Auto merge of #112877 - Nilstrieb:rollup-5g5hegl, r=Nilstrieb

Rollup of 6 pull requests

Successful merges:

 - #112632 (Implement PartialOrd for `Vec`s over different allocators)
 - #112759 (Make closure_saved_names_of_captured_variables a query. )
 - #112772 (Add a fully fledged `Clause` type, rename old `Clause` to `ClauseKind`)
 - #112790 (Syntactically accept `become` expressions (explicit tail calls experiment))
 - #112830 (More codegen cleanups)
 - #112844 (Add retag in MIR transform: `Adt` for `Unique` may contain a reference)

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

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -1295,6 +1295,7 @@ impl Expr {
             ExprKind::Yield(..) => ExprPrecedence::Yield,
             ExprKind::Yeet(..) => ExprPrecedence::Yeet,
             ExprKind::FormatArgs(..) => ExprPrecedence::FormatArgs,
+            ExprKind::Become(..) => ExprPrecedence::Become,
             ExprKind::Err => ExprPrecedence::Err,
         }
     }
@@ -1515,6 +1516,11 @@ pub enum ExprKind {
     /// with an optional value to be returned.
     Yeet(Option<P<Expr>>),
 
+    /// A tail call return, with the value to be returned.
+    ///
+    /// While `.0` must be a function call, we check this later, after parsing.
+    Become(P<Expr>),
+
     /// Bytes included via `include_bytes!`
     /// Added for optimization purposes to avoid the need to escape
     /// large binary blobs - should always behave like [`ExprKind::Lit`]

compiler/rustc_ast/src/mut_visit.rs

@@ -1457,6 +1457,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
         ExprKind::Yeet(expr) => {
             visit_opt(expr, |expr| vis.visit_expr(expr));
         }
+        ExprKind::Become(expr) => vis.visit_expr(expr),
         ExprKind::InlineAsm(asm) => vis.visit_inline_asm(asm),
         ExprKind::FormatArgs(fmt) => vis.visit_format_args(fmt),
         ExprKind::OffsetOf(container, fields) => {

compiler/rustc_ast/src/util/parser.rs

@@ -245,6 +245,7 @@ pub enum ExprPrecedence {
     Ret,
     Yield,
     Yeet,
+    Become,
 
     Range,
 
@@ -298,7 +299,8 @@ impl ExprPrecedence {
             | ExprPrecedence::Continue
             | ExprPrecedence::Ret
             | ExprPrecedence::Yield
-            | ExprPrecedence::Yeet => PREC_JUMP,
+            | ExprPrecedence::Yeet
+            | ExprPrecedence::Become => PREC_JUMP,
 
             // `Range` claims to have higher precedence than `Assign`, but `x .. x = x` fails to
             // parse, instead of parsing as `(x .. x) = x`. Giving `Range` a lower precedence

compiler/rustc_ast/src/visit.rs

@@ -908,6 +908,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::Yeet(optional_expression) => {
             walk_list!(visitor, visit_expr, optional_expression);
         }
+        ExprKind::Become(expr) => visitor.visit_expr(expr),
         ExprKind::MacCall(mac) => visitor.visit_mac_call(mac),
         ExprKind::Paren(subexpression) => visitor.visit_expr(subexpression),
         ExprKind::InlineAsm(asm) => visitor.visit_inline_asm(asm),

compiler/rustc_ast_lowering/src/expr.rs

@@ -275,6 +275,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     hir::ExprKind::Ret(e)
                 }
                 ExprKind::Yeet(sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
+                ExprKind::Become(sub_expr) => {
+                    let sub_expr = self.lower_expr(sub_expr);
+
+                    // FIXME(explicit_tail_calls): Use `hir::ExprKind::Become` once we implemented it
+                    hir::ExprKind::Ret(Some(sub_expr))
+                }
                 ExprKind::InlineAsm(asm) => {
                     hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
                 }

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -555,6 +555,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(dyn_star, "`dyn*` trait objects are experimental");
     gate_all!(const_closures, "const closures are experimental");
     gate_all!(builtin_syntax, "`builtin #` syntax is unstable");
+    gate_all!(explicit_tail_calls, "`become` expression is experimental");
 
     if !visitor.features.negative_bounds {
         for &span in spans.get(&sym::negative_bounds).iter().copied().flatten() {

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -537,6 +537,11 @@ impl<'a> State<'a> {
                     self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
                 }
             }
+            ast::ExprKind::Become(result) => {
+                self.word("become");
+                self.word(" ");
+                self.print_expr_maybe_paren(result, parser::PREC_JUMP);
+            }
             ast::ExprKind::InlineAsm(a) => {
                 // FIXME: This should have its own syntax, distinct from a macro invocation.
                 self.word("asm!");

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -679,7 +679,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
         // Find out if the predicates show that the type is a Fn or FnMut
         let find_fn_kind_from_did = |(pred, _): (ty::Predicate<'tcx>, _)| {
-            if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = pred.kind().skip_binder()
+            if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) = pred.kind().skip_binder()
                 && pred.self_ty() == ty
             {
                 if Some(pred.def_id()) == tcx.lang_items().fn_trait() {
@@ -776,7 +776,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let predicates: Result<Vec<_>, _> = errors
             .into_iter()
             .map(|err| match err.obligation.predicate.kind().skip_binder() {
-                PredicateKind::Clause(ty::Clause::Trait(predicate)) => {
+                PredicateKind::Clause(ty::ClauseKind::Trait(predicate)) => {
                     match predicate.self_ty().kind() {
                         ty::Param(param_ty) => Ok((
                             generics.type_param(param_ty, tcx),

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -939,8 +939,8 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
             {
                 predicates.iter().any(|pred| {
                     match pred.kind().skip_binder() {
-                        ty::PredicateKind::Clause(ty::Clause::Trait(data)) if data.self_ty() == ty => {}
-                        ty::PredicateKind::Clause(ty::Clause::Projection(data)) if data.projection_ty.self_ty() == ty => {}
+                        ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) if data.self_ty() == ty => {}
+                        ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) if data.projection_ty.self_ty() == ty => {}
                         _ => return false,
                     }
                     tcx.any_free_region_meets(pred, |r| {

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -330,8 +330,9 @@ fn check_opaque_type_well_formed<'tcx>(
     // Require the hidden type to be well-formed with only the generics of the opaque type.
     // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
     // hidden type is well formed even without those bounds.
-    let predicate =
-        ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::WellFormed(definition_ty.into())));
+    let predicate = ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(
+        definition_ty.into(),
+    )));
     ocx.register_obligation(Obligation::misc(tcx, definition_span, def_id, param_env, predicate));
 
     // Check that all obligations are satisfied by the implementation's