diff options
Diffstat (limited to 'compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs')
| -rw-r--r-- | compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs | 1134 |
1 files changed, 1134 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs new file mode 100644 index 000000000..561d1354e --- /dev/null +++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs @@ -0,0 +1,1134 @@ +use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; +use crate::infer::InferCtxt; +use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed}; +use rustc_hir as hir; +use rustc_hir::def::Res; +use rustc_hir::def::{CtorOf, DefKind, Namespace}; +use rustc_hir::def_id::DefId; +use rustc_hir::intravisit::{self, Visitor}; +use rustc_hir::{Body, Closure, Expr, ExprKind, FnRetTy, HirId, Local, LocalSource}; +use rustc_middle::hir::nested_filter; +use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind}; +use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability}; +use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Print, Printer}; +use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef}; +use rustc_middle::ty::{self, DefIdTree, InferConst}; +use rustc_middle::ty::{IsSuggestable, Ty, TyCtxt, TypeckResults}; +use rustc_span::symbol::{kw, Ident}; +use rustc_span::{BytePos, Span}; +use std::borrow::Cow; +use std::iter; + +pub enum TypeAnnotationNeeded { + /// ```compile_fail,E0282 + /// let x = "hello".chars().rev().collect(); + /// ``` + E0282, + /// An implementation cannot be chosen unambiguously because of lack of information. + /// ```compile_fail,E0283 + /// let _ = Default::default(); + /// ``` + E0283, + /// ```compile_fail,E0284 + /// let mut d: u64 = 2; + /// d = d % 1u32.into(); + /// ``` + E0284, +} + +impl Into<rustc_errors::DiagnosticId> for TypeAnnotationNeeded { + fn into(self) -> rustc_errors::DiagnosticId { + match self { + Self::E0282 => rustc_errors::error_code!(E0282), + Self::E0283 => rustc_errors::error_code!(E0283), + Self::E0284 => rustc_errors::error_code!(E0284), + } + } +} + +/// Information about a constant or a type containing inference variables. +pub struct InferenceDiagnosticsData { + pub name: String, + pub span: Option<Span>, + pub kind: UnderspecifiedArgKind, + pub parent: Option<InferenceDiagnosticsParentData>, +} + +/// Data on the parent definition where a generic argument was declared. +pub struct InferenceDiagnosticsParentData { + prefix: &'static str, + name: String, +} + +pub enum UnderspecifiedArgKind { + Type { prefix: Cow<'static, str> }, + Const { is_parameter: bool }, +} + +impl InferenceDiagnosticsData { + /// Generate a label for a generic argument which can't be inferred. When not + /// much is known about the argument, `use_diag` may be used to describe the + /// labeled value. + fn cannot_infer_msg(&self) -> String { + if self.name == "_" && matches!(self.kind, UnderspecifiedArgKind::Type { .. }) { + return "cannot infer type".to_string(); + } + + let suffix = match &self.parent { + Some(parent) => parent.suffix_string(), + None => String::new(), + }; + + // For example: "cannot infer type for type parameter `T`" + format!("cannot infer {} `{}`{}", self.kind.prefix_string(), self.name, suffix) + } + + fn where_x_is_specified(&self, in_type: Ty<'_>) -> String { + if in_type.is_ty_infer() { + String::new() + } else if self.name == "_" { + // FIXME: Consider specializing this message if there is a single `_` + // in the type. + ", where the placeholders `_` are specified".to_string() + } else { + format!(", where the {} `{}` is specified", self.kind.prefix_string(), self.name) + } + } +} + +impl InferenceDiagnosticsParentData { + fn for_parent_def_id( + tcx: TyCtxt<'_>, + parent_def_id: DefId, + ) -> Option<InferenceDiagnosticsParentData> { + let parent_name = + tcx.def_key(parent_def_id).disambiguated_data.data.get_opt_name()?.to_string(); + + Some(InferenceDiagnosticsParentData { + prefix: tcx.def_kind(parent_def_id).descr(parent_def_id), + name: parent_name, + }) + } + + fn for_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<InferenceDiagnosticsParentData> { + Self::for_parent_def_id(tcx, tcx.parent(def_id)) + } + + fn suffix_string(&self) -> String { + format!(" declared on the {} `{}`", self.prefix, self.name) + } +} + +impl UnderspecifiedArgKind { + fn prefix_string(&self) -> Cow<'static, str> { + match self { + Self::Type { prefix } => format!("type for {}", prefix).into(), + Self::Const { is_parameter: true } => "the value of const parameter".into(), + Self::Const { is_parameter: false } => "the value of the constant".into(), + } + } +} + +fn fmt_printer<'a, 'tcx>(infcx: &'a InferCtxt<'_, 'tcx>, ns: Namespace) -> FmtPrinter<'a, 'tcx> { + let mut printer = FmtPrinter::new(infcx.tcx, ns); + let ty_getter = move |ty_vid| { + if infcx.probe_ty_var(ty_vid).is_ok() { + warn!("resolved ty var in error message"); + } + if let TypeVariableOriginKind::TypeParameterDefinition(name, _) = + infcx.inner.borrow_mut().type_variables().var_origin(ty_vid).kind + { + Some(name) + } else { + None + } + }; + printer.ty_infer_name_resolver = Some(Box::new(ty_getter)); + let const_getter = move |ct_vid| { + if infcx.probe_const_var(ct_vid).is_ok() { + warn!("resolved const var in error message"); + } + if let ConstVariableOriginKind::ConstParameterDefinition(name, _) = + infcx.inner.borrow_mut().const_unification_table().probe_value(ct_vid).origin.kind + { + return Some(name); + } else { + None + } + }; + printer.const_infer_name_resolver = Some(Box::new(const_getter)); + printer +} + +fn ty_to_string<'tcx>(infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>) -> String { + let printer = fmt_printer(infcx, Namespace::TypeNS); + let ty = infcx.resolve_vars_if_possible(ty); + match ty.kind() { + // We don't want the regular output for `fn`s because it includes its path in + // invalid pseudo-syntax, we want the `fn`-pointer output instead. + ty::FnDef(..) => ty.fn_sig(infcx.tcx).print(printer).unwrap().into_buffer(), + // FIXME: The same thing for closures, but this only works when the closure + // does not capture anything. + // + // We do have to hide the `extern "rust-call"` ABI in that case though, + // which is too much of a bother for now. + _ => ty.print(printer).unwrap().into_buffer(), + } +} + +/// We don't want to directly use `ty_to_string` for closures as their type isn't really +/// something users are familar with. Directly printing the `fn_sig` of closures also +/// doesn't work as they actually use the "rust-call" API. +fn closure_as_fn_str<'tcx>(infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>) -> String { + let ty::Closure(_, substs) = ty.kind() else { unreachable!() }; + let fn_sig = substs.as_closure().sig(); + let args = fn_sig + .inputs() + .skip_binder() + .iter() + .next() + .map(|args| { + args.tuple_fields() + .iter() + .map(|arg| ty_to_string(infcx, arg)) + .collect::<Vec<_>>() + .join(", ") + }) + .unwrap_or_default(); + let ret = if fn_sig.output().skip_binder().is_unit() { + String::new() + } else { + format!(" -> {}", ty_to_string(infcx, fn_sig.output().skip_binder())) + }; + format!("fn({}){}", args, ret) +} + +impl<'a, 'tcx> InferCtxt<'a, 'tcx> { + /// Extracts data used by diagnostic for either types or constants + /// which were stuck during inference. + pub fn extract_inference_diagnostics_data( + &self, + arg: GenericArg<'tcx>, + highlight: Option<ty::print::RegionHighlightMode<'tcx>>, + ) -> InferenceDiagnosticsData { + match arg.unpack() { + GenericArgKind::Type(ty) => { + if let ty::Infer(ty::TyVar(ty_vid)) = *ty.kind() { + let mut inner = self.inner.borrow_mut(); + let ty_vars = &inner.type_variables(); + let var_origin = ty_vars.var_origin(ty_vid); + if let TypeVariableOriginKind::TypeParameterDefinition(name, def_id) = + var_origin.kind + { + if name != kw::SelfUpper { + return InferenceDiagnosticsData { + name: name.to_string(), + span: Some(var_origin.span), + kind: UnderspecifiedArgKind::Type { + prefix: "type parameter".into(), + }, + parent: def_id.and_then(|def_id| { + InferenceDiagnosticsParentData::for_def_id(self.tcx, def_id) + }), + }; + } + } + } + + let mut printer = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS); + if let Some(highlight) = highlight { + printer.region_highlight_mode = highlight; + } + InferenceDiagnosticsData { + name: ty.print(printer).unwrap().into_buffer(), + span: None, + kind: UnderspecifiedArgKind::Type { prefix: ty.prefix_string(self.tcx) }, + parent: None, + } + } + GenericArgKind::Const(ct) => { + if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.kind() { + let origin = + self.inner.borrow_mut().const_unification_table().probe_value(vid).origin; + if let ConstVariableOriginKind::ConstParameterDefinition(name, def_id) = + origin.kind + { + return InferenceDiagnosticsData { + name: name.to_string(), + span: Some(origin.span), + kind: UnderspecifiedArgKind::Const { is_parameter: true }, + parent: InferenceDiagnosticsParentData::for_def_id(self.tcx, def_id), + }; + } + + debug_assert!(!origin.span.is_dummy()); + let mut printer = ty::print::FmtPrinter::new(self.tcx, Namespace::ValueNS); + if let Some(highlight) = highlight { + printer.region_highlight_mode = highlight; + } + InferenceDiagnosticsData { + name: ct.print(printer).unwrap().into_buffer(), + span: Some(origin.span), + kind: UnderspecifiedArgKind::Const { is_parameter: false }, + parent: None, + } + } else { + // If we end up here the `FindInferSourceVisitor` + // won't work, as its expected argument isn't an inference variable. + // + // FIXME: Ideally we should look into the generic constant + // to figure out which inference var is actually unresolved so that + // this path is unreachable. + let mut printer = ty::print::FmtPrinter::new(self.tcx, Namespace::ValueNS); + if let Some(highlight) = highlight { + printer.region_highlight_mode = highlight; + } + InferenceDiagnosticsData { + name: ct.print(printer).unwrap().into_buffer(), + span: None, + kind: UnderspecifiedArgKind::Const { is_parameter: false }, + parent: None, + } + } + } + GenericArgKind::Lifetime(_) => bug!("unexpected lifetime"), + } + } + + /// Used as a fallback in [InferCtxt::emit_inference_failure_err] + /// in case we weren't able to get a better error. + fn bad_inference_failure_err( + &self, + span: Span, + arg_data: InferenceDiagnosticsData, + error_code: TypeAnnotationNeeded, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + let error_code = error_code.into(); + let mut err = + self.tcx.sess.struct_span_err_with_code(span, "type annotations needed", error_code); + err.span_label(span, arg_data.cannot_infer_msg()); + err + } + + pub fn emit_inference_failure_err( + &self, + body_id: Option<hir::BodyId>, + failure_span: Span, + arg: GenericArg<'tcx>, + error_code: TypeAnnotationNeeded, + should_label_span: bool, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + let arg = self.resolve_vars_if_possible(arg); + let arg_data = self.extract_inference_diagnostics_data(arg, None); + + let Some(typeck_results) = self.in_progress_typeck_results else { + // If we don't have any typeck results we're outside + // of a body, so we won't be able to get better info + // here. + return self.bad_inference_failure_err(failure_span, arg_data, error_code); + }; + let typeck_results = typeck_results.borrow(); + let typeck_results = &typeck_results; + + let mut local_visitor = FindInferSourceVisitor::new(&self, typeck_results, arg); + if let Some(body_id) = body_id { + let expr = self.tcx.hir().expect_expr(body_id.hir_id); + local_visitor.visit_expr(expr); + } + + let Some(InferSource { span, kind }) = local_visitor.infer_source else { + return self.bad_inference_failure_err(failure_span, arg_data, error_code) + }; + + let error_code = error_code.into(); + let mut err = self.tcx.sess.struct_span_err_with_code( + span, + &format!("type annotations needed{}", kind.ty_msg(self)), + error_code, + ); + + if should_label_span && !failure_span.overlaps(span) { + err.span_label(failure_span, "type must be known at this point"); + } + + match kind { + InferSourceKind::LetBinding { insert_span, pattern_name, ty } => { + let suggestion_msg = if let Some(name) = pattern_name { + format!( + "consider giving `{}` an explicit type{}", + name, + arg_data.where_x_is_specified(ty) + ) + } else { + format!( + "consider giving this pattern a type{}", + arg_data.where_x_is_specified(ty) + ) + }; + err.span_suggestion_verbose( + insert_span, + &suggestion_msg, + format!(": {}", ty_to_string(self, ty)), + Applicability::HasPlaceholders, + ); + } + InferSourceKind::ClosureArg { insert_span, ty } => { + err.span_suggestion_verbose( + insert_span, + &format!( + "consider giving this closure parameter an explicit type{}", + arg_data.where_x_is_specified(ty) + ), + format!(": {}", ty_to_string(self, ty)), + Applicability::HasPlaceholders, + ); + } + InferSourceKind::GenericArg { + insert_span, + argument_index, + generics_def_id, + def_id: _, + generic_args, + } => { + let generics = self.tcx.generics_of(generics_def_id); + let is_type = matches!(arg.unpack(), GenericArgKind::Type(_)); + + let cannot_infer_msg = format!( + "cannot infer {} of the {} parameter `{}`{}", + if is_type { "type" } else { "the value" }, + if is_type { "type" } else { "const" }, + generics.params[argument_index].name, + // We use the `generics_def_id` here, as even when suggesting `None::<T>`, + // the type parameter `T` was still declared on the enum, not on the + // variant. + InferenceDiagnosticsParentData::for_parent_def_id(self.tcx, generics_def_id) + .map_or(String::new(), |parent| parent.suffix_string()), + ); + + err.span_label(span, cannot_infer_msg); + + let args = fmt_printer(self, Namespace::TypeNS) + .comma_sep(generic_args.iter().copied().map(|arg| { + if arg.is_suggestable(self.tcx, true) { + return arg; + } + + match arg.unpack() { + GenericArgKind::Lifetime(_) => bug!("unexpected lifetime"), + GenericArgKind::Type(_) => self + .next_ty_var(TypeVariableOrigin { + span: rustc_span::DUMMY_SP, + kind: TypeVariableOriginKind::MiscVariable, + }) + .into(), + GenericArgKind::Const(arg) => self + .next_const_var( + arg.ty(), + ConstVariableOrigin { + span: rustc_span::DUMMY_SP, + kind: ConstVariableOriginKind::MiscVariable, + }, + ) + .into(), + } + })) + .unwrap() + .into_buffer(); + + err.span_suggestion_verbose( + insert_span, + &format!( + "consider specifying the generic argument{}", + pluralize!(generic_args.len()), + ), + format!("::<{}>", args), + Applicability::HasPlaceholders, + ); + } + InferSourceKind::FullyQualifiedMethodCall { receiver, successor, substs, def_id } => { + let printer = fmt_printer(self, Namespace::ValueNS); + let def_path = printer.print_def_path(def_id, substs).unwrap().into_buffer(); + + // We only care about whether we have to add `&` or `&mut ` for now. + // This is the case if the last adjustment is a borrow and the + // first adjustment was not a builtin deref. + let adjustment = match typeck_results.expr_adjustments(receiver) { + [ + Adjustment { kind: Adjust::Deref(None), target: _ }, + .., + Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), target: _ }, + ] => "", + [ + .., + Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(_, mut_)), target: _ }, + ] => match mut_ { + AutoBorrowMutability::Mut { .. } => "&mut ", + AutoBorrowMutability::Not => "&", + }, + _ => "", + }; + + let suggestion = vec![ + (receiver.span.shrink_to_lo(), format!("{def_path}({adjustment}")), + (receiver.span.shrink_to_hi().with_hi(successor.1), successor.0.to_string()), + ]; + err.multipart_suggestion_verbose( + "try using a fully qualified path to specify the expected types", + suggestion, + Applicability::HasPlaceholders, + ); + } + InferSourceKind::ClosureReturn { ty, data, should_wrap_expr } => { + let ret = ty_to_string(self, ty); + let (arrow, post) = match data { + FnRetTy::DefaultReturn(_) => ("-> ", " "), + _ => ("", ""), + }; + let suggestion = match should_wrap_expr { + Some(end_span) => vec![ + (data.span(), format!("{}{}{}{{ ", arrow, ret, post)), + (end_span, " }".to_string()), + ], + None => vec![(data.span(), format!("{}{}{}", arrow, ret, post))], + }; + err.multipart_suggestion_verbose( + "try giving this closure an explicit return type", + suggestion, + Applicability::HasPlaceholders, + ); + } + } + err + } + + pub fn need_type_info_err_in_generator( + &self, + kind: hir::GeneratorKind, + span: Span, + ty: Ty<'tcx>, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + let ty = self.resolve_vars_if_possible(ty); + let data = self.extract_inference_diagnostics_data(ty.into(), None); + + let mut err = struct_span_err!( + self.tcx.sess, + span, + E0698, + "type inside {} must be known in this context", + kind, + ); + err.span_label(span, data.cannot_infer_msg()); + err + } +} + +#[derive(Debug)] +struct InferSource<'tcx> { + span: Span, + kind: InferSourceKind<'tcx>, +} + +#[derive(Debug)] +enum InferSourceKind<'tcx> { + LetBinding { + insert_span: Span, + pattern_name: Option<Ident>, + ty: Ty<'tcx>, + }, + ClosureArg { + insert_span: Span, + ty: Ty<'tcx>, + }, + GenericArg { + insert_span: Span, + argument_index: usize, + generics_def_id: DefId, + def_id: DefId, + generic_args: &'tcx [GenericArg<'tcx>], + }, + FullyQualifiedMethodCall { + receiver: &'tcx Expr<'tcx>, + /// If the method has other arguments, this is ", " and the start of the first argument, + /// while for methods without arguments this is ")" and the end of the method call. + successor: (&'static str, BytePos), + substs: SubstsRef<'tcx>, + def_id: DefId, + }, + ClosureReturn { + ty: Ty<'tcx>, + data: &'tcx FnRetTy<'tcx>, + should_wrap_expr: Option<Span>, + }, +} + +impl<'tcx> InferSource<'tcx> { + fn from_expansion(&self) -> bool { + let source_from_expansion = match self.kind { + InferSourceKind::LetBinding { insert_span, .. } + | InferSourceKind::ClosureArg { insert_span, .. } + | InferSourceKind::GenericArg { insert_span, .. } => insert_span.from_expansion(), + InferSourceKind::FullyQualifiedMethodCall { receiver, .. } => { + receiver.span.from_expansion() + } + InferSourceKind::ClosureReturn { data, should_wrap_expr, .. } => { + data.span().from_expansion() || should_wrap_expr.map_or(false, Span::from_expansion) + } + }; + source_from_expansion || self.span.from_expansion() + } +} + +impl<'tcx> InferSourceKind<'tcx> { + fn ty_msg(&self, infcx: &InferCtxt<'_, 'tcx>) -> String { + match *self { + InferSourceKind::LetBinding { ty, .. } + | InferSourceKind::ClosureArg { ty, .. } + | InferSourceKind::ClosureReturn { ty, .. } => { + if ty.is_closure() { + format!(" for the closure `{}`", closure_as_fn_str(infcx, ty)) + } else if !ty.is_ty_infer() { + format!(" for `{}`", ty_to_string(infcx, ty)) + } else { + String::new() + } + } + // FIXME: We should be able to add some additional info here. + InferSourceKind::GenericArg { .. } + | InferSourceKind::FullyQualifiedMethodCall { .. } => String::new(), + } + } +} + +#[derive(Debug)] +struct InsertableGenericArgs<'tcx> { + insert_span: Span, + substs: SubstsRef<'tcx>, + generics_def_id: DefId, + def_id: DefId, +} + +/// A visitor which searches for the "best" spot to use in the inference error. +/// +/// For this it walks over the hir body and tries to check all places where +/// inference variables could be bound. +/// +/// While doing so, the currently best spot is stored in `infer_source`. +/// For details on how we rank spots, see [Self::source_cost] +struct FindInferSourceVisitor<'a, 'tcx> { + infcx: &'a InferCtxt<'a, 'tcx>, + typeck_results: &'a TypeckResults<'tcx>, + + target: GenericArg<'tcx>, + + attempt: usize, + infer_source_cost: usize, + infer_source: Option<InferSource<'tcx>>, +} + +impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> { + fn new( + infcx: &'a InferCtxt<'a, 'tcx>, + typeck_results: &'a TypeckResults<'tcx>, + target: GenericArg<'tcx>, + ) -> Self { + FindInferSourceVisitor { + infcx, + typeck_results, + + target, + + attempt: 0, + infer_source_cost: usize::MAX, + infer_source: None, + } + } + + /// Computes cost for the given source. + /// + /// Sources with a small cost are prefer and should result + /// in a clearer and idiomatic suggestion. + fn source_cost(&self, source: &InferSource<'tcx>) -> usize { + #[derive(Clone, Copy)] + struct CostCtxt<'tcx> { + tcx: TyCtxt<'tcx>, + } + impl<'tcx> CostCtxt<'tcx> { + fn arg_cost(self, arg: GenericArg<'tcx>) -> usize { + match arg.unpack() { + GenericArgKind::Lifetime(_) => 0, // erased + GenericArgKind::Type(ty) => self.ty_cost(ty), + GenericArgKind::Const(_) => 3, // some non-zero value + } + } + fn ty_cost(self, ty: Ty<'tcx>) -> usize { + match *ty.kind() { + ty::Closure(..) => 1000, + ty::FnDef(..) => 150, + ty::FnPtr(..) => 30, + ty::Adt(def, substs) => { + 5 + self + .tcx + .generics_of(def.did()) + .own_substs_no_defaults(self.tcx, substs) + .iter() + .map(|&arg| self.arg_cost(arg)) + .sum::<usize>() + } + ty::Tuple(args) => 5 + args.iter().map(|arg| self.ty_cost(arg)).sum::<usize>(), + ty::Ref(_, ty, _) => 2 + self.ty_cost(ty), + ty::Infer(..) => 0, + _ => 1, + } + } + } + + // The sources are listed in order of preference here. + let tcx = self.infcx.tcx; + let ctx = CostCtxt { tcx }; + let base_cost = match source.kind { + InferSourceKind::LetBinding { ty, .. } => ctx.ty_cost(ty), + InferSourceKind::ClosureArg { ty, .. } => ctx.ty_cost(ty), + InferSourceKind::GenericArg { def_id, generic_args, .. } => { + let variant_cost = match tcx.def_kind(def_id) { + // `None::<u32>` and friends are ugly. + DefKind::Variant | DefKind::Ctor(CtorOf::Variant, _) => 15, + _ => 10, + }; + variant_cost + generic_args.iter().map(|&arg| ctx.arg_cost(arg)).sum::<usize>() + } + InferSourceKind::FullyQualifiedMethodCall { substs, .. } => { + 20 + substs.iter().map(|arg| ctx.arg_cost(arg)).sum::<usize>() + } + InferSourceKind::ClosureReturn { ty, should_wrap_expr, .. } => { + 30 + ctx.ty_cost(ty) + if should_wrap_expr.is_some() { 10 } else { 0 } + } + }; + + let suggestion_may_apply = if source.from_expansion() { 10000 } else { 0 }; + + base_cost + suggestion_may_apply + } + + /// Uses `fn source_cost` to determine whether this inference source is preferable to + /// previous sources. We generally prefer earlier sources. + #[instrument(level = "debug", skip(self))] + fn update_infer_source(&mut self, new_source: InferSource<'tcx>) { + let cost = self.source_cost(&new_source) + self.attempt; + debug!(?cost); + self.attempt += 1; + if cost < self.infer_source_cost { + self.infer_source_cost = cost; + self.infer_source = Some(new_source); + } + } + + fn node_substs_opt(&self, hir_id: HirId) -> Option<SubstsRef<'tcx>> { + let substs = self.typeck_results.node_substs_opt(hir_id); + self.infcx.resolve_vars_if_possible(substs) + } + + fn opt_node_type(&self, hir_id: HirId) -> Option<Ty<'tcx>> { + let ty = self.typeck_results.node_type_opt(hir_id); + self.infcx.resolve_vars_if_possible(ty) + } + + // Check whether this generic argument is the inference variable we + // are looking for. + fn generic_arg_is_target(&self, arg: GenericArg<'tcx>) -> bool { + if arg == self.target { + return true; + } + + match (arg.unpack(), self.target.unpack()) { + (GenericArgKind::Type(inner_ty), GenericArgKind::Type(target_ty)) => { + use ty::{Infer, TyVar}; + match (inner_ty.kind(), target_ty.kind()) { + (&Infer(TyVar(a_vid)), &Infer(TyVar(b_vid))) => { + self.infcx.inner.borrow_mut().type_variables().sub_unified(a_vid, b_vid) + } + _ => false, + } + } + (GenericArgKind::Const(inner_ct), GenericArgKind::Const(target_ct)) => { + use ty::InferConst::*; + match (inner_ct.kind(), target_ct.kind()) { + (ty::ConstKind::Infer(Var(a_vid)), ty::ConstKind::Infer(Var(b_vid))) => self + .infcx + .inner + .borrow_mut() + .const_unification_table() + .unioned(a_vid, b_vid), + _ => false, + } + } + _ => false, + } + } + + /// Does this generic argument contain our target inference variable + /// in a way which can be written by the user. + fn generic_arg_contains_target(&self, arg: GenericArg<'tcx>) -> bool { + let mut walker = arg.walk(); + while let Some(inner) = walker.next() { + if self.generic_arg_is_target(inner) { + return true; + } + match inner.unpack() { + GenericArgKind::Lifetime(_) => {} + GenericArgKind::Type(ty) => { + if matches!(ty.kind(), ty::Opaque(..) | ty::Closure(..) | ty::Generator(..)) { + // Opaque types can't be named by the user right now. + // + // Both the generic arguments of closures and generators can + // also not be named. We may want to only look into the closure + // signature in case it has no captures, as that can be represented + // using `fn(T) -> R`. + + // FIXME(type_alias_impl_trait): These opaque types + // can actually be named, so it would make sense to + // adjust this case and add a test for it. + walker.skip_current_subtree(); + } + } + GenericArgKind::Const(ct) => { + if matches!(ct.kind(), ty::ConstKind::Unevaluated(..)) { + // You can't write the generic arguments for + // unevaluated constants. + walker.skip_current_subtree(); + } + } + } + } + false + } + + fn expr_inferred_subst_iter( + &self, + expr: &'tcx hir::Expr<'tcx>, + ) -> Box<dyn Iterator<Item = InsertableGenericArgs<'tcx>> + 'a> { + let tcx = self.infcx.tcx; + match expr.kind { + hir::ExprKind::Path(ref path) => { + if let Some(substs) = self.node_substs_opt(expr.hir_id) { + return self.path_inferred_subst_iter(expr.hir_id, substs, path); + } + } + // FIXME(#98711): Ideally we would also deal with type relative + // paths here, even if that is quite rare. + // + // See the `need_type_info/expr-struct-type-relative-gat.rs` test + // for an example where that would be needed. + // + // However, the `type_dependent_def_id` for `Self::Output` in an + // impl is currently the `DefId` of `Output` in the trait definition + // which makes this somewhat difficult and prevents us from just + // using `self.path_inferred_subst_iter` here. + hir::ExprKind::Struct(&hir::QPath::Resolved(_self_ty, path), _, _) => { + if let Some(ty) = self.opt_node_type(expr.hir_id) { + if let ty::Adt(_, substs) = ty.kind() { + return Box::new(self.resolved_path_inferred_subst_iter(path, substs)); + } + } + } + hir::ExprKind::MethodCall(segment, _, _) => { + if let Some(def_id) = self.typeck_results.type_dependent_def_id(expr.hir_id) { + let generics = tcx.generics_of(def_id); + let insertable: Option<_> = try { + if generics.has_impl_trait() { + None? + } + let substs = self.node_substs_opt(expr.hir_id)?; + let span = tcx.hir().span(segment.hir_id?); + let insert_span = segment.ident.span.shrink_to_hi().with_hi(span.hi()); + InsertableGenericArgs { + insert_span, + substs, + generics_def_id: def_id, + def_id, + } + }; + return Box::new(insertable.into_iter()); + } + } + _ => {} + } + + Box::new(iter::empty()) + } + + fn resolved_path_inferred_subst_iter( + &self, + path: &'tcx hir::Path<'tcx>, + substs: SubstsRef<'tcx>, + ) -> impl Iterator<Item = InsertableGenericArgs<'tcx>> + 'a { + let tcx = self.infcx.tcx; + // The last segment of a path often has `Res::Err` and the + // correct `Res` is the one of the whole path. + // + // FIXME: We deal with that one separately for now, + // would be good to remove this special case. + let last_segment_using_path_data: Option<_> = try { + let generics_def_id = tcx.res_generics_def_id(path.res)?; + let generics = tcx.generics_of(generics_def_id); + if generics.has_impl_trait() { + None? + } + let insert_span = + path.segments.last().unwrap().ident.span.shrink_to_hi().with_hi(path.span.hi()); + InsertableGenericArgs { + insert_span, + substs, + generics_def_id, + def_id: path.res.def_id(), + } + }; + + path.segments + .iter() + .filter_map(move |segment| { + let res = segment.res?; + let generics_def_id = tcx.res_generics_def_id(res)?; + let generics = tcx.generics_of(generics_def_id); + if generics.has_impl_trait() { + return None; + } + let span = tcx.hir().span(segment.hir_id?); + let insert_span = segment.ident.span.shrink_to_hi().with_hi(span.hi()); + Some(InsertableGenericArgs { + insert_span, + substs, + generics_def_id, + def_id: res.def_id(), + }) + }) + .chain(last_segment_using_path_data) + } + + fn path_inferred_subst_iter( + &self, + hir_id: HirId, + substs: SubstsRef<'tcx>, + qpath: &'tcx hir::QPath<'tcx>, + ) -> Box<dyn Iterator<Item = InsertableGenericArgs<'tcx>> + 'a> { + let tcx = self.infcx.tcx; + match qpath { + hir::QPath::Resolved(_self_ty, path) => { + Box::new(self.resolved_path_inferred_subst_iter(path, substs)) + } + hir::QPath::TypeRelative(ty, segment) => { + let Some(def_id) = self.typeck_results.type_dependent_def_id(hir_id) else { + return Box::new(iter::empty()); + }; + + let generics = tcx.generics_of(def_id); + let segment: Option<_> = try { + if !segment.infer_args || generics.has_impl_trait() { + None?; + } + let span = tcx.hir().span(segment.hir_id?); + let insert_span = segment.ident.span.shrink_to_hi().with_hi(span.hi()); + InsertableGenericArgs { insert_span, substs, generics_def_id: def_id, def_id } + }; + + let parent_def_id = generics.parent.unwrap(); + if tcx.def_kind(parent_def_id) == DefKind::Impl { + let parent_ty = tcx.bound_type_of(parent_def_id).subst(tcx, substs); + match (parent_ty.kind(), &ty.kind) { + ( + ty::Adt(def, substs), + hir::TyKind::Path(hir::QPath::Resolved(_self_ty, path)), + ) => { + if tcx.res_generics_def_id(path.res) != Some(def.did()) { + match path.res { + Res::Def(DefKind::TyAlias, _) => { + // FIXME: Ideally we should support this. For that + // we have to map back from the self type to the + // type alias though. That's difficult. + // + // See the `need_type_info/type-alias.rs` test for + // some examples. + } + // There cannot be inference variables in the self type, + // so there's nothing for us to do here. + Res::SelfTy { .. } => {} + _ => warn!( + "unexpected path: def={:?} substs={:?} path={:?}", + def, substs, path, + ), + } + } else { + return Box::new( + self.resolved_path_inferred_subst_iter(path, substs) + .chain(segment), + ); + } + } + _ => (), + } + } + + Box::new(segment.into_iter()) + } + hir::QPath::LangItem(_, _, _) => Box::new(iter::empty()), + } + } +} + +impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> { + type NestedFilter = nested_filter::OnlyBodies; + + fn nested_visit_map(&mut self) -> Self::Map { + self.infcx.tcx.hir() + } + + fn visit_local(&mut self, local: &'tcx Local<'tcx>) { + intravisit::walk_local(self, local); + + if let Some(ty) = self.opt_node_type(local.hir_id) { + if self.generic_arg_contains_target(ty.into()) { + match local.source { + LocalSource::Normal if local.ty.is_none() => { + self.update_infer_source(InferSource { + span: local.pat.span, + kind: InferSourceKind::LetBinding { + insert_span: local.pat.span.shrink_to_hi(), + pattern_name: local.pat.simple_ident(), + ty, + }, + }) + } + _ => {} + } + } + } + } + + /// For closures, we first visit the parameters and then the content, + /// as we prefer those. + fn visit_body(&mut self, body: &'tcx Body<'tcx>) { + for param in body.params { + debug!( + "param: span {:?}, ty_span {:?}, pat.span {:?}", + param.span, param.ty_span, param.pat.span + ); + if param.ty_span != param.pat.span { + debug!("skipping param: has explicit type"); + continue; + } + + let Some(param_ty) = self.opt_node_type(param.hir_id) else { + continue + }; + + if self.generic_arg_contains_target(param_ty.into()) { + self.update_infer_source(InferSource { + span: param.pat.span, + kind: InferSourceKind::ClosureArg { + insert_span: param.pat.span.shrink_to_hi(), + ty: param_ty, + }, + }) + } + } + intravisit::walk_body(self, body); + } + + #[instrument(level = "debug", skip(self))] + fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) { + let tcx = self.infcx.tcx; + match expr.kind { + // When encountering `func(arg)` first look into `arg` and then `func`, + // as `arg` is "more specific". + ExprKind::Call(func, args) => { + for arg in args { + self.visit_expr(arg); + } + self.visit_expr(func); + } + _ => intravisit::walk_expr(self, expr), + } + + for args in self.expr_inferred_subst_iter(expr) { + debug!(?args); + let InsertableGenericArgs { insert_span, substs, generics_def_id, def_id } = args; + let generics = tcx.generics_of(generics_def_id); + if let Some(argument_index) = generics + .own_substs(substs) + .iter() + .position(|&arg| self.generic_arg_contains_target(arg)) + { + let substs = self.infcx.resolve_vars_if_possible(substs); + let generic_args = &generics.own_substs_no_defaults(tcx, substs) + [generics.own_counts().lifetimes..]; + let span = match expr.kind { + ExprKind::MethodCall(path, _, _) => path.ident.span, + _ => expr.span, + }; + + self.update_infer_source(InferSource { + span, + kind: InferSourceKind::GenericArg { + insert_span, + argument_index, + generics_def_id, + def_id, + generic_args, + }, + }); + } + } + + if let Some(node_ty) = self.opt_node_type(expr.hir_id) { + if let ( + &ExprKind::Closure(&Closure { fn_decl, body, fn_decl_span, .. }), + ty::Closure(_, substs), + ) = (&expr.kind, node_ty.kind()) + { + let output = substs.as_closure().sig().output().skip_binder(); + if self.generic_arg_contains_target(output.into()) { + let body = self.infcx.tcx.hir().body(body); + let should_wrap_expr = if matches!(body.value.kind, ExprKind::Block(..)) { + None + } else { + Some(body.value.span.shrink_to_hi()) + }; + self.update_infer_source(InferSource { + span: fn_decl_span, + kind: InferSourceKind::ClosureReturn { + ty: output, + data: &fn_decl.output, + should_wrap_expr, + }, + }) + } + } + } + + let has_impl_trait = |def_id| { + iter::successors(Some(tcx.generics_of(def_id)), |generics| { + generics.parent.map(|def_id| tcx.generics_of(def_id)) + }) + .any(|generics| generics.has_impl_trait()) + }; + if let ExprKind::MethodCall(path, args, span) = expr.kind + && let Some(substs) = self.node_substs_opt(expr.hir_id) + && substs.iter().any(|arg| self.generic_arg_contains_target(arg)) + && let Some(def_id) = self.typeck_results.type_dependent_def_id(expr.hir_id) + && self.infcx.tcx.trait_of_item(def_id).is_some() + && !has_impl_trait(def_id) + { + let successor = + args.get(1).map_or_else(|| (")", span.hi()), |arg| (", ", arg.span.lo())); + let substs = self.infcx.resolve_vars_if_possible(substs); + self.update_infer_source(InferSource { + span: path.ident.span, + kind: InferSourceKind::FullyQualifiedMethodCall { + receiver: args.first().unwrap(), + successor, + substs, + def_id, + } + }) + } + } +} |