Do not complain about unconstrained params when Self is Ty Error

src/librustc_typeck/constrained_generic_params.rs

@@ -20,10 +20,10 @@ impl From<ty::ParamConst> for Parameter {
 }
 
 /// Returns the set of parameters constrained by the impl header.
-pub fn parameters_for_impl<'tcx>(impl_self_ty: Ty<'tcx>,
-                                 impl_trait_ref: Option<ty::TraitRef<'tcx>>)
-                                 -> FxHashSet<Parameter>
-{
+pub fn parameters_for_impl<'tcx>(
+    impl_self_ty: Ty<'tcx>,
+    impl_trait_ref: Option<ty::TraitRef<'tcx>>,
+) -> FxHashSet<Parameter> {
     let vec = match impl_trait_ref {
         Some(tr) => parameters_for(&tr, false),
         None => parameters_for(&impl_self_ty, false),
@@ -36,12 +36,10 @@ pub fn parameters_for_impl<'tcx>(impl_self_ty: Ty<'tcx>,
 /// uniquely determined by `t` (see RFC 447). If it is true, return the list
 /// of parameters whose values are needed in order to constrain `ty` - these
 /// differ, with the latter being a superset, in the presence of projections.
-pub fn parameters_for<'tcx, T>(t: &T,
-                               include_nonconstraining: bool)
-                               -> Vec<Parameter>
-    where T: TypeFoldable<'tcx>
-{
-
+pub fn parameters_for<'tcx, T: TypeFoldable<'tcx>>(
+    t: &T,
+    include_nonconstraining: bool,
+) -> Vec<Parameter> {
     let mut collector = ParameterCollector {
         parameters: vec![],
         include_nonconstraining,

src/librustc_typeck/impl_wf_check.rs

@@ -99,6 +99,10 @@ fn enforce_impl_params_are_constrained(
 ) {
     // Every lifetime used in an associated type must be constrained.
     let impl_self_ty = tcx.type_of(impl_def_id);
+    if impl_self_ty.sty == ty::Error {
+        // Don't complain about unconstrained type params when self ty doesn't exist. (#36836)
+        return;
+    }
     let impl_generics = tcx.generics_of(impl_def_id);
     let impl_predicates = tcx.predicates_of(impl_def_id);
     let impl_trait_ref = tcx.impl_trait_ref(impl_def_id);

src/test/ui/issues/issue-36836.rs

@@ -0,0 +1,5 @@
+trait Foo {}
+
+impl<T> Foo for Bar<T> {} //~ ERROR cannot find type `Bar` in this scope
+
+fn main() {}

src/test/ui/issues/issue-36836.stderr

@@ -0,0 +1,9 @@
+error[E0412]: cannot find type `Bar` in this scope
+  --> $DIR/issue-36836.rs:3:17
+   |
+LL | impl<T> Foo for Bar<T> {}
+   |                 ^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.