use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed}; use rustc_hir as hir; use rustc_hir::intravisit::Visitor; use rustc_hir::Node; use rustc_middle::hir::map::Map; use rustc_middle::mir::{Mutability, Place, PlaceRef, ProjectionElem}; use rustc_middle::ty::{self, Ty, TyCtxt}; use rustc_middle::{ hir::place::PlaceBase, mir::{self, BindingForm, Local, LocalDecl, LocalInfo, LocalKind, Location}, }; use rustc_span::source_map::DesugaringKind; use rustc_span::symbol::{kw, Symbol}; use rustc_span::{sym, BytePos, Span}; use rustc_target::abi::FieldIdx; use crate::diagnostics::BorrowedContentSource; use crate::util::FindAssignments; use crate::MirBorrowckCtxt; #[derive(Copy, Clone, Debug, Eq, PartialEq)] pub(crate) enum AccessKind { MutableBorrow, Mutate, } impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { pub(crate) fn report_mutability_error( &mut self, access_place: Place<'tcx>, span: Span, the_place_err: PlaceRef<'tcx>, error_access: AccessKind, location: Location, ) { debug!( "report_mutability_error(\ access_place={:?}, span={:?}, the_place_err={:?}, error_access={:?}, location={:?},\ )", access_place, span, the_place_err, error_access, location, ); let mut err; let item_msg; let reason; let mut opt_source = None; let access_place_desc = self.describe_any_place(access_place.as_ref()); debug!("report_mutability_error: access_place_desc={:?}", access_place_desc); match the_place_err { PlaceRef { local, projection: [] } => { item_msg = access_place_desc; if access_place.as_local().is_some() { reason = ", as it is not declared as mutable".to_string(); } else { let name = self.local_names[local].expect("immutable unnamed local"); reason = format!(", as `{name}` is not declared as mutable"); } } PlaceRef { local, projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)], } => { debug_assert!(is_closure_or_generator( Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty )); let imm_borrow_derefed = self.upvars[upvar_index.index()] .place .place .deref_tys() .any(|ty| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not))); // If the place is immutable then: // // - Either we deref an immutable ref to get to our final place. // - We don't capture derefs of raw ptrs // - Or the final place is immut because the root variable of the capture // isn't marked mut and we should suggest that to the user. if imm_borrow_derefed { // If we deref an immutable ref then the suggestion here doesn't help. return; } else { item_msg = access_place_desc; if self.is_upvar_field_projection(access_place.as_ref()).is_some() { reason = ", as it is not declared as mutable".to_string(); } else { let name = self.upvars[upvar_index.index()].place.to_string(self.infcx.tcx); reason = format!(", as `{name}` is not declared as mutable"); } } } PlaceRef { local, projection: [ProjectionElem::Deref] } if self.body.local_decls[local].is_ref_for_guard() => { item_msg = access_place_desc; reason = ", as it is immutable for the pattern guard".to_string(); } PlaceRef { local, projection: [ProjectionElem::Deref] } if self.body.local_decls[local].is_ref_to_static() => { if access_place.projection.len() == 1 { item_msg = format!("immutable static item {access_place_desc}"); reason = String::new(); } else { item_msg = access_place_desc; let local_info = self.body.local_decls[local].local_info(); if let LocalInfo::StaticRef { def_id, .. } = *local_info { let static_name = &self.infcx.tcx.item_name(def_id); reason = format!(", as `{static_name}` is an immutable static item"); } else { bug!("is_ref_to_static return true, but not ref to static?"); } } } PlaceRef { local: _, projection: [proj_base @ .., ProjectionElem::Deref] } => { if the_place_err.local == ty::CAPTURE_STRUCT_LOCAL && proj_base.is_empty() && !self.upvars.is_empty() { item_msg = access_place_desc; debug_assert!(self.body.local_decls[ty::CAPTURE_STRUCT_LOCAL].ty.is_ref()); debug_assert!(is_closure_or_generator( the_place_err.ty(self.body, self.infcx.tcx).ty )); reason = if self.is_upvar_field_projection(access_place.as_ref()).is_some() { ", as it is a captured variable in a `Fn` closure".to_string() } else { ", as `Fn` closures cannot mutate their captured variables".to_string() } } else { let source = self.borrowed_content_source(PlaceRef { local: the_place_err.local, projection: proj_base, }); let pointer_type = source.describe_for_immutable_place(self.infcx.tcx); opt_source = Some(source); if let Some(desc) = self.describe_place(access_place.as_ref()) { item_msg = format!("`{desc}`"); reason = match error_access { AccessKind::Mutate => format!(", which is behind {pointer_type}"), AccessKind::MutableBorrow => { format!(", as it is behind {pointer_type}") } } } else { item_msg = format!("data in {pointer_type}"); reason = String::new(); } } } PlaceRef { local: _, projection: [ .., ProjectionElem::Index(_) | ProjectionElem::ConstantIndex { .. } | ProjectionElem::OpaqueCast { .. } | ProjectionElem::Subslice { .. } | ProjectionElem::Downcast(..), ], } => bug!("Unexpected immutable place."), } debug!("report_mutability_error: item_msg={:?}, reason={:?}", item_msg, reason); // `act` and `acted_on` are strings that let us abstract over // the verbs used in some diagnostic messages. let act; let acted_on; let mut suggest = true; let mut mut_error = None; let mut count = 1; let span = match error_access { AccessKind::Mutate => { err = self.cannot_assign(span, &(item_msg + &reason)); act = "assign"; acted_on = "written"; span } AccessKind::MutableBorrow => { act = "borrow as mutable"; acted_on = "borrowed as mutable"; let borrow_spans = self.borrow_spans(span, location); let borrow_span = borrow_spans.args_or_use(); match the_place_err { PlaceRef { local, projection: [] } if self.body.local_decls[local].can_be_made_mutable() => { let span = self.body.local_decls[local].source_info.span; mut_error = Some(span); if let Some((buffer, c)) = self.get_buffered_mut_error(span) { // We've encountered a second (or more) attempt to mutably borrow an // immutable binding, so the likely problem is with the binding // declaration, not the use. We collect these in a single diagnostic // and make the binding the primary span of the error. err = buffer; count = c + 1; if count == 2 { err.replace_span_with(span, false); err.span_label(span, "not mutable"); } suggest = false; } else { err = self.cannot_borrow_path_as_mutable_because( borrow_span, &item_msg, &reason, ); } } _ => { err = self.cannot_borrow_path_as_mutable_because( borrow_span, &item_msg, &reason, ); } } if suggest { borrow_spans.var_subdiag( None, &mut err, Some(mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default }), |_kind, var_span| { let place = self.describe_any_place(access_place.as_ref()); crate::session_diagnostics::CaptureVarCause::MutableBorrowUsePlaceClosure { place, var_span, } }, ); } borrow_span } }; debug!("report_mutability_error: act={:?}, acted_on={:?}", act, acted_on); match the_place_err { // Suggest making an existing shared borrow in a struct definition a mutable borrow. // // This is applicable when we have a deref of a field access to a deref of a local - // something like `*((*_1).0`. The local that we get will be a reference to the // struct we've got a field access of (it must be a reference since there's a deref // after the field access). PlaceRef { local, projection: [ proj_base @ .., ProjectionElem::Deref, ProjectionElem::Field(field, _), ProjectionElem::Deref, ], } => { err.span_label(span, format!("cannot {act}")); if let Some(span) = get_mut_span_in_struct_field( self.infcx.tcx, Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty, *field, ) { err.span_suggestion_verbose( span, "consider changing this to be mutable", " mut ", Applicability::MaybeIncorrect, ); } } // Suggest removing a `&mut` from the use of a mutable reference. PlaceRef { local, projection: [] } if self .body .local_decls .get(local) .is_some_and(|l| mut_borrow_of_mutable_ref(l, self.local_names[local])) => { let decl = &self.body.local_decls[local]; err.span_label(span, format!("cannot {act}")); if let Some(mir::Statement { source_info, kind: mir::StatementKind::Assign(box ( _, mir::Rvalue::Ref( _, mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default }, _, ), )), .. }) = &self.body[location.block].statements.get(location.statement_index) { match *decl.local_info() { LocalInfo::User(BindingForm::Var(mir::VarBindingForm { binding_mode: ty::BindingMode::BindByValue(Mutability::Not), opt_ty_info: Some(sp), opt_match_place: _, pat_span: _, })) => { if suggest { err.span_note(sp, "the binding is already a mutable borrow"); } } _ => { err.span_note( decl.source_info.span, "the binding is already a mutable borrow", ); } } if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(source_info.span) { if snippet.starts_with("&mut ") { // We don't have access to the HIR to get accurate spans, but we can // give a best effort structured suggestion. err.span_suggestion_verbose( source_info.span.with_hi(source_info.span.lo() + BytePos(5)), "try removing `&mut` here", "", Applicability::MachineApplicable, ); } else { // This can occur with things like `(&mut self).foo()`. err.span_help(source_info.span, "try removing `&mut` here"); } } else { err.span_help(source_info.span, "try removing `&mut` here"); } } else if decl.mutability.is_not() { if matches!( decl.local_info(), LocalInfo::User(BindingForm::ImplicitSelf(hir::ImplicitSelfKind::MutRef)) ) { err.note( "as `Self` may be unsized, this call attempts to take `&mut &mut self`", ); err.note("however, `&mut self` expands to `self: &mut Self`, therefore `self` cannot be borrowed mutably"); } else { err.span_suggestion_verbose( decl.source_info.span.shrink_to_lo(), "consider making the binding mutable", "mut ", Applicability::MachineApplicable, ); }; } } // We want to suggest users use `let mut` for local (user // variable) mutations... PlaceRef { local, projection: [] } if self.body.local_decls[local].can_be_made_mutable() => { // ... but it doesn't make sense to suggest it on // variables that are `ref x`, `ref mut x`, `&self`, // or `&mut self` (such variables are simply not // mutable). let local_decl = &self.body.local_decls[local]; assert_eq!(local_decl.mutability, Mutability::Not); if count < 10 { err.span_label(span, format!("cannot {act}")); } if suggest { err.span_suggestion_verbose( local_decl.source_info.span.shrink_to_lo(), "consider changing this to be mutable", "mut ", Applicability::MachineApplicable, ); let tcx = self.infcx.tcx; if let ty::Closure(id, _) = *the_place_err.ty(self.body, tcx).ty.kind() { self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err); } } } // Also suggest adding mut for upvars PlaceRef { local, projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)], } => { debug_assert!(is_closure_or_generator( Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty )); let captured_place = &self.upvars[upvar_index.index()].place; err.span_label(span, format!("cannot {act}")); let upvar_hir_id = captured_place.get_root_variable(); if let Some(Node::Pat(pat)) = self.infcx.tcx.hir().find(upvar_hir_id) && let hir::PatKind::Binding( hir::BindingAnnotation::NONE, _, upvar_ident, _, ) = pat.kind { if upvar_ident.name == kw::SelfLower { for (_, node) in self.infcx.tcx.hir().parent_iter(upvar_hir_id) { if let Some(fn_decl) = node.fn_decl() { if !matches!(fn_decl.implicit_self, hir::ImplicitSelfKind::ImmRef | hir::ImplicitSelfKind::MutRef) { err.span_suggestion( upvar_ident.span, "consider changing this to be mutable", format!("mut {}", upvar_ident.name), Applicability::MachineApplicable, ); break; } } } } else { err.span_suggestion( upvar_ident.span, "consider changing this to be mutable", format!("mut {}", upvar_ident.name), Applicability::MachineApplicable, ); } } let tcx = self.infcx.tcx; if let ty::Ref(_, ty, Mutability::Mut) = the_place_err.ty(self.body, tcx).ty.kind() && let ty::Closure(id, _) = *ty.kind() { self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err); } } // complete hack to approximate old AST-borrowck // diagnostic: if the span starts with a mutable borrow of // a local variable, then just suggest the user remove it. PlaceRef { local: _, projection: [] } if self .infcx .tcx .sess .source_map() .span_to_snippet(span) .is_ok_and(|snippet| snippet.starts_with("&mut ")) => { err.span_label(span, format!("cannot {act}")); err.span_suggestion( span, "try removing `&mut` here", "", Applicability::MaybeIncorrect, ); } PlaceRef { local, projection: [ProjectionElem::Deref] } if self.body.local_decls[local].is_ref_for_guard() => { err.span_label(span, format!("cannot {act}")); err.note( "variables bound in patterns are immutable until the end of the pattern guard", ); } // We want to point out when a `&` can be readily replaced // with an `&mut`. // // FIXME: can this case be generalized to work for an // arbitrary base for the projection? PlaceRef { local, projection: [ProjectionElem::Deref] } if self.body.local_decls[local].is_user_variable() => { let local_decl = &self.body.local_decls[local]; let (pointer_sigil, pointer_desc) = if local_decl.ty.is_ref() { ("&", "reference") } else { ("*const", "pointer") }; match self.local_names[local] { Some(name) if !local_decl.from_compiler_desugaring() => { err.span_label( span, format!( "`{name}` is a `{pointer_sigil}` {pointer_desc}, \ so the data it refers to cannot be {acted_on}", ), ); self.suggest_make_local_mut(&mut err, local, name); } _ => { err.span_label( span, format!("cannot {act} through `{pointer_sigil}` {pointer_desc}"), ); } } } PlaceRef { local, projection: [ProjectionElem::Deref] } if local == ty::CAPTURE_STRUCT_LOCAL && !self.upvars.is_empty() => { self.expected_fn_found_fn_mut_call(&mut err, span, act); } PlaceRef { local: _, projection: [.., ProjectionElem::Deref] } => { err.span_label(span, format!("cannot {act}")); match opt_source { Some(BorrowedContentSource::OverloadedDeref(ty)) => { err.help(format!( "trait `DerefMut` is required to modify through a dereference, \ but it is not implemented for `{ty}`", )); } Some(BorrowedContentSource::OverloadedIndex(ty)) => { err.help(format!( "trait `IndexMut` is required to modify indexed content, \ but it is not implemented for `{ty}`", )); self.suggest_map_index_mut_alternatives(ty, &mut err, span); } _ => (), } } _ => { err.span_label(span, format!("cannot {act}")); } } if let Some(span) = mut_error { self.buffer_mut_error(span, err, count); } else { self.buffer_error(err); } } 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(); if self.infcx.tcx.is_diagnostic_item(sym::HashMap, did) || self.infcx.tcx.is_diagnostic_item(sym::BTreeMap, did) { struct V<'a, 'tcx> { assign_span: Span, err: &'a mut Diagnostic, ty: Ty<'tcx>, suggested: bool, } impl<'a, 'tcx> Visitor<'tcx> for V<'a, 'tcx> { fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) { hir::intravisit::walk_stmt(self, stmt); let expr = match stmt.kind { hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr) => expr, hir::StmtKind::Local(hir::Local { init: Some(expr), .. }) => expr, _ => { return; } }; if let hir::ExprKind::Assign(place, rv, _sp) = expr.kind && let hir::ExprKind::Index(val, index) = place.kind && (expr.span == self.assign_span || place.span == self.assign_span) { // val[index] = rv; // ---------- place self.err.multipart_suggestions( format!( "to modify a `{}`, use `.get_mut()`, `.insert()` or the entry API", self.ty, ), vec![ vec![ // val.insert(index, rv); ( val.span.shrink_to_hi().with_hi(index.span.lo()), ".insert(".to_string(), ), ( index.span.shrink_to_hi().with_hi(rv.span.lo()), ", ".to_string(), ), (rv.span.shrink_to_hi(), ")".to_string()), ], vec![ // val.get_mut(index).map(|v| { *v = rv; }); ( val.span.shrink_to_hi().with_hi(index.span.lo()), ".get_mut(".to_string(), ), ( index.span.shrink_to_hi().with_hi(place.span.hi()), ").map(|val| { *val".to_string(), ), ( rv.span.shrink_to_hi(), "; })".to_string(), ), ], vec![ // let x = val.entry(index).or_insert(rv); (val.span.shrink_to_lo(), "let val = ".to_string()), ( val.span.shrink_to_hi().with_hi(index.span.lo()), ".entry(".to_string(), ), ( index.span.shrink_to_hi().with_hi(rv.span.lo()), ").or_insert(".to_string(), ), (rv.span.shrink_to_hi(), ")".to_string()), ], ], Applicability::MachineApplicable, ); self.suggested = true; } else if let hir::ExprKind::MethodCall(_path, receiver, _, sp) = expr.kind && let hir::ExprKind::Index(val, index) = receiver.kind && expr.span == self.assign_span { // val[index].path(args..); self.err.multipart_suggestion( format!("to modify a `{}` use `.get_mut()`", self.ty), vec![ ( val.span.shrink_to_hi().with_hi(index.span.lo()), ".get_mut(".to_string(), ), ( index.span.shrink_to_hi().with_hi(receiver.span.hi()), ").map(|val| val".to_string(), ), (sp.shrink_to_hi(), ")".to_string()), ], Applicability::MachineApplicable, ); self.suggested = true; } } } let hir_map = self.infcx.tcx.hir(); let def_id = self.body.source.def_id(); let hir_id = hir_map.local_def_id_to_hir_id(def_id.as_local().unwrap()); let node = hir_map.find(hir_id); let Some(hir::Node::Item(item)) = node else { return; }; let hir::ItemKind::Fn(.., body_id) = item.kind else { return; }; let body = self.infcx.tcx.hir().body(body_id); let mut v = V { assign_span: span, err, ty, suggested: false }; v.visit_body(body); if !v.suggested { err.help(format!( "to modify a `{ty}`, use `.get_mut()`, `.insert()` or the entry API", )); } } } /// User cannot make signature of a trait mutable without changing the /// trait. So we find if this error belongs to a trait and if so we move /// suggestion to the trait or disable it if it is out of scope of this crate fn is_error_in_trait(&self, local: Local) -> (bool, Option) { if self.body.local_kind(local) != LocalKind::Arg { return (false, None); } let hir_map = self.infcx.tcx.hir(); let my_def = self.body.source.def_id(); let my_hir = hir_map.local_def_id_to_hir_id(my_def.as_local().unwrap()); let Some(td) = self.infcx.tcx.impl_of_method(my_def).and_then(|x| self.infcx.tcx.trait_id_of_impl(x)) else { return (false, None); }; ( true, td.as_local().and_then(|tld| match hir_map.find_by_def_id(tld) { Some(Node::Item(hir::Item { kind: hir::ItemKind::Trait(_, _, _, _, items), .. })) => { let mut f_in_trait_opt = None; for hir::TraitItemRef { id: fi, kind: k, .. } in *items { let hi = fi.hir_id(); if !matches!(k, hir::AssocItemKind::Fn { .. }) { continue; } if hir_map.name(hi) != hir_map.name(my_hir) { continue; } f_in_trait_opt = Some(hi); break; } f_in_trait_opt.and_then(|f_in_trait| match hir_map.find(f_in_trait) { Some(Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn( hir::FnSig { decl: hir::FnDecl { inputs, .. }, .. }, _, ), .. })) => { let hir::Ty { span, .. } = inputs[local.index() - 1]; Some(span) } _ => None, }) } _ => None, }), ) } // point to span of upvar making closure call require mutable borrow fn show_mutating_upvar( &self, tcx: TyCtxt<'_>, closure_local_def_id: hir::def_id::LocalDefId, the_place_err: PlaceRef<'tcx>, err: &mut Diagnostic, ) { let tables = tcx.typeck(closure_local_def_id); if let Some((span, closure_kind_origin)) = tcx.closure_kind_origin(closure_local_def_id) { let reason = if let PlaceBase::Upvar(upvar_id) = closure_kind_origin.base { let upvar = ty::place_to_string_for_capture(tcx, closure_kind_origin); let root_hir_id = upvar_id.var_path.hir_id; // we have an origin for this closure kind starting at this root variable so it's safe to unwrap here let captured_places = tables.closure_min_captures[&closure_local_def_id].get(&root_hir_id).unwrap(); let origin_projection = closure_kind_origin .projections .iter() .map(|proj| proj.kind) .collect::>(); let mut capture_reason = String::new(); for captured_place in captured_places { let captured_place_kinds = captured_place .place .projections .iter() .map(|proj| proj.kind) .collect::>(); if rustc_middle::ty::is_ancestor_or_same_capture( &captured_place_kinds, &origin_projection, ) { match captured_place.info.capture_kind { ty::UpvarCapture::ByRef( ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow, ) => { capture_reason = format!("mutable borrow of `{upvar}`"); } ty::UpvarCapture::ByValue => { capture_reason = format!("possible mutation of `{upvar}`"); } _ => bug!("upvar `{upvar}` borrowed, but not mutably"), } break; } } if capture_reason.is_empty() { bug!("upvar `{upvar}` borrowed, but cannot find reason"); } capture_reason } else { bug!("not an upvar") }; err.span_label( *span, format!( "calling `{}` requires mutable binding due to {}", self.describe_place(the_place_err).unwrap(), reason ), ); } } // Attempt to search similar mutable associated items for suggestion. // In the future, attempt in all path but initially for RHS of for_loop fn suggest_similar_mut_method_for_for_loop(&self, err: &mut Diagnostic) { use hir::{ BodyId, Expr, ExprKind::{Block, Call, DropTemps, Match, MethodCall}, HirId, ImplItem, ImplItemKind, Item, ItemKind, }; fn maybe_body_id_of_fn(hir_map: Map<'_>, id: HirId) -> Option { match hir_map.find(id) { Some(Node::Item(Item { kind: ItemKind::Fn(_, _, body_id), .. })) | Some(Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(_, body_id), .. })) => { Some(*body_id) } _ => None, } } let hir_map = self.infcx.tcx.hir(); let mir_body_hir_id = self.mir_hir_id(); if let Some(fn_body_id) = maybe_body_id_of_fn(hir_map, mir_body_hir_id) { if let Block( hir::Block { expr: Some(Expr { kind: DropTemps(Expr { kind: Match( Expr { kind: Call( _, [ Expr { kind: MethodCall(path_segment, _, _, span), hir_id, .. }, .., ], ), .. }, .., ), .. }), .. }), .. }, _, ) = hir_map.body(fn_body_id).value.kind { let opt_suggestions = self .infcx .tcx .typeck(path_segment.hir_id.owner.def_id) .type_dependent_def_id(*hir_id) .and_then(|def_id| self.infcx.tcx.impl_of_method(def_id)) .map(|def_id| self.infcx.tcx.associated_items(def_id)) .map(|assoc_items| { assoc_items .in_definition_order() .map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx)) .filter(|&ident| { let original_method_ident = path_segment.ident; original_method_ident != ident && ident .as_str() .starts_with(&original_method_ident.name.to_string()) }) .map(|ident| format!("{ident}()")) .peekable() }); if let Some(mut suggestions) = opt_suggestions && suggestions.peek().is_some() { err.span_suggestions( *span, "use mutable method", suggestions, Applicability::MaybeIncorrect, ); } } }; } /// Targeted error when encountering an `FnMut` closure where an `Fn` closure was expected. fn expected_fn_found_fn_mut_call(&self, err: &mut Diagnostic, sp: Span, act: &str) { err.span_label(sp, format!("cannot {act}")); let hir = self.infcx.tcx.hir(); let closure_id = self.mir_hir_id(); let closure_span = self.infcx.tcx.def_span(self.mir_def_id()); let fn_call_id = hir.parent_id(closure_id); let node = hir.get(fn_call_id); let def_id = hir.enclosing_body_owner(fn_call_id); let mut look_at_return = true; // If we can detect the expression to be an `fn` call where the closure was an argument, // we point at the `fn` definition argument... if let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Call(func, args), .. }) = node { let arg_pos = args .iter() .enumerate() .filter(|(_, arg)| arg.hir_id == closure_id) .map(|(pos, _)| pos) .next(); let tables = self.infcx.tcx.typeck(def_id); if let Some(ty::FnDef(def_id, _)) = tables.node_type_opt(func.hir_id).as_ref().map(|ty| ty.kind()) { let arg = match hir.get_if_local(*def_id) { Some( hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(sig, ..), .. }) | hir::Node::TraitItem(hir::TraitItem { ident, kind: hir::TraitItemKind::Fn(sig, _), .. }) | hir::Node::ImplItem(hir::ImplItem { ident, kind: hir::ImplItemKind::Fn(sig, _), .. }), ) => Some( arg_pos .and_then(|pos| { sig.decl.inputs.get( pos + if sig.decl.implicit_self.has_implicit_self() { 1 } else { 0 }, ) }) .map(|arg| arg.span) .unwrap_or(ident.span), ), _ => None, }; if let Some(span) = arg { err.span_label(span, "change this to accept `FnMut` instead of `Fn`"); err.span_label(func.span, "expects `Fn` instead of `FnMut`"); err.span_label(closure_span, "in this closure"); look_at_return = false; } } } if look_at_return && hir.get_return_block(closure_id).is_some() { // ...otherwise we are probably in the tail expression of the function, point at the // return type. match hir.get_by_def_id(hir.get_parent_item(fn_call_id).def_id) { hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(sig, ..), .. }) | hir::Node::TraitItem(hir::TraitItem { ident, kind: hir::TraitItemKind::Fn(sig, _), .. }) | hir::Node::ImplItem(hir::ImplItem { ident, kind: hir::ImplItemKind::Fn(sig, _), .. }) => { err.span_label(ident.span, ""); err.span_label( sig.decl.output.span(), "change this to return `FnMut` instead of `Fn`", ); err.span_label(closure_span, "in this closure"); } _ => {} } } } fn suggest_make_local_mut( &self, err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>, local: Local, name: Symbol, ) { let local_decl = &self.body.local_decls[local]; let (pointer_sigil, pointer_desc) = if local_decl.ty.is_ref() { ("&", "reference") } else { ("*const", "pointer") }; let (is_trait_sig, local_trait) = self.is_error_in_trait(local); if is_trait_sig && local_trait.is_none() { return; } let decl_span = match local_trait { Some(span) => span, None => local_decl.source_info.span, }; let label = match *local_decl.local_info() { LocalInfo::User(mir::BindingForm::ImplicitSelf(_)) => { let suggestion = suggest_ampmut_self(self.infcx.tcx, decl_span); Some((true, decl_span, suggestion)) } LocalInfo::User(mir::BindingForm::Var(mir::VarBindingForm { binding_mode: ty::BindingMode::BindByValue(_), opt_ty_info, .. })) => { // check if the RHS is from desugaring let opt_assignment_rhs_span = self.body.find_assignments(local).first().map(|&location| { if let Some(mir::Statement { source_info: _, kind: mir::StatementKind::Assign(box ( _, mir::Rvalue::Use(mir::Operand::Copy(place)), )), }) = self.body[location.block].statements.get(location.statement_index) { self.body.local_decls[place.local].source_info.span } else { self.body.source_info(location).span } }); match opt_assignment_rhs_span.and_then(|s| s.desugaring_kind()) { // on for loops, RHS points to the iterator part Some(DesugaringKind::ForLoop) => { self.suggest_similar_mut_method_for_for_loop(err); err.span_label( opt_assignment_rhs_span.unwrap(), format!("this iterator yields `{pointer_sigil}` {pointer_desc}s",), ); None } // don't create labels for compiler-generated spans Some(_) => None, None => { let label = if name != kw::SelfLower { suggest_ampmut( self.infcx.tcx, local_decl.ty, decl_span, opt_assignment_rhs_span, opt_ty_info, ) } else { match local_decl.local_info() { LocalInfo::User(mir::BindingForm::Var(mir::VarBindingForm { opt_ty_info: None, .. })) => { let sugg = suggest_ampmut_self(self.infcx.tcx, decl_span); (true, decl_span, sugg) } // explicit self (eg `self: &'a Self`) _ => suggest_ampmut( self.infcx.tcx, local_decl.ty, decl_span, opt_assignment_rhs_span, opt_ty_info, ), } }; Some(label) } } } LocalInfo::User(mir::BindingForm::Var(mir::VarBindingForm { binding_mode: ty::BindingMode::BindByReference(_), .. })) => { let pattern_span: Span = local_decl.source_info.span; suggest_ref_mut(self.infcx.tcx, pattern_span) .map(|span| (true, span, "mut ".to_owned())) } _ => unreachable!(), }; match label { Some((true, err_help_span, suggested_code)) => { err.span_suggestion_verbose( err_help_span, format!("consider changing this to be a mutable {pointer_desc}"), suggested_code, Applicability::MachineApplicable, ); } Some((false, err_label_span, message)) => { struct BindingFinder { span: Span, hir_id: Option, } impl<'tcx> Visitor<'tcx> for BindingFinder { fn visit_stmt(&mut self, s: &'tcx hir::Stmt<'tcx>) { if let hir::StmtKind::Local(local) = s.kind { if local.pat.span == self.span { self.hir_id = Some(local.hir_id); } } hir::intravisit::walk_stmt(self, s); } } let hir_map = self.infcx.tcx.hir(); let def_id = self.body.source.def_id(); let hir_id = hir_map.local_def_id_to_hir_id(def_id.expect_local()); let node = hir_map.find(hir_id); let hir_id = if let Some(hir::Node::Item(item)) = node && let hir::ItemKind::Fn(.., body_id) = item.kind { let body = hir_map.body(body_id); let mut v = BindingFinder { span: err_label_span, hir_id: None, }; v.visit_body(body); v.hir_id } else { None }; if let Some(hir_id) = hir_id && let Some(hir::Node::Local(local)) = hir_map.find(hir_id) { let (changing, span, sugg) = match local.ty { Some(ty) => ("changing", ty.span, message), None => ( "specifying", local.pat.span.shrink_to_hi(), format!(": {message}"), ), }; err.span_suggestion_verbose( span, format!("consider {changing} this binding's type"), sugg, Applicability::HasPlaceholders, ); } else { err.span_label( err_label_span, format!( "consider changing this binding's type to be: `{message}`" ), ); } } None => {} } } } pub fn mut_borrow_of_mutable_ref(local_decl: &LocalDecl<'_>, local_name: Option) -> bool { debug!("local_info: {:?}, ty.kind(): {:?}", local_decl.local_info, local_decl.ty.kind()); match *local_decl.local_info() { // Check if mutably borrowing a mutable reference. LocalInfo::User(mir::BindingForm::Var(mir::VarBindingForm { binding_mode: ty::BindingMode::BindByValue(Mutability::Not), .. })) => matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut)), LocalInfo::User(mir::BindingForm::ImplicitSelf(kind)) => { // Check if the user variable is a `&mut self` and we can therefore // suggest removing the `&mut`. // // Deliberately fall into this case for all implicit self types, // so that we don't fall into the next case with them. kind == hir::ImplicitSelfKind::MutRef } _ if Some(kw::SelfLower) == local_name => { // Otherwise, check if the name is the `self` keyword - in which case // we have an explicit self. Do the same thing in this case and check // for a `self: &mut Self` to suggest removing the `&mut`. matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut)) } _ => false, } } fn suggest_ampmut_self<'tcx>(tcx: TyCtxt<'tcx>, span: Span) -> String { match tcx.sess.source_map().span_to_snippet(span) { Ok(snippet) => { let lt_pos = snippet.find('\''); if let Some(lt_pos) = lt_pos { format!("&{}mut self", &snippet[lt_pos..snippet.len() - 4]) } else { "&mut self".to_string() } } _ => "&mut self".to_string(), } } // When we want to suggest a user change a local variable to be a `&mut`, there // are three potential "obvious" things to highlight: // // let ident [: Type] [= RightHandSideExpression]; // ^^^^^ ^^^^ ^^^^^^^^^^^^^^^^^^^^^^^ // (1.) (2.) (3.) // // We can always fallback on highlighting the first. But chances are good that // the user experience will be better if we highlight one of the others if possible; // for example, if the RHS is present and the Type is not, then the type is going to // be inferred *from* the RHS, which means we should highlight that (and suggest // that they borrow the RHS mutably). // // This implementation attempts to emulate AST-borrowck prioritization // by trying (3.), then (2.) and finally falling back on (1.). fn suggest_ampmut<'tcx>( tcx: TyCtxt<'tcx>, decl_ty: Ty<'tcx>, decl_span: Span, opt_assignment_rhs_span: Option, opt_ty_info: Option, ) -> (bool, Span, String) { // if there is a RHS and it starts with a `&` from it, then check if it is // mutable, and if not, put suggest putting `mut ` to make it mutable. // we don't have to worry about lifetime annotations here because they are // not valid when taking a reference. For example, the following is not valid Rust: // // let x: &i32 = &'a 5; // ^^ lifetime annotation not allowed // if let Some(assignment_rhs_span) = opt_assignment_rhs_span && let Ok(src) = tcx.sess.source_map().span_to_snippet(assignment_rhs_span) && let Some(stripped) = src.strip_prefix('&') { let is_mut = if let Some(rest) = stripped.trim_start().strip_prefix("mut") { match rest.chars().next() { // e.g. `&mut x` Some(c) if c.is_whitespace() => true, // e.g. `&mut(x)` Some('(') => true, // e.g. `&mut{x}` Some('{') => true, // e.g. `&mutablevar` _ => false, } } else { false }; // if the reference is already mutable then there is nothing we can do // here. if !is_mut { let span = assignment_rhs_span; // shrink the span to just after the `&` in `&variable` let span = span.with_lo(span.lo() + BytePos(1)).shrink_to_lo(); // FIXME(Ezrashaw): returning is bad because we still might want to // update the annotated type, see #106857. return (true, span, "mut ".to_owned()); } } let (binding_exists, span) = match opt_ty_info { // if this is a variable binding with an explicit type, // then we will suggest changing it to be mutable. // this is `Applicability::MachineApplicable`. Some(ty_span) => (true, ty_span), // otherwise, we'll suggest *adding* an annotated type, we'll suggest // the RHS's type for that. // this is `Applicability::HasPlaceholders`. None => (false, decl_span), }; // if the binding already exists and is a reference with a explicit // lifetime, then we can suggest adding ` mut`. this is special-cased from // the path without a explicit lifetime. if let Ok(src) = tcx.sess.source_map().span_to_snippet(span) && src.starts_with("&'") // note that `& 'a T` is invalid so this is correct. && let Some(ws_pos) = src.find(char::is_whitespace) { let span = span.with_lo(span.lo() + BytePos(ws_pos as u32)).shrink_to_lo(); (true, span, " mut".to_owned()) // if there is already a binding, we modify it to be `mut` } else if binding_exists { // shrink the span to just after the `&` in `&variable` let span = span.with_lo(span.lo() + BytePos(1)).shrink_to_lo(); (true, span, "mut ".to_owned()) } else { // otherwise, suggest that the user annotates the binding; we provide the // type of the local. let ty_mut = decl_ty.builtin_deref(true).unwrap(); assert_eq!(ty_mut.mutbl, hir::Mutability::Not); ( false, span, format!("{}mut {}", if decl_ty.is_ref() {"&"} else {"*"}, ty_mut.ty) ) } } fn is_closure_or_generator(ty: Ty<'_>) -> bool { ty.is_closure() || ty.is_generator() } /// Given a field that needs to be mutable, returns a span where the " mut " could go. /// This function expects the local to be a reference to a struct in order to produce a span. /// /// ```text /// LL | s: &'a String /// | ^^^ returns a span taking up the space here /// ``` fn get_mut_span_in_struct_field<'tcx>( tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, field: FieldIdx, ) -> Option { // Expect our local to be a reference to a struct of some kind. if let ty::Ref(_, ty, _) = ty.kind() && let ty::Adt(def, _) = ty.kind() && let field = def.all_fields().nth(field.index())? // Use the HIR types to construct the diagnostic message. && let node = tcx.hir().find_by_def_id(field.did.as_local()?)? // Now we're dealing with the actual struct that we're going to suggest a change to, // we can expect a field that is an immutable reference to a type. && let hir::Node::Field(field) = node && let hir::TyKind::Ref(lt, hir::MutTy { mutbl: hir::Mutability::Not, ty }) = field.ty.kind { return Some(lt.ident.span.between(ty.span)); } None } /// If possible, suggest replacing `ref` with `ref mut`. fn suggest_ref_mut(tcx: TyCtxt<'_>, span: Span) -> Option { let pattern_str = tcx.sess.source_map().span_to_snippet(span).ok()?; if pattern_str.starts_with("ref") && pattern_str["ref".len()..].starts_with(rustc_lexer::is_whitespace) { let span = span.with_lo(span.lo() + BytePos(4)).shrink_to_lo(); Some(span) } else { None } }