diff --git a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs index e6bde6a8c54dc..efe6f9cd5ce5f 100644 --- a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs +++ b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs @@ -506,9 +506,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { self.expected_fn_found_fn_mut_call(&mut err, span, act); } - PlaceRef { local: _, projection: [.., ProjectionElem::Deref] } => { - err.span_label(span, format!("cannot {act}")); - + PlaceRef { local: _, projection: [proj_base @ .., ProjectionElem::Deref] } => { + let mut span = span; match opt_source { Some(BorrowedContentSource::OverloadedDeref(ty)) => { err.help(format!( @@ -523,8 +522,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { )); self.suggest_map_index_mut_alternatives(ty, &mut err, span); } + Some(BorrowedContentSource::DerefSharedRef) => { + let place_ref = + PlaceRef { local: the_place_err.local, projection: proj_base }; + let ty = place_ref.ty(self.body, self.infcx.tcx).ty; + self.suggest_detailed_hint_for_ref(ty, &mut err, &mut span); + } _ => (), } + err.span_label(span, format!("cannot {act}")); } _ => { @@ -539,6 +545,46 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { } } + fn suggest_detailed_hint_for_ref(&self, ty: Ty<'_>, err: &mut Diagnostic, span: &mut Span) { + struct ExprFinder { + span: Span, + hir_id: Option, + } + + impl<'tcx> Visitor<'tcx> for ExprFinder { + fn visit_expr(&mut self, s: &'tcx hir::Expr<'tcx>) { + if s.span.contains(self.span) { + self.hir_id = Some(s.hir_id); + } + hir::intravisit::walk_expr(self, s); + } + } + let hir_map = self.infcx.tcx.hir(); + let def_id = self.body.source.def_id(); + let hir_id = if let Some(local_def_id) = def_id.as_local() + && let Some(body_id) = hir_map.maybe_body_owned_by(local_def_id) { + let body = hir_map.body(body_id); + let mut v = ExprFinder { + span: *span, + hir_id: None, + }; + v.visit_body(body); + v.hir_id + } else { + None + }; + let expr = if let Some(hir_id) = hir_id { + hir_map.expect_expr(hir_id) + } else { + return; + }; + if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, Mutability::Mut, ex) = expr.kind + && !matches!(ex.kind, hir::ExprKind::Unary(hir::UnOp::Deref, _) | hir::ExprKind::Field(_, _) | hir::ExprKind::Lit(_)) { + *span = ex.span; + err.span_help(ex.span, format!("this expression is of type `{}`, which is an immutable reference", ty)); + } + } + fn suggest_map_index_mut_alternatives(&self, ty: Ty<'tcx>, err: &mut Diagnostic, span: Span) { let Some(adt) = ty.ty_adt_def() else { return }; let did = adt.did(); diff --git a/tests/ui/borrowck/issue-111554.stderr b/tests/ui/borrowck/issue-111554.stderr index 6b7a42e495999..4779b573719c7 100644 --- a/tests/ui/borrowck/issue-111554.stderr +++ b/tests/ui/borrowck/issue-111554.stderr @@ -14,7 +14,15 @@ error[E0596]: cannot borrow data in a `&` reference as mutable --> $DIR/issue-111554.rs:10:16 | LL | || bar(&mut self); - | ^^^^^^^^^ cannot borrow as mutable + | ^^^^^---- + | | + | cannot borrow as mutable + | +help: this expression is of type `&Foo`, which is an immutable reference + --> $DIR/issue-111554.rs:10:21 + | +LL | || bar(&mut self); + | ^^^^ error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable --> $DIR/issue-111554.rs:21:16 diff --git a/tests/ui/borrowck/issue_113842.rs b/tests/ui/borrowck/issue_113842.rs new file mode 100644 index 0000000000000..adb7e40b267b1 --- /dev/null +++ b/tests/ui/borrowck/issue_113842.rs @@ -0,0 +1,22 @@ +mod some_library { + pub fn foo(_: &mut [i32]) {} + pub fn bar<'a>() -> &'a [i32] { + &[] + } + pub fn bar_mut<'a>() -> &'a mut [i32] { + &mut [] + } +} + +struct Foo { + pub x: i32, +} + +fn foo() { + let foo = Foo { x: 0 }; + let _y: &mut Foo = &mut &foo; //~ ERROR cannot borrow data in a `&` reference as mutable +} + +fn main() { + some_library::foo(&mut some_library::bar()); //~ ERROR cannot borrow data in a `&` reference as mutable +} diff --git a/tests/ui/borrowck/issue_113842.stderr b/tests/ui/borrowck/issue_113842.stderr new file mode 100644 index 0000000000000..164574b77f5bb --- /dev/null +++ b/tests/ui/borrowck/issue_113842.stderr @@ -0,0 +1,31 @@ +error[E0596]: cannot borrow data in a `&` reference as mutable + --> $DIR/issue_113842.rs:17:24 + | +LL | let _y: &mut Foo = &mut &foo; + | ^^^^^---- + | | + | cannot borrow as mutable + | +help: this expression is of type `&Foo`, which is an immutable reference + --> $DIR/issue_113842.rs:17:29 + | +LL | let _y: &mut Foo = &mut &foo; + | ^^^^ + +error[E0596]: cannot borrow data in a `&` reference as mutable + --> $DIR/issue_113842.rs:21:23 + | +LL | some_library::foo(&mut some_library::bar()); + | ^^^^^------------------- + | | + | cannot borrow as mutable + | +help: this expression is of type `&[i32]`, which is an immutable reference + --> $DIR/issue_113842.rs:21:28 + | +LL | some_library::foo(&mut some_library::bar()); + | ^^^^^^^^^^^^^^^^^^^ + +error: aborting due to 2 previous errors + +For more information about this error, try `rustc --explain E0596`. diff --git a/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr b/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr index 023fab8fe4a3d..46e60d662de67 100644 --- a/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr +++ b/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr @@ -2,7 +2,15 @@ error[E0596]: cannot borrow data in a `&` reference as mutable --> $DIR/let-else-binding-explicit-mut-borrow.rs:7:37 | LL | let Some(n): &mut Option = &mut &Some(5i32) else { - | ^^^^^^^^^^^^^^^^ cannot borrow as mutable + | ^^^^^----------- + | | + | cannot borrow as mutable + | +help: this expression is of type `&Option`, which is an immutable reference + --> $DIR/let-else-binding-explicit-mut-borrow.rs:7:42 + | +LL | let Some(n): &mut Option = &mut &Some(5i32) else { + | ^^^^^^^^^^^ error: aborting due to previous error diff --git a/tests/ui/nll/issue-51191.rs b/tests/ui/nll/issue-51191.rs index 836587d93b84b..a2076b0db6188 100644 --- a/tests/ui/nll/issue-51191.rs +++ b/tests/ui/nll/issue-51191.rs @@ -22,6 +22,7 @@ impl Struct { (&mut self).bar(); //~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596] //~^^ ERROR cannot borrow data in a `&` reference as mutable [E0596] + //~^^^ HELP this expression is of type `&Struct`, which is an immutable reference } fn mtblref(&mut self) { diff --git a/tests/ui/nll/issue-51191.stderr b/tests/ui/nll/issue-51191.stderr index c14056c3a834b..5da92b2ad6e8f 100644 --- a/tests/ui/nll/issue-51191.stderr +++ b/tests/ui/nll/issue-51191.stderr @@ -48,21 +48,29 @@ error[E0596]: cannot borrow data in a `&` reference as mutable --> $DIR/issue-51191.rs:22:9 | LL | (&mut self).bar(); - | ^^^^^^^^^^^ cannot borrow as mutable + | ^^^^^^----^ + | | + | cannot borrow as mutable + | +help: this expression is of type `&Struct`, which is an immutable reference + --> $DIR/issue-51191.rs:22:15 + | +LL | (&mut self).bar(); + | ^^^^ error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable - --> $DIR/issue-51191.rs:28:9 + --> $DIR/issue-51191.rs:29:9 | LL | (&mut self).bar(); | ^^^^^^^^^^^ cannot borrow as mutable | note: the binding is already a mutable borrow - --> $DIR/issue-51191.rs:27:16 + --> $DIR/issue-51191.rs:28:16 | LL | fn mtblref(&mut self) { | ^^^^^^^^^ help: try removing `&mut` here - --> $DIR/issue-51191.rs:28:9 + --> $DIR/issue-51191.rs:29:9 | LL | (&mut self).bar(); | ^^^^^^^^^^^