Rustup

README.md

@@ -507,6 +507,8 @@ binaries, and as such worth documenting:
   crate currently being compiled.
 * `MIRI_ORIG_RUSTDOC` is set and read by different phases of `cargo-miri` to remember the
   value of `RUSTDOC` from before it was overwritten.
+* `MIRI_REPLACE_LIBRS_IF_NOT_TEST` when set to any value enables a hack that helps bootstrap
+  run the standard library tests in Miri.
 * `MIRI_VERBOSE` when set to any value tells the various `cargo-miri` phases to
   perform verbose logging.
 * `MIRI_HOST_SYSROOT` is set by bootstrap to tell `cargo-miri` which sysroot to use for *host*

cargo-miri/src/phases.rs

@@ -3,7 +3,7 @@
 use std::env;
 use std::fs::{self, File};
 use std::io::BufReader;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::process::Command;
 
 use rustc_version::VersionMeta;
@@ -412,9 +412,25 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
     // Arguments are treated very differently depending on whether this crate is
     // for interpretation by Miri, or for use by a build script / proc macro.
     if target_crate {
-        // Forward arguments, but remove "link" from "--emit" to make this a check-only build.
+        // Forward arguments, but patched.
         let emit_flag = "--emit";
+        // This hack helps bootstrap run standard library tests in Miri. The issue is as follows:
+        // when running `cargo miri test` on libcore, cargo builds a local copy of core and makes it
+        // a dependency of the integration test crate. This copy duplicates all the lang items, so
+        // the build fails. (Regular testing avoids this because the sysroot is a literal copy of
+        // what `cargo build` produces, but since Miri builds its own sysroot this does not work for
+        // us.) So we need to make it so that the locally built libcore contains all the items from
+        // `core`, but does not re-define them -- we want to replace the entire crate but a
+        // re-export of the sysroot crate. We do this by swapping out the source file: if
+        // `MIRI_REPLACE_LIBRS_IF_NOT_TEST` is set and we are building a `lib.rs` file, and a
+        // `lib.miri.rs` file exists in the same folder, we build that instead. But crucially we
+        // only do that for the library, not the unit test crate (which would be runnable) or
+        // rustdoc (which would have a different `phase`).
+        let replace_librs = env::var_os("MIRI_REPLACE_LIBRS_IF_NOT_TEST").is_some()
+            && !runnable_crate
+            && phase == RustcPhase::Build;
         while let Some(arg) = args.next() {
+            // Patch `--emit`: remove "link" from "--emit" to make this a check-only build.
             if let Some(val) = arg.strip_prefix(emit_flag) {
                 // Patch this argument. First, extract its value.
                 let val =
@@ -429,13 +445,36 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
                     }
                 }
                 cmd.arg(format!("{emit_flag}={}", val.join(",")));
-            } else if arg == "--extern" {
-                // Patch `--extern` filenames, since Cargo sometimes passes stub `.rlib` files:
-                // https://github.com/rust-lang/miri/issues/1705
+                continue;
+            }
+            // Patch `--extern` filenames, since Cargo sometimes passes stub `.rlib` files:
+            // https://github.com/rust-lang/miri/issues/1705
+            if arg == "--extern" {
                 forward_patched_extern_arg(&mut args, &mut cmd);
-            } else {
-                cmd.arg(arg);
+                continue;
             }
+            // If the REPLACE_LIBRS hack is enabled and we are building a `lib.rs` file, and a
+            // `lib.miri.rs` file exists, then build that instead. We only consider relative paths
+            // as cargo uses those for files in the workspace; dependencies from crates.io get
+            // absolute paths.
+            if replace_librs {
+                let path = Path::new(&arg);
+                if path.is_relative()
+                    && path.file_name().is_some_and(|f| f == "lib.rs")
+                    && path.is_file()
+                {
+                    let miri_rs = Path::new(&arg).with_extension("miri.rs");
+                    if miri_rs.is_file() {
+                        if verbose > 0 {
+                            eprintln!("Performing REPLACE_LIBRS hack: {arg:?} -> {miri_rs:?}");
+                        }
+                        cmd.arg(miri_rs);
+                        continue;
+                    }
+                }
+            }
+            // Fallback: just propagate the argument.
+            cmd.arg(arg);
         }
 
         // During setup, patch the panic runtime for `libpanic_abort` (mirroring what bootstrap usually does).

rust-version

@@ -1 +1 @@
-0accf4ec4c07d23aa86f6a97aeb8797941abc30e
+23d47dba319331d4418827cfbb8c1af283497d3c

src/helpers.rs

@@ -105,24 +105,41 @@ fn try_resolve_did(tcx: TyCtxt<'_>, path: &[&str], namespace: Option<Namespace>)
         (path, None)
     };
 
-    // First find the crate.
-    let krate =
-        tcx.crates(()).iter().find(|&&krate| tcx.crate_name(krate).as_str() == crate_name)?;
-    let mut cur_item = DefId { krate: *krate, index: CRATE_DEF_INDEX };
-    // Then go over the modules.
-    for &segment in modules {
-        cur_item = find_children(tcx, cur_item, segment)
-            .find(|item| tcx.def_kind(item) == DefKind::Mod)?;
-    }
-    // Finally, look up the desired item in this module, if any.
-    match item {
-        Some((item_name, namespace)) =>
-            Some(
-                find_children(tcx, cur_item, item_name)
-                    .find(|item| tcx.def_kind(item).ns() == Some(namespace))?,
-            ),
-        None => Some(cur_item),
+    // There may be more than one crate with this name. We try them all.
+    // (This is particularly relevant when running `std` tests as then there are two `std` crates:
+    // the one in the sysroot and the one locally built by `cargo test`.)
+    // FIXME: can we prefer the one from the sysroot?
+    'crates: for krate in
+        tcx.crates(()).iter().filter(|&&krate| tcx.crate_name(krate).as_str() == crate_name)
+    {
+        let mut cur_item = DefId { krate: *krate, index: CRATE_DEF_INDEX };
+        // Go over the modules.
+        for &segment in modules {
+            let Some(next_item) = find_children(tcx, cur_item, segment)
+                .find(|item| tcx.def_kind(item) == DefKind::Mod)
+            else {
+                continue 'crates;
+            };
+            cur_item = next_item;
+        }
+        // Finally, look up the desired item in this module, if any.
+        match item {
+            Some((item_name, namespace)) => {
+                let Some(item) = find_children(tcx, cur_item, item_name)
+                    .find(|item| tcx.def_kind(item).ns() == Some(namespace))
+                else {
+                    continue 'crates;
+                };
+                return Some(item);
+            }
+            None => {
+                // Just return the module.
+                return Some(cur_item);
+            }
+        }
     }
+    // Item not found in any of the crates with the right name.
+    None
 }
 
 /// Convert a softfloat type to its corresponding hostfloat type.
@@ -968,10 +985,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
     fn frame_in_std(&self) -> bool {
         let this = self.eval_context_ref();
-        let Some(start_fn) = this.tcx.lang_items().start_fn() else {
-            // no_std situations
-            return false;
-        };
         let frame = this.frame();
         // Make an attempt to get at the instance of the function this is inlined from.
         let instance: Option<_> = try {
@@ -982,13 +995,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         };
         // Fall back to the instance of the function itself.
         let instance = instance.unwrap_or(frame.instance);
-        // Now check if this is in the same crate as start_fn.
-        // As a special exception we also allow unit tests from
-        // <https://github.com/rust-lang/miri-test-libstd/tree/master/std_miri_test> to call these
-        // shims.
+        // Now check the crate it is in. We could try to be clever here and e.g. check if this is
+        // the same crate as `start_fn`, but that would not work for running std tests in Miri, so
+        // we'd need some more hacks anyway. So we just check the name of the crate. If someone
+        // calls their crate `std` then we'll just let them keep the pieces.
         let frame_crate = this.tcx.def_path(instance.def_id()).krate;
-        frame_crate == this.tcx.def_path(start_fn).krate
-            || this.tcx.crate_name(frame_crate).as_str() == "std_miri_test"
+        let crate_name = this.tcx.crate_name(frame_crate);
+        let crate_name = crate_name.as_str();
+        // On miri-test-libstd, the name of the crate is different.
+        crate_name == "std" || crate_name == "std_miri_test"
     }
 
     /// Handler that should be called when unsupported functionality is encountered.

tests/pass/async-closure-captures.rs

@@ -88,4 +88,38 @@ async fn async_main() {
         };
         call_once(c).await;
     }
+
+    fn force_fnonce<T>(f: impl async FnOnce() -> T) -> impl async FnOnce() -> T {
+        f
+    }
+
+    // Capture something with `move`, but infer to `AsyncFnOnce`
+    {
+        let x = Hello(6);
+        let c = force_fnonce(async move || {
+            println!("{x:?}");
+        });
+        call_once(c).await;
+
+        let x = &Hello(7);
+        let c = force_fnonce(async move || {
+            println!("{x:?}");
+        });
+        call_once(c).await;
+    }
+
+    // Capture something by-ref, but infer to `AsyncFnOnce`
+    {
+        let x = Hello(8);
+        let c = force_fnonce(async || {
+            println!("{x:?}");
+        });
+        call_once(c).await;
+
+        let x = &Hello(9);
+        let c = force_fnonce(async || {
+            println!("{x:?}");
+        });
+        call_once(c).await;
+    }
 }

tests/pass/async-closure-captures.stdout

@@ -8,3 +8,7 @@ Hello(3)
 Hello(4)
 Hello(4)
 Hello(5)
+Hello(6)
+Hello(7)
+Hello(8)
+Hello(9)