c_void Libc::unix conflicts with core::ffi

[ghost]

Using rules_rust it seems, that libc::unix::c_void conflicts with core::ffi::c_void type. This used to be the case but according to this the rfc was merged where libc re-exports core::ffi types from November 2018.

I am seeing this problem trying to compile libbacktrace which is a transient dependency for tonic crate. I am seeing the following errors

error[E0308]: mismatched types
   --> external/raze__backtrace__0_3_40/src/symbolize/libbacktrace.rs:100:45
    |
100 |             Symbol::Dladdr(ref s) => return s.addr(),
    |                                             ^^^^^^^^ expected enum `libc::unix::c_void`, found enum `core::ffi::c_void`
    |
    = note: expected type `core::option::Option<*mut libc::unix::c_void>`
               found type `core::option::Option<*mut core::ffi::c_void>`

Any ideas if this is a known behavior of rules_rust?

[ghost]

Sovled. Compiling libc in context of rules_rust require the following flags

    "--cfg=libc_priv_mod_use",
    "--cfg=libc_union",
    "--cfg=libc_const_size_of",
    "--cfg=libc_core_cvoid",
    "--cfg=libc_align",
    "--cfg=libc_packedN",

Hope this helps somehow.

[sholokhov]

Hi @Sythanis !
I'm still getting this error (macOS 10.15.4, Bazel 3.0.0, rules_rust a1d8936161beddadddd17d2b1c335ceac77d1d53) when trying to build backtrace as a transitive dependency:

error[E0308]: mismatched types
   --> external/raze__backtrace__0_3_46/src/symbolize/libbacktrace.rs:100:45
    |
96  |     pub fn addr(&self) -> Option<*mut c_void> {
    |                           ------------------- expected `core::option::Option<*mut libc::unix::c_void>` because of return type
...
100 |             Symbol::Dladdr(ref s) => return s.addr(),
    |                                             ^^^^^^^^ expected enum `libc::unix::c_void`, found enum `core::ffi::c_void`
    |
    = note: expected type `core::option::Option<*mut libc::unix::c_void>`
               found type `core::option::Option<*mut core::ffi::c_void>`

error[E0308]: mismatched types
   --> external/raze__backtrace__0_3_46/src/symbolize/libbacktrace.rs:451:32
    |
451 |         return dladdr_fallback(what.address_or_ip(), cb);
    |                                ^^^^^^^^^^^^^^^^^^^^ expected enum `libc::unix::c_void`, found enum `core::ffi::c_void`
    |
    = note: expected type `*mut libc::unix::c_void`
               found type `*mut core::ffi::c_void`

error[E0308]: mismatched types
   --> external/raze__backtrace__0_3_46/src/symbolize/libbacktrace.rs:479:25
    |
479 |         dladdr_fallback(what.address_or_ip(), cb);
    |                         ^^^^^^^^^^^^^^^^^^^^ expected enum `libc::unix::c_void`, found enum `core::ffi::c_void`
    |
    = note: expected type `*mut libc::unix::c_void`
               found type `*mut core::ffi::c_void`

error[E0308]: mismatched types
   --> external/raze__backtrace__0_3_46/src/symbolize/libbacktrace.rs:484:21
    |
484 |     dladdr::resolve(addr, &mut |sym| {
    |                     ^^^^ expected enum `core::ffi::c_void`, found enum `libc::unix::c_void`
    |
    = note: expected type `*mut core::ffi::c_void`
               found type `*mut libc::unix::c_void`

I've tried to add flags that you've mentioned in Cargo.toml like this (not sure if it's correct since I'm quite new to rules_rust):

[raze.crates.backtrace.'0.3.46']
additional_flags = [
  "--cfg=libc_priv_mod_use",
  "--cfg=libc_union",
  "--cfg=libc_const_size_of",
  "--cfg=libc_core_cvoid",
  "--cfg=libc_align",
  "--cfg=libc_packedN",
]

Do you have any thoughts or ideas how to fix it?

[vrusinov]

@sholokhov and anyone else also wondering: it seems those flags need to be passed to libc. This worked for me:

[raze.crates.libc.'0.2.70']
additional_flags = [
  # https://github.com/bazelbuild/rules_rust/issues/274
  "--cfg=libc_priv_mod_use",
  "--cfg=libc_union",
  "--cfg=libc_const_size_of",
  "--cfg=libc_core_cvoid",
  "--cfg=libc_align",
  "--cfg=libc_packedN",
]

[raze.crates.libc.'0.2.71']
additional_flags = [
  # https://github.com/bazelbuild/rules_rust/issues/274
  "--cfg=libc_priv_mod_use",
  "--cfg=libc_union",
  "--cfg=libc_const_size_of",
  "--cfg=libc_core_cvoid",
  "--cfg=libc_align",
  "--cfg=libc_packedN",
]