Rollup merge of #100129 - RalfJung:miri-test-libstd, r=thomcc

add miri-test-libstd support to libstd

- The first commit mirrors what we already have in liballoc.
- The second commit adds some regression tests that only really make sense to be run in Miri, since they rely on Miri's extra checks to detect anything.
- The third commit makes the MPSC tests work in reasonable time in Miri by reducing iteration counts.
- The fourth commit silences some warnings due to code being disabled with `cfg(miri)`

library/alloc/src/lib.rs

@@ -56,10 +56,6 @@
 //! [`Rc`]: rc
 //! [`RefCell`]: core::cell
 
-// To run liballoc tests without x.py without ending up with two copies of liballoc, Miri needs to be
-// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
-// rustc itself never sets the feature, so this line has no affect there.
-#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
 #![allow(unused_attributes)]
 #![stable(feature = "alloc", since = "1.36.0")]
 #![doc(
@@ -77,6 +73,10 @@
 ))]
 #![no_std]
 #![needs_allocator]
+// To run liballoc tests without x.py without ending up with two copies of liballoc, Miri needs to be
+// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
+// rustc itself never sets the feature, so this line has no affect there.
+#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
 //
 // Lints:
 #![deny(unsafe_op_in_unsafe_fn)]

library/alloc/src/sync/tests.rs

@@ -618,3 +618,22 @@ fn test_arc_cyclic_two_refs() {
     assert_eq!(Arc::strong_count(&two_refs), 3);
     assert_eq!(Arc::weak_count(&two_refs), 2);
 }
+
+/// Test for Arc::drop bug (https://github.com/rust-lang/rust/issues/55005)
+#[test]
+#[cfg(miri)] // relies on Stacked Borrows in Miri
+fn arc_drop_dereferenceable_race() {
+    // The bug seems to take up to 700 iterations to reproduce with most seeds (tested 0-9).
+    for _ in 0..750 {
+        let arc_1 = Arc::new(());
+        let arc_2 = arc_1.clone();
+        let thread = thread::spawn(|| drop(arc_2));
+        // Spin a bit; makes the race more likely to appear
+        let mut i = 0;
+        while i < 256 {
+            i += 1;
+        }
+        drop(arc_1);
+        thread.join().unwrap();
+    }
+}

library/std/src/collections/hash/map/tests.rs

@@ -268,53 +268,56 @@ fn test_lots_of_insertions() {
 
     // Try this a few times to make sure we never screw up the hashmap's
     // internal state.
-    for _ in 0..10 {
+    let loops = if cfg!(miri) { 2 } else { 10 };
+    for _ in 0..loops {
         assert!(m.is_empty());
 
-        for i in 1..1001 {
+        let count = if cfg!(miri) { 101 } else { 1001 };
+
+        for i in 1..count {
             assert!(m.insert(i, i).is_none());
 
             for j in 1..=i {
                 let r = m.get(&j);
                 assert_eq!(r, Some(&j));
             }
 
-            for j in i + 1..1001 {
+            for j in i + 1..count {
                 let r = m.get(&j);
                 assert_eq!(r, None);
             }
         }
 
-        for i in 1001..2001 {
+        for i in count..(2 * count) {
             assert!(!m.contains_key(&i));
         }
 
         // remove forwards
-        for i in 1..1001 {
+        for i in 1..count {
             assert!(m.remove(&i).is_some());
 
             for j in 1..=i {
                 assert!(!m.contains_key(&j));
             }
 
-            for j in i + 1..1001 {
+            for j in i + 1..count {
                 assert!(m.contains_key(&j));
             }
         }
 
-        for i in 1..1001 {
+        for i in 1..count {
             assert!(!m.contains_key(&i));
         }
 
-        for i in 1..1001 {
+        for i in 1..count {
             assert!(m.insert(i, i).is_none());
         }
 
         // remove backwards
-        for i in (1..1001).rev() {
+        for i in (1..count).rev() {
             assert!(m.remove(&i).is_some());
 
-            for j in i..1001 {
+            for j in i..count {
                 assert!(!m.contains_key(&j));
             }
 
@@ -817,6 +820,7 @@ fn test_retain() {
 }
 
 #[test]
+#[cfg_attr(miri, ignore)] // Miri does not support signalling OOM
 #[cfg_attr(target_os = "android", ignore)] // Android used in CI has a broken dlmalloc
 fn test_try_reserve() {
     let mut empty_bytes: HashMap<u8, u8> = HashMap::new();

library/std/src/io/tests.rs

@@ -94,7 +94,7 @@ fn read_to_end() {
     assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
     assert_eq!(v, b"1");
 
-    let cap = 1024 * 1024;
+    let cap = if cfg!(miri) { 1024 } else { 1024 * 1024 };
     let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
     let mut v = Vec::new();
     let (a, b) = data.split_at(data.len() / 2);
@@ -309,6 +309,7 @@ fn chain_zero_length_read_is_not_eof() {
 
 #[bench]
 #[cfg_attr(target_os = "emscripten", ignore)]
+#[cfg_attr(miri, ignore)] // Miri isn't fast...
 fn bench_read_to_end(b: &mut test::Bencher) {
     b.iter(|| {
         let mut lr = repeat(1).take(10000000);

library/std/src/lib.rs

@@ -187,6 +187,7 @@
 //! [rust-discord]: https://discord.gg/rust-lang
 //! [array]: prim@array
 //! [slice]: prim@slice
+
 #![cfg_attr(not(feature = "restricted-std"), stable(feature = "rust1", since = "1.0.0"))]
 #![cfg_attr(feature = "restricted-std", unstable(feature = "restricted_std", issue = "none"))]
 #![doc(
@@ -201,25 +202,35 @@
     no_global_oom_handling,
     not(no_global_oom_handling)
 ))]
+// To run libstd tests without x.py without ending up with two copies of libstd, Miri needs to be
+// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
+// rustc itself never sets the feature, so this line has no affect there.
+#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
+// miri-test-libstd also prefers to make std use the sysroot versions of the dependencies.
+#![cfg_attr(feature = "miri-test-libstd", feature(rustc_private))]
 // Don't link to std. We are std.
 #![no_std]
+// Tell the compiler to link to either panic_abort or panic_unwind
+#![needs_panic_runtime]
+//
+// Lints:
 #![warn(deprecated_in_future)]
 #![warn(missing_docs)]
 #![warn(missing_debug_implementations)]
 #![allow(explicit_outlives_requirements)]
 #![allow(unused_lifetimes)]
-// Tell the compiler to link to either panic_abort or panic_unwind
-#![needs_panic_runtime]
+#![deny(rustc::existing_doc_keyword)]
 // Ensure that std can be linked against panic_abort despite compiled with `-C panic=unwind`
 #![deny(ffi_unwind_calls)]
 // std may use features in a platform-specific way
 #![allow(unused_features)]
+//
+// Features:
 #![cfg_attr(test, feature(internal_output_capture, print_internals, update_panic_count, rt))]
 #![cfg_attr(
     all(target_vendor = "fortanix", target_env = "sgx"),
     feature(slice_index_methods, coerce_unsized, sgx_platform)
 )]
-#![deny(rustc::existing_doc_keyword)]
 //
 // Language features:
 #![feature(alloc_error_handler)]

library/std/src/path/tests.rs

@@ -1768,6 +1768,7 @@ fn test_windows_absolute() {
 }
 
 #[bench]
+#[cfg_attr(miri, ignore)] // Miri isn't fast...
 fn bench_path_cmp_fast_path_buf_sort(b: &mut test::Bencher) {
     let prefix = "my/home";
     let mut paths: Vec<_> =
@@ -1781,6 +1782,7 @@ fn bench_path_cmp_fast_path_buf_sort(b: &mut test::Bencher) {
 }
 
 #[bench]
+#[cfg_attr(miri, ignore)] // Miri isn't fast...
 fn bench_path_cmp_fast_path_long(b: &mut test::Bencher) {
     let prefix = "/my/home/is/my/castle/and/my/castle/has/a/rusty/workbench/";
     let paths: Vec<_> =
@@ -1799,6 +1801,7 @@ fn bench_path_cmp_fast_path_long(b: &mut test::Bencher) {
 }
 
 #[bench]
+#[cfg_attr(miri, ignore)] // Miri isn't fast...
 fn bench_path_cmp_fast_path_short(b: &mut test::Bencher) {
     let prefix = "my/home";
     let paths: Vec<_> =
@@ -1817,6 +1820,7 @@ fn bench_path_cmp_fast_path_short(b: &mut test::Bencher) {
 }
 
 #[bench]
+#[cfg_attr(miri, ignore)] // Miri isn't fast...
 fn bench_path_hashset(b: &mut test::Bencher) {
     let prefix = "/my/home/is/my/castle/and/my/castle/has/a/rusty/workbench/";
     let paths: Vec<_> =
@@ -1835,6 +1839,7 @@ fn bench_path_hashset(b: &mut test::Bencher) {
 }
 
 #[bench]
+#[cfg_attr(miri, ignore)] // Miri isn't fast...
 fn bench_path_hashset_miss(b: &mut test::Bencher) {
     let prefix = "/my/home/is/my/castle/and/my/castle/has/a/rusty/workbench/";
     let paths: Vec<_> =

library/std/src/sync/mpsc/mpsc_queue/tests.rs

@@ -13,7 +13,7 @@ fn test_full() {
 #[test]
 fn test() {
     let nthreads = 8;
-    let nmsgs = 1000;
+    let nmsgs = if cfg!(miri) { 100 } else { 1000 };
     let q = Queue::new();
     match q.pop() {
         Empty => {}

library/std/src/sync/mpsc/spsc_queue/tests.rs

@@ -77,12 +77,13 @@ fn stress() {
     }
 
     unsafe fn stress_bound(bound: usize) {
+        let count = if cfg!(miri) { 1000 } else { 100000 };
         let q = Arc::new(Queue::with_additions(bound, (), ()));
 
         let (tx, rx) = channel();
         let q2 = q.clone();
         let _t = thread::spawn(move || {
-            for _ in 0..100000 {
+            for _ in 0..count {
                 loop {
                     match q2.pop() {
                         Some(1) => break,
@@ -93,7 +94,7 @@ fn stress() {
             }
             tx.send(()).unwrap();
         });
-        for _ in 0..100000 {
+        for _ in 0..count {
             q.push(1);
         }
         rx.recv().unwrap();

library/std/src/sync/mpsc/sync_tests.rs

@@ -113,23 +113,25 @@ fn chan_gone_concurrent() {
 
 #[test]
 fn stress() {
+    let count = if cfg!(miri) { 100 } else { 10000 };
     let (tx, rx) = sync_channel::<i32>(0);
     thread::spawn(move || {
-        for _ in 0..10000 {
+        for _ in 0..count {
             tx.send(1).unwrap();
         }
     });
-    for _ in 0..10000 {
+    for _ in 0..count {
         assert_eq!(rx.recv().unwrap(), 1);
     }
 }
 
 #[test]
 fn stress_recv_timeout_two_threads() {
+    let count = if cfg!(miri) { 100 } else { 10000 };
     let (tx, rx) = sync_channel::<i32>(0);
 
     thread::spawn(move || {
-        for _ in 0..10000 {
+        for _ in 0..count {
             tx.send(1).unwrap();
         }
     });
@@ -146,12 +148,12 @@ fn stress_recv_timeout_two_threads() {
         }
     }
 
-    assert_eq!(recv_count, 10000);
+    assert_eq!(recv_count, count);
 }
 
 #[test]
 fn stress_recv_timeout_shared() {
-    const AMT: u32 = 1000;
+    const AMT: u32 = if cfg!(miri) { 100 } else { 1000 };
     const NTHREADS: u32 = 8;
     let (tx, rx) = sync_channel::<i32>(0);
     let (dtx, drx) = sync_channel::<()>(0);
@@ -191,7 +193,7 @@ fn stress_recv_timeout_shared() {
 
 #[test]
 fn stress_shared() {
-    const AMT: u32 = 1000;
+    const AMT: u32 = if cfg!(miri) { 100 } else { 1000 };
     const NTHREADS: u32 = 8;
     let (tx, rx) = sync_channel::<i32>(0);
     let (dtx, drx) = sync_channel::<()>(0);
@@ -438,12 +440,13 @@ fn stream_send_recv_stress() {
 
 #[test]
 fn recv_a_lot() {
+    let count = if cfg!(miri) { 1000 } else { 10000 };
     // Regression test that we don't run out of stack in scheduler context
-    let (tx, rx) = sync_channel(10000);
-    for _ in 0..10000 {
+    let (tx, rx) = sync_channel(count);
+    for _ in 0..count {
         tx.send(()).unwrap();
     }
-    for _ in 0..10000 {
+    for _ in 0..count {
         rx.recv().unwrap();
     }
 }

library/std/src/sync/mpsc/tests.rs

@@ -120,21 +120,22 @@ fn chan_gone_concurrent() {
 
 #[test]
 fn stress() {
+    let count = if cfg!(miri) { 100 } else { 10000 };
     let (tx, rx) = channel::<i32>();
     let t = thread::spawn(move || {
-        for _ in 0..10000 {
+        for _ in 0..count {
             tx.send(1).unwrap();
         }
     });
-    for _ in 0..10000 {
+    for _ in 0..count {
         assert_eq!(rx.recv().unwrap(), 1);
     }
     t.join().ok().expect("thread panicked");
 }
 
 #[test]
 fn stress_shared() {
-    const AMT: u32 = 10000;
+    const AMT: u32 = if cfg!(miri) { 100 } else { 10000 };
     const NTHREADS: u32 = 8;
     let (tx, rx) = channel::<i32>();
 
@@ -504,12 +505,13 @@ fn very_long_recv_timeout_wont_panic() {
 
 #[test]
 fn recv_a_lot() {
+    let count = if cfg!(miri) { 1000 } else { 10000 };
     // Regression test that we don't run out of stack in scheduler context
     let (tx, rx) = channel();
-    for _ in 0..10000 {
+    for _ in 0..count {
         tx.send(()).unwrap();
     }
-    for _ in 0..10000 {
+    for _ in 0..count {
         rx.recv().unwrap();
     }
 }

library/std/src/sync/rwlock/tests.rs

@@ -19,7 +19,7 @@ fn smoke() {
 #[test]
 fn frob() {
     const N: u32 = 10;
-    const M: usize = 1000;
+    const M: usize = if cfg!(miri) { 100 } else { 1000 };
 
     let r = Arc::new(RwLock::new(()));
 

library/std/src/sys/unix/fs.rs

@@ -829,6 +829,7 @@ impl DirEntry {
         target_os = "fuchsia",
         target_os = "redox"
     )))]
+    #[cfg_attr(miri, allow(unused))]
     fn name_cstr(&self) -> &CStr {
         unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()) }
     }
@@ -840,6 +841,7 @@ impl DirEntry {
         target_os = "fuchsia",
         target_os = "redox"
     ))]
+    #[cfg_attr(miri, allow(unused))]
     fn name_cstr(&self) -> &CStr {
         &self.name
     }