From 16a3601f62e1a2e2ae34668005a317d931e13a09 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 27 Jul 2022 05:06:46 +0000
Subject: [PATCH] Delay a bug when failed to normalize trait ref during
 specialization

---
 .../src/traits/specialize/mod.rs              | 10 ++++++----
 src/test/ui/specialization/issue-43037.rs     | 20 +++++++++++++++++++
 src/test/ui/specialization/issue-43037.stderr | 12 +++++++++++
 src/test/ui/specialization/issue-45814.rs     | 12 +++++++++++
 src/test/ui/specialization/issue-45814.stderr | 14 +++++++++++++
 5 files changed, 64 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/specialization/issue-43037.rs
 create mode 100644 src/test/ui/specialization/issue-43037.stderr
 create mode 100644 src/test/ui/specialization/issue-45814.rs
 create mode 100644 src/test/ui/specialization/issue-45814.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index 5f77aae6f221f..f9c06178368eb 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -149,8 +149,6 @@ pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId,
 
     // Create an infcx, taking the predicates of impl1 as assumptions:
     tcx.infer_ctxt().enter(|infcx| {
-        // Normalize the trait reference. The WF rules ought to ensure
-        // that this always succeeds.
         let impl1_trait_ref = match traits::fully_normalize(
             &infcx,
             FulfillmentContext::new(),
@@ -159,8 +157,12 @@ pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId,
             impl1_trait_ref,
         ) {
             Ok(impl1_trait_ref) => impl1_trait_ref,
-            Err(err) => {
-                bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
+            Err(_errors) => {
+                tcx.sess.delay_span_bug(
+                    tcx.def_span(impl1_def_id),
+                    format!("failed to fully normalize {impl1_trait_ref}"),
+                );
+                impl1_trait_ref
             }
         };
 
diff --git a/src/test/ui/specialization/issue-43037.rs b/src/test/ui/specialization/issue-43037.rs
new file mode 100644
index 0000000000000..c49119f9c095b
--- /dev/null
+++ b/src/test/ui/specialization/issue-43037.rs
@@ -0,0 +1,20 @@
+#![feature(specialization)]
+#![allow(incomplete_features)]
+
+trait X {}
+trait Y: X {}
+trait Z {
+    type Assoc: Y;
+}
+struct A<T>(T);
+
+impl<T> Y for T where T: X {}
+impl<T: X> Z for A<T> {
+    type Assoc = T;
+}
+
+// this impl is invalid, but causes an ICE anyway
+impl<T> From<<A<T> as Z>::Assoc> for T {}
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)
+
+fn main() {}
diff --git a/src/test/ui/specialization/issue-43037.stderr b/src/test/ui/specialization/issue-43037.stderr
new file mode 100644
index 0000000000000..4249cd8947716
--- /dev/null
+++ b/src/test/ui/specialization/issue-43037.stderr
@@ -0,0 +1,12 @@
+error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)
+  --> $DIR/issue-43037.rs:17:6
+   |
+LL | impl<T> From<<A<T> as Z>::Assoc> for T {}
+   |      ^ type parameter `T` must be used as the type parameter for some local type
+   |
+   = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local
+   = note: only traits defined in the current crate can be implemented for a type parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0210`.
diff --git a/src/test/ui/specialization/issue-45814.rs b/src/test/ui/specialization/issue-45814.rs
new file mode 100644
index 0000000000000..8ee5d3e2e58da
--- /dev/null
+++ b/src/test/ui/specialization/issue-45814.rs
@@ -0,0 +1,12 @@
+//~ ERROR overflow evaluating the requirement `T: Trait<_>`
+
+#![feature(specialization)]
+#![allow(incomplete_features)]
+
+pub trait Trait<T> {}
+
+default impl<T, U> Trait<T> for U {}
+
+impl<T> Trait<<T as Iterator>::Item> for T {}
+
+fn main() {}
diff --git a/src/test/ui/specialization/issue-45814.stderr b/src/test/ui/specialization/issue-45814.stderr
new file mode 100644
index 0000000000000..ab6adf477c978
--- /dev/null
+++ b/src/test/ui/specialization/issue-45814.stderr
@@ -0,0 +1,14 @@
+error[E0275]: overflow evaluating the requirement `T: Trait<_>`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_45814`)
+note: required because of the requirements on the impl of `Trait<_>` for `T`
+  --> $DIR/issue-45814.rs:8:20
+   |
+LL | default impl<T, U> Trait<T> for U {}
+   |                    ^^^^^^^^     ^
+   = note: 128 redundant requirements hidden
+   = note: required because of the requirements on the impl of `Trait<_>` for `T`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.