Modify primary span label for E0308

The previous output was unintuitive to users.

Author: estebank

compiler/rustc_hir_analysis/src/check/check.rs

@@ -444,7 +444,10 @@ fn check_opaque_meets_bounds<'tcx>(
         Err(ty_err) => {
             tcx.sess.delay_span_bug(
                 span,
-                &format!("could not unify `{hidden_ty}` with revealed type:\n{ty_err}"),
+                &format!(
+                    "could not unify `{hidden_ty}` with revealed type:\n{}",
+                    ty_err.to_string(tcx)
+                ),
             );
         }
     }

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

@@ -67,6 +67,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::Node;
 use rustc_middle::dep_graph::DepContext;
+use rustc_middle::ty::print::with_forced_trimmed_paths;
 use rustc_middle::ty::relate::{self, RelateResult, TypeRelation};
 use rustc_middle::ty::{
     self, error::TypeError, List, Region, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
@@ -1612,16 +1613,31 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 {
                     format!("expected this to be `{}`", expected)
                 } else {
-                    terr.to_string()
+                    terr.to_string(self.tcx)
                 };
                 label_or_note(sp, &terr);
                 label_or_note(span, &msg);
             } else {
-                label_or_note(span, &terr.to_string());
+                label_or_note(span, &terr.to_string(self.tcx));
                 label_or_note(sp, &msg);
             }
         } else {
-            label_or_note(span, &terr.to_string());
+            if let Some(values) = values
+                && let Some((e, f)) = values.ty()
+                && let TypeError::ArgumentSorts(..) | TypeError::Sorts(_) = terr
+            {
+                let e = self.tcx.erase_regions(e);
+                let f = self.tcx.erase_regions(f);
+                let expected = with_forced_trimmed_paths!(e.sort_string(self.tcx));
+                let found = with_forced_trimmed_paths!(f.sort_string(self.tcx));
+                if expected == found {
+                    label_or_note(span, &terr.to_string(self.tcx));
+                } else {
+                    label_or_note(span, &format!("expected {expected}, found {found}"));
+                }
+            } else {
+                label_or_note(span, &terr.to_string(self.tcx));
+            }
         }
 
         if let Some((expected, found, exp_p, found_p)) = expected_found {

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

@@ -137,25 +137,25 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             diag.help(
                                 "given a type parameter `T` and a method `foo`:
 ```
-trait Trait<T> { fn foo(&tcx) -> T; }
+trait Trait<T> { fn foo(&self) -> T; }
 ```
 the only ways to implement method `foo` are:
 - constrain `T` with an explicit type:
 ```
 impl Trait<String> for X {
-    fn foo(&tcx) -> String { String::new() }
+    fn foo(&self) -> String { String::new() }
 }
 ```
 - add a trait bound to `T` and call a method on that trait that returns `Self`:
 ```
 impl<T: std::default::Default> Trait<T> for X {
-    fn foo(&tcx) -> T { <T as std::default::Default>::default() }
+    fn foo(&self) -> T { <T as std::default::Default>::default() }
 }
 ```
 - change `foo` to return an argument of type `T`:
 ```
 impl<T> Trait<T> for X {
-    fn foo(&tcx, x: T) -> T { x }
+    fn foo(&self, x: T) -> T { x }
 }
 ```",
                             );
@@ -389,14 +389,14 @@ impl<T> Trait<T> for X {
 ```
 trait Trait {
 type T;
-fn foo(&tcx) -> Self::T;
+fn foo(&self) -> Self::T;
 }
 ```
 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
 ```
 impl Trait for X {
 type T = String;
-fn foo(&tcx) -> Self::T { String::new() }
+fn foo(&self) -> Self::T { String::new() }
 }
 ```",
             );