Fix decoding attributes of SyntheticCoroutineBody

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1432,17 +1432,26 @@ impl CrateMetadata {
             .attributes
             .get(self, id)
             .unwrap_or_else(|| {
-                // Structure and variant constructors don't have any attributes encoded for them,
-                // but we assume that someone passing a constructor ID actually wants to look at
-                // the attributes on the corresponding struct or variant.
                 let def_key = self.def_key(id);
-                assert_eq!(def_key.disambiguated_data.data, DefPathData::Ctor);
-                let parent_id = def_key.parent.expect("no parent for a constructor");
-                self.root
-                    .tables
-                    .attributes
-                    .get(self, parent_id)
-                    .expect("no encoded attributes for a structure or variant")
+                match def_key.disambiguated_data.data {
+                    DefPathData::Ctor => {
+                        // Structure and variant constructors don't have any attributes encoded for them,
+                        // but we assume that someone passing a constructor ID actually wants to look at
+                        // the attributes on the corresponding struct or variant.
+                        assert_eq!(def_key.disambiguated_data.data, DefPathData::Ctor);
+                        let parent_id = def_key.parent.expect("no parent for a constructor");
+                        self.root
+                            .tables
+                            .attributes
+                            .get(self, parent_id)
+                            .expect("no encoded attributes for a structure or variant")
+                    }
+                    DefPathData::SyntheticCoroutineBody => {
+                        // SyntheticCoroutineBodies cannot have attributes
+                        LazyArray::default()
+                    }
+                    _ => panic!("Definition key {def_key:?} of type `{:?}` did not have any attributes stored", def_key.disambiguated_data.data)
+                }
             })
             .decode((self, tcx))
     }

src/tools/miri/tests/deps/Cargo.lock

@@ -32,6 +32,13 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
 
+[[package]]
+name = "cross-crate-items"
+version = "0.1.0"
+dependencies = [
+ "futures",
+]
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -290,6 +297,7 @@ dependencies = [
 name = "miri-test-deps"
 version = "0.1.0"
 dependencies = [
+ "cross-crate-items",
  "futures",
  "getrandom 0.1.16",
  "getrandom 0.2.17",

src/tools/miri/tests/deps/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 
 [dependencies]
 # all dependencies (and their transitive ones) listed here can be used in `tests/*-dep`.
+cross-crate-items = { path = "cross-crate-items" } # Used to test things that need multiple crates to check
 libc = "0.2"
 num_cpus = "1.10.1"
 
@@ -35,3 +36,4 @@ windows-sys = { version = "0.61", features = [
 
 # Make sure we are not part of the rustc workspace.
 [workspace]
+members = ["cross-crate-items"]

src/tools/miri/tests/deps/cross-crate-items/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "cross-crate-items"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+futures = { version = "0.3.0", default-features = false, features = ["alloc", "async-await"] }

src/tools/miri/tests/deps/cross-crate-items/src/lib.rs

@@ -0,0 +1,5 @@
+/// Async closure in an external crate — required because decoder.rs is only called for
+/// defs loaded from .rmeta files, not local crate defs.
+pub fn returns_async_closure() -> impl futures::Sink<(), Error = std::io::Error> {
+    futures::sink::unfold((), async |(), ()| Ok::<_, std::io::Error>(()))
+}

src/tools/miri/tests/pass-dep/cross_crate_async_closure_ice.rs

@@ -0,0 +1,26 @@
+//@compile-flags: -Zmiri-tree-borrows -Zmiri-tree-borrows-implicit-writes
+
+// This is a regression test for a Miri ICE when encountering a `SyntheticCoroutineBody` from an external crate (see
+// `cross_crate_items` for details). Calling the async closure triggered the ICE: https://github.com/rust-lang/rust/issues/156905
+
+use std::future::Future;
+use std::task::{Context, Poll, Waker};
+
+use futures::SinkExt as _;
+
+// Taken from tests/pass/async-fn.rs.
+fn run_fut<T>(fut: impl Future<Output = T>) -> T {
+    let mut context = Context::from_waker(Waker::noop());
+    let mut pinned = Box::pin(fut);
+    loop {
+        match pinned.as_mut().poll(&mut context) {
+            Poll::Pending => continue,
+            Poll::Ready(v) => return v,
+        }
+    }
+}
+
+fn main() {
+    let mut sink = Box::pin(cross_crate_items::returns_async_closure());
+    run_fut(sink.send(())).unwrap();
+}