| use super::deconstruct_pat::{Constructor, DeconstructedPat}; |
| use super::usefulness::{ |
| compute_match_usefulness, MatchArm, MatchCheckCtxt, Reachability, UsefulnessReport, |
| }; |
| use super::{PatCtxt, PatternError}; |
| |
| use rustc_arena::TypedArena; |
| use rustc_ast::Mutability; |
| use rustc_errors::{ |
| error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, |
| ErrorGuaranteed, MultiSpan, |
| }; |
| use rustc_hir as hir; |
| use rustc_hir::def::*; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::intravisit::{self, Visitor}; |
| use rustc_hir::{HirId, Pat}; |
| use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt}; |
| use rustc_session::lint::builtin::{ |
| BINDINGS_WITH_VARIANT_NAME, IRREFUTABLE_LET_PATTERNS, UNREACHABLE_PATTERNS, |
| }; |
| use rustc_session::Session; |
| use rustc_span::source_map::Spanned; |
| use rustc_span::{BytePos, DesugaringKind, ExpnKind, Span}; |
| |
| 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 pattern_arena = TypedArena::default(); |
| let mut visitor = MatchVisitor { |
| tcx, |
| typeck_results: tcx.typeck_body(body_id), |
| param_env: tcx.param_env(def_id), |
| pattern_arena: &pattern_arena, |
| }; |
| visitor.visit_body(tcx.hir().body(body_id)); |
| } |
| |
| fn create_e0004( |
| sess: &Session, |
| sp: Span, |
| error_message: String, |
| ) -> DiagnosticBuilder<'_, ErrorGuaranteed> { |
| struct_span_err!(sess, sp, E0004, "{}", &error_message) |
| } |
| |
| #[derive(PartialEq)] |
| enum RefutableFlag { |
| Irrefutable, |
| Refutable, |
| } |
| use RefutableFlag::*; |
| |
| struct MatchVisitor<'a, 'p, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| typeck_results: &'a ty::TypeckResults<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| pattern_arena: &'p TypedArena<DeconstructedPat<'p, 'tcx>>, |
| } |
| |
| impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, '_, 'tcx> { |
| fn visit_expr(&mut self, ex: &'tcx hir::Expr<'tcx>) { |
| intravisit::walk_expr(self, ex); |
| match &ex.kind { |
| hir::ExprKind::Match(scrut, arms, source) => { |
| self.check_match(scrut, arms, *source, ex.span) |
| } |
| hir::ExprKind::Let(hir::Let { pat, init, span, .. }) => { |
| self.check_let(pat, init, *span) |
| } |
| _ => {} |
| } |
| } |
| |
| 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::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); |
| } |
| |
| fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) { |
| intravisit::walk_param(self, param); |
| self.check_irrefutable(¶m.pat, "function argument", None); |
| } |
| } |
| |
| impl PatCtxt<'_, '_> { |
| fn report_inlining_errors(&self) { |
| 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::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<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> { |
| fn check_patterns(&self, pat: &Pat<'_>, rf: RefutableFlag) { |
| pat.walk_always(|pat| check_borrow_conflicts_in_at_patterns(self, pat)); |
| check_for_bindings_named_same_as_variants(self, pat, rf); |
| } |
| |
| fn lower_pattern( |
| &self, |
| cx: &mut MatchCheckCtxt<'p, 'tcx>, |
| pat: &'tcx hir::Pat<'tcx>, |
| have_errors: &mut bool, |
| ) -> &'p DeconstructedPat<'p, '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: &_ = cx.pattern_arena.alloc(DeconstructedPat::from_pat(cx, &pattern)); |
| if !patcx.errors.is_empty() { |
| *have_errors = true; |
| patcx.report_inlining_errors(); |
| } |
| pattern |
| } |
| |
| fn new_cx(&self, hir_id: HirId) -> MatchCheckCtxt<'p, '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_let(&mut self, pat: &'tcx hir::Pat<'tcx>, scrutinee: &hir::Expr<'_>, span: Span) { |
| self.check_patterns(pat, Refutable); |
| let mut cx = self.new_cx(scrutinee.hir_id); |
| let tpat = self.lower_pattern(&mut cx, pat, &mut false); |
| self.check_let_reachability(&mut cx, pat.hir_id, tpat, span); |
| } |
| |
| fn check_match( |
| &mut self, |
| scrut: &hir::Expr<'_>, |
| hir_arms: &'tcx [hir::Arm<'tcx>], |
| source: hir::MatchSource, |
| expr_span: Span, |
| ) { |
| let mut cx = self.new_cx(scrut.hir_id); |
| |
| for arm in hir_arms { |
| // Check the arm for some things unrelated to exhaustiveness. |
| self.check_patterns(&arm.pat, Refutable); |
| if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard { |
| self.check_patterns(pat, Refutable); |
| let tpat = self.lower_pattern(&mut cx, pat, &mut false); |
| self.check_let_reachability(&mut cx, pat.hir_id, tpat, tpat.span()); |
| } |
| } |
| |
| let mut have_errors = false; |
| |
| let arms: Vec<_> = hir_arms |
| .iter() |
| .map(|hir::Arm { pat, guard, .. }| MatchArm { |
| pat: self.lower_pattern(&mut cx, pat, &mut have_errors), |
| 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); |
| |
| match source { |
| // Don't report arm reachability of desugared `match $iter.into_iter() { iter => .. }` |
| // when the iterator is an uninhabited type. unreachable_code will trigger instead. |
| hir::MatchSource::ForLoopDesugar if arms.len() == 1 => {} |
| hir::MatchSource::ForLoopDesugar | hir::MatchSource::Normal => { |
| report_arm_reachability(&cx, &report) |
| } |
| // 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 => {} |
| } |
| |
| // Check if the match is exhaustive. |
| let witnesses = report.non_exhaustiveness_witnesses; |
| if !witnesses.is_empty() { |
| if source == hir::MatchSource::ForLoopDesugar && hir_arms.len() == 2 { |
| // the for loop pattern is not irrefutable |
| let pat = hir_arms[1].pat.for_loop_some().unwrap(); |
| self.check_irrefutable(pat, "`for` loop binding", None); |
| } else { |
| non_exhaustive_match(&cx, scrut_ty, scrut.span, witnesses, hir_arms, expr_span); |
| } |
| } |
| } |
| |
| fn check_let_reachability( |
| &mut self, |
| cx: &mut MatchCheckCtxt<'p, 'tcx>, |
| pat_id: HirId, |
| pat: &'p DeconstructedPat<'p, 'tcx>, |
| span: Span, |
| ) { |
| if self.check_let_chain(cx, pat_id) { |
| return; |
| } |
| |
| if is_let_irrefutable(cx, pat_id, pat) { |
| irrefutable_let_pattern(cx.tcx, pat_id, span); |
| } |
| } |
| |
| fn check_let_chain(&mut self, cx: &mut MatchCheckCtxt<'p, 'tcx>, pat_id: HirId) -> bool { |
| let hir = self.tcx.hir(); |
| let parent = hir.get_parent_node(pat_id); |
| |
| // First, figure out if the given pattern is part of a let chain, |
| // and if so, obtain the top node of the chain. |
| let mut top = parent; |
| let mut part_of_chain = false; |
| loop { |
| let new_top = hir.get_parent_node(top); |
| if let hir::Node::Expr( |
| hir::Expr { |
| kind: hir::ExprKind::Binary(Spanned { node: hir::BinOpKind::And, .. }, lhs, rhs), |
| .. |
| }, |
| .., |
| ) = hir.get(new_top) |
| { |
| // If this isn't the first iteration, we need to check |
| // if there is a let expr before us in the chain, so |
| // that we avoid doubly checking the let chain. |
| |
| // The way a chain of &&s is encoded is ((let ... && let ...) && let ...) && let ... |
| // as && is left-to-right associative. Thus, we need to check rhs. |
| if part_of_chain && matches!(rhs.kind, hir::ExprKind::Let(..)) { |
| return true; |
| } |
| // If there is a let at the lhs, and we provide the rhs, we don't do any checking either. |
| if !part_of_chain && matches!(lhs.kind, hir::ExprKind::Let(..)) && rhs.hir_id == top |
| { |
| return true; |
| } |
| } else { |
| // We've reached the top. |
| break; |
| } |
| |
| // Since this function is called within a let context, it is reasonable to assume that any parent |
| // `&&` infers a let chain |
| part_of_chain = true; |
| top = new_top; |
| } |
| if !part_of_chain { |
| return false; |
| } |
| |
| // Second, obtain the refutabilities of all exprs in the chain, |
| // and record chain members that aren't let exprs. |
| let mut chain_refutabilities = Vec::new(); |
| let hir::Node::Expr(top_expr) = hir.get(top) else { |
| // We ensure right above that it's an Expr |
| unreachable!() |
| }; |
| let mut cur_expr = top_expr; |
| loop { |
| let mut add = |expr: &hir::Expr<'tcx>| { |
| let refutability = match expr.kind { |
| hir::ExprKind::Let(hir::Let { pat, init, span, .. }) => { |
| let mut ncx = self.new_cx(init.hir_id); |
| let tpat = self.lower_pattern(&mut ncx, pat, &mut false); |
| |
| let refutable = !is_let_irrefutable(&mut ncx, pat.hir_id, tpat); |
| Some((*span, refutable)) |
| } |
| _ => None, |
| }; |
| chain_refutabilities.push(refutability); |
| }; |
| if let hir::Expr { |
| kind: hir::ExprKind::Binary(Spanned { node: hir::BinOpKind::And, .. }, lhs, rhs), |
| .. |
| } = cur_expr |
| { |
| add(rhs); |
| cur_expr = lhs; |
| } else { |
| add(cur_expr); |
| break; |
| } |
| } |
| chain_refutabilities.reverse(); |
| |
| // Third, emit the actual warnings. |
| |
| if chain_refutabilities.iter().all(|r| matches!(*r, Some((_, false)))) { |
| // The entire chain is made up of irrefutable `let` statements |
| let let_source = let_source_parent(self.tcx, top, None); |
| irrefutable_let_patterns( |
| cx.tcx, |
| top, |
| let_source, |
| chain_refutabilities.len(), |
| top_expr.span, |
| ); |
| return true; |
| } |
| let lint_affix = |affix: &[Option<(Span, bool)>], kind, suggestion| { |
| let span_start = affix[0].unwrap().0; |
| let span_end = affix.last().unwrap().unwrap().0; |
| let span = span_start.to(span_end); |
| let cnt = affix.len(); |
| cx.tcx.struct_span_lint_hir(IRREFUTABLE_LET_PATTERNS, top, span, |lint| { |
| let s = pluralize!(cnt); |
| let mut diag = lint.build(&format!("{kind} irrefutable pattern{s} in let chain")); |
| diag.note(&format!( |
| "{these} pattern{s} will always match", |
| these = pluralize!("this", cnt), |
| )); |
| diag.help(&format!( |
| "consider moving {} {suggestion}", |
| if cnt > 1 { "them" } else { "it" } |
| )); |
| diag.emit() |
| }); |
| }; |
| if let Some(until) = chain_refutabilities.iter().position(|r| !matches!(*r, Some((_, false)))) && until > 0 { |
| // The chain has a non-zero prefix of irrefutable `let` statements. |
| |
| // Check if the let source is while, for there is no alternative place to put a prefix, |
| // and we shouldn't lint. |
| let let_source = let_source_parent(self.tcx, top, None); |
| if !matches!(let_source, LetSource::WhileLet) { |
| // Emit the lint |
| let prefix = &chain_refutabilities[..until]; |
| lint_affix(prefix, "leading", "outside of the construct"); |
| } |
| } |
| if let Some(from) = chain_refutabilities.iter().rposition(|r| !matches!(*r, Some((_, false)))) && from != (chain_refutabilities.len() - 1) { |
| // The chain has a non-empty suffix of irrefutable `let` statements |
| let suffix = &chain_refutabilities[from + 1..]; |
| lint_affix(suffix, "trailing", "into the body"); |
| } |
| true |
| } |
| |
| fn check_irrefutable(&self, pat: &'tcx Pat<'tcx>, origin: &str, sp: Option<Span>) { |
| let mut cx = self.new_cx(pat.hir_id); |
| |
| let pattern = self.lower_pattern(&mut cx, pat, &mut false); |
| let pattern_ty = pattern.ty(); |
| 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. |
| self.check_patterns(pat, Irrefutable); |
| return; |
| } |
| |
| let joined_patterns = joined_uncovered_patterns(&cx, &witnesses); |
| |
| let mut bindings = vec![]; |
| |
| 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 |
| } |
| _ => { |
| pat.walk(&mut |pat: &hir::Pat<'_>| { |
| match pat.kind { |
| hir::PatKind::Binding(_, _, ident, _) => { |
| bindings.push(ident); |
| } |
| _ => {} |
| } |
| true |
| }); |
| |
| 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 self.tcx.sess.source_map().span_to_snippet(span).is_ok() { |
| let semi_span = span.shrink_to_hi().with_lo(span.hi() - BytePos(1)); |
| let start_span = span.shrink_to_lo(); |
| let end_span = semi_span.shrink_to_lo(); |
| err.multipart_suggestion( |
| &format!( |
| "you might want to use `if let` to ignore the variant{} that {} matched", |
| pluralize!(witnesses.len()), |
| match witnesses.len() { |
| 1 => "isn't", |
| _ => "aren't", |
| }, |
| ), |
| vec![ |
| match &bindings[..] { |
| [] => (start_span, "if ".to_string()), |
| [binding] => (start_span, format!("let {} = if ", binding)), |
| bindings => ( |
| start_span, |
| format!( |
| "let ({}) = if ", |
| bindings |
| .iter() |
| .map(|ident| ident.to_string()) |
| .collect::<Vec<_>>() |
| .join(", ") |
| ), |
| ), |
| }, |
| match &bindings[..] { |
| [] => (semi_span, " { todo!() }".to_string()), |
| [binding] => { |
| (end_span, format!(" {{ {} }} else {{ todo!() }}", binding)) |
| } |
| bindings => ( |
| end_span, |
| format!( |
| " {{ ({}) }} else {{ todo!() }}", |
| bindings |
| .iter() |
| .map(|ident| ident.to_string()) |
| .collect::<Vec<_>>() |
| .join(", ") |
| ), |
| ), |
| }, |
| ], |
| Applicability::HasPlaceholders, |
| ); |
| if !bindings.is_empty() && cx.tcx.sess.is_nightly_build() { |
| err.span_suggestion_verbose( |
| semi_span.shrink_to_lo(), |
| &format!( |
| "alternatively, on nightly, you might want to use \ |
| `#![feature(let_else)]` to handle the variant{} that {} matched", |
| pluralize!(witnesses.len()), |
| match witnesses.len() { |
| 1 => "isn't", |
| _ => "aren't", |
| }, |
| ), |
| " else { todo!() }".to_string(), |
| 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 Diagnostic, 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<'_>, |
| rf: RefutableFlag, |
| ) { |
| pat.walk_always(|p| { |
| if let hir::PatKind::Binding(_, _, ident, None) = p.kind |
| && 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() |
| && let ty::Adt(edef, _) = pat_ty.kind() |
| && edef.is_enum() |
| && edef.variants().iter().any(|variant| { |
| variant.ident(cx.tcx) == ident && variant.ctor_kind == CtorKind::Const |
| }) |
| { |
| let variant_count = edef.variants().len(); |
| 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()); |
| let mut err = lint.build(&format!( |
| "pattern binding `{}` is named the same as one \ |
| of the variants of the type `{}`", |
| ident, ty_path |
| )); |
| err.code(error_code!(E0170)); |
| // If this is an irrefutable pattern, and there's > 1 variant, |
| // then we can't actually match on this. Applying the below |
| // suggestion would produce code that breaks on `check_irrefutable`. |
| if rf == Refutable || variant_count == 1 { |
| err.span_suggestion( |
| p.span, |
| "to match on the variant, qualify the path", |
| format!("{}::{}", ty_path, ident), |
| Applicability::MachineApplicable, |
| ); |
| } |
| err.emit(); |
| }, |
| ) |
| } |
| }); |
| } |
| |
| /// Checks for common cases of "catchall" patterns that may not be intended as such. |
| fn pat_is_catchall(pat: &DeconstructedPat<'_, '_>) -> bool { |
| use Constructor::*; |
| match pat.ctor() { |
| Wildcard => true, |
| Single => pat.iter_fields().all(|pat| pat_is_catchall(pat)), |
| _ => 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<'_>, id: HirId, span: Span) { |
| let source = let_source(tcx, id); |
| irrefutable_let_patterns(tcx, id, source, 1, span); |
| } |
| |
| fn irrefutable_let_patterns( |
| tcx: TyCtxt<'_>, |
| id: HirId, |
| source: LetSource, |
| count: usize, |
| span: Span, |
| ) { |
| macro_rules! emit_diag { |
| ( |
| $lint:expr, |
| $source_name:expr, |
| $note_sufix:expr, |
| $help_sufix:expr |
| ) => {{ |
| let s = pluralize!(count); |
| let these = pluralize!("this", count); |
| let mut diag = $lint.build(&format!("irrefutable {} pattern{s}", $source_name)); |
| diag.note(&format!("{these} pattern{s} will always match, so the {}", $note_sufix)); |
| diag.help(concat!("consider ", $help_sufix)); |
| diag.emit() |
| }}; |
| } |
| |
| let span = match source { |
| LetSource::LetElse(span) => span, |
| _ => span, |
| }; |
| tcx.struct_span_lint_hir(IRREFUTABLE_LET_PATTERNS, id, span, |lint| match source { |
| LetSource::GenericLet => { |
| emit_diag!(lint, "`let`", "`let` is useless", "removing `let`"); |
| } |
| LetSource::IfLet => { |
| emit_diag!( |
| lint, |
| "`if let`", |
| "`if let` is useless", |
| "replacing the `if let` with a `let`" |
| ); |
| } |
| LetSource::IfLetGuard => { |
| emit_diag!( |
| lint, |
| "`if let` guard", |
| "guard is useless", |
| "removing the guard and adding a `let` inside the match arm" |
| ); |
| } |
| LetSource::LetElse(..) => { |
| emit_diag!( |
| lint, |
| "`let...else`", |
| "`else` clause is useless", |
| "removing the `else` clause" |
| ); |
| } |
| LetSource::WhileLet => { |
| emit_diag!( |
| lint, |
| "`while let`", |
| "loop will never exit", |
| "instead using a `loop { ... }` with a `let` inside it" |
| ); |
| } |
| }); |
| } |
| |
| fn is_let_irrefutable<'p, 'tcx>( |
| cx: &mut MatchCheckCtxt<'p, 'tcx>, |
| pat_id: HirId, |
| pat: &'p DeconstructedPat<'p, 'tcx>, |
| ) -> bool { |
| let arms = [MatchArm { pat, hir_id: pat_id, has_guard: false }]; |
| let report = compute_match_usefulness(&cx, &arms, pat_id, pat.ty()); |
| |
| // Report if the pattern is unreachable, which can only occur when the type is uninhabited. |
| // This also reports unreachable sub-patterns though, so we can't just replace it with an |
| // `is_uninhabited` check. |
| report_arm_reachability(&cx, &report); |
| |
| // If the list of witnesses is empty, the match is exhaustive, |
| // i.e. the `if let` pattern is irrefutable. |
| report.non_exhaustiveness_witnesses.is_empty() |
| } |
| |
| /// Report unreachable arms, if any. |
| fn report_arm_reachability<'p, 'tcx>( |
| cx: &MatchCheckCtxt<'p, 'tcx>, |
| report: &UsefulnessReport<'p, 'tcx>, |
| ) { |
| use Reachability::*; |
| let mut catchall = None; |
| for (arm, is_useful) in report.arm_usefulness.iter() { |
| match is_useful { |
| Unreachable => unreachable_pattern(cx.tcx, arm.pat.span(), arm.hir_id, catchall), |
| Reachable(unreachables) if unreachables.is_empty() => {} |
| // The arm is reachable, but contains unreachable subpatterns (from or-patterns). |
| Reachable(unreachables) => { |
| let mut unreachables = unreachables.clone(); |
| // 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); |
| } |
| } |
| } |
| 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<DeconstructedPat<'p, 'tcx>>, |
| arms: &[hir::Arm<'tcx>], |
| expr_span: Span, |
| ) { |
| let is_empty_match = arms.is_empty(); |
| 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; |
| let pattern; |
| let mut patterns_len = 0; |
| if is_empty_match && !non_empty_enum { |
| err = create_e0004( |
| cx.tcx.sess, |
| sp, |
| format!("non-exhaustive patterns: type `{}` is non-empty", scrut_ty), |
| ); |
| pattern = "_".to_string(); |
| } else { |
| let joined_patterns = joined_uncovered_patterns(cx, &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)); |
| patterns_len = witnesses.len(); |
| pattern = if witnesses.len() < 4 { |
| witnesses |
| .iter() |
| .map(|witness| witness.to_pat(cx).to_string()) |
| .collect::<Vec<String>>() |
| .join(" | ") |
| } else { |
| "_".to_string() |
| }; |
| }; |
| |
| let is_variant_list_non_exhaustive = match scrut_ty.kind() { |
| ty::Adt(def, _) if def.is_variant_list_non_exhaustive() && !def.did().is_local() => true, |
| _ => false, |
| }; |
| |
| adt_defined_here(cx, &mut err, scrut_ty, &witnesses); |
| err.note(&format!( |
| "the matched value is of type `{}`{}", |
| scrut_ty, |
| if is_variant_list_non_exhaustive { ", which is marked as non-exhaustive" } else { "" } |
| )); |
| if (scrut_ty == cx.tcx.types.usize || scrut_ty == cx.tcx.types.isize) |
| && !is_empty_match |
| && witnesses.len() == 1 |
| && matches!(witnesses[0].ctor(), Constructor::NonExhaustive) |
| { |
| 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, |
| )); |
| } |
| } |
| if let ty::Ref(_, sub_ty, _) = scrut_ty.kind() { |
| if cx.tcx.is_ty_uninhabited_from(cx.module, *sub_ty, cx.param_env) { |
| err.note("references are always considered inhabited"); |
| } |
| } |
| |
| let mut suggestion = None; |
| let sm = cx.tcx.sess.source_map(); |
| match arms { |
| [] if sp.ctxt() == expr_span.ctxt() => { |
| // Get the span for the empty match body `{}`. |
| let (indentation, more) = if let Some(snippet) = sm.indentation_before(sp) { |
| (format!("\n{}", snippet), " ") |
| } else { |
| (" ".to_string(), "") |
| }; |
| suggestion = Some(( |
| sp.shrink_to_hi().with_hi(expr_span.hi()), |
| format!( |
| " {{{indentation}{more}{pattern} => todo!(),{indentation}}}", |
| indentation = indentation, |
| more = more, |
| pattern = pattern, |
| ), |
| )); |
| } |
| [only] => { |
| let pre_indentation = if let (Some(snippet), true) = ( |
| sm.indentation_before(only.span), |
| sm.is_multiline(sp.shrink_to_hi().with_hi(only.span.lo())), |
| ) { |
| format!("\n{}", snippet) |
| } else { |
| " ".to_string() |
| }; |
| let comma = if matches!(only.body.kind, hir::ExprKind::Block(..)) { "" } else { "," }; |
| suggestion = Some(( |
| only.span.shrink_to_hi(), |
| format!("{}{}{} => todo!()", comma, pre_indentation, pattern), |
| )); |
| } |
| [.., prev, last] if prev.span.ctxt() == last.span.ctxt() => { |
| if let Ok(snippet) = sm.span_to_snippet(prev.span.between(last.span)) { |
| let comma = |
| if matches!(last.body.kind, hir::ExprKind::Block(..)) { "" } else { "," }; |
| suggestion = Some(( |
| last.span.shrink_to_hi(), |
| format!( |
| "{}{}{} => todo!()", |
| comma, |
| snippet.strip_prefix(',').unwrap_or(&snippet), |
| pattern |
| ), |
| )); |
| } |
| } |
| _ => {} |
| } |
| |
| let msg = format!( |
| "ensure that all possible cases are being handled by adding a match arm with a wildcard \ |
| pattern{}{}", |
| if patterns_len > 1 && patterns_len < 4 && suggestion.is_some() { |
| ", a match arm with multiple or-patterns" |
| } else { |
| // we are either not suggesting anything, or suggesting `_` |
| "" |
| }, |
| match patterns_len { |
| // non-exhaustive enum case |
| 0 if suggestion.is_some() => " as shown", |
| 0 => "", |
| 1 if suggestion.is_some() => " or an explicit pattern as shown", |
| 1 => " or an explicit pattern", |
| _ if suggestion.is_some() => " as shown, or multiple match arms", |
| _ => " or multiple match arms", |
| }, |
| ); |
| if let Some((span, sugg)) = suggestion { |
| err.span_suggestion_verbose(span, &msg, sugg, Applicability::HasPlaceholders); |
| } else { |
| err.help(&msg); |
| } |
| err.emit(); |
| } |
| |
| crate fn joined_uncovered_patterns<'p, 'tcx>( |
| cx: &MatchCheckCtxt<'p, 'tcx>, |
| witnesses: &[DeconstructedPat<'p, 'tcx>], |
| ) -> String { |
| const LIMIT: usize = 3; |
| let pat_to_str = |pat: &DeconstructedPat<'p, 'tcx>| pat.to_pat(cx).to_string(); |
| match witnesses { |
| [] => bug!(), |
| [witness] => format!("`{}`", witness.to_pat(cx)), |
| [head @ .., tail] if head.len() < LIMIT => { |
| let head: Vec<_> = head.iter().map(pat_to_str).collect(); |
| format!("`{}` and `{}`", head.join("`, `"), tail.to_pat(cx)) |
| } |
| _ => { |
| let (head, tail) = witnesses.split_at(LIMIT); |
| let head: Vec<_> = head.iter().map(pat_to_str).collect(); |
| format!("`{}` and {} more", head.join("`, `"), tail.len()) |
| } |
| } |
| } |
| |
| crate fn pattern_not_covered_label( |
| witnesses: &[DeconstructedPat<'_, '_>], |
| 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<'p, 'tcx>( |
| cx: &MatchCheckCtxt<'p, 'tcx>, |
| err: &mut Diagnostic, |
| ty: Ty<'tcx>, |
| witnesses: &[DeconstructedPat<'p, 'tcx>], |
| ) { |
| let ty = ty.peel_refs(); |
| if let ty::Adt(def, _) = ty.kind() { |
| let mut spans = vec![]; |
| if witnesses.len() < 5 { |
| for sp in maybe_point_at_variant(cx, *def, witnesses.iter()) { |
| spans.push(sp); |
| } |
| } |
| let def_span = cx |
| .tcx |
| .hir() |
| .get_if_local(def.did()) |
| .and_then(|node| node.ident()) |
| .map(|ident| ident.span) |
| .unwrap_or_else(|| cx.tcx.def_span(def.did())); |
| let mut span: MultiSpan = |
| if spans.is_empty() { def_span.into() } else { spans.clone().into() }; |
| |
| span.push_span_label(def_span, String::new()); |
| for pat in spans { |
| span.push_span_label(pat, "not covered".to_string()); |
| } |
| err.span_note(span, &format!("`{}` defined here", ty)); |
| } |
| } |
| |
| fn maybe_point_at_variant<'a, 'p: 'a, 'tcx: 'a>( |
| cx: &MatchCheckCtxt<'p, 'tcx>, |
| def: AdtDef<'tcx>, |
| patterns: impl Iterator<Item = &'a DeconstructedPat<'p, 'tcx>>, |
| ) -> Vec<Span> { |
| use Constructor::*; |
| let mut covered = vec![]; |
| for pattern in patterns { |
| if let Variant(variant_index) = pattern.ctor() { |
| if let ty::Adt(this_def, _) = pattern.ty().kind() && this_def.did() != def.did() { |
| continue; |
| } |
| let sp = def.variant(*variant_index).ident(cx.tcx).span; |
| if covered.contains(&sp) { |
| // Don't point at variants that have already been covered due to other patterns to avoid |
| // visual clutter. |
| continue; |
| } |
| covered.push(sp); |
| } |
| covered.extend(maybe_point_at_variant(cx, def, pattern.iter_fields())); |
| } |
| 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(); |
| } |
| } |
| |
| #[derive(Clone, Copy, Debug)] |
| pub enum LetSource { |
| GenericLet, |
| IfLet, |
| IfLetGuard, |
| LetElse(Span), |
| WhileLet, |
| } |
| |
| fn let_source(tcx: TyCtxt<'_>, pat_id: HirId) -> LetSource { |
| let hir = tcx.hir(); |
| |
| let parent = hir.get_parent_node(pat_id); |
| let_source_parent(tcx, parent, Some(pat_id)) |
| } |
| |
| fn let_source_parent(tcx: TyCtxt<'_>, parent: HirId, pat_id: Option<HirId>) -> LetSource { |
| let hir = tcx.hir(); |
| |
| let parent_node = hir.get(parent); |
| |
| match parent_node { |
| hir::Node::Arm(hir::Arm { |
| guard: Some(hir::Guard::IfLet(&hir::Pat { hir_id, .. }, _)), |
| .. |
| }) if Some(hir_id) == pat_id => { |
| return LetSource::IfLetGuard; |
| } |
| hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Let(..), span, .. }) => { |
| let expn_data = span.ctxt().outer_expn_data(); |
| if let ExpnKind::Desugaring(DesugaringKind::LetElse) = expn_data.kind { |
| return LetSource::LetElse(expn_data.call_site); |
| } |
| } |
| _ => {} |
| } |
| |
| let parent_parent = hir.get_parent_node(parent); |
| let parent_parent_node = hir.get(parent_parent); |
| |
| let parent_parent_parent = hir.get_parent_node(parent_parent); |
| let parent_parent_parent_parent = hir.get_parent_node(parent_parent_parent); |
| let parent_parent_parent_parent_node = hir.get(parent_parent_parent_parent); |
| |
| if let hir::Node::Expr(hir::Expr { |
| kind: hir::ExprKind::Loop(_, _, hir::LoopSource::While, _), |
| .. |
| }) = parent_parent_parent_parent_node |
| { |
| return LetSource::WhileLet; |
| } |
| |
| if let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::If(..), .. }) = parent_parent_node { |
| return LetSource::IfLet; |
| } |
| |
| LetSource::GenericLet |
| } |
