Properly report error when object type param default references self

3 files changed, 13 insertions, 15 deletions

diff --git a/compiler/rustc_error_codes/src/error_codes/E0393.md b/compiler/rustc_error_codes/src/error_codes/E0393.md
index 50225b25163..c7260815905 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0393.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0393.md
@@ -3,12 +3,10 @@ A type parameter which references `Self` in its default value was not specified.
 Erroneous code example:
 
 ```compile_fail,E0393
-trait A<T=Self> {}
+trait A<T = Self> {}
 
-fn together_we_will_rule_the_galaxy(son: &A) {}
-// error: the type parameter `T` must be explicitly specified in an
-//        object type because its default value `Self` references the
-//        type `Self`
+fn together_we_will_rule_the_galaxy(son: &dyn A) {}
+// error: the type parameter `T` must be explicitly specified
 ```
 
 A trait object is defined over a single, fully-defined trait. With a regular
@@ -23,7 +21,7 @@ disallowed. Making the trait concrete by explicitly specifying the value of the
 defaulted parameter will fix this issue. Fixed example:
 
 ```
-trait A<T=Self> {}
+trait A<T = Self> {}
 
-fn together_we_will_rule_the_galaxy(son: &A<i32>) {} // Ok!
+fn together_we_will_rule_the_galaxy(son: &dyn A<i32>) {} // Ok!
 ```
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 512d379687b..be4004f5904 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -353,7 +353,13 @@ hir_analysis_missing_type_params =
         [one] reference
         *[other] references
     } to {$parameters}
-    .note = because of the default `Self` reference, type parameters must be specified on object types
+    .note = because the parameter {$parameterCount ->
+        [one] default references
+        *[other] defaults reference
+    } `Self`, the {$parameterCount ->
+        [one] parameter
+        *[other] parameters
+    } must be specified on the object type
 
 hir_analysis_multiple_relaxed_default_bounds =
     type parameter has more than one relaxed default bound, only one is supported
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
index 72ad190df7e..e59ff02642c 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
@@ -237,16 +237,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     // Skip `Self`
                     .skip(1)
                     .map(|(index, arg)| {
-                        if arg == dummy_self.into() {
+                        if arg.walk().any(|arg| arg == dummy_self.into()) {
                             let param = &generics.own_params[index];
                             missing_type_params.push(param.name);
                             Ty::new_misc_error(tcx).into()
-                        } else if arg.walk().any(|arg| arg == dummy_self.into()) {
-                            let guar = self.dcx().span_delayed_bug(
-                                span,
-                                "trait object trait bounds reference `Self`",
-                            );
-                            replace_dummy_self_with_error(tcx, arg, guar)
                         } else {
                             arg
                         }