T-compiler Meeting Agenda 2023-10-26

Announcements

• Compiler Team Steering Meeting - P-high review at time:2023-10-27T10:00:00-04:00
• Types team meeting: roadmap draft review [jackh726] at time:2023-10-30T10:00:00-04:00
• Reminder: if you see a PR/issue that seems like there might be legal implications due to copyright/IP/etc, please let us know (or at least message @davidtwco or @Wesley Wiser so we can pass it along).

Other WG meetings (calendar link)

• AFIT/RPITIT Impl Triage at time:2023-10-26T16:00:00-04:00
• [Types] Rotating new solver / formality / polonius deep dive at time:2023-10-30T11:00:00-04:00

MCPs/FCPs

• New MCPs (take a look, see if you like them!)
  • None at this time
• Pending FCP requests (check your boxes!)
  • “Add $message_type field to distinguish json diagnostic outputs” compiler-team#673
  • “Add a new --build-id flag to rustc” compiler-team#635 (Zulip)
  • “Retire the mailing list and make all decisions on zulip” compiler-team#649 (Zulip)
  • “Stabilize --json=unused-externs(-silent)” compiler-team#674 (Zulip)
  • “Tracking issue for dyn upcasting coercion” rust#65991
  • “Support overriding warnings level for a specific lint via command line” rust#113307
  • “Update Windows platform support” rust#115141
  • “make soft_unstable show up in future breakage reports” rust#116274
• Things in FCP (make sure you’re good with it)
  • “Add a stable flag to enable/disable codegen UB checks” compiler-team#625 (Zulip)
  • “Report all lints, even if other errors already occurred.” compiler-team#633 (Zulip)
  • “Match the behavior of strip and split-debuginfo across platforms” compiler-team#669 (Zulip)
  • “Add infrastructure to “compute the ABI of a Rust type, described as a C type”” compiler-team#672 (Zulip)
  • “Stabilize --json=unused-externs(-silent)” compiler-team#674 (Zulip)
  • “Have rustc produce a local log of execution metrics” compiler-team#679 (Zulip)
  • “Remove support for compiler plugins.” rust#116412
• Accepted MCPs
  • “Enable Parallel Rustc Front End In Nightly Builds” compiler-team#681 (Zulip)
  • “Rename generator to coroutine” compiler-team#682 (Zulip)
• Finalized FCPs (disposition merge)
  • “rustdoc: align stability badge to baseline instead of bottom” rust#105666
  • “document ABI compatibility” rust#115476

WG checkins

• @_WG-diagnostics by @Esteban Küber and @oli (previous checkin):

  Checkin text

• @_WG-rustc-dev-guide by @Santiago Pastorino and @Yuki Okushi|217081 (previous checkin):

  Most notable changes

  • Start a chapter about the evolving const effect system #1808
  • Document subtle implied bounds issue in RPITIT inference #1807
  • update new trait solver docs #1802
  • Clarify all the {AP,RP}IT{,IT} impl trait types #1798
  • Add deep dive document about early/late bound parameters interacting with turbofish #1794
  • explain the MIR const vs TY const situation #1793
  • Document the coverage-map and run-coverage test suites #1790
  • Add section about building an optimized version of rustc #1787
  • Add dropck documentation #1767
  • Add RPITIT documentation #1764
  • Explain more in depth what early and late bound generic parameters are #1732
  • add section for normalization with the new solver #1731
  • various fixes/improvements to Contributing chapter #1723
  • document ./x test --rustc-args option #1719

  Most notable WIPs

  • Update some outdated descriptions of coverage instrumentation #1809
  • update some of the diagnostic translations info #1711
  • rewrite bootstrapping stages #1650
  • new chapter with examples of diagnostic translation PRs #1621
  • Add back the canonicalization chapter. #1532
  • Improve documentation of MIR queries & passes #1434
  • Document inert vs active attributes #1110

Backport nominations

T-compiler stable / T-compiler beta

• :beta: “dropck_outlives check whether generator witness needs_drop” rust#117134
  • Currently waiting on perf. results and RFC voting
  • T-compiler label was removed so is it fair to assume it’s now fully in T-types hands?

• :beta: “Avoid unbounded O(n^2) when parsing nested type args” rust#117143
  • “When encountering code like f::<f::<f::<f::<f::<f::<f::<f::<… with unmatched closing angle brackets, add a linear check that avoids the exponential behavior of the parse recovery mechanism.”
  • Fixes #117080 and #115414 (compiler OOMs)

• No stable nominations for T-compiler this time.

PRs S-waiting-on-team

T-compiler

• Other issues in progress or waiting on other teams

Issues of Note

Short Summary

• 1 T-compiler P-critical issues
  • 0 of those are unassigned
• 65 T-compiler P-high issues
  • 36 of those are unassigned
• 1 P-critical, 3 P-high, 2 P-medium, 1 P-low regression-from-stable-to-beta
• 0 P-critical, 1 P-high, 3 P-medium, 2 P-low regression-from-stable-to-nightly
• 0 P-critical, 41 P-high, 100 P-medium, 19 P-low regression-from-stable-to-stable

P-critical

T-compiler

• “Code no longer compiles after -Zdrop-tracking-mir was enabled by default” rust#116242
  • being handled by @lcnr + @Santiago Pastorino in rust#117134, thanks!

T-types

• No P-critical issues for T-types this time.

P-high regressions

P-high beta regressions

• “regression: parameter type may not live long enough” rust#117055
  • RFC’d by T-types (comment). Decided it’s an acceptable breaking change for a fix (downstream crates will need to update their code)
• “regression: new resolution failures in 1.74” rust#117056
  • @lqd bisected to possibly #115834 (comment)
  • @Michael (compiler-errors) Goulet will be looking into it
• “regression: change in async capture rules?” rust#117059
  • Duplicate of rust#116242, under T-types scrutiny (I-types-nominated)

Unassigned P-high nightly regressions

• No unassigned P-high nightly regressions this time.

Performance logs

triage logs for 2023-10-24?

TODO

Nominated Issues

T-compiler

• “tidy watcher” rust#114209
  • Creates a static watchlist of code in different places, checks when not in sync anymore (relevant code)
  • nominated by @cjgillot for visibility (comment) i.e. “is this potentially useful work?”
• “Code no longer compiles after -Zdrop-tracking-mir was enabled by default” rust#116242
  • Probably handled by T-types and solved by #117134
  • anything to add? can remove I-compiler-nominated?

RFC

• No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

T-compiler

• “Require type_map::stub callers to supply file information” rust#104342 (last review activity: 4 months ago)
  • @Wesley Wiser rerolling this one, if it’s ok for you?
• “Try to use approximate placeholder regions when outputting an AscribeUserType error in borrowck” rust#116097 (last review activity: about 31 days ago)
  • cc: @Wesley Wiser
• “Stabilize target_feature_11” rust#116114 (last review activity: about 31 days ago)
  • RFC#2396
  • Unsure if the review at this stage is more for T-lang or T-compiler

Next week’s WG checkins

• Impl Trait initiative by @oli
• @_WG-llvm by @nagisa and @Nikita Popov

Next meetings' agenda draft: hackmd link