Implement .use keyword as an alias of clone

compiler/rustc_ast/src/ast.rs

@@ -1399,6 +1399,7 @@ impl Expr {
             // Never need parens
             ExprKind::Array(_)
             | ExprKind::Await(..)
+            | ExprKind::Use(..)
             | ExprKind::Block(..)
             | ExprKind::Call(..)
             | ExprKind::ConstBlock(_)
@@ -1588,6 +1589,8 @@ pub enum ExprKind {
     Gen(CaptureBy, P<Block>, GenBlockKind, Span),
     /// An await expression (`my_future.await`). Span is of await keyword.
     Await(P<Expr>, Span),
+    /// A use expression (`x.use`). Span is of use keyword.
+    Use(P<Expr>, Span),
 
     /// A try block (`try { ... }`).
     TryBlock(P<Block>),

compiler/rustc_ast/src/mut_visit.rs

@@ -1745,6 +1745,10 @@ pub fn walk_expr<T: MutVisitor>(vis: &mut T, Expr { kind, id, span, attrs, token
             vis.visit_expr(expr);
             vis.visit_span(await_kw_span);
         }
+        ExprKind::Use(expr, use_kw_span) => {
+            vis.visit_expr(expr);
+            vis.visit_span(use_kw_span);
+        }
         ExprKind::Assign(el, er, span) => {
             vis.visit_expr(el);
             vis.visit_expr(er);

compiler/rustc_ast/src/util/classify.rs

@@ -108,6 +108,7 @@ pub fn leading_labeled_expr(mut expr: &ast::Expr) -> bool {
             Assign(e, _, _)
             | AssignOp(_, e, _)
             | Await(e, _)
+            | Use(e, _)
             | Binary(_, e, _)
             | Call(e, _)
             | Cast(e, _)
@@ -224,6 +225,7 @@ pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<TrailingBrace<'_>> {
             | Lit(_)
             | Type(_, _)
             | Await(_, _)
+            | Use(_, _)
             | Field(_, _)
             | Index(_, _, _)
             | Underscore

compiler/rustc_ast/src/visit.rs

@@ -1211,6 +1211,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) -> V
         }
         ExprKind::Gen(_capt, body, _kind, _decl_span) => try_visit!(visitor.visit_block(body)),
         ExprKind::Await(expr, _span) => try_visit!(visitor.visit_expr(expr)),
+        ExprKind::Use(expr, _span) => try_visit!(visitor.visit_expr(expr)),
         ExprKind::Assign(lhs, rhs, _span) => {
             try_visit!(visitor.visit_expr(lhs));
             try_visit!(visitor.visit_expr(rhs));

compiler/rustc_ast_lowering/src/expr.rs

@@ -207,6 +207,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     },
                 ),
                 ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
+                ExprKind::Use(expr, use_kw_span) => self.lower_expr_use(*use_kw_span, expr),
                 ExprKind::Closure(box Closure {
                     binder,
                     capture_clause,
@@ -1067,6 +1068,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         )
     }
 
+    fn lower_expr_use(&mut self, use_kw_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
+        hir::ExprKind::Use(self.lower_expr(expr), use_kw_span)
+    }
+
     fn lower_expr_closure(
         &mut self,
         binder: &ClosureBinder,

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

@@ -574,6 +574,14 @@ impl<'a> State<'a> {
                 );
                 self.word(".await");
             }
+            ast::ExprKind::Use(expr, _) => {
+                self.print_expr_cond_paren(
+                    expr,
+                    expr.precedence() < ExprPrecedence::Unambiguous,
+                    fixup,
+                );
+                self.word(".use");
+            }
             ast::ExprKind::Assign(lhs, rhs, _) => {
                 self.print_expr_cond_paren(
                     lhs,

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -297,6 +297,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::AssignOp(_, _, _)
             | ExprKind::Gen(_, _, _, _)
             | ExprKind::Await(_, _)
+            | ExprKind::Use(_, _)
             | ExprKind::Block(_, _)
             | ExprKind::Break(_, _)
             | ExprKind::Closure(_)

compiler/rustc_hir/src/hir.rs

@@ -2166,6 +2166,7 @@ impl Expr<'_> {
             | ExprKind::Tup(_)
             | ExprKind::Type(..)
             | ExprKind::UnsafeBinderCast(..)
+            | ExprKind::Use(..)
             | ExprKind::Err(_) => ExprPrecedence::Unambiguous,
 
             ExprKind::DropTemps(expr, ..) => expr.precedence(),
@@ -2212,6 +2213,7 @@ impl Expr<'_> {
             ExprKind::Path(QPath::TypeRelative(..))
             | ExprKind::Call(..)
             | ExprKind::MethodCall(..)
+            | ExprKind::Use(..)
             | ExprKind::Struct(..)
             | ExprKind::Tup(..)
             | ExprKind::If(..)
@@ -2285,7 +2287,9 @@ impl Expr<'_> {
 
     pub fn can_have_side_effects(&self) -> bool {
         match self.peel_drop_temps().kind {
-            ExprKind::Path(_) | ExprKind::Lit(_) | ExprKind::OffsetOf(..) => false,
+            ExprKind::Path(_) | ExprKind::Lit(_) | ExprKind::OffsetOf(..) | ExprKind::Use(..) => {
+                false
+            }
             ExprKind::Type(base, _)
             | ExprKind::Unary(_, base)
             | ExprKind::Field(base, _)
@@ -2547,6 +2551,8 @@ pub enum ExprKind<'hir> {
     ///
     /// [`type_dependent_def_id`]: ../../rustc_middle/ty/struct.TypeckResults.html#method.type_dependent_def_id
     MethodCall(&'hir PathSegment<'hir>, &'hir Expr<'hir>, &'hir [Expr<'hir>], Span),
+    /// An use expression (e.g., `var.use`).
+    Use(&'hir Expr<'hir>, Span),
     /// A tuple (e.g., `(a, b, c, d)`).
     Tup(&'hir [Expr<'hir>]),
     /// A binary operation (e.g., `a + b`, `a * b`).

compiler/rustc_hir/src/intravisit.rs

@@ -821,6 +821,9 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
             try_visit!(visitor.visit_expr(receiver));
             walk_list!(visitor, visit_expr, arguments);
         }
+        ExprKind::Use(expr, _) => {
+            try_visit!(visitor.visit_expr(expr));
+        }
         ExprKind::Binary(_, ref left_expression, ref right_expression) => {
             try_visit!(visitor.visit_expr(left_expression));
             try_visit!(visitor.visit_expr(right_expression));

compiler/rustc_hir_pretty/src/lib.rs

@@ -1544,6 +1544,10 @@ impl<'a> State<'a> {
             hir::ExprKind::MethodCall(segment, receiver, args, _) => {
                 self.print_expr_method_call(segment, receiver, args);
             }
+            hir::ExprKind::Use(expr, _) => {
+                self.print_expr(expr);
+                self.word(".use");
+            }
             hir::ExprKind::Binary(op, lhs, rhs) => {
                 self.print_expr_binary(op, lhs, rhs);
             }

compiler/rustc_hir_typeck/src/expr.rs

@@ -362,6 +362,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // Any expression child of these expressions constitute reads.
                     ExprKind::Array(_)
                     | ExprKind::Call(_, _)
+                    | ExprKind::Use(_, _)
                     | ExprKind::MethodCall(_, _, _, _)
                     | ExprKind::Tup(_)
                     | ExprKind::Binary(_, _, _)
@@ -552,6 +553,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ExprKind::Closure(closure) => self.check_expr_closure(closure, expr.span, expected),
             ExprKind::Block(body, _) => self.check_expr_block(body, expected),
             ExprKind::Call(callee, args) => self.check_expr_call(expr, callee, args, expected),
+            ExprKind::Use(used_expr, _) => self.check_expr_use(used_expr, expected),
             ExprKind::MethodCall(segment, receiver, args, _) => {
                 self.check_expr_method_call(expr, segment, receiver, args, expected)
             }
@@ -1616,6 +1618,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         )
     }
 
+    /// Checks use `x.use`.
+    fn check_expr_use(
+        &self,
+        used_expr: &'tcx hir::Expr<'tcx>,
+        expected: Expectation<'tcx>,
+    ) -> Ty<'tcx> {
+        self.check_expr_with_expectation(used_expr, expected)
+    }
+
     fn check_expr_cast(
         &self,
         e: &'tcx hir::Expr<'tcx>,

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -366,6 +366,10 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 self.consume_exprs(args)?;
             }
 
+            hir::ExprKind::Use(expr, _) => {
+                self.consume_expr(expr)?;
+            }
+
             hir::ExprKind::MethodCall(.., receiver, args, _) => {
                 // callee.m(args)
                 self.consume_expr(receiver)?;
@@ -1386,6 +1390,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
 
             hir::ExprKind::AddrOf(..)
             | hir::ExprKind::Call(..)
+            | hir::ExprKind::Use(..)
             | hir::ExprKind::Assign(..)
             | hir::ExprKind::AssignOp(..)
             | hir::ExprKind::Closure { .. }

compiler/rustc_lint/src/dangling.rs

@@ -159,7 +159,10 @@ fn is_temporary_rvalue(expr: &Expr<'_>) -> bool {
         ExprKind::Path(..) => false,
 
         // Calls return rvalues.
-        ExprKind::Call(..) | ExprKind::MethodCall(..) | ExprKind::Binary(..) => true,
+        ExprKind::Call(..)
+        | ExprKind::MethodCall(..)
+        | ExprKind::Use(..)
+        | ExprKind::Binary(..) => true,
 
         // Inner blocks are rvalues.
         ExprKind::If(..) | ExprKind::Loop(..) | ExprKind::Match(..) | ExprKind::Block(..) => true,

compiler/rustc_middle/src/thir.rs

@@ -312,6 +312,14 @@ pub enum ExprKind<'tcx> {
         /// (e.g. `foo(a, b)` in `x.foo(a, b)`).
         fn_span: Span,
     },
+    /// A use expression `x.use`.
+    ByUse {
+        /// The expression on which use is applied.
+        expr: ExprId,
+        /// The span of use, without the dot and receiver
+        /// (e.g. `use` in `x.use`).
+        span: Span,
+    },
     /// A *non-overloaded* dereference.
     Deref {
         arg: ExprId,

compiler/rustc_middle/src/thir/visit.rs

@@ -59,6 +59,9 @@ pub fn walk_expr<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
                 visitor.visit_expr(&visitor.thir()[arg]);
             }
         }
+        ByUse { expr, span: _ } => {
+            visitor.visit_expr(&visitor.thir()[expr]);
+        }
         Deref { arg } => visitor.visit_expr(&visitor.thir()[arg]),
         Binary { lhs, rhs, op: _ } | LogicalOp { lhs, rhs, op: _ } => {
             visitor.visit_expr(&visitor.thir()[lhs]);

compiler/rustc_mir_build/src/builder/expr/as_place.rs

@@ -582,6 +582,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | ExprKind::Yield { .. }
             | ExprKind::ThreadLocalRef(_)
             | ExprKind::Call { .. }
+            | ExprKind::ByUse { .. }
             | ExprKind::WrapUnsafeBinder { .. } => {
                 // these are not places, so we need to make a temporary.
                 debug_assert!(!matches!(Category::of(&expr.kind), Some(Category::Place)));

compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs

@@ -572,6 +572,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 );
                 block.and(Rvalue::Use(operand))
             }
+
+            ExprKind::ByUse { expr, span: _ } => {
+                let operand = unpack!(
+                    block =
+                        this.as_operand(block, scope, expr, LocalInfo::Boring, NeedsTemporary::No)
+                );
+                block.and(Rvalue::Use(operand))
+            }
         }
     }
 

compiler/rustc_mir_build/src/builder/expr/category.rs

@@ -56,6 +56,7 @@ impl Category {
             | ExprKind::RawBorrow { .. }
             | ExprKind::Yield { .. }
             | ExprKind::Call { .. }
+            | ExprKind::ByUse { .. }
             | ExprKind::InlineAsm { .. } => Some(Category::Rvalue(RvalueFunc::Into)),
 
             ExprKind::Array { .. }

compiler/rustc_mir_build/src/builder/expr/into.rs

@@ -4,10 +4,12 @@ use rustc_ast::{AsmMacro, InlineAsmOptions};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir as hir;
+use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::*;
 use rustc_middle::span_bug;
 use rustc_middle::thir::*;
-use rustc_middle::ty::CanonicalUserTypeAnnotation;
+use rustc_middle::ty::{CanonicalUserTypeAnnotation, Ty};
+use rustc_span::DUMMY_SP;
 use rustc_span::source_map::Spanned;
 use tracing::{debug, instrument};
 
@@ -289,6 +291,38 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 this.diverge_from(block);
                 success.unit()
             }
+            ExprKind::ByUse { expr, span } => {
+                let place = unpack!(block = this.as_place(block, expr));
+                let ty = place.ty(&this.local_decls, this.tcx).ty;
+
+                // Convert `expr.use` to a call like `Clone::clone(&expr)`
+                let success = this.cfg.start_new_block();
+                let clone_trait = this.tcx.require_lang_item(LangItem::Clone, None);
+                let clone_fn = this.tcx.associated_item_def_ids(clone_trait)[0];
+                let func = Operand::function_handle(this.tcx, clone_fn, [ty.into()], expr_span);
+                let ref_ty = Ty::new_imm_ref(this.tcx, this.tcx.lifetimes.re_erased, ty);
+                let ref_place = this.temp(ref_ty, span);
+                this.cfg.push_assign(
+                    block,
+                    source_info,
+                    ref_place,
+                    Rvalue::Ref(this.tcx.lifetimes.re_erased, BorrowKind::Shared, place),
+                );
+                this.cfg.terminate(
+                    block,
+                    source_info,
+                    TerminatorKind::Call {
+                        func,
+                        args: [Spanned { node: Operand::Move(ref_place), span: DUMMY_SP }].into(),
+                        destination,
+                        target: Some(success),
+                        unwind: UnwindAction::Unreachable,
+                        call_source: CallSource::Misc,
+                        fn_span: expr_span,
+                    },
+                );
+                success.unit()
+            }
             ExprKind::Use { source } => this.expr_into_dest(destination, block, source),
             ExprKind::Borrow { arg, borrow_kind } => {
                 // We don't do this in `as_rvalue` because we use `as_place`

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -451,6 +451,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
             | ExprKind::Tuple { .. }
             | ExprKind::Unary { .. }
             | ExprKind::Call { .. }
+            | ExprKind::ByUse { .. }
             | ExprKind::Assign { .. }
             | ExprKind::AssignOp { .. }
             | ExprKind::Break { .. }

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -464,6 +464,10 @@ impl<'tcx> ThirBuildCx<'tcx> {
                 }
             }
 
+            hir::ExprKind::Use(expr, span) => {
+                ExprKind::ByUse { expr: self.mirror_expr(expr), span }
+            }
+
             hir::ExprKind::AddrOf(hir::BorrowKind::Ref, mutbl, arg) => {
                 ExprKind::Borrow { borrow_kind: mutbl.to_borrow_kind(), arg: self.mirror_expr(arg) }
             }

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -345,6 +345,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             | Borrow { .. }
             | Box { .. }
             | Call { .. }
+            | ByUse { .. }
             | Closure { .. }
             | ConstBlock { .. }
             | ConstParam { .. }

compiler/rustc_mir_build/src/thir/print.rs

@@ -246,6 +246,13 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
 
                 print_indented!(self, "}", depth_lvl);
             }
+            ByUse { expr, span } => {
+                print_indented!(self, "ByUse {", depth_lvl);
+                print_indented!(self, "expr:", depth_lvl + 1);
+                self.print_expr(*expr, depth_lvl + 2);
+                print_indented!(self, format!("span: {:?}", span), depth_lvl + 1);
+                print_indented!(self, "}", depth_lvl);
+            }
             Deref { arg } => {
                 print_indented!(self, "Deref {", depth_lvl);
                 self.print_expr(*arg, depth_lvl + 1);

compiler/rustc_parse/messages.ftl

@@ -348,6 +348,9 @@ parse_incorrect_use_of_await = incorrect use of `await`
 
 parse_incorrect_use_of_await_postfix_suggestion = `await` is a postfix operation
 
+parse_incorrect_use_of_use = incorrect use of `use`
+    .parentheses_suggestion = `use` is not a method call, try removing the parentheses
+
 parse_incorrect_visibility_restriction = incorrect visibility restriction
     .help = some possible visibility restrictions are:
             `pub(crate)`: visible only on the current crate

compiler/rustc_parse/src/errors.rs

@@ -106,6 +106,19 @@ pub(crate) struct IncorrectUseOfAwait {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_incorrect_use_of_use)]
+pub(crate) struct IncorrectUseOfUse {
+    #[primary_span]
+    #[suggestion(
+        parse_parentheses_suggestion,
+        style = "verbose",
+        code = "",
+        applicability = "machine-applicable"
+    )]
+    pub span: Span,
+}
+
 #[derive(Subdiagnostic)]
 #[multipart_suggestion(
     parse_incorrect_use_of_await_postfix_suggestion,

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -38,8 +38,8 @@ use crate::errors::{
     DoubleColonInBound, ExpectedIdentifier, ExpectedSemi, ExpectedSemiSugg,
     GenericParamsWithoutAngleBrackets, GenericParamsWithoutAngleBracketsSugg,
     HelpIdentifierStartsWithNumber, HelpUseLatestEdition, InInTypo, IncorrectAwait,
-    IncorrectSemicolon, IncorrectUseOfAwait, PatternMethodParamWithoutBody, QuestionMarkInType,
+    IncorrectSemicolon, IncorrectUseOfAwait, IncorrectUseOfUse, PatternMethodParamWithoutBody,
-    QuestionMarkInTypeSugg, SelfParamNotFirst, StructLiteralBodyWithoutPath,
+    QuestionMarkInType, QuestionMarkInTypeSugg, SelfParamNotFirst, StructLiteralBodyWithoutPath,
     StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens, StructLiteralNeedingParensSugg,
     SuggAddMissingLetStmt, SuggEscapeIdentifier, SuggRemoveComma, TernaryOperator,
     UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
@@ -1991,7 +1991,7 @@ impl<'a> Parser<'a> {
             self.parse_expr()
         }
         .map_err(|mut err| {
-            err.span_label(await_sp, "while parsing this incorrect await expression");
+            err.span_label(await_sp, format!("while parsing this incorrect await expression"));
             err
         })?;
         Ok((expr.span, expr, is_question))
@@ -2030,6 +2030,21 @@ impl<'a> Parser<'a> {
             self.dcx().emit_err(IncorrectUseOfAwait { span });
         }
     }
+    ///
+    /// If encountering `x.use()`, consumes and emits an error.
+    pub(super) fn recover_from_use(&mut self) {
+        if self.token == token::OpenDelim(Delimiter::Parenthesis)
+            && self.look_ahead(1, |t| t == &token::CloseDelim(Delimiter::Parenthesis))
+        {
+            // var.use()
+            let lo = self.token.span;
+            self.bump(); // (
+            let span = lo.to(self.token.span);
+            self.bump(); // )
+
+            self.dcx().emit_err(IncorrectUseOfUse { span });
+        }
+    }
 
     pub(super) fn try_macro_suggestion(&mut self) -> PResult<'a, P<Expr>> {
         let is_try = self.token.is_keyword(kw::Try);

compiler/rustc_parse/src/parser/expr.rs

@@ -778,6 +778,7 @@ impl<'a> Parser<'a> {
                     ExprKind::MethodCall(_) => "a method call",
                     ExprKind::Call(_, _) => "a function call",
                     ExprKind::Await(_, _) => "`.await`",
+                    ExprKind::Use(_, _) => "`.use`",
                     ExprKind::Match(_, _, MatchKind::Postfix) => "a postfix match",
                     ExprKind::Err(_) => return Ok(with_postfix),
                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
@@ -1296,6 +1297,12 @@ impl<'a> Parser<'a> {
             return Ok(self.mk_await_expr(self_arg, lo));
         }
 
+        if self.eat_keyword(exp!(Use)) {
+            let use_span = self.prev_token.span;
+            self.psess.gated_spans.gate(sym::ergonomic_clones, use_span);
+            return Ok(self.mk_use_expr(self_arg, lo));
+        }
+
         // Post-fix match
         if self.eat_keyword(exp!(Match)) {
             let match_span = self.prev_token.span;
@@ -3818,6 +3825,13 @@ impl<'a> Parser<'a> {
         await_expr
     }
 
+    fn mk_use_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
+        let span = lo.to(self.prev_token.span);
+        let use_expr = self.mk_expr(span, ExprKind::Use(self_arg, self.prev_token.span));
+        self.recover_from_use();
+        use_expr
+    }
+
     pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
     }
@@ -3966,6 +3980,7 @@ impl MutVisitor for CondChecker<'_> {
             }
             ExprKind::Unary(_, _)
             | ExprKind::Await(_, _)
+            | ExprKind::Use(_, _)
             | ExprKind::AssignOp(_, _, _)
             | ExprKind::Range(_, _, _)
             | ExprKind::Try(_)

compiler/rustc_passes/src/input_stats.rs

@@ -328,6 +328,7 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
                 Array,
                 Call,
                 MethodCall,
+                Use,
                 Tup,
                 Binary,
                 Unary,
@@ -626,7 +627,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
             (self, e, e.kind, None, ast, Expr, ExprKind),
             [
                 Array, ConstBlock, Call, MethodCall, Tup, Binary, Unary, Lit, Cast, Type, Let,
-                If, While, ForLoop, Loop, Match, Closure, Block, Await, TryBlock, Assign,
+                If, While, ForLoop, Loop, Match, Closure, Block, Await, Use, TryBlock, Assign,
                 AssignOp, Field, Index, Range, Underscore, Path, AddrOf, Break, Continue, Ret,
                 InlineAsm, FormatArgs, OffsetOf, MacCall, Struct, Repeat, Paren, Try, Yield, Yeet,
                 Become, IncludedBytes, Gen, UnsafeBinderCast, Err, Dummy

compiler/rustc_passes/src/liveness.rs

@@ -426,6 +426,7 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
             | hir::ExprKind::Array(..)
             | hir::ExprKind::Call(..)
             | hir::ExprKind::MethodCall(..)
+            | hir::ExprKind::Use(..)
             | hir::ExprKind::Tup(..)
             | hir::ExprKind::Binary(..)
             | hir::ExprKind::AddrOf(..)
@@ -1031,6 +1032,11 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 self.propagate_through_expr(receiver, succ)
             }
 
+            hir::ExprKind::Use(expr, _) => {
+                let succ = self.check_is_ty_uninhabited(expr, succ);
+                self.propagate_through_expr(expr, succ)
+            }
+
             hir::ExprKind::Tup(exprs) => self.propagate_through_exprs(exprs, succ),
 
             hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => {
@@ -1418,6 +1424,7 @@ fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) {
         // no correctness conditions related to liveness
         hir::ExprKind::Call(..)
         | hir::ExprKind::MethodCall(..)
+        | hir::ExprKind::Use(..)
         | hir::ExprKind::Match(..)
         | hir::ExprKind::Loop(..)
         | hir::ExprKind::Index(..)

compiler/rustc_passes/src/naked_functions.rs

@@ -182,6 +182,7 @@ impl CheckInlineAssembly {
             | ExprKind::Array(..)
             | ExprKind::Call(..)
             | ExprKind::MethodCall(..)
+            | ExprKind::Use(..)
             | ExprKind::Tup(..)
             | ExprKind::Binary(..)
             | ExprKind::Unary(..)

compiler/rustc_ty_utils/messages.ftl

@@ -14,6 +14,8 @@ ty_utils_borrow_not_supported = borrowing is not supported in generic constants
 
 ty_utils_box_not_supported = allocations are not allowed in generic constants
 
+ty_utils_by_use_not_supported = .use is not allowed in generic constants
+
 ty_utils_closure_and_return_not_supported = closures and function keywords are not supported in generic constants
 
 ty_utils_const_block_not_supported = const blocks are not supported in generic constants

compiler/rustc_ty_utils/src/consts.rs

@@ -230,7 +230,9 @@ fn recurse_build<'tcx>(
             error(GenericConstantTooComplexSub::LoopNotSupported(node.span))?
         }
         ExprKind::Box { .. } => error(GenericConstantTooComplexSub::BoxNotSupported(node.span))?,
-
+        ExprKind::ByUse { .. } => {
+            error(GenericConstantTooComplexSub::ByUseNotSupported(node.span))?
+        }
         ExprKind::Unary { .. } => unreachable!(),
         // we handle valid unary/binary ops above
         ExprKind::Binary { .. } => {
@@ -317,6 +319,7 @@ impl<'a, 'tcx> IsThirPolymorphic<'a, 'tcx> {
             | thir::ExprKind::Box { .. }
             | thir::ExprKind::If { .. }
             | thir::ExprKind::Call { .. }
+            | thir::ExprKind::ByUse { .. }
             | thir::ExprKind::Deref { .. }
             | thir::ExprKind::Binary { .. }
             | thir::ExprKind::LogicalOp { .. }

compiler/rustc_ty_utils/src/errors.rs

@@ -55,6 +55,8 @@ pub(crate) enum GenericConstantTooComplexSub {
     BoxNotSupported(#[primary_span] Span),
     #[label(ty_utils_binary_not_supported)]
     BinaryNotSupported(#[primary_span] Span),
+    #[label(ty_utils_by_use_not_supported)]
+    ByUseNotSupported(#[primary_span] Span),
     #[label(ty_utils_logical_op_not_supported)]
     LogicalOpNotSupported(#[primary_span] Span),
     #[label(ty_utils_assign_not_supported)]

tests/ui/ergonomic-clones/dotuse.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+
+#![feature(ergonomic_clones)]
+
+fn basic_test(x: i32) -> i32 {
+    x.use.use.abs()
+}
+
+fn do_not_move_test(x: String) -> String {
+    let s = x.use;
+    x
+}
+
+fn main() {}

tests/ui/feature-gates/feature-gate-ergonomic-clones.rs

@@ -1,18 +1,18 @@
 fn ergonomic_clone(x: i32) -> i32 {
     x.use
-    //~^ ERROR expected identifier, found keyword `use`
+    //~^ ERROR `.use` calls are experimental [E0658]
-    //~| ERROR `i32` is a primitive type and therefore doesn't have fields [E0610]
 }
 
 fn ergonomic_closure_clone() {
     let s1 = String::from("hi!");
 
     let s2 = use || {
-        //~^ ERROR expected expression, found keyword `use`
+        //~^ ERROR incorrect use of `use`
         s1
     };
 
     let s3 = use || {
+        //~^ ERROR incorrect use of `use`
         s1
     };
 }

tests/ui/feature-gates/feature-gate-ergonomic-clones.stderr

@@ -1,26 +1,49 @@
-error: expected identifier, found keyword `use`
+error: incorrect use of `use`
-  --> $DIR/feature-gate-ergonomic-clones.rs:2:7
+  --> $DIR/feature-gate-ergonomic-clones.rs:9:14
    |
-LL |     x.use
+LL |       let s2 = use || {
-   |       ^^^ expected identifier, found keyword
+   |  ______________^
+LL | |
+LL | |         s1
+LL | |     };
+   | |_____^
    |
-help: escape `use` to use it as an identifier
+help: `use` is a postfix operation
+   |
+LL ~     let s2 = || {
+LL |
+LL |         s1
+LL ~     }.use;
    |
-LL |     x.r#use
-   |       ++
 
-error: expected expression, found keyword `use`
+error: incorrect use of `use`
-  --> $DIR/feature-gate-ergonomic-clones.rs:10:14
+  --> $DIR/feature-gate-ergonomic-clones.rs:14:14
+   |
+LL |       let s3 = use || {
+   |  ______________^
+LL | |
+LL | |         s1
+LL | |     };
+   | |_____^
+   |
+help: `use` is a postfix operation
+   |
+LL ~     let s3 = || {
+LL |
+LL |         s1
+LL ~     }.use;
    |
-LL |     let s2 = use || {
-   |              ^^^ expected expression
 
-error[E0610]: `i32` is a primitive type and therefore doesn't have fields
+error[E0658]: `.use` calls are experimental
   --> $DIR/feature-gate-ergonomic-clones.rs:2:7
    |
 LL |     x.use
    |       ^^^
+   |
+   = note: see issue #132290 <https://github.com/rust-lang/rust/issues/132290> for more information
+   = help: add `#![feature(ergonomic_clones)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0610`.
+For more information about this error, try `rustc --explain E0658`.