dtolnay/cxx

Improve error message on signatures containing self by value

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#577 opened on Dec 13, 2020

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help wanted

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Description

The current error is shown as:

error[cxxbridge]: unsupported signature
  ┌─ /dev/stdin:1:54
  │
1 │ #[cxx::bridge] mod ffi { extern "C++" { type T; fn f(self); }}
  │                                                      ^^^^ unsupported signature

Instead it should say what to use instead. &self or &mut self for shared structs and opaque Rust types, self: Pin<&mut Self> for an opaque C++ type, Box<T> or UniquePtr<T> if ownership needs to be transferred depending on opaque Rust or opaque C++ type.

Contributor guide

Research direction
Locate the error generation point for unsupported signatures and add logic to suggest alternatives based on the type: &self, &mut self, self: Pin<&mut Self>, Box<T>, or UniquePtr<T>.
Tech stack
rust
Domain
developer experience
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Rust
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75