2020-09-28.md

Error Handling Project Group Agenda - 2020-09-28

tags: Error Handling Minutes

Agenda Items

• Prototyping an implementation of std::core::Error and stabilizing #[feature(backtrace)]
• Identifying existing issues and RFCs that we should track
  • rust-lang/rfcs#2895
• Planning for "Communicating best practices"
• "How users expect error handling to be, As in, we take a leap into the future and assume all this was implemented into the language, then how it would potentially look"

Meeting Minutes

Participants

People in attendance:

• Jane Lusby
• Sean Chen
• Ashley Mannix
• DPC
• Mukund Lakshman
• Jakub Duchniewicz
• must-compute
• Lance Zhang
• Oliver
• Charles Ellis O'Riley Jr.
• Kyle Strand
• Lokathor
• Jubilee Young

Topic 1: Discussing stabilizing Backtrace

• Global hooks vs Boxing vs a trait-based approach for stabilizing Backtrace in core.
• Going with the trait-based impl for Backtrace in core.
  • Private trait + public newtype wrapper.
  • Start with eddyb's impl and see how many hooks are necessary along the way.
• private trait with a public newtype wrapper
  • newtype wrapper is an interface not subject to coherence so we can add new methods without worrying about breaking changes downstream
• https://doc.rust-lang.org/stable/src/std/io/error.rs.html#67-71
• trait-based approaches have fewer magic compiler pieces and so would be easier to put together
• write_backtrace_to(&mut dyn FormatterThing) -> Result<(),FormatterThing::Error>
  • ultimately about moving Error to core
• should we do a trait object based solution internally with an unstable Backtrace trait in core and a stable Backtrace type in core or should it use global hooks like panic_impl
• need a prototype solution for exposing Backtrace as a type in core with the interface it currently provides in std

Topic 2: What RFCs should this group be tracking?

• This group will have its own Project board to track relevant issues/RFCs.
• Prep status reports on relevant issues we're tracking for future meetings.
• Pulled from the tracking board
  • #58520 tracking issue for error source iterators
  • #53487 tracking issue for RFC 2504, "fix the error trait"
  • #44838 tracking issue for RFC 2011: nicer assert messages
  • #2895 RFC: generic member access for dyn error trait objects
• #58520 tracking issue for error source iterators

Topic 3: Planning for "Communicating Best Practices"

• Facilitate communication of best practices via a Book/documentation.
  • Should include some guidance on FFI error handling.
• Adding a book section to the project repo (using mdbook).
• Publish The Rust Error Book (name subject to change) and potentially contribute to The Book to make its error handling recommendations consistent with what this group decides.

Topic 4: What is the long-term vision of what error handling in Rust looks like?

• Error in core.
• Stabilization of unstable Error interfaces.
• Iterator API on Backtrace.
• Generic member access (possibly with two-way flow).
• Error return traces.
• Some way to universally hook into all error reporting points for consistent error reporting.
• Better handling of error enums
• Guidance on FFI error handling.
• Ways of recovering from recoverable errors.
  • enum-convergance as errors propagate up the stack