use crate::FnCtxt;
use rustc_hir as hir;
use rustc_hir::def::Res;
-use rustc_middle::ty::{self, DefIdTree, Ty};
+use rustc_hir::def_id::DefId;
+use rustc_infer::traits::ObligationCauseCode;
+use rustc_middle::ty::{self, DefIdTree, Ty, TypeSuperVisitable, TypeVisitable, TypeVisitor};
+use rustc_span::{self, Span};
use rustc_trait_selection::traits;
+use std::ops::ControlFlow;
+
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+ pub fn adjust_fulfillment_error_for_expr_obligation(
+ &self,
+ error: &mut traits::FulfillmentError<'tcx>,
+ ) -> bool {
+ let (traits::ExprItemObligation(def_id, hir_id, idx) | traits::ExprBindingObligation(def_id, _, hir_id, idx))
+ = *error.obligation.cause.code().peel_derives() else { return false; };
+ let hir = self.tcx.hir();
+ let hir::Node::Expr(expr) = hir.get(hir_id) else { return false; };
+
+ let Some(unsubstituted_pred) =
+ self.tcx.predicates_of(def_id).instantiate_identity(self.tcx).predicates.into_iter().nth(idx)
+ else { return false; };
+
+ let generics = self.tcx.generics_of(def_id);
+ let predicate_substs = match unsubstituted_pred.kind().skip_binder() {
+ ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => pred.trait_ref.substs,
+ ty::PredicateKind::Clause(ty::Clause::Projection(pred)) => pred.projection_ty.substs,
+ _ => ty::List::empty(),
+ };
+
+ let find_param_matching = |matches: &dyn Fn(&ty::ParamTy) -> bool| {
+ predicate_substs.types().find_map(|ty| {
+ ty.walk().find_map(|arg| {
+ if let ty::GenericArgKind::Type(ty) = arg.unpack()
+ && let ty::Param(param_ty) = ty.kind()
+ && matches(param_ty)
+ {
+ Some(arg)
+ } else {
+ None
+ }
+ })
+ })
+ };
+
+ // Prefer generics that are local to the fn item, since these are likely
+ // to be the cause of the unsatisfied predicate.
+ let mut param_to_point_at = find_param_matching(&|param_ty| {
+ self.tcx.parent(generics.type_param(param_ty, self.tcx).def_id) == def_id
+ });
+ // Fall back to generic that isn't local to the fn item. This will come
+ // from a trait or impl, for example.
+ let mut fallback_param_to_point_at = find_param_matching(&|param_ty| {
+ self.tcx.parent(generics.type_param(param_ty, self.tcx).def_id) != def_id
+ && param_ty.name != rustc_span::symbol::kw::SelfUpper
+ });
+ // Finally, the `Self` parameter is possibly the reason that the predicate
+ // is unsatisfied. This is less likely to be true for methods, because
+ // method probe means that we already kinda check that the predicates due
+ // to the `Self` type are true.
+ let mut self_param_to_point_at =
+ find_param_matching(&|param_ty| param_ty.name == rustc_span::symbol::kw::SelfUpper);
+
+ // Finally, for ambiguity-related errors, we actually want to look
+ // for a parameter that is the source of the inference type left
+ // over in this predicate.
+ if let traits::FulfillmentErrorCode::CodeAmbiguity = error.code {
+ fallback_param_to_point_at = None;
+ self_param_to_point_at = None;
+ param_to_point_at =
+ self.find_ambiguous_parameter_in(def_id, error.root_obligation.predicate);
+ }
+
+ if self.closure_span_overlaps_error(error, expr.span) {
+ return false;
+ }
+
+ match &expr.kind {
+ hir::ExprKind::Path(qpath) => {
+ if let hir::Node::Expr(hir::Expr {
+ kind: hir::ExprKind::Call(callee, args),
+ hir_id: call_hir_id,
+ span: call_span,
+ ..
+ }) = hir.get_parent(expr.hir_id)
+ && callee.hir_id == expr.hir_id
+ {
+ if self.closure_span_overlaps_error(error, *call_span) {
+ return false;
+ }
+
+ for param in
+ [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
+ .into_iter()
+ .flatten()
+ {
+ if self.blame_specific_arg_if_possible(
+ error,
+ def_id,
+ param,
+ *call_hir_id,
+ callee.span,
+ None,
+ args,
+ )
+ {
+ return true;
+ }
+ }
+ }
+ // Notably, we only point to params that are local to the
+ // item we're checking, since those are the ones we are able
+ // to look in the final `hir::PathSegment` for. Everything else
+ // would require a deeper search into the `qpath` than I think
+ // is worthwhile.
+ if let Some(param_to_point_at) = param_to_point_at
+ && self.point_at_path_if_possible(error, def_id, param_to_point_at, qpath)
+ {
+ return true;
+ }
+ }
+ hir::ExprKind::MethodCall(segment, receiver, args, ..) => {
+ for param in [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
+ .into_iter()
+ .flatten()
+ {
+ if self.blame_specific_arg_if_possible(
+ error,
+ def_id,
+ param,
+ hir_id,
+ segment.ident.span,
+ Some(receiver),
+ args,
+ ) {
+ return true;
+ }
+ }
+ if let Some(param_to_point_at) = param_to_point_at
+ && self.point_at_generic_if_possible(error, def_id, param_to_point_at, segment)
+ {
+ return true;
+ }
+ }
+ hir::ExprKind::Struct(qpath, fields, ..) => {
+ if let Res::Def(
+ hir::def::DefKind::Struct | hir::def::DefKind::Variant,
+ variant_def_id,
+ ) = self.typeck_results.borrow().qpath_res(qpath, hir_id)
+ {
+ for param in
+ [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
+ {
+ if let Some(param) = param {
+ let refined_expr = self.point_at_field_if_possible(
+ def_id,
+ param,
+ variant_def_id,
+ fields,
+ );
+
+ match refined_expr {
+ None => {}
+ Some((refined_expr, _)) => {
+ error.obligation.cause.span = refined_expr
+ .span
+ .find_ancestor_in_same_ctxt(error.obligation.cause.span)
+ .unwrap_or(refined_expr.span);
+ return true;
+ }
+ }
+ }
+ }
+ }
+ if let Some(param_to_point_at) = param_to_point_at
+ && self.point_at_path_if_possible(error, def_id, param_to_point_at, qpath)
+ {
+ return true;
+ }
+ }
+ _ => {}
+ }
+
+ false
+ }
+
+ fn point_at_path_if_possible(
+ &self,
+ error: &mut traits::FulfillmentError<'tcx>,
+ def_id: DefId,
+ param: ty::GenericArg<'tcx>,
+ qpath: &hir::QPath<'tcx>,
+ ) -> bool {
+ match qpath {
+ hir::QPath::Resolved(_, path) => {
+ if let Some(segment) = path.segments.last()
+ && self.point_at_generic_if_possible(error, def_id, param, segment)
+ {
+ return true;
+ }
+ }
+ hir::QPath::TypeRelative(_, segment) => {
+ if self.point_at_generic_if_possible(error, def_id, param, segment) {
+ return true;
+ }
+ }
+ _ => {}
+ }
+
+ false
+ }
+
+ fn point_at_generic_if_possible(
+ &self,
+ error: &mut traits::FulfillmentError<'tcx>,
+ def_id: DefId,
+ param_to_point_at: ty::GenericArg<'tcx>,
+ segment: &hir::PathSegment<'tcx>,
+ ) -> bool {
+ let own_substs = self
+ .tcx
+ .generics_of(def_id)
+ .own_substs(ty::InternalSubsts::identity_for_item(self.tcx, def_id));
+ let Some((index, _)) = own_substs
+ .iter()
+ .filter(|arg| matches!(arg.unpack(), ty::GenericArgKind::Type(_)))
+ .enumerate()
+ .find(|(_, arg)| **arg == param_to_point_at) else { return false };
+ let Some(arg) = segment
+ .args()
+ .args
+ .iter()
+ .filter(|arg| matches!(arg, hir::GenericArg::Type(_)))
+ .nth(index) else { return false; };
+ error.obligation.cause.span = arg
+ .span()
+ .find_ancestor_in_same_ctxt(error.obligation.cause.span)
+ .unwrap_or(arg.span());
+ true
+ }
+
+ fn find_ambiguous_parameter_in<T: TypeVisitable<'tcx>>(
+ &self,
+ item_def_id: DefId,
+ t: T,
+ ) -> Option<ty::GenericArg<'tcx>> {
+ struct FindAmbiguousParameter<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, DefId);
+ impl<'tcx> TypeVisitor<'tcx> for FindAmbiguousParameter<'_, 'tcx> {
+ type BreakTy = ty::GenericArg<'tcx>;
+ fn visit_ty(&mut self, ty: Ty<'tcx>) -> std::ops::ControlFlow<Self::BreakTy> {
+ if let Some(origin) = self.0.type_var_origin(ty)
+ && let rustc_infer::infer::type_variable::TypeVariableOriginKind::TypeParameterDefinition(_, Some(def_id)) =
+ origin.kind
+ && let generics = self.0.tcx.generics_of(self.1)
+ && let Some(index) = generics.param_def_id_to_index(self.0.tcx, def_id)
+ && let Some(subst) = ty::InternalSubsts::identity_for_item(self.0.tcx, self.1)
+ .get(index as usize)
+ {
+ ControlFlow::Break(*subst)
+ } else {
+ ty.super_visit_with(self)
+ }
+ }
+ }
+ t.visit_with(&mut FindAmbiguousParameter(self, item_def_id)).break_value()
+ }
+
+ fn closure_span_overlaps_error(
+ &self,
+ error: &traits::FulfillmentError<'tcx>,
+ span: Span,
+ ) -> bool {
+ if let traits::FulfillmentErrorCode::CodeSelectionError(
+ traits::SelectionError::OutputTypeParameterMismatch(_, expected, _),
+ ) = error.code
+ && let ty::Closure(def_id, _) | ty::Generator(def_id, ..) = expected.skip_binder().self_ty().kind()
+ && span.overlaps(self.tcx.def_span(*def_id))
+ {
+ true
+ } else {
+ false
+ }
+ }
+
+ fn point_at_field_if_possible(
+ &self,
+ def_id: DefId,
+ param_to_point_at: ty::GenericArg<'tcx>,
+ variant_def_id: DefId,
+ expr_fields: &[hir::ExprField<'tcx>],
+ ) -> Option<(&'tcx hir::Expr<'tcx>, Ty<'tcx>)> {
+ let def = self.tcx.adt_def(def_id);
+
+ let identity_substs = ty::InternalSubsts::identity_for_item(self.tcx, def_id);
+ let fields_referencing_param: Vec<_> = def
+ .variant_with_id(variant_def_id)
+ .fields
+ .iter()
+ .filter(|field| {
+ let field_ty = field.ty(self.tcx, identity_substs);
+ Self::find_param_in_ty(field_ty.into(), param_to_point_at)
+ })
+ .collect();
+
+ if let [field] = fields_referencing_param.as_slice() {
+ for expr_field in expr_fields {
+ // Look for the ExprField that matches the field, using the
+ // same rules that check_expr_struct uses for macro hygiene.
+ if self.tcx.adjust_ident(expr_field.ident, variant_def_id) == field.ident(self.tcx)
+ {
+ return Some((expr_field.expr, self.tcx.type_of(field.did)));
+ }
+ }
+ }
+
+ None
+ }
+
+ /// - `blame_specific_*` means that the function will recursively traverse the expression,
+ /// looking for the most-specific-possible span to blame.
+ ///
+ /// - `point_at_*` means that the function will only go "one level", pointing at the specific
+ /// expression mentioned.
+ ///
+ /// `blame_specific_arg_if_possible` will find the most-specific expression anywhere inside
+ /// the provided function call expression, and mark it as responsible for the fullfillment
+ /// error.
+ fn blame_specific_arg_if_possible(
+ &self,
+ error: &mut traits::FulfillmentError<'tcx>,
+ def_id: DefId,
+ param_to_point_at: ty::GenericArg<'tcx>,
+ call_hir_id: hir::HirId,
+ callee_span: Span,
+ receiver: Option<&'tcx hir::Expr<'tcx>>,
+ args: &'tcx [hir::Expr<'tcx>],
+ ) -> bool {
+ let ty = self.tcx.type_of(def_id);
+ if !ty.is_fn() {
+ return false;
+ }
+ let sig = ty.fn_sig(self.tcx).skip_binder();
+ let args_referencing_param: Vec<_> = sig
+ .inputs()
+ .iter()
+ .enumerate()
+ .filter(|(_, ty)| Self::find_param_in_ty((**ty).into(), param_to_point_at))
+ .collect();
+ // If there's one field that references the given generic, great!
+ if let [(idx, _)] = args_referencing_param.as_slice()
+ && let Some(arg) = receiver
+ .map_or(args.get(*idx), |rcvr| if *idx == 0 { Some(rcvr) } else { args.get(*idx - 1) }) {
+
+ error.obligation.cause.span = arg.span.find_ancestor_in_same_ctxt(error.obligation.cause.span).unwrap_or(arg.span);
+
+ if let hir::Node::Expr(arg_expr) = self.tcx.hir().get(arg.hir_id) {
+ // This is more specific than pointing at the entire argument.
+ self.blame_specific_expr_if_possible(error, arg_expr)
+ }
+
+ error.obligation.cause.map_code(|parent_code| {
+ ObligationCauseCode::FunctionArgumentObligation {
+ arg_hir_id: arg.hir_id,
+ call_hir_id,
+ parent_code,
+ }
+ });
+ return true;
+ } else if args_referencing_param.len() > 0 {
+ // If more than one argument applies, then point to the callee span at least...
+ // We have chance to fix this up further in `point_at_generics_if_possible`
+ error.obligation.cause.span = callee_span;
+ }
+
+ false
+ }
+
/**
* Recursively searches for the most-specific blamable expression.
* For example, if you have a chain of constraints like:
projects / rust.git / blobdiff