From b7a5f3a41c6613033f0e6be9307c40e3174a9381 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 7 Mar 2023 05:40:55 +0000
Subject: [PATCH] Instantiate instead of erasing binder when probing param
 methods

---
 compiler/rustc_hir_typeck/src/method/probe.rs | 27 ++++++++++++-------
 .../non_lifetime_binders/method-probe.rs      | 16 +++++++++++
 .../non_lifetime_binders/method-probe.stderr  | 11 ++++++++
 3 files changed, 45 insertions(+), 9 deletions(-)
 create mode 100644 tests/ui/traits/non_lifetime_binders/method-probe.rs
 create mode 100644 tests/ui/traits/non_lifetime_binders/method-probe.stderr

diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 3bef5cfcd780e..2c8c9ed69d31c 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -792,6 +792,14 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         // a `&self` method will wind up with an argument type like `&dyn Trait`.
         let trait_ref = principal.with_self_ty(self.tcx, self_ty);
         self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
+            if new_trait_ref.has_non_region_late_bound() {
+                this.tcx.sess.delay_span_bug(
+                    this.span,
+                    "tried to select method from HRTB with non-lifetime bound vars",
+                );
+                return;
+            }
+
             let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
 
             let (xform_self_ty, xform_ret_ty) =
@@ -842,18 +850,15 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         });
 
         self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
-            let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
+            let trait_ref = this.instantiate_binder_with_fresh_vars(
+                this.span,
+                infer::LateBoundRegionConversionTime::FnCall,
+                poly_trait_ref,
+            );
 
             let (xform_self_ty, xform_ret_ty) =
                 this.xform_self_ty(item, trait_ref.self_ty(), trait_ref.substs);
 
-            // Because this trait derives from a where-clause, it
-            // should not contain any inference variables or other
-            // artifacts. This means it is safe to put into the
-            // `WhereClauseCandidate` and (eventually) into the
-            // `WhereClausePick`.
-            assert!(!trait_ref.substs.needs_infer());
-
             this.push_candidate(
                 Candidate {
                     xform_self_ty,
@@ -963,7 +968,11 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                             bound_trait_ref.def_id(),
                         ));
                     } else {
-                        let new_trait_ref = self.erase_late_bound_regions(bound_trait_ref);
+                        let new_trait_ref = self.instantiate_binder_with_fresh_vars(
+                            self.span,
+                            infer::LateBoundRegionConversionTime::FnCall,
+                            bound_trait_ref,
+                        );
 
                         let (xform_self_ty, xform_ret_ty) =
                             self.xform_self_ty(item, new_trait_ref.self_ty(), new_trait_ref.substs);
diff --git a/tests/ui/traits/non_lifetime_binders/method-probe.rs b/tests/ui/traits/non_lifetime_binders/method-probe.rs
new file mode 100644
index 0000000000000..8df240c2082b7
--- /dev/null
+++ b/tests/ui/traits/non_lifetime_binders/method-probe.rs
@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(non_lifetime_binders)]
+//~^ WARN the feature `non_lifetime_binders` is incomplete
+
+trait Foo: for<T> Bar<T> {}
+
+trait Bar<T> {
+    fn method() -> T;
+}
+
+fn x<T: Foo>() {
+    let _: i32 = T::method();
+}
+
+fn main() {}
diff --git a/tests/ui/traits/non_lifetime_binders/method-probe.stderr b/tests/ui/traits/non_lifetime_binders/method-probe.stderr
new file mode 100644
index 0000000000000..8f61792e6ce7f
--- /dev/null
+++ b/tests/ui/traits/non_lifetime_binders/method-probe.stderr
@@ -0,0 +1,11 @@
+warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/method-probe.rs:3:12
+   |
+LL | #![feature(non_lifetime_binders)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+