//! Error Reporting Code for the inference engine //! //! Because of the way inference, and in particular region inference, //! works, it often happens that errors are not detected until far after //! the relevant line of code has been type-checked. Therefore, there is //! an elaborate system to track why a particular constraint in the //! inference graph arose so that we can explain to the user what gave //! rise to a particular error. //! //! The basis of the system are the "origin" types. An "origin" is the //! reason that a constraint or inference variable arose. There are //! different "origin" enums for different kinds of constraints/variables //! (e.g., `TypeOrigin`, `RegionVariableOrigin`). An origin always has //! a span, but also more information so that we can generate a meaningful //! error message. //! //! Having a catalog of all the different reasons an error can arise is //! also useful for other reasons, like cross-referencing FAQs etc, though //! we are not really taking advantage of this yet. //! //! # Region Inference //! //! Region inference is particularly tricky because it always succeeds "in //! the moment" and simply registers a constraint. Then, at the end, we //! can compute the full graph and report errors, so we need to be able to //! store and later report what gave rise to the conflicting constraints. //! //! # Subtype Trace //! //! Determining whether `T1 <: T2` often involves a number of subtypes and //! subconstraints along the way. A "TypeTrace" is an extended version //! of an origin that traces the types and other values that were being //! compared. It is not necessarily comprehensive (in fact, at the time of //! this writing it only tracks the root values being compared) but I'd //! like to extend it to include significant "waypoints". For example, if //! you are comparing `(T1, T2) <: (T3, T4)`, and the problem is that `T2 //! <: T4` fails, I'd like the trace to include enough information to say //! "in the 2nd element of the tuple". Similarly, failures when comparing //! arguments or return types in fn types should be able to cite the //! specific position, etc. //! //! # Reality vs plan //! //! Of course, there is still a LOT of code in typeck that has yet to be //! ported to this system, and which relies on string concatenation at the //! time of error detection. use super::lexical_region_resolve::RegionResolutionError; use super::region_constraints::GenericKind; use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs}; use crate::infer::{self, SuppressRegionErrors}; use crate::hir; use crate::hir::def_id::DefId; use crate::hir::Node; use crate::middle::region; use crate::traits::{ObligationCause, ObligationCauseCode}; use crate::ty::error::TypeError; use crate::ty::{self, subst::{Subst, SubstsRef}, Region, Ty, TyCtxt, TypeFoldable}; use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString}; use std::{cmp, fmt}; use syntax_pos::{Pos, Span}; mod note; mod need_type_info; pub mod nice_region_error; impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { pub fn note_and_explain_region( self, region_scope_tree: ®ion::ScopeTree, err: &mut DiagnosticBuilder<'_>, prefix: &str, region: ty::Region<'tcx>, suffix: &str, ) { let (description, span) = match *region { ty::ReScope(scope) => { let new_string; let unknown_scope = || { format!( "{}unknown scope: {:?}{}. Please report a bug.", prefix, scope, suffix ) }; let span = scope.span(self, region_scope_tree); let tag = match self.hir().find(scope.node_id(self, region_scope_tree)) { Some(Node::Block(_)) => "block", Some(Node::Expr(expr)) => match expr.node { hir::ExprKind::Call(..) => "call", hir::ExprKind::MethodCall(..) => "method call", hir::ExprKind::Match(.., hir::MatchSource::IfLetDesugar { .. }) => "if let", hir::ExprKind::Match(.., hir::MatchSource::WhileLetDesugar) => "while let", hir::ExprKind::Match(.., hir::MatchSource::ForLoopDesugar) => "for", hir::ExprKind::Match(..) => "match", _ => "expression", }, Some(Node::Stmt(_)) => "statement", Some(Node::Item(it)) => Self::item_scope_tag(&it), Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it), Some(Node::ImplItem(it)) => Self::impl_item_scope_tag(&it), Some(_) | None => { err.span_note(span, &unknown_scope()); return; } }; let scope_decorated_tag = match scope.data { region::ScopeData::Node => tag, region::ScopeData::CallSite => "scope of call-site for function", region::ScopeData::Arguments => "scope of function body", region::ScopeData::Destruction => { new_string = format!("destruction scope surrounding {}", tag); &new_string[..] } region::ScopeData::Remainder(first_statement_index) => { new_string = format!( "block suffix following statement {}", first_statement_index.index() ); &new_string[..] } }; self.explain_span(scope_decorated_tag, span) } ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => { self.msg_span_from_free_region(region) } ty::ReEmpty => ("the empty lifetime".to_owned(), None), ty::RePlaceholder(_) => (format!("any other region"), None), // FIXME(#13998) RePlaceholder should probably print like // ReFree rather than dumping Debug output on the user. // // We shouldn't really be having unification failures with ReVar // and ReLateBound though. ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => { (format!("lifetime {:?}", region), None) } // We shouldn't encounter an error message with ReClosureBound. ty::ReClosureBound(..) => { bug!("encountered unexpected ReClosureBound: {:?}", region,); } }; TyCtxt::emit_msg_span(err, prefix, description, span, suffix); } pub fn note_and_explain_free_region( self, err: &mut DiagnosticBuilder<'_>, prefix: &str, region: ty::Region<'tcx>, suffix: &str, ) { let (description, span) = self.msg_span_from_free_region(region); TyCtxt::emit_msg_span(err, prefix, description, span, suffix); } fn msg_span_from_free_region(self, region: ty::Region<'tcx>) -> (String, Option) { match *region { ty::ReEarlyBound(_) | ty::ReFree(_) => { self.msg_span_from_early_bound_and_free_regions(region) } ty::ReStatic => ("the static lifetime".to_owned(), None), ty::ReEmpty => ("an empty lifetime".to_owned(), None), _ => bug!("{:?}", region), } } fn msg_span_from_early_bound_and_free_regions( self, region: ty::Region<'tcx>, ) -> (String, Option) { let cm = self.sess.source_map(); let scope = region.free_region_binding_scope(self); let node = self.hir().as_local_hir_id(scope).unwrap_or(hir::DUMMY_HIR_ID); let tag = match self.hir().find_by_hir_id(node) { Some(Node::Block(_)) | Some(Node::Expr(_)) => "body", Some(Node::Item(it)) => Self::item_scope_tag(&it), Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it), Some(Node::ImplItem(it)) => Self::impl_item_scope_tag(&it), _ => unreachable!(), }; let (prefix, span) = match *region { ty::ReEarlyBound(ref br) => { let mut sp = cm.def_span(self.hir().span_by_hir_id(node)); if let Some(param) = self.hir() .get_generics(scope) .and_then(|generics| generics.get_named(&br.name)) { sp = param.span; } (format!("the lifetime {} as defined on", br.name), sp) } ty::ReFree(ty::FreeRegion { bound_region: ty::BoundRegion::BrNamed(_, ref name), .. }) => { let mut sp = cm.def_span(self.hir().span_by_hir_id(node)); if let Some(param) = self.hir() .get_generics(scope) .and_then(|generics| generics.get_named(&name)) { sp = param.span; } (format!("the lifetime {} as defined on", name), sp) } ty::ReFree(ref fr) => match fr.bound_region { ty::BrAnon(idx) => ( format!("the anonymous lifetime #{} defined on", idx + 1), self.hir().span_by_hir_id(node), ), ty::BrFresh(_) => ( "an anonymous lifetime defined on".to_owned(), self.hir().span_by_hir_id(node), ), _ => ( format!("the lifetime {} as defined on", region), cm.def_span(self.hir().span_by_hir_id(node)), ), }, _ => bug!(), }; let (msg, opt_span) = self.explain_span(tag, span); (format!("{} {}", prefix, msg), opt_span) } fn emit_msg_span( err: &mut DiagnosticBuilder<'_>, prefix: &str, description: String, span: Option, suffix: &str, ) { let message = format!("{}{}{}", prefix, description, suffix); if let Some(span) = span { err.span_note(span, &message); } else { err.note(&message); } } fn item_scope_tag(item: &hir::Item) -> &'static str { match item.node { hir::ItemKind::Impl(..) => "impl", hir::ItemKind::Struct(..) => "struct", hir::ItemKind::Union(..) => "union", hir::ItemKind::Enum(..) => "enum", hir::ItemKind::Trait(..) => "trait", hir::ItemKind::Fn(..) => "function body", _ => "item", } } fn trait_item_scope_tag(item: &hir::TraitItem) -> &'static str { match item.node { hir::TraitItemKind::Method(..) => "method body", hir::TraitItemKind::Const(..) | hir::TraitItemKind::Type(..) => "associated item", } } fn impl_item_scope_tag(item: &hir::ImplItem) -> &'static str { match item.node { hir::ImplItemKind::Method(..) => "method body", hir::ImplItemKind::Const(..) | hir::ImplItemKind::Existential(..) | hir::ImplItemKind::Type(..) => "associated item", } } fn explain_span(self, heading: &str, span: Span) -> (String, Option) { let lo = self.sess.source_map().lookup_char_pos(span.lo()); ( format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize() + 1), Some(span), ) } } impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { pub fn report_region_errors( &self, region_scope_tree: ®ion::ScopeTree, errors: &Vec>, suppress: SuppressRegionErrors, ) { debug!( "report_region_errors(): {} errors to start, suppress = {:?}", errors.len(), suppress ); if suppress.suppressed() { return; } // try to pre-process the errors, which will group some of them // together into a `ProcessedErrors` group: let errors = self.process_errors(errors); debug!( "report_region_errors: {} errors after preprocessing", errors.len() ); for error in errors { debug!("report_region_errors: error = {:?}", error); if !self.try_report_nice_region_error(&error) { match error.clone() { // These errors could indicate all manner of different // problems with many different solutions. Rather // than generate a "one size fits all" error, what we // attempt to do is go through a number of specific // scenarios and try to find the best way to present // the error. If all of these fails, we fall back to a rather // general bit of code that displays the error information RegionResolutionError::ConcreteFailure(origin, sub, sup) => { if sub.is_placeholder() || sup.is_placeholder() { self.report_placeholder_failure(region_scope_tree, origin, sub, sup) .emit(); } else { self.report_concrete_failure(region_scope_tree, origin, sub, sup) .emit(); } } RegionResolutionError::GenericBoundFailure(origin, param_ty, sub) => { self.report_generic_bound_failure( region_scope_tree, origin.span(), Some(origin), param_ty, sub, ); } RegionResolutionError::SubSupConflict( _, var_origin, sub_origin, sub_r, sup_origin, sup_r, ) => { if sub_r.is_placeholder() { self.report_placeholder_failure( region_scope_tree, sub_origin, sub_r, sup_r, ) .emit(); } else if sup_r.is_placeholder() { self.report_placeholder_failure( region_scope_tree, sup_origin, sub_r, sup_r, ) .emit(); } else { self.report_sub_sup_conflict( region_scope_tree, var_origin, sub_origin, sub_r, sup_origin, sup_r, ); } } } } } } // This method goes through all the errors and try to group certain types // of error together, for the purpose of suggesting explicit lifetime // parameters to the user. This is done so that we can have a more // complete view of what lifetimes should be the same. // If the return value is an empty vector, it means that processing // failed (so the return value of this method should not be used). // // The method also attempts to weed out messages that seem like // duplicates that will be unhelpful to the end-user. But // obviously it never weeds out ALL errors. fn process_errors( &self, errors: &Vec>, ) -> Vec> { debug!("process_errors()"); // We want to avoid reporting generic-bound failures if we can // avoid it: these have a very high rate of being unhelpful in // practice. This is because they are basically secondary // checks that test the state of the region graph after the // rest of inference is done, and the other kinds of errors // indicate that the region constraint graph is internally // inconsistent, so these test results are likely to be // meaningless. // // Therefore, we filter them out of the list unless they are // the only thing in the list. let is_bound_failure = |e: &RegionResolutionError<'tcx>| match *e { RegionResolutionError::GenericBoundFailure(..) => true, RegionResolutionError::ConcreteFailure(..) | RegionResolutionError::SubSupConflict(..) => false, }; let mut errors = if errors.iter().all(|e| is_bound_failure(e)) { errors.clone() } else { errors .iter() .filter(|&e| !is_bound_failure(e)) .cloned() .collect() }; // sort the errors by span, for better error message stability. errors.sort_by_key(|u| match *u { RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(), RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(), RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _) => rvo.span(), }); errors } /// Adds a note if the types come from similarly named crates fn check_and_note_conflicting_crates( &self, err: &mut DiagnosticBuilder<'_>, terr: &TypeError<'tcx>, sp: Span, ) { use hir::def_id::CrateNum; use hir::map::DisambiguatedDefPathData; use ty::print::Printer; use ty::subst::Kind; struct AbsolutePathPrinter<'a, 'gcx, 'tcx> { tcx: TyCtxt<'a, 'gcx, 'tcx>, } struct NonTrivialPath; impl<'gcx, 'tcx> Printer<'gcx, 'tcx> for AbsolutePathPrinter<'_, 'gcx, 'tcx> { type Error = NonTrivialPath; type Path = Vec; type Region = !; type Type = !; type DynExistential = !; fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx> { self.tcx } fn print_region( self, _region: ty::Region<'_>, ) -> Result { Err(NonTrivialPath) } fn print_type( self, _ty: Ty<'tcx>, ) -> Result { Err(NonTrivialPath) } fn print_dyn_existential( self, _predicates: &'tcx ty::List>, ) -> Result { Err(NonTrivialPath) } fn path_crate( self, cnum: CrateNum, ) -> Result { Ok(vec![self.tcx.original_crate_name(cnum).to_string()]) } fn path_qualified( self, _self_ty: Ty<'tcx>, _trait_ref: Option>, ) -> Result { Err(NonTrivialPath) } fn path_append_impl( self, _print_prefix: impl FnOnce(Self) -> Result, _disambiguated_data: &DisambiguatedDefPathData, _self_ty: Ty<'tcx>, _trait_ref: Option>, ) -> Result { Err(NonTrivialPath) } fn path_append( self, print_prefix: impl FnOnce(Self) -> Result, disambiguated_data: &DisambiguatedDefPathData, ) -> Result { let mut path = print_prefix(self)?; path.push(disambiguated_data.data.as_interned_str().to_string()); Ok(path) } fn path_generic_args( self, print_prefix: impl FnOnce(Self) -> Result, _args: &[Kind<'tcx>], ) -> Result { print_prefix(self) } } let report_path_match = |err: &mut DiagnosticBuilder<'_>, did1: DefId, did2: DefId| { // Only external crates, if either is from a local // module we could have false positives if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate { let abs_path = |def_id| { AbsolutePathPrinter { tcx: self.tcx } .print_def_path(def_id, &[]) }; // We compare strings because DefPath can be different // for imported and non-imported crates let same_path = || -> Result<_, NonTrivialPath> { Ok( self.tcx.def_path_str(did1) == self.tcx.def_path_str(did2) || abs_path(did1)? == abs_path(did2)? ) }; if same_path().unwrap_or(false) { let crate_name = self.tcx.crate_name(did1.krate); err.span_note( sp, &format!( "Perhaps two different versions \ of crate `{}` are being used?", crate_name ), ); } } }; match *terr { TypeError::Sorts(ref exp_found) => { // if they are both "path types", there's a chance of ambiguity // due to different versions of the same crate if let (&ty::Adt(exp_adt, _), &ty::Adt(found_adt, _)) = (&exp_found.expected.sty, &exp_found.found.sty) { report_path_match(err, exp_adt.did, found_adt.did); } } TypeError::Traits(ref exp_found) => { report_path_match(err, exp_found.expected, exp_found.found); } _ => (), // FIXME(#22750) handle traits and stuff } } fn note_error_origin( &self, err: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>, exp_found: Option>>, ) { match cause.code { ObligationCauseCode::MatchExpressionArmPattern { span, ty } => { if ty.is_suggestable() { // don't show type `_` err.span_label(span, format!("this match expression has type `{}`", ty)); } if let Some(ty::error::ExpectedFound { found, .. }) = exp_found { if ty.is_box() && ty.boxed_ty() == found { if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) { err.span_suggestion( span, "consider dereferencing the boxed value", format!("*{}", snippet), Applicability::MachineApplicable, ); } } } } ObligationCauseCode::MatchExpressionArm { source, ref prior_arms, last_ty, discrim_hir_id, .. } => match source { hir::MatchSource::IfLetDesugar { .. } => { let msg = "`if let` arms have incompatible types"; err.span_label(cause.span, msg); } hir::MatchSource::TryDesugar => { if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found { let discrim_expr = self.tcx.hir().expect_expr_by_hir_id(discrim_hir_id); let discrim_ty = if let hir::ExprKind::Call(_, args) = &discrim_expr.node { let arg_expr = args.first().expect("try desugaring call w/out arg"); self.in_progress_tables.and_then(|tables| { tables.borrow().expr_ty_opt(arg_expr) }) } else { bug!("try desugaring w/out call expr as discriminant"); }; match discrim_ty { Some(ty) if expected == ty => { let source_map = self.tcx.sess.source_map(); err.span_suggestion( source_map.end_point(cause.span), "try removing this `?`", "".to_string(), Applicability::MachineApplicable, ); }, _ => {}, } } } _ => { let msg = "`match` arms have incompatible types"; err.span_label(cause.span, msg); if prior_arms.len() <= 4 { for sp in prior_arms { err.span_label(*sp, format!( "this is found to be of type `{}`", last_ty, )); } } else if let Some(sp) = prior_arms.last() { err.span_label(*sp, format!( "this and all prior arms are found to be of type `{}`", last_ty, )); } } }, ObligationCauseCode::IfExpression { then, outer, semicolon } => { err.span_label(then, "expected because of this"); outer.map(|sp| err.span_label(sp, "if and else have incompatible types")); if let Some(sp) = semicolon { err.span_suggestion_short( sp, "consider removing this semicolon", String::new(), Applicability::MachineApplicable, ); } } _ => (), } } /// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value` /// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and /// populate `other_value` with `other_ty`. /// /// ```text /// Foo> /// ^^^^--------^ this is highlighted /// | | /// | this type argument is exactly the same as the other type, not highlighted /// this is highlighted /// Bar /// -------- this type is the same as a type argument in the other type, not highlighted /// ``` fn highlight_outer( &self, value: &mut DiagnosticStyledString, other_value: &mut DiagnosticStyledString, name: String, sub: ty::subst::SubstsRef<'tcx>, pos: usize, other_ty: Ty<'tcx>, ) { // `value` and `other_value` hold two incomplete type representation for display. // `name` is the path of both types being compared. `sub` value.push_highlighted(name); let len = sub.len(); if len > 0 { value.push_highlighted("<"); } // Output the lifetimes for the first type let lifetimes = sub.regions() .map(|lifetime| { let s = lifetime.to_string(); if s.is_empty() { "'_".to_string() } else { s } }) .collect::>() .join(", "); if !lifetimes.is_empty() { if sub.regions().count() < len { value.push_normal(lifetimes + &", "); } else { value.push_normal(lifetimes); } } // Highlight all the type arguments that aren't at `pos` and compare the type argument at // `pos` and `other_ty`. for (i, type_arg) in sub.types().enumerate() { if i == pos { let values = self.cmp(type_arg, other_ty); value.0.extend((values.0).0); other_value.0.extend((values.1).0); } else { value.push_highlighted(type_arg.to_string()); } if len > 0 && i != len - 1 { value.push_normal(", "); } //self.push_comma(&mut value, &mut other_value, len, i); } if len > 0 { value.push_highlighted(">"); } } /// If `other_ty` is the same as a type argument present in `sub`, highlight `path` in `t1_out`, /// as that is the difference to the other type. /// /// For the following code: /// /// ```norun /// let x: Foo> = foo::>(); /// ``` /// /// The type error output will behave in the following way: /// /// ```text /// Foo> /// ^^^^--------^ this is highlighted /// | | /// | this type argument is exactly the same as the other type, not highlighted /// this is highlighted /// Bar /// -------- this type is the same as a type argument in the other type, not highlighted /// ``` fn cmp_type_arg( &self, mut t1_out: &mut DiagnosticStyledString, mut t2_out: &mut DiagnosticStyledString, path: String, sub: ty::subst::SubstsRef<'tcx>, other_path: String, other_ty: Ty<'tcx>, ) -> Option<()> { for (i, ta) in sub.types().enumerate() { if ta == other_ty { self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty); return Some(()); } if let &ty::Adt(def, _) = &ta.sty { let path_ = self.tcx.def_path_str(def.did.clone()); if path_ == other_path { self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty); return Some(()); } } } None } /// Adds a `,` to the type representation only if it is appropriate. fn push_comma( &self, value: &mut DiagnosticStyledString, other_value: &mut DiagnosticStyledString, len: usize, pos: usize, ) { if len > 0 && pos != len - 1 { value.push_normal(", "); other_value.push_normal(", "); } } /// For generic types with parameters with defaults, remove the parameters corresponding to /// the defaults. This repeats a lot of the logic found in `ty::print::pretty`. fn strip_generic_default_params( &self, def_id: DefId, substs: ty::subst::SubstsRef<'tcx>, ) -> SubstsRef<'tcx> { let generics = self.tcx.generics_of(def_id); let mut num_supplied_defaults = 0; let mut type_params = generics.params.iter().rev().filter_map(|param| match param.kind { ty::GenericParamDefKind::Lifetime => None, ty::GenericParamDefKind::Type { has_default, .. } => Some((param.def_id, has_default)), ty::GenericParamDefKind::Const => None, // FIXME(const_generics:defaults) }).peekable(); let has_default = { let has_default = type_params.peek().map(|(_, has_default)| has_default); *has_default.unwrap_or(&false) }; if has_default { let types = substs.types().rev(); for ((def_id, has_default), actual) in type_params.zip(types) { if !has_default { break; } if self.tcx.type_of(def_id).subst(self.tcx, substs) != actual { break; } num_supplied_defaults += 1; } } let len = generics.params.len(); let mut generics = generics.clone(); generics.params.truncate(len - num_supplied_defaults); substs.truncate_to(self.tcx, &generics) } /// Compares two given types, eliding parts that are the same between them and highlighting /// relevant differences, and return two representation of those types for highlighted printing. fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) { fn equals<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool { match (&a.sty, &b.sty) { (a, b) if *a == *b => true, (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_))) | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Int(_)) | (&ty::Infer(ty::InferTy::IntVar(_)), &ty::Infer(ty::InferTy::IntVar(_))) | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_))) | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Float(_)) | (&ty::Infer(ty::InferTy::FloatVar(_)), &ty::Infer(ty::InferTy::FloatVar(_))) => { true } _ => false, } } fn push_ty_ref<'tcx>( r: &ty::Region<'tcx>, ty: Ty<'tcx>, mutbl: hir::Mutability, s: &mut DiagnosticStyledString, ) { let mut r = r.to_string(); if r == "'_" { r.clear(); } else { r.push(' '); } s.push_highlighted(format!( "&{}{}", r, if mutbl == hir::MutMutable { "mut " } else { "" } )); s.push_normal(ty.to_string()); } match (&t1.sty, &t2.sty) { (&ty::Adt(def1, sub1), &ty::Adt(def2, sub2)) => { let sub_no_defaults_1 = self.strip_generic_default_params(def1.did, sub1); let sub_no_defaults_2 = self.strip_generic_default_params(def2.did, sub2); let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new()); let path1 = self.tcx.def_path_str(def1.did.clone()); let path2 = self.tcx.def_path_str(def2.did.clone()); if def1.did == def2.did { // Easy case. Replace same types with `_` to shorten the output and highlight // the differing ones. // let x: Foo = y::>(); // Foo // Foo // --- ^ type argument elided // | // highlighted in output values.0.push_normal(path1); values.1.push_normal(path2); // Avoid printing out default generic parameters that are common to both // types. let len1 = sub_no_defaults_1.len(); let len2 = sub_no_defaults_2.len(); let common_len = cmp::min(len1, len2); let remainder1: Vec<_> = sub1.types().skip(common_len).collect(); let remainder2: Vec<_> = sub2.types().skip(common_len).collect(); let common_default_params = remainder1 .iter() .rev() .zip(remainder2.iter().rev()) .filter(|(a, b)| a == b) .count(); let len = sub1.len() - common_default_params; // Only draw `<...>` if there're lifetime/type arguments. if len > 0 { values.0.push_normal("<"); values.1.push_normal("<"); } fn lifetime_display(lifetime: Region<'_>) -> String { let s = lifetime.to_string(); if s.is_empty() { "'_".to_string() } else { s } } // At one point we'd like to elide all lifetimes here, they are irrelevant for // all diagnostics that use this output // // Foo<'x, '_, Bar> // Foo<'y, '_, Qux> // ^^ ^^ --- type arguments are not elided // | | // | elided as they were the same // not elided, they were different, but irrelevant let lifetimes = sub1.regions().zip(sub2.regions()); for (i, lifetimes) in lifetimes.enumerate() { let l1 = lifetime_display(lifetimes.0); let l2 = lifetime_display(lifetimes.1); if l1 == l2 { values.0.push_normal("'_"); values.1.push_normal("'_"); } else { values.0.push_highlighted(l1); values.1.push_highlighted(l2); } self.push_comma(&mut values.0, &mut values.1, len, i); } // We're comparing two types with the same path, so we compare the type // arguments for both. If they are the same, do not highlight and elide from the // output. // Foo<_, Bar> // Foo<_, Qux> // ^ elided type as this type argument was the same in both sides let type_arguments = sub1.types().zip(sub2.types()); let regions_len = sub1.regions().count(); for (i, (ta1, ta2)) in type_arguments.take(len).enumerate() { let i = i + regions_len; if ta1 == ta2 { values.0.push_normal("_"); values.1.push_normal("_"); } else { let (x1, x2) = self.cmp(ta1, ta2); (values.0).0.extend(x1.0); (values.1).0.extend(x2.0); } self.push_comma(&mut values.0, &mut values.1, len, i); } // Close the type argument bracket. // Only draw `<...>` if there're lifetime/type arguments. if len > 0 { values.0.push_normal(">"); values.1.push_normal(">"); } values } else { // Check for case: // let x: Foo = foo::>(); // Foo // ------- this type argument is exactly the same as the other type // Bar if self.cmp_type_arg( &mut values.0, &mut values.1, path1.clone(), sub_no_defaults_1, path2.clone(), &t2, ).is_some() { return values; } // Check for case: // let x: Bar = y:>>(); // Bar // Foo> // ------- this type argument is exactly the same as the other type if self.cmp_type_arg( &mut values.1, &mut values.0, path2, sub_no_defaults_2, path1, &t1, ).is_some() { return values; } // We couldn't find anything in common, highlight everything. // let x: Bar = y::>(); ( DiagnosticStyledString::highlighted(t1.to_string()), DiagnosticStyledString::highlighted(t2.to_string()), ) } } // When finding T != &T, highlight only the borrow (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(&ref_ty1, &t2) => { let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new()); push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0); values.1.push_normal(t2.to_string()); values } (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(&t1, &ref_ty2) => { let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new()); values.0.push_normal(t1.to_string()); push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1); values } // When encountering &T != &mut T, highlight only the borrow (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2)) if equals(&ref_ty1, &ref_ty2) => { let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new()); push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0); push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1); values } _ => { if t1 == t2 { // The two types are the same, elide and don't highlight. ( DiagnosticStyledString::normal("_"), DiagnosticStyledString::normal("_"), ) } else { // We couldn't find anything in common, highlight everything. ( DiagnosticStyledString::highlighted(t1.to_string()), DiagnosticStyledString::highlighted(t2.to_string()), ) } } } } pub fn note_type_err( &self, diag: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>, secondary_span: Option<(Span, String)>, mut values: Option>, terr: &TypeError<'tcx>, ) { // For some types of errors, expected-found does not make // sense, so just ignore the values we were given. match terr { TypeError::CyclicTy(_) => { values = None; } _ => {} } let (expected_found, exp_found, is_simple_error) = match values { None => (None, None, false), Some(values) => { let (is_simple_error, exp_found) = match values { ValuePairs::Types(exp_found) => { let is_simple_err = exp_found.expected.is_primitive() && exp_found.found.is_primitive(); (is_simple_err, Some(exp_found)) } _ => (false, None), }; let vals = match self.values_str(&values) { Some((expected, found)) => Some((expected, found)), None => { // Derived error. Cancel the emitter. self.tcx.sess.diagnostic().cancel(diag); return; } }; (vals, exp_found, is_simple_error) } }; let span = cause.span(self.tcx); diag.span_label(span, terr.to_string()); if let Some((sp, msg)) = secondary_span { diag.span_label(sp, msg); } if let Some((expected, found)) = expected_found { match (terr, is_simple_error, expected == found) { (&TypeError::Sorts(ref values), false, true) => { diag.note_expected_found_extra( &"type", expected, found, &format!(" ({})", values.expected.sort_string(self.tcx)), &format!(" ({})", values.found.sort_string(self.tcx)), ); } (_, false, _) => { if let Some(exp_found) = exp_found { let (def_id, ret_ty) = match exp_found.found.sty { ty::FnDef(def, _) => { (Some(def), Some(self.tcx.fn_sig(def).output())) } _ => (None, None), }; let exp_is_struct = match exp_found.expected.sty { ty::Adt(def, _) => def.is_struct(), _ => false, }; if let (Some(def_id), Some(ret_ty)) = (def_id, ret_ty) { if exp_is_struct && &exp_found.expected == ret_ty.skip_binder() { let message = format!( "did you mean `{}(/* fields */)`?", self.tcx.def_path_str(def_id) ); diag.span_label(span, message); } } self.suggest_as_ref_where_appropriate(span, &exp_found, diag); } diag.note_expected_found(&"type", expected, found); } _ => (), } } self.check_and_note_conflicting_crates(diag, terr, span); self.tcx.note_and_explain_type_err(diag, terr, span); // It reads better to have the error origin as the final // thing. self.note_error_origin(diag, &cause, exp_found); } /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate, /// suggest it. fn suggest_as_ref_where_appropriate( &self, span: Span, exp_found: &ty::error::ExpectedFound>, diag: &mut DiagnosticBuilder<'tcx>, ) { match (&exp_found.expected.sty, &exp_found.found.sty) { (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) => { if let ty::Adt(found_def, found_substs) = found_ty.sty { let path_str = format!("{:?}", exp_def); if exp_def == &found_def { let opt_msg = "you can convert from `&Option` to `Option<&T>` using \ `.as_ref()`"; let result_msg = "you can convert from `&Result` to \ `Result<&T, &E>` using `.as_ref()`"; let have_as_ref = &[ ("std::option::Option", opt_msg), ("core::option::Option", opt_msg), ("std::result::Result", result_msg), ("core::result::Result", result_msg), ]; if let Some(msg) = have_as_ref.iter() .filter_map(|(path, msg)| if &path_str == path { Some(msg) } else { None }).next() { let mut show_suggestion = true; for (exp_ty, found_ty) in exp_substs.types().zip(found_substs.types()) { match exp_ty.sty { ty::Ref(_, exp_ty, _) => { match (&exp_ty.sty, &found_ty.sty) { (_, ty::Param(_)) | (_, ty::Infer(_)) | (ty::Param(_), _) | (ty::Infer(_), _) => {} _ if ty::TyS::same_type(exp_ty, found_ty) => {} _ => show_suggestion = false, }; } ty::Param(_) | ty::Infer(_) => {} _ => show_suggestion = false, } } if let (Ok(snippet), true) = ( self.tcx.sess.source_map().span_to_snippet(span), show_suggestion, ) { diag.span_suggestion( span, msg, format!("{}.as_ref()", snippet), Applicability::MachineApplicable, ); } } } } } _ => {} } } pub fn report_and_explain_type_error( &self, trace: TypeTrace<'tcx>, terr: &TypeError<'tcx>, ) -> DiagnosticBuilder<'tcx> { debug!( "report_and_explain_type_error(trace={:?}, terr={:?})", trace, terr ); let span = trace.cause.span(self.tcx); let failure_code = trace.cause.as_failure_code(terr); let mut diag = match failure_code { FailureCode::Error0317(failure_str) => { struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str) } FailureCode::Error0580(failure_str) => { struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str) } FailureCode::Error0308(failure_str) => { struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str) } FailureCode::Error0644(failure_str) => { struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str) } }; self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr); diag } fn values_str( &self, values: &ValuePairs<'tcx>, ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> { match *values { infer::Types(ref exp_found) => self.expected_found_str_ty(exp_found), infer::Regions(ref exp_found) => self.expected_found_str(exp_found), infer::TraitRefs(ref exp_found) => self.expected_found_str(exp_found), infer::PolyTraitRefs(ref exp_found) => self.expected_found_str(exp_found), } } fn expected_found_str_ty( &self, exp_found: &ty::error::ExpectedFound>, ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> { let exp_found = self.resolve_type_vars_if_possible(exp_found); if exp_found.references_error() { return None; } Some(self.cmp(exp_found.expected, exp_found.found)) } /// Returns a string of the form "expected `{}`, found `{}`". fn expected_found_str>( &self, exp_found: &ty::error::ExpectedFound, ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> { let exp_found = self.resolve_type_vars_if_possible(exp_found); if exp_found.references_error() { return None; } Some(( DiagnosticStyledString::highlighted(exp_found.expected.to_string()), DiagnosticStyledString::highlighted(exp_found.found.to_string()), )) } pub fn report_generic_bound_failure( &self, region_scope_tree: ®ion::ScopeTree, span: Span, origin: Option>, bound_kind: GenericKind<'tcx>, sub: Region<'tcx>, ) { self.construct_generic_bound_failure(region_scope_tree, span, origin, bound_kind, sub) .emit() } pub fn construct_generic_bound_failure( &self, region_scope_tree: ®ion::ScopeTree, span: Span, origin: Option>, bound_kind: GenericKind<'tcx>, sub: Region<'tcx>, ) -> DiagnosticBuilder<'a> { // Attempt to obtain the span of the parameter so we can // suggest adding an explicit lifetime bound to it. let type_param_span = match (self.in_progress_tables, bound_kind) { (Some(ref table), GenericKind::Param(ref param)) => { let table = table.borrow(); table.local_id_root.and_then(|did| { let generics = self.tcx.generics_of(did); // Account for the case where `did` corresponds to `Self`, which doesn't have // the expected type argument. if !param.is_self() { let type_param = generics.type_param(param, self.tcx); let hir = &self.tcx.hir(); hir.as_local_node_id(type_param.def_id).map(|id| { // Get the `hir::Param` to verify whether it already has any bounds. // We do this to avoid suggesting code that ends up as `T: 'a'b`, // instead we suggest `T: 'a + 'b` in that case. let mut has_bounds = false; if let Node::GenericParam(ref param) = hir.get(id) { has_bounds = !param.bounds.is_empty(); } let sp = hir.span(id); // `sp` only covers `T`, change it so that it covers // `T:` when appropriate let is_impl_trait = bound_kind.to_string().starts_with("impl "); let sp = if has_bounds && !is_impl_trait { sp.to(self.tcx .sess .source_map() .next_point(self.tcx.sess.source_map().next_point(sp))) } else { sp }; (sp, has_bounds, is_impl_trait) }) } else { None } }) } _ => None, }; let labeled_user_string = match bound_kind { GenericKind::Param(ref p) => format!("the parameter type `{}`", p), GenericKind::Projection(ref p) => format!("the associated type `{}`", p), }; if let Some(SubregionOrigin::CompareImplMethodObligation { span, item_name, impl_item_def_id, trait_item_def_id, }) = origin { return self.report_extra_impl_obligation( span, item_name, impl_item_def_id, trait_item_def_id, &format!("`{}: {}`", bound_kind, sub), ); } fn binding_suggestion<'tcx, S: fmt::Display>( err: &mut DiagnosticBuilder<'tcx>, type_param_span: Option<(Span, bool, bool)>, bound_kind: GenericKind<'tcx>, sub: S, ) { let consider = format!( "consider adding an explicit lifetime bound {}", if type_param_span.map(|(_, _, is_impl_trait)| is_impl_trait).unwrap_or(false) { format!(" `{}` to `{}`...", sub, bound_kind) } else { format!("`{}: {}`...", bound_kind, sub) }, ); if let Some((sp, has_lifetimes, is_impl_trait)) = type_param_span { let suggestion = if is_impl_trait { format!("{} + {}", bound_kind, sub) } else { let tail = if has_lifetimes { " + " } else { "" }; format!("{}: {}{}", bound_kind, sub, tail) }; err.span_suggestion_short( sp, &consider, suggestion, Applicability::MaybeIncorrect, // Issue #41966 ); } else { err.help(&consider); } } let mut err = match *sub { ty::ReEarlyBound(_) | ty::ReFree(ty::FreeRegion { bound_region: ty::BrNamed(..), .. }) => { // Does the required lifetime have a nice name we can print? let mut err = struct_span_err!( self.tcx.sess, span, E0309, "{} may not live long enough", labeled_user_string ); binding_suggestion(&mut err, type_param_span, bound_kind, sub); err } ty::ReStatic => { // Does the required lifetime have a nice name we can print? let mut err = struct_span_err!( self.tcx.sess, span, E0310, "{} may not live long enough", labeled_user_string ); binding_suggestion(&mut err, type_param_span, bound_kind, "'static"); err } _ => { // If not, be less specific. let mut err = struct_span_err!( self.tcx.sess, span, E0311, "{} may not live long enough", labeled_user_string ); err.help(&format!( "consider adding an explicit lifetime bound for `{}`", bound_kind )); self.tcx.note_and_explain_region( region_scope_tree, &mut err, &format!("{} must be valid for ", labeled_user_string), sub, "...", ); err } }; if let Some(origin) = origin { self.note_region_origin(&mut err, &origin); } err } fn report_sub_sup_conflict( &self, region_scope_tree: ®ion::ScopeTree, var_origin: RegionVariableOrigin, sub_origin: SubregionOrigin<'tcx>, sub_region: Region<'tcx>, sup_origin: SubregionOrigin<'tcx>, sup_region: Region<'tcx>, ) { let mut err = self.report_inference_failure(var_origin); self.tcx.note_and_explain_region( region_scope_tree, &mut err, "first, the lifetime cannot outlive ", sup_region, "...", ); match (&sup_origin, &sub_origin) { (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) => { debug!("report_sub_sup_conflict: var_origin={:?}", var_origin); debug!("report_sub_sup_conflict: sub_region={:?}", sub_region); debug!("report_sub_sup_conflict: sub_origin={:?}", sub_origin); debug!("report_sub_sup_conflict: sup_region={:?}", sup_region); debug!("report_sub_sup_conflict: sup_origin={:?}", sup_origin); debug!("report_sub_sup_conflict: sup_trace={:?}", sup_trace); debug!("report_sub_sup_conflict: sub_trace={:?}", sub_trace); debug!("report_sub_sup_conflict: sup_trace.values={:?}", sup_trace.values); debug!("report_sub_sup_conflict: sub_trace.values={:?}", sub_trace.values); if let (Some((sup_expected, sup_found)), Some((sub_expected, sub_found))) = ( self.values_str(&sup_trace.values), self.values_str(&sub_trace.values), ) { if sub_expected == sup_expected && sub_found == sup_found { self.tcx.note_and_explain_region( region_scope_tree, &mut err, "...but the lifetime must also be valid for ", sub_region, "...", ); err.note(&format!( "...so that the {}:\nexpected {}\n found {}", sup_trace.cause.as_requirement_str(), sup_expected.content(), sup_found.content() )); err.emit(); return; } } } _ => {} } self.note_region_origin(&mut err, &sup_origin); self.tcx.note_and_explain_region( region_scope_tree, &mut err, "but, the lifetime must be valid for ", sub_region, "...", ); self.note_region_origin(&mut err, &sub_origin); err.emit(); } } impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { fn report_inference_failure( &self, var_origin: RegionVariableOrigin, ) -> DiagnosticBuilder<'tcx> { let br_string = |br: ty::BoundRegion| { let mut s = match br { ty::BrNamed(_, name) => name.to_string(), _ => String::new(), }; if !s.is_empty() { s.push_str(" "); } s }; let var_description = match var_origin { infer::MiscVariable(_) => String::new(), infer::PatternRegion(_) => " for pattern".to_string(), infer::AddrOfRegion(_) => " for borrow expression".to_string(), infer::Autoref(_) => " for autoref".to_string(), infer::Coercion(_) => " for automatic coercion".to_string(), infer::LateBoundRegion(_, br, infer::FnCall) => { format!(" for lifetime parameter {}in function call", br_string(br)) } infer::LateBoundRegion(_, br, infer::HigherRankedType) => { format!(" for lifetime parameter {}in generic type", br_string(br)) } infer::LateBoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!( " for lifetime parameter {}in trait containing associated type `{}`", br_string(br), self.tcx.associated_item(def_id).ident ), infer::EarlyBoundRegion(_, name) => format!(" for lifetime parameter `{}`", name), infer::BoundRegionInCoherence(name) => { format!(" for lifetime parameter `{}` in coherence check", name) } infer::UpvarRegion(ref upvar_id, _) => { let var_name = self.tcx.hir().name_by_hir_id(upvar_id.var_path.hir_id); format!(" for capture of `{}` by closure", var_name) } infer::NLL(..) => bug!("NLL variable found in lexical phase"), }; struct_span_err!( self.tcx.sess, var_origin.span(), E0495, "cannot infer an appropriate lifetime{} \ due to conflicting requirements", var_description ) } } enum FailureCode { Error0317(&'static str), Error0580(&'static str), Error0308(&'static str), Error0644(&'static str), } impl<'tcx> ObligationCause<'tcx> { fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode { use self::FailureCode::*; use crate::traits::ObligationCauseCode::*; match self.code { CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"), MatchExpressionArm { source, .. } => Error0308(match source { hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have incompatible types", hir::MatchSource::TryDesugar => { "try expression alternatives have incompatible types" } _ => "match arms have incompatible types", }), IfExpression { .. } => Error0308("if and else have incompatible types"), IfExpressionWithNoElse => Error0317("if may be missing an else clause"), MainFunctionType => Error0580("main function has wrong type"), StartFunctionType => Error0308("start function has wrong type"), IntrinsicType => Error0308("intrinsic has wrong type"), MethodReceiver => Error0308("mismatched method receiver"), // In the case where we have no more specific thing to // say, also take a look at the error code, maybe we can // tailor to that. _ => match terr { TypeError::CyclicTy(ty) if ty.is_closure() || ty.is_generator() => { Error0644("closure/generator type that references itself") } _ => Error0308("mismatched types"), }, } } fn as_requirement_str(&self) -> &'static str { use crate::traits::ObligationCauseCode::*; match self.code { CompareImplMethodObligation { .. } => "method type is compatible with trait", ExprAssignable => "expression is assignable", MatchExpressionArm { source, .. } => match source { hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have compatible types", _ => "match arms have compatible types", }, IfExpression { .. } => "if and else have compatible types", IfExpressionWithNoElse => "if missing an else returns ()", MainFunctionType => "`main` function has the correct type", StartFunctionType => "`start` function has the correct type", IntrinsicType => "intrinsic has the correct type", MethodReceiver => "method receiver has the correct type", _ => "types are compatible", } } }