Implement .use keyword as an alias of clone

spastorino · spastorino · commit 05c516446a0f · 2025-03-06T17:58:32.000-03:00
diff --git a/compiler/rustc_ast/src/ast.rs b/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>),
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/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);
diff --git a/compiler/rustc_ast/src/util/classify.rs b/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
diff --git a/compiler/rustc_ast/src/visit.rs b/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));
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/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,
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/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,
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/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(_)
diff --git a/compiler/rustc_hir/src/hir.rs b/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`).
diff --git a/compiler/rustc_hir/src/intravisit.rs 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));
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/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);
             }
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/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>,
diff --git a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs b/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 { .. }
diff --git a/compiler/rustc_lint/src/dangling.rs b/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,
diff --git a/compiler/rustc_middle/src/thir.rs b/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,
diff --git a/compiler/rustc_middle/src/thir/visit.rs b/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]);
diff --git a/compiler/rustc_mir_build/src/builder/expr/as_place.rs b/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)));
diff --git a/compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs b/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))
+            }
         }
     }
 
diff --git a/compiler/rustc_mir_build/src/builder/expr/category.rs b/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 { .. }
diff --git a/compiler/rustc_mir_build/src/builder/expr/into.rs b/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`
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/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 { .. }
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/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) }
             }
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/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 { .. }
diff --git a/compiler/rustc_mir_build/src/thir/print.rs b/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);
diff --git a/compiler/rustc_parse/messages.ftl b/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
diff --git a/compiler/rustc_parse/src/errors.rs b/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,
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
diff --git a/compiler/rustc_passes/src/input_stats.rs b/compiler/rustc_passes/src/input_stats.rs
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs
diff --git a/compiler/rustc_passes/src/naked_functions.rs b/compiler/rustc_passes/src/naked_functions.rs
diff --git a/compiler/rustc_ty_utils/messages.ftl b/compiler/rustc_ty_utils/messages.ftl
diff --git a/compiler/rustc_ty_utils/src/consts.rs b/compiler/rustc_ty_utils/src/consts.rs
diff --git a/compiler/rustc_ty_utils/src/errors.rs b/compiler/rustc_ty_utils/src/errors.rs
diff --git a/tests/ui/ergonomic-clones/dotuse.rs b/tests/ui/ergonomic-clones/dotuse.rs
diff --git a/tests/ui/feature-gates/feature-gate-ergonomic-clones.rs b/tests/ui/feature-gates/feature-gate-ergonomic-clones.rs
diff --git a/tests/ui/feature-gates/feature-gate-ergonomic-clones.stderr b/tests/ui/feature-gates/feature-gate-ergonomic-clones.stderr

Original file line number	Diff line number	Diff line change
`@@ -1211,6 +1211,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) -> V`
`1211`	`1211`	`}`
`1212`	`1212`	`ExprKind::Gen(_capt, body, _kind, _decl_span) => try_visit!(visitor.visit_block(body)),`
`1213`	`1213`	`ExprKind::Await(expr, _span) => try_visit!(visitor.visit_expr(expr)),`
	`1214`	`+ ExprKind::Use(expr, _span) => try_visit!(visitor.visit_expr(expr)),`
`1214`	`1215`	`ExprKind::Assign(lhs, rhs, _span) => {`
`1215`	`1216`	`try_visit!(visitor.visit_expr(lhs));`
`1216`	`1217`	`try_visit!(visitor.visit_expr(rhs));`
Original file line number	Diff line number	Diff line change
`@@ -1544,6 +1544,10 @@ impl<'a> State<'a> {`
`1544`	`1544`	`hir::ExprKind::MethodCall(segment, receiver, args, _) => {`
`1545`	`1545`	`self.print_expr_method_call(segment, receiver, args);`
`1546`	`1546`	`}`
	`1547`	`+ hir::ExprKind::Use(expr, _) => {`
	`1548`	`+ self.print_expr(expr);`
	`1549`	`+ self.word(".use");`
	`1550`	`+ }`
`1547`	`1551`	`hir::ExprKind::Binary(op, lhs, rhs) => {`
`1548`	`1552`	`self.print_expr_binary(op, lhs, rhs);`
`1549`	`1553`	`}`