Auto merge of #87413 - JohnTitor:rollup-dht22jk, r=JohnTitor

Rollup of 14 pull requests

Successful merges:

 - #86410 (VecMap::get_value_matching should return just one element)
 - #86790 (Document iteration order of `retain` functions)
 - #87171 (Remove Option from BufWriter)
 - #87175 (Stabilize `into_parts()` and `into_error()`)
 - #87185 (Fix panics on Windows when the build was cancelled)
 - #87191 (Package LLVM libs for the target rather than the build host)
 - #87255 (better support for running libcore tests with Miri)
 - #87266 (Add testcase for 87076)
 - #87283 (Add `--codegen-backends=foo,bar` configure flag)
 - #87322 (fix: clarify suggestion that `&T` must refer to `T: Sync` for `&T: Send`)
 - #87358 (Fix `--dry-run` when download-ci-llvm is set)
 - #87380 (Don't default to `submodules = true` unless the rust repo has a .git directory)
 - #87398 (Add test for fonts used for module items)
 - #87412 (Add missing article)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_data_structures/src/vec_map.rs

@@ -1,4 +1,5 @@
 use std::borrow::Borrow;
+use std::fmt::Debug;
 use std::iter::FromIterator;
 use std::slice::Iter;
 use std::vec::IntoIter;
@@ -12,7 +13,8 @@ pub struct VecMap<K, V>(Vec<(K, V)>);
 
 impl<K, V> VecMap<K, V>
 where
-    K: PartialEq,
+    K: Debug + PartialEq,
+    V: Debug,
 {
     pub fn new() -> Self {
         VecMap(Default::default())
@@ -37,14 +39,31 @@ where
         self.0.iter().find(|(key, _)| k == key.borrow()).map(|elem| &elem.1)
     }
 
-    /// Returns the value corresponding to the supplied predicate filter.
+    /// Returns the any value corresponding to the supplied predicate filter.
     ///
     /// The supplied predicate will be applied to each (key, value) pair and it will return a
     /// reference to the values where the predicate returns `true`.
-    pub fn get_by(&self, mut predicate: impl FnMut(&(K, V)) -> bool) -> Option<&V> {
+    pub fn any_value_matching(&self, mut predicate: impl FnMut(&(K, V)) -> bool) -> Option<&V> {
         self.0.iter().find(|kv| predicate(kv)).map(|elem| &elem.1)
     }
 
+    /// Returns the value corresponding to the supplied predicate filter. It crashes if there's
+    /// more than one matching element.
+    ///
+    /// The supplied predicate will be applied to each (key, value) pair and it will return a
+    /// reference to the value where the predicate returns `true`.
+    pub fn get_value_matching(&self, mut predicate: impl FnMut(&(K, V)) -> bool) -> Option<&V> {
+        let mut filter = self.0.iter().filter(|kv| predicate(kv));
+        let (_, value) = filter.next()?;
+        // This should return just one element, otherwise it's a bug
+        assert!(
+            filter.next().is_none(),
+            "Collection {:?} should have just one matching element",
+            self
+        );
+        Some(value)
+    }
+
     /// Returns `true` if the map contains a value for the specified key.
     ///
     /// The key may be any borrowed form of the map's key type,
@@ -131,7 +150,7 @@ impl<K, V> IntoIterator for VecMap<K, V> {
     }
 }
 
-impl<K: PartialEq, V> Extend<(K, V)> for VecMap<K, V> {
+impl<K: PartialEq + Debug, V: Debug> Extend<(K, V)> for VecMap<K, V> {
     fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iter: I) {
         for (k, v) in iter {
             self.insert(k, v);

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1857,12 +1857,37 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 }
             }
             GeneratorInteriorOrUpvar::Upvar(upvar_span) => {
+                // `Some(ref_ty)` if `target_ty` is `&T` and `T` fails to impl `Sync`
+                let refers_to_non_sync = match target_ty.kind() {
+                    ty::Ref(_, ref_ty, _) => match self.evaluate_obligation(&obligation) {
+                        Ok(eval) if !eval.may_apply() => Some(ref_ty),
+                        _ => None,
+                    },
+                    _ => None,
+                };
+
+                let (span_label, span_note) = match refers_to_non_sync {
+                    // if `target_ty` is `&T` and `T` fails to impl `Sync`,
+                    // include suggestions to make `T: Sync` so that `&T: Send`
+                    Some(ref_ty) => (
+                        format!(
+                            "has type `{}` which {}, because `{}` is not `Sync`",
+                            target_ty, trait_explanation, ref_ty
+                        ),
+                        format!(
+                            "captured value {} because `&` references cannot be sent unless their referent is `Sync`",
+                            trait_explanation
+                        ),
+                    ),
+                    None => (
+                        format!("has type `{}` which {}", target_ty, trait_explanation),
+                        format!("captured value {}", trait_explanation),
+                    ),
+                };
+
                 let mut span = MultiSpan::from_span(upvar_span);
-                span.push_span_label(
-                    upvar_span,
-                    format!("has type `{}` which {}", target_ty, trait_explanation),
-                );
-                err.span_note(span, &format!("captured value {}", trait_explanation));
+                span.push_span_label(upvar_span, span_label);
+                err.span_note(span, &span_note);
             }
         }
 

compiler/rustc_typeck/src/collect/type_of.rs

@@ -364,7 +364,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     let concrete_ty = tcx
                         .mir_borrowck(owner.expect_local())
                         .concrete_opaque_types
-                        .get_by(|(key, _)| key.def_id == def_id.to_def_id())
+                        .get_value_matching(|(key, _)| key.def_id == def_id.to_def_id())
                         .map(|concrete_ty| *concrete_ty)
                         .unwrap_or_else(|| {
                             tcx.sess.delay_span_bug(
@@ -512,8 +512,15 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
 
     struct ConstraintLocator<'tcx> {
         tcx: TyCtxt<'tcx>,
+
+        /// def_id of the opaque type whose defining uses are being checked
         def_id: DefId,
-        // (first found type span, actual type)
+
+        /// as we walk the defining uses, we are checking that all of them
+        /// define the same hidden type. This variable is set to `Some`
+        /// with the first type that we find, and then later types are
+        /// checked against it (we also carry the span of that first
+        /// type).
         found: Option<(Span, Ty<'tcx>)>,
     }
 
@@ -531,7 +538,7 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
                 .tcx
                 .typeck(def_id)
                 .concrete_opaque_types
-                .get_by(|(key, _)| key.def_id == self.def_id)
+                .any_value_matching(|(key, _)| key.def_id == self.def_id)
                 .is_none()
             {
                 debug!("no constraints in typeck results");

config.toml.example

@@ -38,7 +38,7 @@ changelog-seen = 2
 # This is false by default so that distributions don't unexpectedly download
 # LLVM from the internet.
 #
-# All tier 1 targets are currently supported; set this to `"if-supported"` if
+# All tier 1 targets are currently supported; set this to `"if-available"` if
 # you are not sure whether you're on a tier 1 target.
 #
 # We also currently only support this when building LLVM for the build triple.

library/alloc/src/collections/btree/map.rs

@@ -935,6 +935,7 @@ impl<K, V> BTreeMap<K, V> {
     /// Retains only the elements specified by the predicate.
     ///
     /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns `false`.
+    /// The elements are visited in ascending key order.
     ///
     /// # Examples
     ///

library/alloc/src/collections/btree/set.rs

@@ -846,6 +846,7 @@ impl<T> BTreeSet<T> {
     /// Retains only the elements specified by the predicate.
     ///
     /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
+    /// The elements are visited in ascending order.
     ///
     /// # Examples
     ///

library/alloc/src/lib.rs

@@ -56,6 +56,10 @@
 //! [`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(

library/core/src/lib.rs

@@ -49,6 +49,10 @@
 //
 // This cfg won't affect doc tests.
 #![cfg(not(test))]
+// To run libcore tests without x.py without ending up with two copies of libcore, 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))]
 #![stable(feature = "core", since = "1.6.0")]
 #![doc(
     html_playground_url = "https://play.rust-lang.org/",

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

@@ -934,6 +934,7 @@ where
     /// Retains only the elements specified by the predicate.
     ///
     /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns `false`.
+    /// The elements are visited in unsorted (and unspecified) order.
     ///
     /// # Examples
     ///

library/std/src/collections/hash/set.rs

@@ -912,6 +912,7 @@ where
     /// Retains only the elements specified by the predicate.
     ///
     /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
+    /// The elements are visited in unsorted (and unspecified) order.
     ///
     /// # Examples
     ///

library/std/src/io/buffered/bufwriter.rs

@@ -68,7 +68,7 @@ use crate::ptr;
 /// [`flush`]: BufWriter::flush
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct BufWriter<W: Write> {
-    inner: Option<W>,
+    inner: W,
     // The buffer. Avoid using this like a normal `Vec` in common code paths.
     // That is, don't use `buf.push`, `buf.extend_from_slice`, or any other
     // methods that require bounds checking or the like. This makes an enormous
@@ -112,7 +112,7 @@ impl<W: Write> BufWriter<W> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> {
-        BufWriter { inner: Some(inner), buf: Vec::with_capacity(capacity), panicked: false }
+        BufWriter { inner, buf: Vec::with_capacity(capacity), panicked: false }
     }
 
     /// Send data in our local buffer into the inner writer, looping as
@@ -161,10 +161,9 @@ impl<W: Write> BufWriter<W> {
         }
 
         let mut guard = BufGuard::new(&mut self.buf);
-        let inner = self.inner.as_mut().unwrap();
         while !guard.done() {
             self.panicked = true;
-            let r = inner.write(guard.remaining());
+            let r = self.inner.write(guard.remaining());
             self.panicked = false;
 
             match r {
@@ -212,7 +211,7 @@ impl<W: Write> BufWriter<W> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_ref(&self) -> &W {
-        self.inner.as_ref().unwrap()
+        &self.inner
     }
 
     /// Gets a mutable reference to the underlying writer.
@@ -232,7 +231,7 @@ impl<W: Write> BufWriter<W> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut(&mut self) -> &mut W {
-        self.inner.as_mut().unwrap()
+        &mut self.inner
     }
 
     /// Returns a reference to the internally buffered data.
@@ -308,7 +307,7 @@ impl<W: Write> BufWriter<W> {
     pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
         match self.flush_buf() {
             Err(e) => Err(IntoInnerError::new(self, e)),
-            Ok(()) => Ok(self.inner.take().unwrap()),
+            Ok(()) => Ok(self.into_raw_parts().0),
         }
     }
 
@@ -339,7 +338,12 @@ impl<W: Write> BufWriter<W> {
     pub fn into_raw_parts(mut self) -> (W, Result<Vec<u8>, WriterPanicked>) {
         let buf = mem::take(&mut self.buf);
         let buf = if !self.panicked { Ok(buf) } else { Err(WriterPanicked { buf }) };
-        (self.inner.take().unwrap(), buf)
+
+        // SAFETY: forget(self) prevents double dropping inner
+        let inner = unsafe { ptr::read(&mut self.inner) };
+        mem::forget(self);
+
+        (inner, buf)
     }
 
     // Ensure this function does not get inlined into `write`, so that it
@@ -643,7 +647,7 @@ where
 {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("BufWriter")
-            .field("writer", &self.inner.as_ref().unwrap())
+            .field("writer", &self.inner)
             .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity()))
             .finish()
     }
@@ -663,7 +667,7 @@ impl<W: Write + Seek> Seek for BufWriter<W> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write> Drop for BufWriter<W> {
     fn drop(&mut self) {
-        if self.inner.is_some() && !self.panicked {
+        if !self.panicked {
             // dtors should not panic, so we ignore a failed flush
             let _r = self.flush_buf();
         }

library/std/src/io/buffered/mod.rs

@@ -133,7 +133,6 @@ impl<W> IntoInnerError<W> {
     ///
     /// # Example
     /// ```
-    /// #![feature(io_into_inner_error_parts)]
     /// use std::io::{BufWriter, ErrorKind, Write};
     ///
     /// let mut not_enough_space = [0u8; 10];
@@ -143,7 +142,7 @@ impl<W> IntoInnerError<W> {
     /// let err = into_inner_err.into_error();
     /// assert_eq!(err.kind(), ErrorKind::WriteZero);
     /// ```
-    #[unstable(feature = "io_into_inner_error_parts", issue = "79704")]
+    #[stable(feature = "io_into_inner_error_parts", since = "1.55.0")]
     pub fn into_error(self) -> Error {
         self.1
     }
@@ -156,7 +155,6 @@ impl<W> IntoInnerError<W> {
     ///
     /// # Example
     /// ```
-    /// #![feature(io_into_inner_error_parts)]
     /// use std::io::{BufWriter, ErrorKind, Write};
     ///
     /// let mut not_enough_space = [0u8; 10];
@@ -167,7 +165,7 @@ impl<W> IntoInnerError<W> {
     /// assert_eq!(err.kind(), ErrorKind::WriteZero);
     /// assert_eq!(recovered_writer.buffer(), b"t be actually written");
     /// ```
-    #[unstable(feature = "io_into_inner_error_parts", issue = "79704")]
+    #[stable(feature = "io_into_inner_error_parts", since = "1.55.0")]
     pub fn into_parts(self) -> (Error, W) {
         (self.1, self.0)
     }

src/bootstrap/compile.rs

@@ -3,7 +3,7 @@
 //!
 //! This module contains some of the real meat in the rustbuild build system
 //! which is where Cargo is used to compile the standard library, libtest, and
-//! compiler. This module is also responsible for assembling the sysroot as it
+//! the compiler. This module is also responsible for assembling the sysroot as it
 //! goes along from the output of the previous stage.
 
 use std::borrow::Cow;

src/bootstrap/config.rs

@@ -13,6 +13,7 @@ use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
 use crate::cache::{Interned, INTERNER};
+use crate::channel::GitInfo;
 pub use crate::flags::Subcommand;
 use crate::flags::{Color, Flags};
 use crate::util::exe;
@@ -48,7 +49,7 @@ pub struct Config {
     /// Call Build::ninja() instead of this.
     pub ninja_in_file: bool,
     pub verbose: usize,
-    pub submodules: bool,
+    pub submodules: Option<bool>,
     pub fast_submodules: bool,
     pub compiler_docs: bool,
     pub docs_minification: bool,
@@ -552,7 +553,7 @@ impl Config {
         config.backtrace = true;
         config.rust_optimize = true;
         config.rust_optimize_tests = true;
-        config.submodules = true;
+        config.submodules = None;
         config.fast_submodules = true;
         config.docs = true;
         config.docs_minification = true;
@@ -658,11 +659,11 @@ impl Config {
         config.npm = build.npm.map(PathBuf::from);
         config.gdb = build.gdb.map(PathBuf::from);
         config.python = build.python.map(PathBuf::from);
+        config.submodules = build.submodules;
         set(&mut config.low_priority, build.low_priority);
         set(&mut config.compiler_docs, build.compiler_docs);
         set(&mut config.docs_minification, build.docs_minification);
         set(&mut config.docs, build.docs);
-        set(&mut config.submodules, build.submodules);
         set(&mut config.fast_submodules, build.fast_submodules);
         set(&mut config.locked_deps, build.locked_deps);
         set(&mut config.vendor, build.vendor);
@@ -792,8 +793,16 @@ impl Config {
 
                 // CI-built LLVM can be either dynamic or static.
                 let ci_llvm = config.out.join(&*config.build.triple).join("ci-llvm");
-                let link_type = t!(std::fs::read_to_string(ci_llvm.join("link-type.txt")));
-                config.llvm_link_shared = link_type == "dynamic";
+                config.llvm_link_shared = if config.dry_run {
+                    // just assume dynamic for now
+                    true
+                } else {
+                    let link_type = t!(
+                        std::fs::read_to_string(ci_llvm.join("link-type.txt")),
+                        format!("CI llvm missing: {}", ci_llvm.display())
+                    );
+                    link_type == "dynamic"
+                };
             }
 
             if config.llvm_thin_lto {
@@ -1075,6 +1084,10 @@ impl Config {
     pub fn llvm_enabled(&self) -> bool {
         self.rust_codegen_backends.contains(&INTERNER.intern_str("llvm"))
     }
+
+    pub fn submodules(&self, rust_info: &GitInfo) -> bool {
+        self.submodules.unwrap_or(rust_info.is_git())
+    }
 }
 
 fn set<T>(field: &mut T, val: Option<T>) {

src/bootstrap/configure.py

@@ -160,6 +160,7 @@ o("full-bootstrap", "build.full-bootstrap", "build three compilers instead of tw
 o("extended", "build.extended", "build an extended rust tool set")
 
 v("tools", None, "List of extended tools will be installed")
+v("codegen-backends", None, "List of codegen backends to build")
 v("build", "build.build", "GNUs ./configure syntax LLVM build triple")
 v("host", None, "GNUs ./configure syntax LLVM host triples")
 v("target", None, "GNUs ./configure syntax LLVM target triples")
@@ -339,6 +340,8 @@ for key in known_args:
         set('target.{}.llvm-filecheck'.format(build()), value)
     elif option.name == 'tools':
         set('build.tools', value.split(','))
+    elif option.name == 'codegen-backends':
+        set('rust.codegen-backends', value.split(','))
     elif option.name == 'host':
         set('build.host', value.split(','))
     elif option.name == 'target':

src/bootstrap/dist.rs

@@ -1955,8 +1955,16 @@ fn maybe_install_llvm(builder: &Builder<'_>, target: TargetSelection, dst_libdir
         cmd.arg("--libfiles");
         builder.verbose(&format!("running {:?}", cmd));
         let files = output(&mut cmd);
+        let build_llvm_out = &builder.llvm_out(builder.config.build);
+        let target_llvm_out = &builder.llvm_out(target);
         for file in files.trim_end().split(' ') {
-            builder.install(Path::new(file), dst_libdir, 0o644);
+            // If we're not using a custom LLVM, make sure we package for the target.
+            let file = if let Ok(relative_path) = Path::new(file).strip_prefix(build_llvm_out) {
+                target_llvm_out.join(relative_path)
+            } else {
+                PathBuf::from(file)
+            };
+            builder.install(&file, dst_libdir, 0o644);
         }
         !builder.config.dry_run
     } else {

src/bootstrap/job.rs

@@ -103,12 +103,20 @@ pub unsafe fn setup(build: &mut Build) {
     };
 
     let parent = OpenProcess(PROCESS_DUP_HANDLE, FALSE, pid.parse().unwrap());
-    assert!(
-        !parent.is_null(),
-        "PID `{}` doesn't seem to exist: {}",
-        pid,
-        io::Error::last_os_error()
-    );
+
+    // If we get a null parent pointer here, it is possible that either
+    // we have got an invalid pid or the parent process has been closed.
+    // Since the first case rarely happens
+    // (only when wrongly setting the environmental variable),
+    // so it might be better to improve the experience of the second case
+    // when users have interrupted the parent process and we don't finish
+    // duplicating the handle yet.
+    // We just need close the job object if that occurs.
+    if parent.is_null() {
+        CloseHandle(job);
+        return;
+    }
+
     let mut parent_handle = ptr::null_mut();
     let r = DuplicateHandle(
         GetCurrentProcess(),

src/bootstrap/lib.rs

@@ -486,7 +486,7 @@ impl Build {
             t!(std::fs::read_dir(dir)).next().is_none()
         }
 
-        if !self.config.submodules {
+        if !self.config.submodules(&self.rust_info) {
             return;
         }
 
@@ -562,7 +562,7 @@ impl Build {
             "library/stdarch",
         ];
         // Avoid running git when there isn't a git checkout.
-        if !self.config.submodules {
+        if !self.config.submodules(&self.rust_info) {
             return;
         }
         let output = output(

src/test/rustdoc-gui/module-items-font.goml

@@ -0,0 +1,4 @@
+// This test checks that the correct font is used on module items (in index.html pages).
+goto: file://|DOC_PATH|/test_docs/index.html
+assert-css: (".item-table .module-item a", {"font-family": '"Fira Sans", Arial, sans-serif'}, ALL)
+assert-css: (".item-table .docblock-short", {"font-family": '"Source Serif 4", "Noto Sans KR", serif'}, ALL)

src/test/ui/async-await/issue-86507.rs

@@ -0,0 +1,25 @@
+// edition:2018
+
+use ::core::pin::Pin;
+use ::core::future::Future;
+use ::core::marker::Send;
+
+trait Foo {
+    fn bar<'me, 'async_trait, T: Send>(x: &'me T)
+        -> Pin<Box<dyn Future<Output = ()> + Send + 'async_trait>>
+        where 'me: 'async_trait;
+}
+
+impl Foo for () {
+    fn bar<'me, 'async_trait, T: Send>(x: &'me T)
+        -> Pin<Box<dyn Future<Output = ()> + Send + 'async_trait>>
+        where 'me:'async_trait {
+            Box::pin( //~ ERROR future cannot be sent between threads safely
+                async move {
+                    let x = x;
+                }
+            )
+         }
+}
+
+fn main() { }

src/test/ui/async-await/issue-86507.stderr

@@ -0,0 +1,23 @@
+error: future cannot be sent between threads safely
+  --> $DIR/issue-86507.rs:17:13
+   |
+LL | /             Box::pin(
+LL | |                 async move {
+LL | |                     let x = x;
+LL | |                 }
+LL | |             )
+   | |_____________^ future created by async block is not `Send`
+   |
+note: captured value is not `Send` because `&` references cannot be sent unless their referent is `Sync`
+  --> $DIR/issue-86507.rs:19:29
+   |
+LL |                     let x = x;
+   |                             ^ has type `&T` which is not `Send`, because `T` is not `Sync`
+   = note: required for the cast to the object type `dyn Future<Output = ()> + Send`
+help: consider further restricting type parameter `T`
+   |
+LL |         where 'me:'async_trait, T: std::marker::Sync {
+   |                               ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/const-generics/issues/issue-87076.rs

@@ -0,0 +1,20 @@
+// build-pass
+
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+#[derive(PartialEq, Eq)]
+pub struct UnitDims {
+    pub time: u8,
+    pub length: u8,
+}
+
+pub struct UnitValue<const DIMS: UnitDims>;
+
+impl<const DIMS: UnitDims> UnitValue<DIMS> {
+    fn crash() {}
+}
+
+fn main() {
+    UnitValue::<{ UnitDims { time: 1, length: 2 } }>::crash();
+}

src/tools/clippy/tests/ui/future_not_send.stderr

@@ -55,11 +55,11 @@ note: captured value is not `Send`
 LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
    |                          ^^ has type `std::rc::Rc<[u8]>` which is not `Send`
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Send`
-note: captured value is not `Send`
+note: captured value is not `Send` because `&` references cannot be sent unless their referent is `Sync`
   --> $DIR/future_not_send.rs:20:40
    |
 LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
-   |                                        ^^^^ has type `&std::cell::Cell<usize>` which is not `Send`
+   |                                        ^^^^ has type `&std::cell::Cell<usize>` which is not `Send`, because `std::cell::Cell<usize>` is not `Sync`
    = note: `std::cell::Cell<usize>` doesn't implement `std::marker::Sync`
 
 error: future cannot be sent between threads safely