dtolnay/cxx

Implement glob import semantics for builtin type names

Open

#682 opened on Jan 16, 2021

View on GitHub
 (6 comments) (0 reactions) (0 assignees)Rust (4,472 stars) (253 forks)batch import
help wanted

Description

Currently we disallow any user-defined type name that collides with one of the builtin type names.

error[cxxbridge]: reserved name
  ┌─ src/main.rs:3:12
  │
3 │     struct UniquePtr { broken: bool }
  │            ^^^^^^^^^ reserved name

error[cxxbridge]: reserved name
  ┌─ src/main.rs:5:12
  │
5 │     struct c_char { broken: bool }
  │            ^^^^^^ reserved name

However, this is bad because it makes it a breaking change for us to add new builtin bindings, such as #681. If the user already had their own type with the same name as the new binding, that code needs to continue to work.

We need to implement basically the same semantics that Rust has for prelude types and glob imports — a user-defined type replaces any builtin binding of the same name.

Contributor guide

Tech stack
rust
Domain
developer experiencetooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Rust programmingUnderstanding of cxx crate APIFamiliarity with Rust's glob imports
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Examine the cxx crate's source code for the reserved name validation logic (likely around the code generation step). Study how Rust implements glob import semantics for prelude types, and design a similar mechanism where user defined types shadow builtin bindings. The issue mentions #681 as an example of a new builtin binding that could break existing code; review that PR for context. Look at the error message output and the parsing of type names to understand where to implement the fallback.