Compilation error when building with --cfg doc

[fpoli]

Is there some known limitation regarding generating the documentation of socket2?

I tried generating the documentation with links to definitions of a crate depending on socket2:

cargo init
cargo add socket2@0.4.7
RUSTDOCFLAGS="--generate-link-to-definition -Zunstable-options" cargo +nightly-2023-01-15 doc

I expected the cargo doc above to succeed. Instead, I get some compilation errors:

   Compiling libc v0.2.139
 Documenting libc v0.2.139
    Checking socket2 v0.4.7
 Documenting socket2 v0.4.7
error[E0433]: failed to resolve: could not resolve path `sys::socketpair`
   --> /home/fpoli/.cargo/registry/src/gh.loli.garden-1ecc6299db9ec823/socket2-0.4.7/src/socket.rs:172:9
    |
172 |         sys::socketpair(domain.0, ty.0, protocol)
    |         ^^^^^^^^^^^^^^^ could not resolve path `sys::socketpair`
    |
    = note: this error was originally ignored because you are running `rustdoc`
    = note: try running again with `rustc` or `cargo check` and you may get a more detailed error

error[E0433]: failed to resolve: could not resolve path `sys::keepalive_time`
    --> /home/fpoli/.cargo/registry/src/gh.loli.garden-1ecc6299db9ec823/socket2-0.4.7/src/socket.rs:1663:9
     |
1663 |         sys::keepalive_time(self.as_raw())
     |         ^^^^^^^^^^^^^^^^^^^ could not resolve path `sys::keepalive_time`
     |
     = note: this error was originally ignored because you are running `rustdoc`
     = note: try running again with `rustc` or `cargo check` and you may get a more detailed error

For more information about this error, try `rustc --explain E0433`.
error: could not document `socket2`

Even without using nightly Rust, the following fails to compile (suggested in rust-lang/rust#107063):

RUSTFLAGS="--cfg doc" cargo build

   Compiling libc v0.2.139
   Compiling socket2 v0.4.7
error[E0425]: cannot find function `socketpair` in module `sys`
   --> /home/fpoli/.cargo/registry/src/gh.loli.garden-1ecc6299db9ec823/socket2-0.4.7/src/socket.rs:172:14
    |
172 |         sys::socketpair(domain.0, ty.0, protocol)
    |              ^^^^^^^^^^ not found in `sys`
    |
help: consider importing this function
    |
9   | use libc::socketpair;
    |
help: if you import `socketpair`, refer to it directly
    |
172 -         sys::socketpair(domain.0, ty.0, protocol)
172 +         socketpair(domain.0, ty.0, protocol)
    |

error[E0425]: cannot find function `keepalive_time` in module `sys`
    --> /home/fpoli/.cargo/registry/src/gh.loli.garden-1ecc6299db9ec823/socket2-0.4.7/src/socket.rs:1663:14
     |
1663 |         sys::keepalive_time(self.as_raw())
     |              ^^^^^^^^^^^^^^ help: a constant with a similar name exists: `KEEPALIVE_TIME`
     |
    ::: /home/fpoli/.cargo/registry/src/gh.loli.garden-1ecc6299db9ec823/libc-0.2.139/src/unix/linux_like/mod.rs:964:1
     |
964  | pub const TCP_KEEPIDLE: ::c_int = 4;
     | ------------------------------- similarly named constant `KEEPALIVE_TIME` defined here

For more information about this error, try `rustc --explain E0425`.
error: could not compile `socket2` due to 2 previous errors

[Thomasdezeeuw]

I think we're missing the #[cfg_attr(docsrs, doc(cfg(all(feature = "all", unix))))] attribute, see

socket2/src/socket.rs

Line 168 in 5b68514

#[cfg_attr(docsrs, doc(cfg(all(feature = "all", unix))))]

on the socketpair in the sys module:

socket2/src/sys/unix.rs

Lines 612 to 613 in a6d6587

	#[cfg(feature = "all")]
	pub(crate) fn socketpair(family: c_int, ty: c_int, protocol: c_int) -> io::Result<[Socket; 2]> {

We should probably add this to the CI.