Get rid of infer vars in inherent assoc types selection by using probe

Author: spastorino

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1620,19 +1620,22 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             self_ty,
             |self_ty| {
                 let tcx = self.tcx();
-                let InferOk { value: self_ty, obligations } =
-                    infcx.at(&cause, param_env).normalize(self_ty);
 
-                let (impl_, (assoc_item, def_scope)) = self.select_inherent_assoc_type_candidates(
-                    infcx,
-                    name,
-                    span,
-                    self_ty,
-                    cause,
-                    param_env,
-                    obligations,
-                    candidates,
-                )?;
+                let (impl_, (assoc_item, def_scope)) = infcx.probe(|_| {
+                    let InferOk { value: self_ty, obligations } =
+                        infcx.at(&cause, param_env).normalize(self_ty);
+
+                    self.select_inherent_assoc_type_candidates(
+                        infcx,
+                        name,
+                        span,
+                        self_ty,
+                        cause,
+                        param_env,
+                        obligations,
+                        candidates,
+                    )
+                })?;
 
                 self.check_assoc_ty(assoc_item, name, def_scope, block, span);
 

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1455,7 +1455,12 @@ pub fn compute_inherent_assoc_ty_args<'a, 'b, 'tcx>(
     // Infer the generic parameters of the impl by unifying the
     // impl type with the self type of the projection.
     let self_ty = alias_ty.self_ty();
-    match selcx.infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, impl_ty, self_ty) {
+    let infcx = selcx.infcx.at(&cause, param_env);
+    let InferOk { value: self_ty, obligations: mut normalize_obligations } =
+        infcx.normalize(self_ty);
+    obligations.append(&mut normalize_obligations);
+
+    match infcx.eq(DefineOpaqueTypes::No, impl_ty, self_ty) {
         Ok(mut ok) => obligations.append(&mut ok.obligations),
         Err(_) => {
             tcx.sess.delay_span_bug(

tests/ui/associated-inherent-types/assoc-inherent-late-bound.rs

@@ -0,0 +1,14 @@
+// check-pass
+
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+struct Foo<T>(T);
+
+impl<'a> Foo<fn(&'a ())> {
+    type Assoc = &'a ();
+}
+
+fn bar(_: for<'a> fn(Foo<fn(Foo<fn(&'static ())>::Assoc)>::Assoc)) {}
+
+fn main() {}