fix cargo doc

Introduce a dummy feature to hack around `cargo doc --all-features`
always hitting the compile_error!(...) in vhost/src/lib.rs about
incompatible features.

This is happening because when documenting vhost-user-backend, cargo
does not pass --cfg doc to dependencies, meaning the cfg(not(doc))
attribute that is supposed to eliminate this compile_error!() invokation
when building docs does not actually trigger. Hence cargo doc fails.

Instead, introduce a dummy feature that will automatically be picked up
by doing 'cargo doc --all-features` (as docs.rs does), which then
definitely kills the compile_error!().

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

vhost-user-backend/Cargo.toml

@@ -8,9 +8,13 @@ repository = "https://github.com/rust-vmm/vhost"
 edition = "2021"
 license = "Apache-2.0"
 
+[package.metadata.docs.rs]
+all-features = true
+
 [features]
 xen = ["vm-memory/xen", "vhost/xen"]
 postcopy = ["vhost/postcopy", "userfaultfd"]
+DUMMY_FEATURE_disable_compile_error = ["vhost/DUMMY_FEATURE_disable_compile_error"]
 
 [dependencies]
 libc = "0.2.39"
@@ -32,4 +36,6 @@ tempfile = "3.2.0"
 [package.metadata.cargo-all-features]
 skip_feature_sets = [
     ["xen", "postcopy"]
-]
+]
+
+denylist = ["DUMMY_FEATURE_disable_compile_error"]

vhost-user-backend/src/lib.rs

@@ -36,10 +36,14 @@ pub use self::vring::{
     VringMutex, VringRwLock, VringState, VringStateGuard, VringStateMutGuard, VringT,
 };
 
-/// Due to the way `xen` handles memory mappings we can not combine it with
-/// `postcopy` feature which relies on persistent memory mappings. Thus we
-/// disallow enabling both features at the same time.
-#[cfg(all(feature = "postcopy", feature = "xen"))]
+// Due to the way `xen` handles memory mappings we can not combine it with
+// `postcopy` feature which relies on persistent memory mappings. Thus we
+// disallow enabling both features at the same time.
+#[cfg(all(
+    not(feature = "DUMMY_FEATURE_disable_compile_error"),
+    feature = "postcopy",
+    feature = "xen"
+))]
 compile_error!("Both `postcopy` and `xen` features can not be enabled at the same time.");
 
 /// An alias for `GuestMemoryAtomic<GuestMemoryMmap<B>>` to simplify code.

vhost/Cargo.toml

@@ -25,6 +25,7 @@ vhost-user-frontend = ["vhost-user"]
 vhost-user-backend = ["vhost-user"]
 xen = ["vm-memory/xen"]
 postcopy = []
+DUMMY_FEATURE_disable_compile_error = []
 
 [dependencies]
 bitflags = "2.4"
@@ -43,4 +44,4 @@ skip_feature_sets = [
     ["xen", "postcopy"]
 ]
 
-denylist = ["test_utils"]
+denylist = ["test_utils", "DUMMY_FEATURE_disable_compile_error"]

vhost/src/lib.rs

@@ -51,10 +51,14 @@ pub mod vhost_user;
 #[cfg(feature = "vhost-vsock")]
 pub mod vsock;
 
-/// Due to the way `xen` handles memory mappings we can not combine it with
-/// `postcopy` feature which relies on persistent memory mappings. Thus we
-/// disallow enabling both features at the same time.
-#[cfg(all(not(doc), feature = "postcopy", feature = "xen"))]
+// Due to the way `xen` handles memory mappings we can not combine it with
+// `postcopy` feature which relies on persistent memory mappings. Thus we
+// disallow enabling both features at the same time.
+#[cfg(all(
+    not(feature = "DUMMY_FEATURE_disable_compile_error"),
+    feature = "postcopy",
+    feature = "xen"
+))]
 compile_error!("Both `postcopy` and `xen` features can not be enabled at the same time.");
 
 /// Error codes for vhost operations