Rollup merge of rust-lang#64151 - estebank:binding-error, r=varkor

On obligation errors point at the unfulfilled binding when possible

CC rust-lang#42855, rust-lang#64130, rust-lang#64135.

Author: Centril

src/etc/generate-deriving-span-tests.py

@@ -14,6 +14,8 @@
     os.path.join(os.path.dirname(__file__), '../test/ui/derives/'))
 
 TEMPLATE = """\
+// ignore-musl
+// ^ due to stderr output differences
 // This file was auto-generated using 'src/etc/generate-deriving-span-tests.py'
 
 {error_deriving}

src/librustc/hir/lowering.rs

@@ -1893,10 +1893,13 @@ impl<'a> LoweringContext<'a> {
                         if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
                             // Do not suggest going from `Trait()` to `Trait<>`
                             if data.inputs.len() > 0 {
+                                let split = snippet.find('(').unwrap();
+                                let trait_name = &snippet[0..split];
+                                let args = &snippet[split + 1 .. snippet.len() - 1];
                                 err.span_suggestion(
                                     data.span,
                                     "use angle brackets instead",
-                                    format!("<{}>", &snippet[1..snippet.len() - 1]),
+                                    format!("{}<{}>", trait_name, args),
                                     Applicability::MaybeIncorrect,
                                 );
                             }

src/librustc/hir/mod.rs

@@ -2750,3 +2750,15 @@ pub enum Node<'hir> {
 
     Crate,
 }
+
+impl Node<'_> {
+    pub fn ident(&self) -> Option<Ident> {
+        match self {
+            Node::TraitItem(TraitItem { ident, .. }) |
+            Node::ImplItem(ImplItem { ident, .. }) |
+            Node::ForeignItem(ForeignItem { ident, .. }) |
+            Node::Item(Item { ident, .. }) => Some(*ident),
+            _ => None,
+        }
+    }
+}

src/librustc/traits/error_reporting.rs

@@ -40,10 +40,12 @@ use syntax::symbol::{sym, kw};
 use syntax_pos::{DUMMY_SP, Span, ExpnKind};
 
 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
-    pub fn report_fulfillment_errors(&self,
-                                     errors: &[FulfillmentError<'tcx>],
-                                     body_id: Option<hir::BodyId>,
-                                     fallback_has_occurred: bool) {
+    pub fn report_fulfillment_errors(
+        &self,
+        errors: &[FulfillmentError<'tcx>],
+        body_id: Option<hir::BodyId>,
+        fallback_has_occurred: bool,
+    ) {
         #[derive(Debug)]
         struct ErrorDescriptor<'tcx> {
             predicate: ty::Predicate<'tcx>,
@@ -1623,6 +1625,18 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     err.note(&msg);
                 }
             }
+            ObligationCauseCode::BindingObligation(item_def_id, span) => {
+                let item_name = tcx.def_path_str(item_def_id);
+                let msg = format!("required by this bound in `{}`", item_name);
+                if let Some(ident) = tcx.opt_item_name(item_def_id) {
+                    err.span_label(ident.span, "");
+                }
+                if span != DUMMY_SP {
+                    err.span_label(span, &msg);
+                } else {
+                    err.note(&msg);
+                }
+            }
             ObligationCauseCode::ObjectCastObligation(object_ty) => {
                 err.note(&format!("required for the cast to the object type `{}`",
                                   self.ty_to_string(object_ty)));

src/librustc/traits/mod.rs

@@ -176,6 +176,9 @@ pub enum ObligationCauseCode<'tcx> {
     /// also implement all supertraits of `X`.
     ItemObligation(DefId),
 
+    /// Like `ItemObligation`, but with extra detail on the source of the obligation.
+    BindingObligation(DefId, Span),
+
     /// A type like `&'a T` is WF only if `T: 'a`.
     ReferenceOutlivesReferent(Ty<'tcx>),
 

src/librustc/traits/structural_impls.rs

@@ -472,6 +472,7 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
             super::TupleElem => Some(super::TupleElem),
             super::ProjectionWf(proj) => tcx.lift(&proj).map(super::ProjectionWf),
             super::ItemObligation(def_id) => Some(super::ItemObligation(def_id)),
+            super::BindingObligation(def_id, span) => Some(super::BindingObligation(def_id, span)),
             super::ReferenceOutlivesReferent(ty) => {
                 tcx.lift(&ty).map(super::ReferenceOutlivesReferent)
             }

src/librustc/ty/mod.rs

@@ -2797,6 +2797,10 @@ impl<'tcx> TyCtxt<'tcx> {
         })
     }
 
+    pub fn opt_item_name(self, def_id: DefId) -> Option<Ident> {
+        self.hir().as_local_hir_id(def_id).and_then(|hir_id| self.hir().get(hir_id).ident())
+    }
+
     pub fn opt_associated_item(self, def_id: DefId) -> Option<AssocItem> {
         let is_associated_item = if let Some(hir_id) = self.hir().as_local_hir_id(def_id) {
             match self.hir().get(hir_id) {

src/librustc_typeck/check/mod.rs

@@ -2579,16 +2579,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     /// As `instantiate_type_scheme`, but for the bounds found in a
     /// generic type scheme.
-    fn instantiate_bounds(&self, span: Span, def_id: DefId, substs: SubstsRef<'tcx>)
-                          -> ty::InstantiatedPredicates<'tcx> {
+    fn instantiate_bounds(
+        &self,
+        span: Span,
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
+    ) -> (ty::InstantiatedPredicates<'tcx>, Vec<Span>) {
         let bounds = self.tcx.predicates_of(def_id);
+        let spans: Vec<Span> = bounds.predicates.iter().map(|(_, span)| *span).collect();
         let result = bounds.instantiate(self.tcx, substs);
         let result = self.normalize_associated_types_in(span, &result);
-        debug!("instantiate_bounds(bounds={:?}, substs={:?}) = {:?}",
+        debug!(
+            "instantiate_bounds(bounds={:?}, substs={:?}) = {:?}, {:?}",
                bounds,
                substs,
-               result);
-        result
+            result,
+            spans,
+        );
+        (result, spans)
     }
 
     /// Replaces the opaque types from the given value with type variables,
@@ -3151,8 +3159,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // All the input types from the fn signature must outlive the call
         // so as to validate implied bounds.
-        for &fn_input_ty in fn_inputs {
-            self.register_wf_obligation(fn_input_ty, sp, traits::MiscObligation);
+        for (fn_input_ty, arg_expr) in fn_inputs.iter().zip(args.iter()) {
+            self.register_wf_obligation(fn_input_ty, arg_expr.span, traits::MiscObligation);
         }
 
         let expected_arg_count = fn_inputs.len();
@@ -3513,7 +3521,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.write_user_type_annotation_from_substs(hir_id, did, substs, None);
 
             // Check bounds on type arguments used in the path.
-            let bounds = self.instantiate_bounds(path_span, did, substs);
+            let (bounds, _) = self.instantiate_bounds(path_span, did, substs);
             let cause = traits::ObligationCause::new(path_span, self.body_id,
                                                      traits::ItemObligation(did));
             self.add_obligations_for_parameters(cause, &bounds);
@@ -4634,12 +4642,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // First, store the "user substs" for later.
         self.write_user_type_annotation_from_substs(hir_id, def_id, substs, user_self_ty);
 
-        // Add all the obligations that are required, substituting and
-        // normalized appropriately.
-        let bounds = self.instantiate_bounds(span, def_id, &substs);
-        self.add_obligations_for_parameters(
-            traits::ObligationCause::new(span, self.body_id, traits::ItemObligation(def_id)),
-            &bounds);
+        self.add_required_obligations(span, def_id, &substs);
 
         // Substitute the values for the type parameters into the type of
         // the referenced item.
@@ -4676,6 +4679,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         (ty_substituted, res)
     }
 
+    /// Add all the obligations that are required, substituting and normalized appropriately.
+    fn add_required_obligations(&self, span: Span, def_id: DefId, substs: &SubstsRef<'tcx>) {
+        let (bounds, spans) = self.instantiate_bounds(span, def_id, &substs);
+
+        for (i, mut obligation) in traits::predicates_for_generics(
+            traits::ObligationCause::new(
+                span,
+                self.body_id,
+                traits::ItemObligation(def_id),
+            ),
+            self.param_env,
+            &bounds,
+        ).into_iter().enumerate() {
+            // This makes the error point at the bound, but we want to point at the argument
+            if let Some(span) = spans.get(i) {
+                obligation.cause.code = traits::BindingObligation(def_id, *span);
+            }
+            self.register_predicate(obligation);
+        }
+    }
+
     fn check_rustc_args_require_const(&self,
                                       def_id: DefId,
                                       hir_id: hir::HirId,

src/libsyntax/parse/parser/path.rs

@@ -129,10 +129,11 @@ impl<'a> Parser<'a> {
         self.parse_path(style)
     }
 
-    crate fn parse_path_segments(&mut self,
-                           segments: &mut Vec<PathSegment>,
-                           style: PathStyle)
-                           -> PResult<'a, ()> {
+    crate fn parse_path_segments(
+        &mut self,
+        segments: &mut Vec<PathSegment>,
+        style: PathStyle,
+    ) -> PResult<'a, ()> {
         loop {
             let segment = self.parse_path_segment(style)?;
             if style == PathStyle::Expr {
@@ -201,7 +202,7 @@ impl<'a> Parser<'a> {
             } else {
                 // `(T, U) -> R`
                 let (inputs, _) = self.parse_paren_comma_seq(|p| p.parse_ty())?;
-                let span = lo.to(self.prev_span);
+                let span = ident.span.to(self.prev_span);
                 let output = if self.eat(&token::RArrow) {
                     Some(self.parse_ty_common(false, false, false)?)
                 } else {