2020-10-12.md

PEH Meeting Agenda - 2020-10-12

tags: Error Handling Minutes

• 2020-09-28 Meeting Minutes

Action Items

• Implement trait based proof of concept for Backtrace in core (Jane Lusby)
• Setup The Rust Error Book (must-compute, Charles Ellis O'Riley Jr, and Jakub Duchniewicz)
• Draft a blog post detailing the long-term vision of what this group thinks Rust error handling should look like (Sean Chen)
• Status Updates on Tracked issues (What's the current status, what are the next steps, what are the blockers, is it actively being worked on)
  • Generic Member Access (Jane Lusby)
  • Fix the error trait / Stabilizing Backtrace (Jane Lusby)
  • stabilizing error source iterators (Oliver)
  • Box error alias (unassigned)
  • stabilizing Error::type_id (Jakub Duchniewicz)
  • PanicInfo::message (DPC)
  • nicer assert messages (Charles Ellis O'Riley Jr.)
• Moving forward with adding an iterator API to backtrace (Sean Chen)

Agenda Items

• Review action items from last meeting
• Review open issues on project group repository
• Anything to buble up to the Libs meeting?

Meeting Minutes

Participants

People in attendance:

• Jane Lusby
• Sean Chen
• Ashley Mannix
• Kyle Strand
• Lance Zhang
• Jeremiah Senkpiel
• Jakub Duchniewicz
• DPC
• oliver
• Charles Ellis O'Riley Jr.
• must-compute
• Jubilee Young

Backtrace in core

• So far the implementation is moving forward fine, but there are questions around the hooks
• Not clear how to set them up with a default in no_std so users don't need to write one like #[panic_handler]
• Current work in progress here
• There's enough sketched out that it shouldn't be a blocker for stabilizing backtrace anymore

The Rust Error Book

• We now have a folder in the project-error-handling repository for content

Log-term project group vision and goals

• Draft here: https://hackmd.io/GMLcORX_R7W4de0ZryDIxg?view

Generic member access RFC

• There's an updated API in object-provider that the RFC would like to use
• Once the content is updated it needs some Libs input
• There could be some tie in with tide's Response type?

Fix the Error trait / Stabilizing backtrace

• Covered in the earlier discussion on Backtrace in core
• There could be some documentation work to do on backtrace

Stabilizing Error source iterators

• stabilizing error source iterators
  • trait objects vs. provided methods
  • stabilization report 2020-09-14
    • unergonomic use-cases ---> difficulties stabilizing
    • bugs
  • blocked on #53487
• #75180 might feed into this too
• related crate error-chain

Stabilizing Error::type_id

• Several possible approaches, but all are waiting for other stabilizations/RFCs
  • #[marker] trait stabilization: rust-lang/rust#29864
  • negative trait impls
  • dynamic vtable type_id (like C++ typeid keyword) rust-lang/rfcs#2580
  • final keyword -> no overriding of trait any more
  • new trait TypeInfo rust-lang/rfcs#2738
• Not clear it's something we want to stabilize
• Looks like a rabbit hole we don't want to go down right now

PanicInfo::message

• No progress made here

Nicer Assert Messages

• RFC has been approved, with no implementation started yet
• Does this need to be implemented using the compiler's built-in proc macros, or can it be done as an external crate using pro-macros and syn?
  • Need external thoughts/mentorship on this question

Iterating over Backtrace frames

• Just starting out, so there hasn't been much discussion yet
• The backtrace crate has a frames() fn that already exposes its individual frames
• We could propose basically the same thing for std's Backtrace type

Outcomes

Backtrace in core

• @KodrAus to ping rust-lang/rust#72981 and raise at Libs meeting RE backtrace stabilization

Long-term project group vision and goals blog post

• @Jane Lusby @Jakub Duchniewicz @KodrAus to review draft content

Generic member access RFC

• @Jane Lusby to incorporate changes from object-provider
• @KodrAus to review RFC and ping Libs

Stabilizing Error source iterators

• Looks like many parts of this are stuck on fixing the Error trait, so our efforts should be focused here to push this forward

Stabilizing Error::type_id

• Putting this one on the back burner

Nicer Assert Messages

• Look into whether we can implement an external POC for this ourselves
• Need external advice/mentorship (possibly from t-libs-impl) before we can get started on it

Iterator API on Backtrace

• @Sean Chen to look more into this initiative
• Export an identical fn frames(&self) -> &[BacktraceFrame] to std
• Add it as an unstable API to Backtrace without an RFC to start with (just an FCP on the implementation itself)