rust-lang/rust-clippy

Warn about uses of Rust types where a C (raw) type is expected

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#1631 opened on Mar 20, 2017

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 (4 comments) (3 reactions) (0 assignees)Rust (10,406 stars) (1,391 forks)batch import
A-lintE-hardL-correctnessT-ASTgood first issue

Description

I started using Rust on ARMv7 and run twice into issues where Rust types where used instead of c_* types.

  1. It should not be possible to use a C type in a function declaration and a Rust type when calling it (or vice versa.)
  2. Functions like CStr::from_ptr should not allow the use of a Rust type. It is clearly intended for use with c_char.

A few examples

This really should be libc::c_char (c_char is an alias for u8 on ARMv7)

CStr::from_ptr(ptr as *const i8)

Use of libc::c_char in declaration but when using the function i8 is used instead:

pub fn rados_append(io: rados_ioctx_t, oid: *const ::libc::c_char, buf: *const ::libc::c_char, len: size_t)
…
unsafe {
    rados_append(ctx, obj_name_str.as_ptr(), buffer.as_ptr() as *const i8, buffer.len());
}

Use of i64 instead of c_time (32bit on ARMv7):

   pub fn rados_ioctx_snap_get_stamp(io: rados_ioctx_t, id: rados_snap_t, t: *mut time_t) -> ::libc::c_int;
   …
    let mut time_id: i64 = 0;
    unsafe {
        rados_ioctx_snap_get_stamp(ctx, snap_id, &mut time_id);
   }

Contributor guide

Tech stack
rust
Domain
developer experiencebackend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
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.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
basic Rust knowledgefamiliarity with FFI types
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Examine existing clippy lints like `c cast` or `c str` to see how they detect mismatches. Consult the Rustonomicon for `c char` behavior across platforms. The issue provides concrete examples; new lint should flag uses of `i8` instead of `c char` in functions like `CStr::from ptr` and mismatches between declaration and call.