Design meeting: Non-local errors (aka post-monomorphization errors)

[tmandry]

Summary

A non-local error is a compile-time error that appears in code only in some cases, contingent on external factors not controlled by the code itself. Examples:

• Static assertions about the value of a const generic, or the size of a generic type
• Errors that only appear when certain APIs are used from main, or flags like -C link-dead-code are passed
• Errors that appear in cargo build, but not cargo check

The lang team needs to decide its stance on these errors, their tradeoffs, and in particular, how they relate to the discussion to stabilize inline_const.

Background reading

Non-local errors in Rust

About this issue

This issue corresponds to a lang-team design meeting proposal. It corresponds to a possible topic of discussion that may be scheduled for deeper discussion during one of our design meetings.

[tmandry]

This meeting has been scheduled for Feb 22. Calendar

[tmandry]

Meeting notes: Non-local errors in Rust. There is a summary of the discussion at the bottom.

Summary of consensus on the question of stabilizing inline_const specifically is in rust-lang/rust#104087 (comment). It's possible the outcomes of the resulting investigations/discussion may trigger one or more follow-up meetings, but those will need new issues.