| use super::usefulness::Usefulness::*; |
| use super::usefulness::{ |
| compute_match_usefulness, expand_pattern, MatchArm, MatchCheckCtxt, UsefulnessReport, |
| }; |
| use super::{PatCtxt, PatKind, PatternError}; |
| |
| use rustc_arena::TypedArena; |
| use rustc_ast::Mutability; |
| use rustc_errors::{error_code, struct_span_err, Applicability, DiagnosticBuilder}; |
| use rustc_hir as hir; |
| use rustc_hir::def::*; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor}; |
| use rustc_hir::{HirId, Pat}; |
| use rustc_middle::ty::{self, Ty, TyCtxt}; |
| use rustc_session::lint::builtin::BINDINGS_WITH_VARIANT_NAME; |
| use rustc_session::lint::builtin::{IRREFUTABLE_LET_PATTERNS, UNREACHABLE_PATTERNS}; |
| use rustc_session::parse::feature_err; |
| use rustc_session::Session; |
| use rustc_span::{sym, Span}; |
| use std::slice; |
| |
| crate fn check_match(tcx: TyCtxt<'_>, def_id: DefId) { |
| let body_id = match def_id.as_local() { |
| None => return, |
| Some(id) => tcx.hir().body_owned_by(tcx.hir().local_def_id_to_hir_id(id)), |
| }; |
| |
| let mut visitor = MatchVisitor { |
| tcx, |
| typeck_results: tcx.typeck_body(body_id), |
| param_env: tcx.param_env(def_id), |
| pattern_arena: TypedArena::default(), |
| }; |
| visitor.visit_body(tcx.hir().body(body_id)); |
| } |
| |
| fn create_e0004(sess: &Session, sp: Span, error_message: String) -> DiagnosticBuilder<'_> { |
| struct_span_err!(sess, sp, E0004, "{}", &error_message) |
| } |
| |
| struct MatchVisitor<'a, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| typeck_results: &'a ty::TypeckResults<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| pattern_arena: TypedArena<super::Pat<'tcx>>, |
| } |
| |
| impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, 'tcx> { |
| type Map = intravisit::ErasedMap<'tcx>; |
| |
| fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { |
| NestedVisitorMap::None |
| } |
| |
| fn visit_expr(&mut self, ex: &'tcx hir::Expr<'tcx>) { |
| intravisit::walk_expr(self, ex); |
| |
| if let hir::ExprKind::Match(ref scrut, ref arms, source) = ex.kind { |
| self.check_match(scrut, arms, source); |
| } |
| } |
| |
| fn visit_local(&mut self, loc: &'tcx hir::Local<'tcx>) { |
| intravisit::walk_local(self, loc); |
| |
| let (msg, sp) = match loc.source { |
| hir::LocalSource::Normal => ("local binding", Some(loc.span)), |
| hir::LocalSource::ForLoopDesugar => ("`for` loop binding", None), |
| hir::LocalSource::AsyncFn => ("async fn binding", None), |
| hir::LocalSource::AwaitDesugar => ("`await` future binding", None), |
| hir::LocalSource::AssignDesugar(_) => ("destructuring assignment binding", None), |
| }; |
| self.check_irrefutable(&loc.pat, msg, sp); |
| self.check_patterns(&loc.pat); |
| } |
| |
| fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) { |
| intravisit::walk_param(self, param); |
| self.check_irrefutable(¶m.pat, "function argument", None); |
| self.check_patterns(¶m.pat); |
| } |
| } |
| |
| impl PatCtxt<'_, '_> { |
| fn report_inlining_errors(&self, pat_span: Span) { |
| for error in &self.errors { |
| match *error { |
| PatternError::StaticInPattern(span) => { |
| self.span_e0158(span, "statics cannot be referenced in patterns") |
| } |
| PatternError::AssocConstInPattern(span) => { |
| self.span_e0158(span, "associated consts cannot be referenced in patterns") |
| } |
| PatternError::ConstParamInPattern(span) => { |
| self.span_e0158(span, "const parameters cannot be referenced in patterns") |
| } |
| PatternError::FloatBug => { |
| // FIXME(#31407) this is only necessary because float parsing is buggy |
| rustc_middle::mir::interpret::struct_error( |
| self.tcx.at(pat_span), |
| "could not evaluate float literal (see issue #31407)", |
| ) |
| .emit(); |
| } |
| PatternError::NonConstPath(span) => { |
| rustc_middle::mir::interpret::struct_error( |
| self.tcx.at(span), |
| "runtime values cannot be referenced in patterns", |
| ) |
| .emit(); |
| } |
| } |
| } |
| } |
| |
| fn span_e0158(&self, span: Span, text: &str) { |
| struct_span_err!(self.tcx.sess, span, E0158, "{}", text).emit(); |
| } |
| } |
| |
| impl<'tcx> MatchVisitor<'_, 'tcx> { |
| fn check_patterns(&mut self, pat: &Pat<'_>) { |
| pat.walk_always(|pat| check_borrow_conflicts_in_at_patterns(self, pat)); |
| if !self.tcx.features().bindings_after_at { |
| check_legality_of_bindings_in_at_patterns(self, pat); |
| } |
| check_for_bindings_named_same_as_variants(self, pat); |
| } |
| |
| fn lower_pattern<'p>( |
| &self, |
| cx: &mut MatchCheckCtxt<'p, 'tcx>, |
| pat: &'tcx hir::Pat<'tcx>, |
| have_errors: &mut bool, |
| ) -> (&'p super::Pat<'tcx>, Ty<'tcx>) { |
| let mut patcx = PatCtxt::new(self.tcx, self.param_env, self.typeck_results); |
| patcx.include_lint_checks(); |
| let pattern = patcx.lower_pattern(pat); |
| let pattern_ty = pattern.ty; |
| let pattern: &_ = cx.pattern_arena.alloc(expand_pattern(pattern)); |
| if !patcx.errors.is_empty() { |
| *have_errors = true; |
| patcx.report_inlining_errors(pat.span); |
| } |
| (pattern, pattern_ty) |
| } |
| |
| fn new_cx(&self, hir_id: HirId) -> MatchCheckCtxt<'_, 'tcx> { |
| MatchCheckCtxt { |
| tcx: self.tcx, |
| param_env: self.param_env, |
| module: self.tcx.parent_module(hir_id).to_def_id(), |
| pattern_arena: &self.pattern_arena, |
| } |
| } |
| |
| fn check_match( |
| &mut self, |
| scrut: &hir::Expr<'_>, |
| arms: &'tcx [hir::Arm<'tcx>], |
| source: hir::MatchSource, |
| ) { |
| for arm in arms { |
| // Check the arm for some things unrelated to exhaustiveness. |
| self.check_patterns(&arm.pat); |
| if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard { |
| self.check_patterns(pat); |
| } |
| } |
| |
| let mut cx = self.new_cx(scrut.hir_id); |
| |
| for arm in arms { |
| if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard { |
| let tpat = self.lower_pattern(&mut cx, pat, &mut false).0; |
| check_if_let_guard(&mut cx, &tpat, pat.hir_id); |
| } |
| } |
| |
| let mut have_errors = false; |
| |
| let arms: Vec<_> = arms |
| .iter() |
| .map(|hir::Arm { pat, guard, .. }| MatchArm { |
| pat: self.lower_pattern(&mut cx, pat, &mut have_errors).0, |
| hir_id: pat.hir_id, |
| has_guard: guard.is_some(), |
| }) |
| .collect(); |
| |
| // Bail out early if lowering failed. |
| if have_errors { |
| return; |
| } |
| |
| let scrut_ty = self.typeck_results.expr_ty_adjusted(scrut); |
| let report = compute_match_usefulness(&cx, &arms, scrut.hir_id, scrut_ty); |
| |
| // Report unreachable arms. |
| report_arm_reachability(&cx, &report, source); |
| |
| // Check if the match is exhaustive. |
| // Note: An empty match isn't the same as an empty matrix for diagnostics purposes, |
| // since an empty matrix can occur when there are arms, if those arms all have guards. |
| let is_empty_match = arms.is_empty(); |
| let witnesses = report.non_exhaustiveness_witnesses; |
| if !witnesses.is_empty() { |
| non_exhaustive_match(&cx, scrut_ty, scrut.span, witnesses, is_empty_match); |
| } |
| } |
| |
| fn check_irrefutable(&self, pat: &'tcx Pat<'tcx>, origin: &str, sp: Option<Span>) { |
| let mut cx = self.new_cx(pat.hir_id); |
| |
| let (pattern, pattern_ty) = self.lower_pattern(&mut cx, pat, &mut false); |
| let arms = vec![MatchArm { pat: pattern, hir_id: pat.hir_id, has_guard: false }]; |
| let report = compute_match_usefulness(&cx, &arms, pat.hir_id, pattern_ty); |
| |
| // Note: we ignore whether the pattern is unreachable (i.e. whether the type is empty). We |
| // only care about exhaustiveness here. |
| let witnesses = report.non_exhaustiveness_witnesses; |
| if witnesses.is_empty() { |
| // The pattern is irrefutable. |
| return; |
| } |
| |
| let joined_patterns = joined_uncovered_patterns(&witnesses); |
| let mut err = struct_span_err!( |
| self.tcx.sess, |
| pat.span, |
| E0005, |
| "refutable pattern in {}: {} not covered", |
| origin, |
| joined_patterns |
| ); |
| let suggest_if_let = match &pat.kind { |
| hir::PatKind::Path(hir::QPath::Resolved(None, path)) |
| if path.segments.len() == 1 && path.segments[0].args.is_none() => |
| { |
| const_not_var(&mut err, cx.tcx, pat, path); |
| false |
| } |
| _ => { |
| err.span_label(pat.span, pattern_not_covered_label(&witnesses, &joined_patterns)); |
| true |
| } |
| }; |
| |
| if let (Some(span), true) = (sp, suggest_if_let) { |
| err.note( |
| "`let` bindings require an \"irrefutable pattern\", like a `struct` or \ |
| an `enum` with only one variant", |
| ); |
| if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) { |
| err.span_suggestion( |
| span, |
| "you might want to use `if let` to ignore the variant that isn't matched", |
| format!("if {} {{ /* */ }}", &snippet[..snippet.len() - 1]), |
| Applicability::HasPlaceholders, |
| ); |
| } |
| err.note( |
| "for more information, visit \ |
| https://doc.rust-lang.org/book/ch18-02-refutability.html", |
| ); |
| } |
| |
| adt_defined_here(&cx, &mut err, pattern_ty, &witnesses); |
| err.note(&format!("the matched value is of type `{}`", pattern_ty)); |
| err.emit(); |
| } |
| } |
| |
| /// A path pattern was interpreted as a constant, not a new variable. |
| /// This caused an irrefutable match failure in e.g. `let`. |
| fn const_not_var( |
| err: &mut DiagnosticBuilder<'_>, |
| tcx: TyCtxt<'_>, |
| pat: &Pat<'_>, |
| path: &hir::Path<'_>, |
| ) { |
| let descr = path.res.descr(); |
| err.span_label( |
| pat.span, |
| format!("interpreted as {} {} pattern, not a new variable", path.res.article(), descr,), |
| ); |
| |
| err.span_suggestion( |
| pat.span, |
| "introduce a variable instead", |
| format!("{}_var", path.segments[0].ident).to_lowercase(), |
| // Cannot use `MachineApplicable` as it's not really *always* correct |
| // because there may be such an identifier in scope or the user maybe |
| // really wanted to match against the constant. This is quite unlikely however. |
| Applicability::MaybeIncorrect, |
| ); |
| |
| if let Some(span) = tcx.hir().res_span(path.res) { |
| err.span_label(span, format!("{} defined here", descr)); |
| } |
| } |
| |
| fn check_for_bindings_named_same_as_variants(cx: &MatchVisitor<'_, '_>, pat: &Pat<'_>) { |
| pat.walk_always(|p| { |
| if let hir::PatKind::Binding(_, _, ident, None) = p.kind { |
| if let Some(ty::BindByValue(hir::Mutability::Not)) = |
| cx.typeck_results.extract_binding_mode(cx.tcx.sess, p.hir_id, p.span) |
| { |
| let pat_ty = cx.typeck_results.pat_ty(p).peel_refs(); |
| if let ty::Adt(edef, _) = pat_ty.kind() { |
| if edef.is_enum() |
| && edef.variants.iter().any(|variant| { |
| variant.ident == ident && variant.ctor_kind == CtorKind::Const |
| }) |
| { |
| cx.tcx.struct_span_lint_hir( |
| BINDINGS_WITH_VARIANT_NAME, |
| p.hir_id, |
| p.span, |
| |lint| { |
| let ty_path = cx.tcx.def_path_str(edef.did); |
| lint.build(&format!( |
| "pattern binding `{}` is named the same as one \ |
| of the variants of the type `{}`", |
| ident, ty_path |
| )) |
| .code(error_code!(E0170)) |
| .span_suggestion( |
| p.span, |
| "to match on the variant, qualify the path", |
| format!("{}::{}", ty_path, ident), |
| Applicability::MachineApplicable, |
| ) |
| .emit(); |
| }, |
| ) |
| } |
| } |
| } |
| } |
| }); |
| } |
| |
| /// Checks for common cases of "catchall" patterns that may not be intended as such. |
| fn pat_is_catchall(pat: &super::Pat<'_>) -> bool { |
| use super::PatKind::*; |
| match &*pat.kind { |
| Binding { subpattern: None, .. } => true, |
| Binding { subpattern: Some(s), .. } | Deref { subpattern: s } => pat_is_catchall(s), |
| Leaf { subpatterns: s } => s.iter().all(|p| pat_is_catchall(&p.pattern)), |
| _ => false, |
| } |
| } |
| |
| fn unreachable_pattern(tcx: TyCtxt<'_>, span: Span, id: HirId, catchall: Option<Span>) { |
| tcx.struct_span_lint_hir(UNREACHABLE_PATTERNS, id, span, |lint| { |
| let mut err = lint.build("unreachable pattern"); |
| if let Some(catchall) = catchall { |
| // We had a catchall pattern, hint at that. |
| err.span_label(span, "unreachable pattern"); |
| err.span_label(catchall, "matches any value"); |
| } |
| err.emit(); |
| }); |
| } |
| |
| fn irrefutable_let_pattern(tcx: TyCtxt<'_>, span: Span, id: HirId, source: hir::MatchSource) { |
| tcx.struct_span_lint_hir(IRREFUTABLE_LET_PATTERNS, id, span, |lint| { |
| let msg = match source { |
| hir::MatchSource::IfLetDesugar { .. } => "irrefutable if-let pattern", |
| hir::MatchSource::WhileLetDesugar => "irrefutable while-let pattern", |
| hir::MatchSource::IfLetGuardDesugar => "irrefutable if-let guard", |
| _ => bug!(), |
| }; |
| lint.build(msg).emit() |
| }); |
| } |
| |
| fn check_if_let_guard<'p, 'tcx>( |
| cx: &mut MatchCheckCtxt<'p, 'tcx>, |
| pat: &'p super::Pat<'tcx>, |
| pat_id: HirId, |
| ) { |
| let arms = [MatchArm { pat, hir_id: pat_id, has_guard: false }]; |
| let report = compute_match_usefulness(&cx, &arms, pat_id, pat.ty); |
| report_arm_reachability(&cx, &report, hir::MatchSource::IfLetGuardDesugar); |
| |
| if report.non_exhaustiveness_witnesses.is_empty() { |
| // The match is exhaustive, i.e. the if let pattern is irrefutable. |
| irrefutable_let_pattern(cx.tcx, pat.span, pat_id, hir::MatchSource::IfLetGuardDesugar) |
| } |
| } |
| |
| /// Report unreachable arms, if any. |
| fn report_arm_reachability<'p, 'tcx>( |
| cx: &MatchCheckCtxt<'p, 'tcx>, |
| report: &UsefulnessReport<'p, 'tcx>, |
| source: hir::MatchSource, |
| ) { |
| let mut catchall = None; |
| for (arm_index, (arm, is_useful)) in report.arm_usefulness.iter().enumerate() { |
| match is_useful { |
| NotUseful => { |
| match source { |
| hir::MatchSource::IfDesugar { .. } | hir::MatchSource::WhileDesugar => bug!(), |
| |
| hir::MatchSource::IfLetDesugar { .. } | hir::MatchSource::WhileLetDesugar => { |
| // Check which arm we're on. |
| match arm_index { |
| // The arm with the user-specified pattern. |
| 0 => unreachable_pattern(cx.tcx, arm.pat.span, arm.hir_id, None), |
| // The arm with the wildcard pattern. |
| 1 => irrefutable_let_pattern(cx.tcx, arm.pat.span, arm.hir_id, source), |
| _ => bug!(), |
| } |
| } |
| |
| hir::MatchSource::IfLetGuardDesugar => { |
| assert_eq!(arm_index, 0); |
| unreachable_pattern(cx.tcx, arm.pat.span, arm.hir_id, None); |
| } |
| |
| hir::MatchSource::ForLoopDesugar | hir::MatchSource::Normal => { |
| unreachable_pattern(cx.tcx, arm.pat.span, arm.hir_id, catchall); |
| } |
| |
| // Unreachable patterns in try and await expressions occur when one of |
| // the arms are an uninhabited type. Which is OK. |
| hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {} |
| } |
| } |
| Useful(unreachables) if unreachables.is_empty() => {} |
| // The arm is reachable, but contains unreachable subpatterns (from or-patterns). |
| Useful(unreachables) => { |
| let mut unreachables: Vec<_> = unreachables.iter().collect(); |
| // Emit lints in the order in which they occur in the file. |
| unreachables.sort_unstable(); |
| for span in unreachables { |
| unreachable_pattern(cx.tcx, span, arm.hir_id, None); |
| } |
| } |
| UsefulWithWitness(_) => bug!(), |
| } |
| if !arm.has_guard && catchall.is_none() && pat_is_catchall(arm.pat) { |
| catchall = Some(arm.pat.span); |
| } |
| } |
| } |
| |
| /// Report that a match is not exhaustive. |
| fn non_exhaustive_match<'p, 'tcx>( |
| cx: &MatchCheckCtxt<'p, 'tcx>, |
| scrut_ty: Ty<'tcx>, |
| sp: Span, |
| witnesses: Vec<super::Pat<'tcx>>, |
| is_empty_match: bool, |
| ) { |
| let non_empty_enum = match scrut_ty.kind() { |
| ty::Adt(def, _) => def.is_enum() && !def.variants.is_empty(), |
| _ => false, |
| }; |
| // In the case of an empty match, replace the '`_` not covered' diagnostic with something more |
| // informative. |
| let mut err; |
| if is_empty_match && !non_empty_enum { |
| err = create_e0004( |
| cx.tcx.sess, |
| sp, |
| format!("non-exhaustive patterns: type `{}` is non-empty", scrut_ty), |
| ); |
| } else { |
| let joined_patterns = joined_uncovered_patterns(&witnesses); |
| err = create_e0004( |
| cx.tcx.sess, |
| sp, |
| format!("non-exhaustive patterns: {} not covered", joined_patterns), |
| ); |
| err.span_label(sp, pattern_not_covered_label(&witnesses, &joined_patterns)); |
| }; |
| |
| adt_defined_here(cx, &mut err, scrut_ty, &witnesses); |
| err.help( |
| "ensure that all possible cases are being handled, \ |
| possibly by adding wildcards or more match arms", |
| ); |
| err.note(&format!("the matched value is of type `{}`", scrut_ty)); |
| if (scrut_ty == cx.tcx.types.usize || scrut_ty == cx.tcx.types.isize) |
| && !is_empty_match |
| && witnesses.len() == 1 |
| && witnesses[0].is_wildcard() |
| { |
| err.note(&format!( |
| "`{}` does not have a fixed maximum value, \ |
| so a wildcard `_` is necessary to match exhaustively", |
| scrut_ty, |
| )); |
| if cx.tcx.sess.is_nightly_build() { |
| err.help(&format!( |
| "add `#![feature(precise_pointer_size_matching)]` \ |
| to the crate attributes to enable precise `{}` matching", |
| scrut_ty, |
| )); |
| } |
| } |
| err.emit(); |
| } |
| |
| fn joined_uncovered_patterns(witnesses: &[super::Pat<'_>]) -> String { |
| const LIMIT: usize = 3; |
| match witnesses { |
| [] => bug!(), |
| [witness] => format!("`{}`", witness), |
| [head @ .., tail] if head.len() < LIMIT => { |
| let head: Vec<_> = head.iter().map(<_>::to_string).collect(); |
| format!("`{}` and `{}`", head.join("`, `"), tail) |
| } |
| _ => { |
| let (head, tail) = witnesses.split_at(LIMIT); |
| let head: Vec<_> = head.iter().map(<_>::to_string).collect(); |
| format!("`{}` and {} more", head.join("`, `"), tail.len()) |
| } |
| } |
| } |
| |
| fn pattern_not_covered_label(witnesses: &[super::Pat<'_>], joined_patterns: &str) -> String { |
| format!("pattern{} {} not covered", rustc_errors::pluralize!(witnesses.len()), joined_patterns) |
| } |
| |
| /// Point at the definition of non-covered `enum` variants. |
| fn adt_defined_here( |
| cx: &MatchCheckCtxt<'_, '_>, |
| err: &mut DiagnosticBuilder<'_>, |
| ty: Ty<'_>, |
| witnesses: &[super::Pat<'_>], |
| ) { |
| let ty = ty.peel_refs(); |
| if let ty::Adt(def, _) = ty.kind() { |
| if let Some(sp) = cx.tcx.hir().span_if_local(def.did) { |
| err.span_label(sp, format!("`{}` defined here", ty)); |
| } |
| |
| if witnesses.len() < 4 { |
| for sp in maybe_point_at_variant(ty, &witnesses) { |
| err.span_label(sp, "not covered"); |
| } |
| } |
| } |
| } |
| |
| fn maybe_point_at_variant(ty: Ty<'_>, patterns: &[super::Pat<'_>]) -> Vec<Span> { |
| let mut covered = vec![]; |
| if let ty::Adt(def, _) = ty.kind() { |
| // Don't point at variants that have already been covered due to other patterns to avoid |
| // visual clutter. |
| for pattern in patterns { |
| use PatKind::{AscribeUserType, Deref, Leaf, Or, Variant}; |
| match &*pattern.kind { |
| AscribeUserType { subpattern, .. } | Deref { subpattern } => { |
| covered.extend(maybe_point_at_variant(ty, slice::from_ref(&subpattern))); |
| } |
| Variant { adt_def, variant_index, subpatterns, .. } if adt_def.did == def.did => { |
| let sp = def.variants[*variant_index].ident.span; |
| if covered.contains(&sp) { |
| continue; |
| } |
| covered.push(sp); |
| |
| let pats = subpatterns |
| .iter() |
| .map(|field_pattern| field_pattern.pattern.clone()) |
| .collect::<Box<[_]>>(); |
| covered.extend(maybe_point_at_variant(ty, &pats)); |
| } |
| Leaf { subpatterns } => { |
| let pats = subpatterns |
| .iter() |
| .map(|field_pattern| field_pattern.pattern.clone()) |
| .collect::<Box<[_]>>(); |
| covered.extend(maybe_point_at_variant(ty, &pats)); |
| } |
| Or { pats } => { |
| let pats = pats.iter().cloned().collect::<Box<[_]>>(); |
| covered.extend(maybe_point_at_variant(ty, &pats)); |
| } |
| _ => {} |
| } |
| } |
| } |
| covered |
| } |
| |
| /// Check if a by-value binding is by-value. That is, check if the binding's type is not `Copy`. |
| fn is_binding_by_move(cx: &MatchVisitor<'_, '_>, hir_id: HirId, span: Span) -> bool { |
| !cx.typeck_results.node_type(hir_id).is_copy_modulo_regions(cx.tcx.at(span), cx.param_env) |
| } |
| |
| /// Check that there are no borrow or move conflicts in `binding @ subpat` patterns. |
| /// |
| /// For example, this would reject: |
| /// - `ref x @ Some(ref mut y)`, |
| /// - `ref mut x @ Some(ref y)`, |
| /// - `ref mut x @ Some(ref mut y)`, |
| /// - `ref mut? x @ Some(y)`, and |
| /// - `x @ Some(ref mut? y)`. |
| /// |
| /// This analysis is *not* subsumed by NLL. |
| fn check_borrow_conflicts_in_at_patterns(cx: &MatchVisitor<'_, '_>, pat: &Pat<'_>) { |
| // Extract `sub` in `binding @ sub`. |
| let (name, sub) = match &pat.kind { |
| hir::PatKind::Binding(.., name, Some(sub)) => (*name, sub), |
| _ => return, |
| }; |
| let binding_span = pat.span.with_hi(name.span.hi()); |
| |
| let typeck_results = cx.typeck_results; |
| let sess = cx.tcx.sess; |
| |
| // Get the binding move, extract the mutability if by-ref. |
| let mut_outer = match typeck_results.extract_binding_mode(sess, pat.hir_id, pat.span) { |
| Some(ty::BindByValue(_)) if is_binding_by_move(cx, pat.hir_id, pat.span) => { |
| // We have `x @ pat` where `x` is by-move. Reject all borrows in `pat`. |
| let mut conflicts_ref = Vec::new(); |
| sub.each_binding(|_, hir_id, span, _| { |
| match typeck_results.extract_binding_mode(sess, hir_id, span) { |
| Some(ty::BindByValue(_)) | None => {} |
| Some(ty::BindByReference(_)) => conflicts_ref.push(span), |
| } |
| }); |
| if !conflicts_ref.is_empty() { |
| let occurs_because = format!( |
| "move occurs because `{}` has type `{}` which does not implement the `Copy` trait", |
| name, |
| typeck_results.node_type(pat.hir_id), |
| ); |
| sess.struct_span_err(pat.span, "borrow of moved value") |
| .span_label(binding_span, format!("value moved into `{}` here", name)) |
| .span_label(binding_span, occurs_because) |
| .span_labels(conflicts_ref, "value borrowed here after move") |
| .emit(); |
| } |
| return; |
| } |
| Some(ty::BindByValue(_)) | None => return, |
| Some(ty::BindByReference(m)) => m, |
| }; |
| |
| // We now have `ref $mut_outer binding @ sub` (semantically). |
| // Recurse into each binding in `sub` and find mutability or move conflicts. |
| let mut conflicts_move = Vec::new(); |
| let mut conflicts_mut_mut = Vec::new(); |
| let mut conflicts_mut_ref = Vec::new(); |
| sub.each_binding(|_, hir_id, span, name| { |
| match typeck_results.extract_binding_mode(sess, hir_id, span) { |
| Some(ty::BindByReference(mut_inner)) => match (mut_outer, mut_inner) { |
| (Mutability::Not, Mutability::Not) => {} // Both sides are `ref`. |
| (Mutability::Mut, Mutability::Mut) => conflicts_mut_mut.push((span, name)), // 2x `ref mut`. |
| _ => conflicts_mut_ref.push((span, name)), // `ref` + `ref mut` in either direction. |
| }, |
| Some(ty::BindByValue(_)) if is_binding_by_move(cx, hir_id, span) => { |
| conflicts_move.push((span, name)) // `ref mut?` + by-move conflict. |
| } |
| Some(ty::BindByValue(_)) | None => {} // `ref mut?` + by-copy is fine. |
| } |
| }); |
| |
| // Report errors if any. |
| if !conflicts_mut_mut.is_empty() { |
| // Report mutability conflicts for e.g. `ref mut x @ Some(ref mut y)`. |
| let mut err = sess |
| .struct_span_err(pat.span, "cannot borrow value as mutable more than once at a time"); |
| err.span_label(binding_span, format!("first mutable borrow, by `{}`, occurs here", name)); |
| for (span, name) in conflicts_mut_mut { |
| err.span_label(span, format!("another mutable borrow, by `{}`, occurs here", name)); |
| } |
| for (span, name) in conflicts_mut_ref { |
| err.span_label(span, format!("also borrowed as immutable, by `{}`, here", name)); |
| } |
| for (span, name) in conflicts_move { |
| err.span_label(span, format!("also moved into `{}` here", name)); |
| } |
| err.emit(); |
| } else if !conflicts_mut_ref.is_empty() { |
| // Report mutability conflicts for e.g. `ref x @ Some(ref mut y)` or the converse. |
| let (primary, also) = match mut_outer { |
| Mutability::Mut => ("mutable", "immutable"), |
| Mutability::Not => ("immutable", "mutable"), |
| }; |
| let msg = |
| format!("cannot borrow value as {} because it is also borrowed as {}", also, primary); |
| let mut err = sess.struct_span_err(pat.span, &msg); |
| err.span_label(binding_span, format!("{} borrow, by `{}`, occurs here", primary, name)); |
| for (span, name) in conflicts_mut_ref { |
| err.span_label(span, format!("{} borrow, by `{}`, occurs here", also, name)); |
| } |
| for (span, name) in conflicts_move { |
| err.span_label(span, format!("also moved into `{}` here", name)); |
| } |
| err.emit(); |
| } else if !conflicts_move.is_empty() { |
| // Report by-ref and by-move conflicts, e.g. `ref x @ y`. |
| let mut err = |
| sess.struct_span_err(pat.span, "cannot move out of value because it is borrowed"); |
| err.span_label(binding_span, format!("value borrowed, by `{}`, here", name)); |
| for (span, name) in conflicts_move { |
| err.span_label(span, format!("value moved into `{}` here", name)); |
| } |
| err.emit(); |
| } |
| } |
| |
| /// Forbids bindings in `@` patterns. This used to be is necessary for memory safety, |
| /// because of the way rvalues were handled in the borrow check. (See issue #14587.) |
| fn check_legality_of_bindings_in_at_patterns(cx: &MatchVisitor<'_, '_>, pat: &Pat<'_>) { |
| AtBindingPatternVisitor { cx, bindings_allowed: true }.visit_pat(pat); |
| |
| struct AtBindingPatternVisitor<'a, 'b, 'tcx> { |
| cx: &'a MatchVisitor<'b, 'tcx>, |
| bindings_allowed: bool, |
| } |
| |
| impl<'v> Visitor<'v> for AtBindingPatternVisitor<'_, '_, '_> { |
| type Map = intravisit::ErasedMap<'v>; |
| |
| fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { |
| NestedVisitorMap::None |
| } |
| |
| fn visit_pat(&mut self, pat: &Pat<'_>) { |
| match pat.kind { |
| hir::PatKind::Binding(.., ref subpat) => { |
| if !self.bindings_allowed { |
| feature_err( |
| &self.cx.tcx.sess.parse_sess, |
| sym::bindings_after_at, |
| pat.span, |
| "pattern bindings after an `@` are unstable", |
| ) |
| .emit(); |
| } |
| |
| if subpat.is_some() { |
| let bindings_were_allowed = self.bindings_allowed; |
| self.bindings_allowed = false; |
| intravisit::walk_pat(self, pat); |
| self.bindings_allowed = bindings_were_allowed; |
| } |
| } |
| _ => intravisit::walk_pat(self, pat), |
| } |
| } |
| } |
| } |
