tests: ring_buf: remove dependency on allocator_api

Reuse examples/error.rs so that the error returned by EvenU64::new2() is
not core::alloc::AllocError.  This will allow running the test without
the allocator_api feature.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: bonzini

examples/error.rs

@@ -1,6 +1,8 @@
-#![feature(allocator_api)]
+#![cfg_attr(feature = "alloc", feature(allocator_api))]
 
 use core::convert::Infallible;
+
+#[cfg(feature = "alloc")]
 use std::alloc::AllocError;
 
 #[derive(Debug)]
@@ -12,6 +14,7 @@ impl From<Infallible> for Error {
     }
 }
 
+#[cfg(feature = "alloc")]
 impl From<AllocError> for Error {
     fn from(_: AllocError) -> Self {
         Self

tests/ring_buf.rs

@@ -1,6 +1,6 @@
-#![feature(allocator_api)]
+#![cfg_attr(feature = "alloc", feature(allocator_api))]
+
 use core::{
-    alloc::AllocError,
     convert::Infallible,
     marker::PhantomPinned,
     mem::MaybeUninit,
@@ -14,6 +14,10 @@ use std::sync::Arc;
 mod mutex;
 use mutex::*;
 
+#[path = "../examples/error.rs"]
+mod error;
+use error::Error;
+
 #[pin_data(PinnedDrop)]
 pub struct RingBuffer<T, const SIZE: usize> {
     buffer: [MaybeUninit<T>; SIZE],
@@ -152,15 +156,15 @@ pub struct EvenU64 {
 }
 
 impl EvenU64 {
-    pub fn new2(value: u64) -> impl Init<Self, AllocError> {
+    pub fn new2(value: u64) -> impl Init<Self, Error> {
         try_init!(Self {
             info: "Hello world!".to_owned(),
             data: if value % 2 == 0 {
                 value
             } else {
-                return Err(AllocError);
+                return Err(Error);
             },
-        }? AllocError)
+        }? Error)
     }
     pub fn new(value: u64) -> impl Init<Self, ()> {
         try_init!(Self {
@@ -190,16 +194,10 @@ fn even_stack() {
 
 #[test]
 fn even_failing() {
-    assert!(matches!(
-        Box::try_pin_init(EvenU64::new2(3)),
-        Err(AllocError)
-    ));
-    assert!(matches!(
-        Arc::try_pin_init(EvenU64::new2(5)),
-        Err(AllocError)
-    ));
-    assert!(matches!(Box::try_init(EvenU64::new2(3)), Err(AllocError)));
-    assert!(matches!(Arc::try_init(EvenU64::new2(5)), Err(AllocError)));
+    assert!(matches!(Box::try_pin_init(EvenU64::new2(3)), Err(Error)));
+    assert!(matches!(Arc::try_pin_init(EvenU64::new2(5)), Err(Error)));
+    assert!(matches!(Box::try_init(EvenU64::new2(3)), Err(Error)));
+    assert!(matches!(Arc::try_init(EvenU64::new2(5)), Err(Error)));
 }
 
 #[test]