Better method call error messages

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1448,6 +1448,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         mut values: Option<ValuePairs<'tcx>>,
         terr: &TypeError<'tcx>,
         swap_secondary_and_primary: bool,
+        force_label: bool,
     ) {
         let span = cause.span(self.tcx);
         debug!("note_type_err cause={:?} values={:?}, terr={:?}", cause, values, terr);
@@ -1623,7 +1624,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             TypeError::ObjectUnsafeCoercion(_) => {}
             _ => {
                 let mut label_or_note = |span: Span, msg: &str| {
-                    if &[span] == diag.span.primary_spans() {
+                    if force_label || &[span] == diag.span.primary_spans() {
                         diag.span_label(span, msg);
                     } else {
                         diag.span_note(span, msg);
@@ -2171,7 +2172,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 struct_span_err!(self.tcx.sess, span, E0644, "{}", failure_str)
             }
         };
-        self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr, false);
+        self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr, false, false);
         diag
     }
 
@@ -2765,15 +2766,15 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 }
 
-enum FailureCode {
+pub enum FailureCode {
     Error0038(DefId),
     Error0317(&'static str),
     Error0580(&'static str),
     Error0308(&'static str),
     Error0644(&'static str),
 }
 
-trait ObligationCauseExt<'tcx> {
+pub trait ObligationCauseExt<'tcx> {
     fn as_failure_code(&self, terr: &TypeError<'tcx>) -> FailureCode;
     fn as_requirement_str(&self) -> &'static str;
 }

compiler/rustc_infer/src/infer/mod.rs

@@ -385,8 +385,8 @@ impl<'tcx> ValuePairs<'tcx> {
 /// See the `error_reporting` module for more details.
 #[derive(Clone, Debug)]
 pub struct TypeTrace<'tcx> {
-    cause: ObligationCause<'tcx>,
-    values: ValuePairs<'tcx>,
+    pub cause: ObligationCause<'tcx>,
+    pub values: ValuePairs<'tcx>,
 }
 
 /// The origin of a `r1 <= r2` constraint.

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1654,7 +1654,15 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                     }),
                 _ => None,
             };
-            self.note_type_err(&mut diag, &obligation.cause, secondary_span, values, err, true);
+            self.note_type_err(
+                &mut diag,
+                &obligation.cause,
+                secondary_span,
+                values,
+                err,
+                true,
+                false,
+            );
             self.note_obligation_cause(&mut diag, obligation);
             diag.emit();
         });

compiler/rustc_typeck/src/check/coercion.rs

@@ -1502,7 +1502,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                         found,
                         expected,
                         None,
-                        coercion_error,
+                        Some(coercion_error),
                     );
                 }
 

compiler/rustc_typeck/src/check/compare_method.rs

@@ -384,6 +384,7 @@ fn compare_predicate_entailment<'tcx>(
                 })),
                 &terr,
                 false,
+                false,
             );
 
             return Err(diag.emit());
@@ -1074,6 +1075,7 @@ crate fn compare_const_impl<'tcx>(
                 })),
                 &terr,
                 false,
+                false,
             );
             diag.emit();
         }

compiler/rustc_typeck/src/check/demand.rs

@@ -28,7 +28,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expr_ty: Ty<'tcx>,
         expected: Ty<'tcx>,
         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
-        error: TypeError<'tcx>,
+        error: Option<TypeError<'tcx>>,
     ) {
         self.annotate_expected_due_to_let_ty(err, expr, error);
         self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr);
@@ -150,7 +150,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
 
-        self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr, e);
+        self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr, Some(e));
 
         (expected, Some(err))
     }
@@ -159,7 +159,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         err: &mut Diagnostic,
         expr: &hir::Expr<'_>,
-        error: TypeError<'_>,
+        error: Option<TypeError<'_>>,
     ) {
         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
         match (self.tcx.hir().find(parent), error) {
@@ -173,7 +173,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Some(hir::Node::Expr(hir::Expr {
                     kind: hir::ExprKind::Assign(lhs, rhs, _), ..
                 })),
-                TypeError::Sorts(ExpectedFound { expected, .. }),
+                Some(TypeError::Sorts(ExpectedFound { expected, .. })),
             ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
                 // We ignore closures explicitly because we already point at them elsewhere.
                 // Point at the assigned-to binding.

compiler/rustc_typeck/src/check/expr.rs

@@ -259,7 +259,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     #[instrument(skip(self, expr), level = "debug")]
-    fn check_expr_kind(
+    pub(super) fn check_expr_kind(
         &self,
         expr: &'tcx hir::Expr<'tcx>,
         expected: Expectation<'tcx>,
@@ -1367,11 +1367,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) {
         let tcx = self.tcx;
 
-        let adt_ty_hint = self
-            .expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
-            .get(0)
-            .cloned()
-            .unwrap_or(adt_ty);
+        let expected_inputs =
+            self.expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty]);
+        let adt_ty_hint = if let Some(expected_inputs) = expected_inputs {
+            expected_inputs.get(0).cloned().unwrap_or(adt_ty)
+        } else {
+            adt_ty
+        };
         // re-link the regions that EIfEO can erase.
         self.demand_eqtype(span, adt_ty_hint, adt_ty);
 

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -755,9 +755,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected_ret: Expectation<'tcx>,
         formal_ret: Ty<'tcx>,
         formal_args: &[Ty<'tcx>],
-    ) -> Vec<Ty<'tcx>> {
+    ) -> Option<Vec<Ty<'tcx>>> {
         let formal_ret = self.resolve_vars_with_obligations(formal_ret);
-        let Some(ret_ty) = expected_ret.only_has_type(self) else { return Vec::new() };
+        let Some(ret_ty) = expected_ret.only_has_type(self) else { return None };
 
         // HACK(oli-obk): This is a hack to keep RPIT and TAIT in sync wrt their behaviour.
         // Without it, the inference
@@ -779,7 +779,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 if let ty::subst::GenericArgKind::Type(ty) = ty.unpack() {
                     if let ty::Opaque(def_id, _) = *ty.kind() {
                         if self.infcx.opaque_type_origin(def_id, DUMMY_SP).is_some() {
-                            return Vec::new();
+                            return None;
                         }
                     }
                 }
@@ -820,7 +820,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                 // Record all the argument types, with the substitutions
                 // produced from the above subtyping unification.
-                Ok(formal_args.iter().map(|&ty| self.resolve_vars_if_possible(ty)).collect())
+                Ok(Some(formal_args.iter().map(|&ty| self.resolve_vars_if_possible(ty)).collect()))
             })
             .unwrap_or_default();
         debug!(?formal_args, ?formal_ret, ?expect_args, ?expected_ret);