Rollup of 9 pull requests

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -38,6 +38,13 @@ enum SelfSemantic {
     No,
 }
 
+/// What is the context that prevents using `~const`?
+enum DisallowTildeConstContext<'a> {
+    TraitObject,
+    ImplTrait,
+    Fn(FnKind<'a>),
+}
+
 struct AstValidator<'a> {
     session: &'a Session,
 
@@ -56,7 +63,7 @@ struct AstValidator<'a> {
     /// e.g., `impl Iterator<Item = impl Debug>`.
     outer_impl_trait: Option<Span>,
 
-    is_tilde_const_allowed: bool,
+    disallow_tilde_const: Option<DisallowTildeConstContext<'a>>,
 
     /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
     /// or `Foo::Bar<impl Trait>`
@@ -93,18 +100,26 @@ impl<'a> AstValidator<'a> {
         self.is_impl_trait_banned = old;
     }
 
-    fn with_tilde_const(&mut self, allowed: bool, f: impl FnOnce(&mut Self)) {
-        let old = mem::replace(&mut self.is_tilde_const_allowed, allowed);
+    fn with_tilde_const(
+        &mut self,
+        disallowed: Option<DisallowTildeConstContext<'a>>,
+        f: impl FnOnce(&mut Self),
+    ) {
+        let old = mem::replace(&mut self.disallow_tilde_const, disallowed);
         f(self);
-        self.is_tilde_const_allowed = old;
+        self.disallow_tilde_const = old;
     }
 
     fn with_tilde_const_allowed(&mut self, f: impl FnOnce(&mut Self)) {
-        self.with_tilde_const(true, f)
+        self.with_tilde_const(None, f)
     }
 
-    fn with_banned_tilde_const(&mut self, f: impl FnOnce(&mut Self)) {
-        self.with_tilde_const(false, f)
+    fn with_banned_tilde_const(
+        &mut self,
+        ctx: DisallowTildeConstContext<'a>,
+        f: impl FnOnce(&mut Self),
+    ) {
+        self.with_tilde_const(Some(ctx), f)
     }
 
     fn with_let_management(
@@ -172,7 +187,7 @@ impl<'a> AstValidator<'a> {
     fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
         let old = mem::replace(&mut self.outer_impl_trait, outer);
         if outer.is_some() {
-            self.with_banned_tilde_const(f);
+            self.with_banned_tilde_const(DisallowTildeConstContext::ImplTrait, f);
         } else {
             f(self);
         }
@@ -197,7 +212,10 @@ impl<'a> AstValidator<'a> {
             TyKind::ImplTrait(..) => {
                 self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
             }
-            TyKind::TraitObject(..) => self.with_banned_tilde_const(|this| visit::walk_ty(this, t)),
+            TyKind::TraitObject(..) => self
+                .with_banned_tilde_const(DisallowTildeConstContext::TraitObject, |this| {
+                    visit::walk_ty(this, t)
+                }),
             TyKind::Path(ref qself, ref path) => {
                 // We allow these:
                 //  - `Option<impl Trait>`
@@ -1411,13 +1429,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     );
                     err.emit();
                 }
-                (_, TraitBoundModifier::MaybeConst) => {
-                    if !self.is_tilde_const_allowed {
-                        self.err_handler()
-                            .struct_span_err(bound.span(), "`~const` is not allowed here")
-                            .note("only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions")
-                            .emit();
-                    }
+                (_, TraitBoundModifier::MaybeConst) if let Some(reason) = &self.disallow_tilde_const => {
+                    let mut err = self.err_handler().struct_span_err(bound.span(), "`~const` is not allowed here");
+                    match reason {
+                        DisallowTildeConstContext::TraitObject => err.note("trait objects cannot have `~const` trait bounds"),
+                        DisallowTildeConstContext::ImplTrait => err.note("`impl Trait`s cannot have `~const` trait bounds"),
+                        DisallowTildeConstContext::Fn(FnKind::Closure(..)) => err.note("closures cannot have `~const` trait bounds"),
+                        DisallowTildeConstContext::Fn(FnKind::Fn(_, ident, ..)) => err.span_note(ident.span, "this function is not `const`, so it cannot have `~const` trait bounds"),
+                    };
+                    err.emit();
                 }
                 (_, TraitBoundModifier::MaybeConstMaybe) => {
                     self.err_handler()
@@ -1523,10 +1543,13 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             });
         }
 
-        let tilde_const_allowed = matches!(fk.header(), Some(FnHeader { .. }))
-            || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
+        let tilde_const_allowed =
+            matches!(fk.header(), Some(FnHeader { constness: ast::Const::Yes(_), .. }))
+                || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
+
+        let disallowed = (!tilde_const_allowed).then(|| DisallowTildeConstContext::Fn(fk));
 
-        self.with_tilde_const(tilde_const_allowed, |this| visit::walk_fn(this, fk));
+        self.with_tilde_const(disallowed, |this| visit::walk_fn(this, fk));
     }
 
     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
@@ -1770,7 +1793,7 @@ pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) ->
         in_const_trait_impl: false,
         has_proc_macro_decls: false,
         outer_impl_trait: None,
-        is_tilde_const_allowed: false,
+        disallow_tilde_const: None,
         is_impl_trait_banned: false,
         is_assoc_ty_bound_banned: false,
         forbidden_let_reason: Some(ForbiddenLetReason::GenericForbidden),

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -35,7 +35,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 assert_eq!(discr.layout.ty, switch_ty);
 
                 // Branch to the `otherwise` case by default, if no match is found.
-                assert!(!targets.iter().is_empty());
                 let mut target_block = targets.otherwise();
 
                 for (const_int, target) in targets.iter() {

compiler/rustc_driver/src/lib.rs

@@ -190,6 +190,7 @@ impl<'a, 'b> RunCompiler<'a, 'b> {
         run_compiler(self.at_args, self.callbacks, self.file_loader, self.make_codegen_backend)
     }
 }
+
 fn run_compiler(
     at_args: &[String],
     callbacks: &mut (dyn Callbacks + Send),

compiler/rustc_interface/src/interface.rs

@@ -25,7 +25,10 @@ use std::result;
 
 pub type Result<T> = result::Result<T, ErrorGuaranteed>;
 
-/// Represents a compiler session.
+/// Represents a compiler session. Note that every `Compiler` contains a
+/// `Session`, but `Compiler` also contains some things that cannot be in
+/// `Session`, due to `Session` being in a crate that has many fewer
+/// dependencies than this crate.
 ///
 /// Can be used to run `rustc_interface` queries.
 /// Created by passing [`Config`] to [`run_compiler`].

compiler/rustc_interface/src/util.rs

@@ -3,14 +3,8 @@ use libloading::Library;
 use rustc_ast as ast;
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-#[cfg(parallel_compiler)]
-use rustc_data_structures::jobserver;
 use rustc_errors::registry::Registry;
-#[cfg(parallel_compiler)]
-use rustc_middle::ty::tls;
 use rustc_parse::validate_attr;
-#[cfg(parallel_compiler)]
-use rustc_query_impl::{QueryContext, QueryCtxt};
 use rustc_session as session;
 use rustc_session::config::CheckCfg;
 use rustc_session::config::{self, CrateType};
@@ -25,8 +19,6 @@ use rustc_span::symbol::{sym, Symbol};
 use std::env;
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
 use std::mem;
-#[cfg(not(parallel_compiler))]
-use std::panic;
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::OnceLock;
@@ -135,13 +127,20 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
     _threads: usize,
     f: F,
 ) -> R {
-    // The thread pool is a single thread in the non-parallel compiler.
-    thread::scope(|s| {
-        let mut builder = thread::Builder::new().name("rustc".to_string());
-        if let Some(size) = get_stack_size() {
-            builder = builder.stack_size(size);
-        }
+    // The "thread pool" is a single spawned thread in the non-parallel
+    // compiler. We run on a spawned thread instead of the main thread (a) to
+    // provide control over the stack size, and (b) to increase similarity with
+    // the parallel compiler, in particular to ensure there is no accidental
+    // sharing of data between the main thread and the compilation thread
+    // (which might cause problems for the parallel compiler).
+    let mut builder = thread::Builder::new().name("rustc".to_string());
+    if let Some(size) = get_stack_size() {
+        builder = builder.stack_size(size);
+    }
 
+    // We build the session globals and run `f` on the spawned thread, because
+    // `SessionGlobals` does not impl `Send` in the non-parallel compiler.
+    thread::scope(|s| {
         // `unwrap` is ok here because `spawn_scoped` only panics if the thread
         // name contains null bytes.
         let r = builder
@@ -151,55 +150,57 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
 
         match r {
             Ok(v) => v,
-            Err(e) => panic::resume_unwind(e),
+            Err(e) => std::panic::resume_unwind(e),
         }
     })
 }
 
-/// Creates a new thread and forwards information in thread locals to it.
-/// The new thread runs the deadlock handler.
-/// Must only be called when a deadlock is about to happen.
-#[cfg(parallel_compiler)]
-unsafe fn handle_deadlock() {
-    let registry = rustc_rayon_core::Registry::current();
-
-    let query_map = tls::with(|tcx| {
-        QueryCtxt::from_tcx(tcx)
-            .try_collect_active_jobs()
-            .expect("active jobs shouldn't be locked in deadlock handler")
-    });
-    thread::spawn(move || rustc_query_impl::deadlock(query_map, &registry));
-}
-
 #[cfg(parallel_compiler)]
 pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
     edition: Edition,
     threads: usize,
     f: F,
 ) -> R {
-    let mut config = rayon::ThreadPoolBuilder::new()
+    use rustc_data_structures::jobserver;
+    use rustc_middle::ty::tls;
+    use rustc_query_impl::{deadlock, QueryContext, QueryCtxt};
+
+    let mut builder = rayon::ThreadPoolBuilder::new()
         .thread_name(|_| "rustc".to_string())
         .acquire_thread_handler(jobserver::acquire_thread)
         .release_thread_handler(jobserver::release_thread)
         .num_threads(threads)
-        .deadlock_handler(|| unsafe { handle_deadlock() });
-
+        .deadlock_handler(|| {
+            // On deadlock, creates a new thread and forwards information in thread
+            // locals to it. The new thread runs the deadlock handler.
+            let query_map = tls::with(|tcx| {
+                QueryCtxt::from_tcx(tcx)
+                    .try_collect_active_jobs()
+                    .expect("active jobs shouldn't be locked in deadlock handler")
+            });
+            let registry = rustc_rayon_core::Registry::current();
+            thread::spawn(move || deadlock(query_map, &registry));
+        });
     if let Some(size) = get_stack_size() {
-        config = config.stack_size(size);
+        builder = builder.stack_size(size);
     }
 
-    let with_pool = move |pool: &rayon::ThreadPool| pool.install(f);
-
+    // We create the session globals on the main thread, then create the thread
+    // pool. Upon creation, each worker thread created gets a copy of the
+    // session globals in TLS. This is possible because `SessionGlobals` impls
+    // `Send` in the parallel compiler.
     rustc_span::create_session_globals_then(edition, || {
         rustc_span::with_session_globals(|session_globals| {
-            // The main handler runs for each Rayon worker thread and sets up
-            // the thread local rustc uses. `session_globals` is captured and set
-            // on the new threads.
-            let main_handler = move |thread: rayon::ThreadBuilder| {
-                rustc_span::set_session_globals_then(session_globals, || thread.run())
-            };
-
-            config.build_scoped(main_handler, with_pool).unwrap()
+            builder
+                .build_scoped(
+                    // Initialize each new worker thread when created.
+                    move |thread: rayon::ThreadBuilder| {
+                        rustc_span::set_session_globals_then(session_globals, || thread.run())
+                    },
+                    // Run `f` on the first thread in the thread pool.
+                    move |pool: &rayon::ThreadPool| pool.install(f),
+                )
+                .unwrap()
         })
     })
 }

compiler/rustc_resolve/src/late.rs

@@ -1939,11 +1939,11 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 match ty.kind {
                     TyKind::ImplicitSelf => true,
                     TyKind::Path(None, _) => {
-                        let path_res = self.r.partial_res_map[&ty.id].expect_full_res();
-                        if let Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } = path_res {
+                        let path_res = self.r.partial_res_map[&ty.id].full_res();
+                        if let Some(Res::SelfTyParam { .. } | Res::SelfTyAlias { .. }) = path_res {
                             return true;
                         }
-                        Some(path_res) == self.impl_self
+                        self.impl_self.is_some() && path_res == self.impl_self
                     }
                     _ => false,
                 }

library/core/src/intrinsics.rs

@@ -994,14 +994,14 @@ extern "rust-intrinsic" {
     /// `transmute` is semantically equivalent to a bitwise move of one type
     /// into another. It copies the bits from the source value into the
     /// destination value, then forgets the original. Note that source and destination
-    /// are passed by-value, which means if `T` or `U` contain padding, that padding
+    /// are passed by-value, which means if `Src` or `Dst` contain padding, that padding
     /// is *not* guaranteed to be preserved by `transmute`.
     ///
     /// Both the argument and the result must be [valid](../../nomicon/what-unsafe-does.html) at
     /// their given type. Violating this condition leads to [undefined behavior][ub]. The compiler
     /// will generate code *assuming that you, the programmer, ensure that there will never be
     /// undefined behavior*. It is therefore your responsibility to guarantee that every value
-    /// passed to `transmute` is valid at both types `T` and `U`. Failing to uphold this condition
+    /// passed to `transmute` is valid at both types `Src` and `Dst`. Failing to uphold this condition
     /// may lead to unexpected and unstable compilation results. This makes `transmute` **incredibly
     /// unsafe**. `transmute` should be the absolute last resort.
     ///
@@ -1012,7 +1012,7 @@ extern "rust-intrinsic" {
     ///
     /// Because `transmute` is a by-value operation, alignment of the *transmuted values
     /// themselves* is not a concern. As with any other function, the compiler already ensures
-    /// both `T` and `U` are properly aligned. However, when transmuting values that *point
+    /// both `Src` and `Dst` are properly aligned. However, when transmuting values that *point
     /// elsewhere* (such as pointers, references, boxes…), the caller has to ensure proper
     /// alignment of the pointed-to values.
     ///
@@ -1248,7 +1248,7 @@ extern "rust-intrinsic" {
     #[rustc_allowed_through_unstable_modules]
     #[rustc_const_stable(feature = "const_transmute", since = "1.56.0")]
     #[rustc_diagnostic_item = "transmute"]
-    pub fn transmute<T, U>(e: T) -> U;
+    pub fn transmute<Src, Dst>(src: Src) -> Dst;
 
     /// Returns `true` if the actual type given as `T` requires drop
     /// glue; returns `false` if the actual type provided for `T`