| use rustc::hir; |
| use rustc::hir::Node; |
| use rustc::mir::{self, ClearCrossCrate, Local, LocalInfo, Location, ReadOnlyBodyCache}; |
| use rustc::mir::{Mutability, Place, PlaceRef, PlaceBase, ProjectionElem}; |
| use rustc::ty::{self, Ty, TyCtxt}; |
| use rustc_index::vec::Idx; |
| use syntax_pos::Span; |
| use syntax_pos::symbol::kw; |
| |
| use crate::borrow_check::MirBorrowckCtxt; |
| use crate::borrow_check::diagnostics::BorrowedContentSource; |
| use crate::util::collect_writes::FindAssignments; |
| use rustc_errors::Applicability; |
| |
| #[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<'cx, '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_place(access_place.as_ref()); |
| debug!("report_mutability_error: access_place_desc={:?}", access_place_desc); |
| |
| match the_place_err { |
| PlaceRef { |
| base: PlaceBase::Local(local), |
| projection: [], |
| } => { |
| item_msg = format!("`{}`", access_place_desc.unwrap()); |
| 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 `{}` is not declared as mutable", name); |
| } |
| } |
| |
| PlaceRef { |
| base: _, |
| projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)], |
| } => { |
| debug_assert!(is_closure_or_generator( |
| Place::ty_from( |
| &the_place_err.base, |
| proj_base, |
| *self.body, |
| self.infcx.tcx |
| ).ty)); |
| |
| item_msg = format!("`{}`", access_place_desc.unwrap()); |
| 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()].name; |
| reason = format!(", as `{}` is not declared as mutable", name); |
| } |
| } |
| |
| PlaceRef { |
| base: &PlaceBase::Local(local), |
| projection: [ProjectionElem::Deref], |
| } if self.body.local_decls[local].is_ref_for_guard() => { |
| item_msg = format!("`{}`", access_place_desc.unwrap()); |
| reason = ", as it is immutable for the pattern guard".to_string(); |
| } |
| PlaceRef { |
| base: &PlaceBase::Local(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.unwrap()); |
| reason = String::new(); |
| } else { |
| item_msg = format!("`{}`", access_place_desc.unwrap()); |
| 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 `{}` is an immutable static item", static_name); |
| } else { |
| bug!("is_ref_to_static return true, but not ref to static?"); |
| } |
| } |
| } |
| PlaceRef { |
| base: _, |
| projection: [proj_base @ .., ProjectionElem::Deref], |
| } => { |
| if the_place_err.base == &PlaceBase::Local(Local::new(1)) && |
| proj_base.is_empty() && |
| !self.upvars.is_empty() { |
| item_msg = format!("`{}`", access_place_desc.unwrap()); |
| debug_assert!(self.body.local_decls[Local::new(1)].ty.is_region_ptr()); |
| debug_assert!(is_closure_or_generator( |
| Place::ty_from( |
| the_place_err.base, |
| the_place_err.projection, |
| *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 { |
| base: the_place_err.base, |
| projection: proj_base, |
| }); |
| let pointer_type = source.describe_for_immutable_place(); |
| opt_source = Some(source); |
| if let Some(desc) = access_place_desc { |
| 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 { |
| base: PlaceBase::Static(_), |
| .. |
| } |
| | PlaceRef { |
| base: _, |
| projection: [.., ProjectionElem::Index(_)], |
| } |
| | PlaceRef { |
| base: _, |
| projection: [.., ProjectionElem::ConstantIndex { .. }], |
| } |
| | PlaceRef { |
| base: _, |
| projection: [.., ProjectionElem::Subslice { .. }], |
| } |
| | PlaceRef { |
| base: _, |
| projection: [.., 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 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(); |
| err = self.cannot_borrow_path_as_mutable_because( |
| borrow_span, |
| &item_msg, |
| &reason, |
| ); |
| borrow_spans.var_span_label( |
| &mut err, |
| format!( |
| "mutable borrow occurs due to use of `{}` in closure", |
| // always Some() if the message is printed. |
| self.describe_place(access_place.as_ref()).unwrap_or_default(), |
| ) |
| ); |
| 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 { |
| base, |
| projection: [proj_base @ .., |
| ProjectionElem::Deref, |
| ProjectionElem::Field(field, _), |
| ProjectionElem::Deref, |
| ], |
| } => { |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| |
| if let Some((span, message)) = annotate_struct_field( |
| self.infcx.tcx, |
| Place::ty_from(base, proj_base, *self.body, self.infcx.tcx).ty, |
| field, |
| ) { |
| err.span_suggestion( |
| span, |
| "consider changing this to be mutable", |
| message, |
| Applicability::MaybeIncorrect, |
| ); |
| } |
| }, |
| |
| // Suggest removing a `&mut` from the use of a mutable reference. |
| PlaceRef { |
| base: PlaceBase::Local(local), |
| projection: [], |
| } if { |
| self.body.local_decls.get(*local).map(|local_decl| { |
| if let LocalInfo::User(ClearCrossCrate::Set( |
| mir::BindingForm::ImplicitSelf(kind) |
| )) = local_decl.local_info { |
| // 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 in to the next case with them. |
| kind == mir::ImplicitSelfKind::MutRef |
| } else if Some(kw::SelfLower) == self.local_names[*local] { |
| // Otherwise, check if the name is the self kewyord - 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`. |
| if let ty::Ref( |
| _, _, hir::Mutability::Mutable |
| ) = local_decl.ty.kind { |
| true |
| } else { |
| false |
| } |
| } else { |
| false |
| } |
| }).unwrap_or(false) |
| } => { |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| err.span_label(span, "try removing `&mut` here"); |
| }, |
| |
| // We want to suggest users use `let mut` for local (user |
| // variable) mutations... |
| PlaceRef { |
| base: PlaceBase::Local(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); |
| |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| err.span_suggestion( |
| local_decl.source_info.span, |
| "consider changing this to be mutable", |
| format!("mut {}", self.local_names[*local].unwrap()), |
| Applicability::MachineApplicable, |
| ); |
| } |
| |
| // Also suggest adding mut for upvars |
| PlaceRef { |
| base, |
| projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)], |
| } => { |
| debug_assert!(is_closure_or_generator( |
| Place::ty_from(base, proj_base, *self.body, self.infcx.tcx).ty |
| )); |
| |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| |
| let upvar_hir_id = self.upvars[upvar_index.index()].var_hir_id; |
| if let Some(Node::Binding(pat)) = self.infcx.tcx.hir().find(upvar_hir_id) |
| { |
| if let hir::PatKind::Binding( |
| hir::BindingAnnotation::Unannotated, |
| _, |
| upvar_ident, |
| _, |
| ) = pat.kind |
| { |
| err.span_suggestion( |
| upvar_ident.span, |
| "consider changing this to be mutable", |
| format!("mut {}", upvar_ident.name), |
| Applicability::MachineApplicable, |
| ); |
| } |
| } |
| } |
| |
| // 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 { |
| base: PlaceBase::Local(_), |
| projection: [], |
| } if { |
| if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) { |
| snippet.starts_with("&mut ") |
| } else { |
| false |
| } |
| } => |
| { |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| err.span_label(span, "try removing `&mut` here"); |
| } |
| |
| PlaceRef { |
| base: PlaceBase::Local(local), |
| projection: [ProjectionElem::Deref], |
| } if self.body.local_decls[*local].is_ref_for_guard() => { |
| err.span_label(span, format!("cannot {ACT}", ACT = 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 { |
| base: PlaceBase::Local(local), |
| projection: [ProjectionElem::Deref], |
| } if self.body.local_decls[*local].is_user_variable() => |
| { |
| let local_decl = &self.body.local_decls[*local]; |
| let suggestion = match local_decl.local_info { |
| LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::ImplicitSelf(_))) => { |
| Some(suggest_ampmut_self(self.infcx.tcx, local_decl)) |
| } |
| |
| LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var( |
| mir::VarBindingForm { |
| binding_mode: ty::BindingMode::BindByValue(_), |
| opt_ty_info, |
| .. |
| }, |
| ))) => Some(suggest_ampmut( |
| self.infcx.tcx, |
| self.body, |
| *local, |
| local_decl, |
| opt_ty_info, |
| )), |
| |
| LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var( |
| mir::VarBindingForm { |
| binding_mode: ty::BindingMode::BindByReference(_), |
| .. |
| }, |
| ))) => { |
| let pattern_span = local_decl.source_info.span; |
| suggest_ref_mut(self.infcx.tcx, pattern_span) |
| .map(|replacement| (pattern_span, replacement)) |
| } |
| |
| LocalInfo::User(ClearCrossCrate::Clear) => bug!("saw cleared local state"), |
| |
| _ => unreachable!(), |
| }; |
| |
| let (pointer_sigil, pointer_desc) = if local_decl.ty.is_region_ptr() { |
| ("&", "reference") |
| } else { |
| ("*const", "pointer") |
| }; |
| |
| if let Some((err_help_span, suggested_code)) = suggestion { |
| err.span_suggestion( |
| err_help_span, |
| &format!("consider changing this to be a mutable {}", pointer_desc), |
| suggested_code, |
| Applicability::MachineApplicable, |
| ); |
| } |
| |
| match self.local_names[*local] { |
| Some(name) if !local_decl.from_compiler_desugaring() => { |
| err.span_label( |
| span, |
| format!( |
| "`{NAME}` is a `{SIGIL}` {DESC}, \ |
| so the data it refers to cannot be {ACTED_ON}", |
| NAME = name, |
| SIGIL = pointer_sigil, |
| DESC = pointer_desc, |
| ACTED_ON = acted_on |
| ), |
| ); |
| } |
| _ => { |
| err.span_label( |
| span, |
| format!( |
| "cannot {ACT} through `{SIGIL}` {DESC}", |
| ACT = act, |
| SIGIL = pointer_sigil, |
| DESC = pointer_desc |
| ), |
| ); |
| } |
| } |
| } |
| |
| PlaceRef { |
| base, |
| projection: [ProjectionElem::Deref], |
| // FIXME document what is this 1 magic number about |
| } if *base == PlaceBase::Local(Local::new(1)) && |
| !self.upvars.is_empty() => |
| { |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| err.span_help( |
| self.body.span, |
| "consider changing this to accept closures that implement `FnMut`" |
| ); |
| } |
| |
| PlaceRef { |
| base: _, |
| projection: [.., ProjectionElem::Deref], |
| } => { |
| err.span_label(span, format!("cannot {ACT}", ACT = 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, |
| ), |
| ); |
| } |
| _ => (), |
| } |
| } |
| |
| _ => { |
| err.span_label(span, format!("cannot {ACT}", ACT = act)); |
| } |
| } |
| |
| err.buffer(&mut self.errors_buffer); |
| } |
| } |
| |
| fn suggest_ampmut_self<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| local_decl: &mir::LocalDecl<'tcx>, |
| ) -> (Span, String) { |
| let sp = local_decl.source_info.span; |
| (sp, match tcx.sess.source_map().span_to_snippet(sp) { |
| 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>, |
| body: ReadOnlyBodyCache<'_, 'tcx>, |
| local: Local, |
| local_decl: &mir::LocalDecl<'tcx>, |
| opt_ty_info: Option<Span>, |
| ) -> (Span, String) { |
| let locations = body.find_assignments(local); |
| if !locations.is_empty() { |
| let assignment_rhs_span = body.source_info(locations[0]).span; |
| if let Ok(src) = tcx.sess.source_map().span_to_snippet(assignment_rhs_span) { |
| if let (true, Some(ws_pos)) = ( |
| src.starts_with("&'"), |
| src.find(|c: char| -> bool { c.is_whitespace() }), |
| ) { |
| let lt_name = &src[1..ws_pos]; |
| let ty = &src[ws_pos..]; |
| return (assignment_rhs_span, format!("&{} mut {}", lt_name, ty)); |
| } else if src.starts_with('&') { |
| let borrowed_expr = &src[1..]; |
| return (assignment_rhs_span, format!("&mut {}", borrowed_expr)); |
| } |
| } |
| } |
| |
| let highlight_span = match opt_ty_info { |
| // if this is a variable binding with an explicit type, |
| // try to highlight that for the suggestion. |
| Some(ty_span) => ty_span, |
| |
| // otherwise, just highlight the span associated with |
| // the (MIR) LocalDecl. |
| None => local_decl.source_info.span, |
| }; |
| |
| if let Ok(src) = tcx.sess.source_map().span_to_snippet(highlight_span) { |
| if let (true, Some(ws_pos)) = ( |
| src.starts_with("&'"), |
| src.find(|c: char| -> bool { c.is_whitespace() }), |
| ) { |
| let lt_name = &src[1..ws_pos]; |
| let ty = &src[ws_pos..]; |
| return (highlight_span, format!("&{} mut{}", lt_name, ty)); |
| } |
| } |
| |
| let ty_mut = local_decl.ty.builtin_deref(true).unwrap(); |
| assert_eq!(ty_mut.mutbl, hir::Mutability::Immutable); |
| (highlight_span, |
| if local_decl.ty.is_region_ptr() { |
| format!("&mut {}", ty_mut.ty) |
| } else { |
| format!("*mut {}", ty_mut.ty) |
| }) |
| } |
| |
| fn is_closure_or_generator(ty: Ty<'_>) -> bool { |
| ty.is_closure() || ty.is_generator() |
| } |
| |
| /// Adds a suggestion to a struct definition given a field access to a local. |
| /// This function expects the local to be a reference to a struct in order to produce a suggestion. |
| /// |
| /// ```text |
| /// LL | s: &'a String |
| /// | ---------- use `&'a mut String` here to make mutable |
| /// ``` |
| fn annotate_struct_field( |
| tcx: TyCtxt<'tcx>, |
| ty: Ty<'tcx>, |
| field: &mir::Field, |
| ) -> Option<(Span, String)> { |
| // Expect our local to be a reference to a struct of some kind. |
| if let ty::Ref(_, ty, _) = ty.kind { |
| if let ty::Adt(def, _) = ty.kind { |
| let field = def.all_fields().nth(field.index())?; |
| // Use the HIR types to construct the diagnostic message. |
| let hir_id = tcx.hir().as_local_hir_id(field.did)?; |
| let node = tcx.hir().find(hir_id)?; |
| // 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. |
| if let hir::Node::Field(field) = node { |
| if let hir::TyKind::Rptr(lifetime, hir::MutTy { |
| mutbl: hir::Mutability::Immutable, |
| ref ty |
| }) = field.ty.kind { |
| // Get the snippets in two parts - the named lifetime (if there is one) and |
| // type being referenced, that way we can reconstruct the snippet without loss |
| // of detail. |
| let type_snippet = tcx.sess.source_map().span_to_snippet(ty.span).ok()?; |
| let lifetime_snippet = if !lifetime.is_elided() { |
| format!("{} ", tcx.sess.source_map().span_to_snippet(lifetime.span).ok()?) |
| } else { |
| String::new() |
| }; |
| |
| return Some(( |
| field.ty.span, |
| format!( |
| "&{}mut {}", |
| lifetime_snippet, &*type_snippet, |
| ), |
| )); |
| } |
| } |
| } |
| } |
| |
| None |
| } |
| |
| /// If possible, suggest replacing `ref` with `ref mut`. |
| fn suggest_ref_mut(tcx: TyCtxt<'_>, binding_span: Span) -> Option<String> { |
| let hi_src = tcx.sess.source_map().span_to_snippet(binding_span).ok()?; |
| if hi_src.starts_with("ref") |
| && hi_src["ref".len()..].starts_with(rustc_lexer::is_whitespace) |
| { |
| let replacement = format!("ref mut{}", &hi_src["ref".len()..]); |
| Some(replacement) |
| } else { |
| None |
| } |
| } |
