter We now build archives through strictly additive means rather than taking an existing archive and potentially substracting parts. This is simpler and makes it easier to swap out the archive writer in https://github.com/rust-lang/rust/pull/97485.
2022-06-19Small refactoringbjorn3-9/+5
2022-06-19Remove the source archive functionality of ArchiveWriterbjorn3-33/+2
We now build archives through strictly additive means rather than taking an existing archive and potentially substracting parts.
2022-06-19Fix "Remove src_files and remove_file"bjorn3-5/+6
2022-06-19Rollup merge of #98165 - WaffleLapkin:once_things_renamings, r=m-ou-seMatthias Krüger-1/+1
once cell renamings This PR does the renamings proposed in https://github.com/rust-lang/rust/issues/74465#issuecomment-1153703128 - Move/rename `lazy::{OnceCell, Lazy}` to `cell::{OnceCell, LazyCell}` - Move/rename `lazy::{SyncOnceCell, SyncLazy}` to `sync::{OnceLock, LazyLock}` (I used `Lazy...` instead of `...Lazy` as it seems to be more consistent, easier to pronounce, etc) ```@rustbot``` label +T-libs-api -T-libs
2022-06-18rustc_target: Remove some redundant target propertiesVadim Petrochenkov-2/+2
2022-06-16Move/rename `lazy::{OnceCell, Lazy}` to `cell::{OnceCell, LazyCell}`Maybe Waffle-1/+1
2022-06-16Rollup merge of #97757 - xFrednet:rfc-2383-expect-with-force-warn, ↵Matthias Krüger-1/+1
r=wesleywiser,flip1995 Support lint expectations for `--force-warn` lints (RFC 2383) Rustc has a `--force-warn` flag, which overrides lint level attributes and forces the diagnostics to always be warn. This means, that for lint expectations, the diagnostic can't be suppressed as usual. This also means that the expectation would not be fulfilled, even if a lint had been triggered in the expected scope. This PR now also tracks the expectation ID in the `ForceWarn` level. I've also made some minor adjustments, to possibly catch more bugs and make the whole implementation more robust. This will probably conflict with https://github.com/rust-lang/rust/pull/97718. That PR should ideally be reviewed and merged first. The conflict itself will be trivial to fix. --- r? `@wesleywiser` cc: `@flip1995` since you've helped with the initial review and also discussed this topic with me. :upside_down_face: Follow-up of: https://github.com/rust-lang/rust/pull/87835 Issue: https://github.com/rust-lang/rust/issues/85549 Yeah, and that's it.
2022-06-16Support lint expectations for `--force-warn` lints (RFC 2383)xFrednet-1/+1
2022-06-15Rollup merge of #98067 - klensy:compiler-deps2, r=Dylan-DPCYuki Okushi-1/+0
compiler: remove unused deps Removed unused dependencies in compiler crates and moves few `libc` under `target.cfg(unix)` .
2022-06-14Remove src_files and remove_filebjorn3-29/+0
They only apply to the main source archive and their role can be fulfilled through the skip argument of add_archive too.
2022-06-14Inline ArchiveConfig struct into LlvmArchiveBuilderbjorn3-28/+21
2022-06-14Add metadata generation for vtables when using VFEflip1995-7/+100
This adds the typeid and `vcall_visibility` metadata to vtables when the -Cvirtual-function-elimination flag is set. The typeid is generated in the same way as for the `llvm.type.checked.load` intrinsic from the trait_ref. The offset that is added to the typeid is always 0. This is because LLVM assumes that vtables are constructed according to the definition in the Itanium ABI. This includes an "address point" of the vtable. In C++ this is the offset in the vtable where information for RTTI is placed. Since there is no RTTI information in Rust's vtables, this "address point" is always 0. This "address point" in combination with the offset passed to the `llvm.type.checked.load` intrinsic determines the final function that should be loaded from the vtable in the `WholeProgramDevirtualization` pass in LLVM. That's why the `llvm.type.checked.load` intrinsics are generated with the typeid of the trait, rather than with that of the function that is called. This matches what `clang` does for C++. The vcall_visibility metadata depends on three factors: 1. LTO level: Currently this is always fat LTO, because LLVM only supports this optimization with fat LTO. 2. Visibility of the trait: If the trait is publicly visible, VFE can only act on its vtables after linking. 3. Number of CGUs: if there is more than one CGU, also vtables with restricted visibility could be seen outside of the CGU, so VFE can only act on them after linking. To reflect this, there are three visibility levels: Public, LinkageUnit, and TranslationUnit.
2022-06-14Add llvm.type.checked.load intrinsicflip1995-3/+15
Add the intrinsic declare {i8*, i1} @llvm.type.checked.load(i8* %ptr, i32 %offset, metadata %type) This is used in the VFE optimization when lowering loading functions from vtables to LLVM IR. The `metadata` is used to map the function to all vtables this function could belong to. This ensures that functions from vtables that might be used somewhere won't get removed.
2022-06-14Add LLVM module flags required for the VFE optflip1995-1/+23
To apply the optimization the `Virtual Function Elim` module flag has to be set. To apply this optimization post-link the `LTOPostLink` module flag has to be set.
2022-06-14Rollup merge of #95243 - vladimir-ea:compiler_watch_os, r=nagisaYuki Okushi-1/+2
Add Apple WatchOS compile targets Hello, I would like to add the following target triples for Apple WatchOS as Tier 3 platforms: armv7k-apple-watchos arm64_32-apple-watchos x86_64-apple-watchos-sim There are some pre-requisites Pull Requests: https://github.com/rust-lang/compiler-builtins/pull/456 (merged) https://github.com/alexcrichton/cc-rs/pull/662 (pending) https://github.com/rust-lang/libc/pull/2717 (merged) There will be a subsequent PR with standard library changes for WatchOS. Previous compiler and library changes were in a single PR (https://github.com/rust-lang/rust/pull/94736) which is now closed in favour of separate PRs. Many thanks! Vlad. ### Tier 3 Target Requirements Adds support for Apple WatchOS compile targets. Below are details on how this target meets the requirements for tier 3: > tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.) `@deg4uss3r` has volunteered to be the target maintainer. I am also happy to help if a second maintainer is required. > Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target. Uses the same naming as the LLVM target, and the same convention as other Apple targets. > Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it. I don't believe there is any ambiguity here. > Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users. I don't see any legal issues here. > The target must not introduce license incompatibilities. > Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0). > The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements. > If the target supports building host tools (such as rustc or cargo), those host tools must not depend on proprietary (non-FOSS) libraries, other than ordinary runtime libraries supplied by the platform and commonly used by other binaries built for the target. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3. > Targets should not require proprietary (non-FOSS) components to link a functional binary or library. > "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users. I see no issues with any of the above. > Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions. > This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements. Only relevant to those making approval decisions. > Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions. core and alloc can be used. std support will be added in a subsequent PR. > The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running tests (even if they do not pass), the documentation must explain how to run tests for the target, using emulation if possible or dedicated hardware if necessary. Use --target=<target> option to cross compile, just like any target. Tests can be run using the WatchOS simulator (see https://developer.apple.com/documentation/xcode/running-your-app-in-the-simulator-or-on-a-device). > Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via `@)` to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages. > Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications. I don't foresee this being a problem. > Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target. > In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target. No other targets should be affected by the pull request.
2022-06-13remove currently unused depsklensy-1/+0
2022-06-13Add Apple WatchOS compile targetsVladimir Michael Eatwell-1/+2
2022-06-11Rollup merge of #97969 - inglorion:prelinkpasses, r=nikicMatthias Krüger-1/+1
Make -Cpasses= only apply to pre-link optimization This change causes passes specified in -Cpasses= to be applied only during pre-link optimization, not during LTO. This avoids such passes running multiple times, which they may not be designed for. Fixes https://github.com/rust-lang/rust/issues/97713
2022-06-10Make -Cpasses= only apply to pre-link optimizationBob Haarman-1/+1
This change causes passes specified in -Cpasses= to be applied only during pre-link optimization, not during LTO. This avoids such passes running multiple times, which they may not be designed for. Fixes https://github.com/rust-lang/rust/issues/97713
2022-06-09refactor write_output_file to merge two invocation paths into one.Felix S. Klock II-18/+14
2022-06-08Rollup merge of #97846 - pcwalton:align-bits, r=michaelwoeristerDylan DPC-1/+1
Specify DWARF alignment in bits, not bytes. In DWARF, alignment of types is specified in bits, as is made clear by the parameter name `AlignInBits`. However, `rustc` was incorrectly passing a byte alignment. This commit fixes that. This was noticed in upstream LLVM when I tried to check in a test consisting of LLVM IR generated from `rustc` and it triggered assertions [1]. [1]: https://reviews.llvm.org/D126835
2022-06-07Specify DWARF alignment in bits, not bytes.Patrick Walton-1/+1
In DWARF, alignment of types is specified in bits, as is made clear by the parameter name `AlignInBits`. However, `rustc` was incorrectly passing a byte alignment. This commit fixes that. This was noticed in upstream LLVM when I tried to check in a test consisting of LLVM IR generated from `rustc` and it triggered assertions [1]. [1]: https://reviews.llvm.org/D126835
2022-06-07Auto merge of #97512 - scottmcm:add-coldcc, r=nagisa,lcnrbors-0/+1
Add support for emitting functions with `coldcc` to LLVM The eventual goal is to try using this for things like the internal panicking stuff, to see whether it helps.
2022-06-07Auto merge of #95565 - jackh726:remove-borrowck-mode, r=nikomatsakisbors-1/+0
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](https://github.com/rust-lang/rust/issues/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](https://github.com/rust-lang/rust/issues/43234) * On 2017-07-20, [initial empty MIR pass added](https://github.com/rust-lang/rust/pull/43271) * On 2017-08-29, [RFC opened](https://github.com/rust-lang/rfcs/pull/2094) * On 2017-11-16, [Integrate MIR type-checker with NLL](https://github.com/rust-lang/rust/pull/45825) * On 2017-12-20, [NLL feature complete](https://github.com/rust-lang/rust/pull/46862) * On 2018-07-07, [Don't run AST borrowck on mir mode](https://github.com/rust-lang/rust/pull/52083) * On 2018-07-27, [Add migrate mode](https://github.com/rust-lang/rust/pull/52681) * On 2019-04-22, [Enable migrate mode on 2015 edition](https://github.com/rust-lang/rust/pull/59114) * On 2019-08-26, [Don't downgrade errors on 2015 edition](https://github.com/rust-lang/rust/pull/64221) * On 2019-08-27, [Remove AST borrowck](https://github.com/rust-lang/rust/pull/64790)