From b57ddfe079cbd9974f0b1f68a50f8f1b901cfdaf Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 27 Feb 2024 16:11:35 +0000
Subject: [PATCH] Print RPITIT like an opaque

---
 compiler/rustc_middle/src/ty/print/pretty.rs  | 20 +++++++++++--------
 .../impl-trait/in-trait/async-and-ret-ref.rs  |  2 +-
 .../in-trait/async-and-ret-ref.stderr         |  4 ++--
 .../missing-static-bound-from-impl.rs         |  2 +-
 .../missing-static-bound-from-impl.stderr     |  4 ++--
 5 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 1910841f268..87acca9e945 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -715,13 +715,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 p!(print_def_path(def_id, &[]));
             }
             ty::Alias(ty::Projection | ty::Inherent | ty::Weak, ref data) => {
-                if !(self.should_print_verbose() || with_no_queries())
-                    && self.tcx().is_impl_trait_in_trait(data.def_id)
-                {
-                    return self.pretty_print_opaque_impl_type(data.def_id, data.args);
-                } else {
-                    p!(print(data))
-                }
+                p!(print(data))
             }
             ty::Placeholder(placeholder) => match placeholder.bound.kind {
                 ty::BoundTyKind::Anon => p!(write("{placeholder:?}")),
@@ -3053,7 +3047,17 @@ define_print_and_forward_display! {
         if let DefKind::Impl { of_trait: false } = cx.tcx().def_kind(cx.tcx().parent(self.def_id)) {
             p!(pretty_print_inherent_projection(self))
         } else {
-            p!(print_def_path(self.def_id, self.args));
+            // If we're printing verbosely, or don't want to invoke queries
+            // (`is_impl_trait_in_trait`), then fall back to printing the def path.
+            // This is likely what you want if you're debugging the compiler anyways.
+            if !(cx.should_print_verbose() || with_no_queries())
+                && cx.tcx().is_impl_trait_in_trait(self.def_id)
+            {
+                return cx.pretty_print_opaque_impl_type(self.def_id, self.args);
+            } else {
+                p!(print_def_path(self.def_id, self.args));
+            }
+
         }
     }
 
diff --git a/tests/ui/impl-trait/in-trait/async-and-ret-ref.rs b/tests/ui/impl-trait/in-trait/async-and-ret-ref.rs
index e991b74a0f8..e0a7aef2c5f 100644
--- a/tests/ui/impl-trait/in-trait/async-and-ret-ref.rs
+++ b/tests/ui/impl-trait/in-trait/async-and-ret-ref.rs
@@ -5,7 +5,7 @@ trait T {}
 
 trait MyTrait {
     async fn foo() -> &'static impl T;
-    //~^ ERROR the associated type `<Self as MyTrait>::{opaque#0}` may not live long enough
+    //~^ ERROR the associated type `impl T` may not live long enough
 }
 
 fn main() {}
diff --git a/tests/ui/impl-trait/in-trait/async-and-ret-ref.stderr b/tests/ui/impl-trait/in-trait/async-and-ret-ref.stderr
index a17653496db..19ffff9d3f2 100644
--- a/tests/ui/impl-trait/in-trait/async-and-ret-ref.stderr
+++ b/tests/ui/impl-trait/in-trait/async-and-ret-ref.stderr
@@ -1,10 +1,10 @@
-error[E0310]: the associated type `<Self as MyTrait>::{synthetic#0}` may not live long enough
+error[E0310]: the associated type `impl T` may not live long enough
   --> $DIR/async-and-ret-ref.rs:7:5
    |
 LL |     async fn foo() -> &'static impl T;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |     |
-   |     the associated type `<Self as MyTrait>::{synthetic#0}` must be valid for the static lifetime...
+   |     the associated type `impl T` must be valid for the static lifetime...
    |     ...so that the reference type `&'static impl T` does not outlive the data it points at
 
 error: aborting due to 1 previous error
diff --git a/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.rs b/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.rs
index a36799c3ebd..ee9ecdda902 100644
--- a/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.rs
+++ b/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.rs
@@ -9,7 +9,7 @@ trait Erased {
 impl<T: Original> Erased for T {
     fn f(&self) -> Box<dyn Fn()> {
         Box::new(<T as Original>::f())
-        //~^ ERROR the associated type `<T as Original>::{opaque#0}` may not live long enough
+        //~^ ERROR the associated type `impl Fn()` may not live long enough
     }
 }
 
diff --git a/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.stderr b/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.stderr
index 7fa4b8dbd49..1f787c1842c 100644
--- a/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.stderr
+++ b/tests/ui/impl-trait/in-trait/missing-static-bound-from-impl.stderr
@@ -1,10 +1,10 @@
-error[E0310]: the associated type `<T as Original>::{synthetic#0}` may not live long enough
+error[E0310]: the associated type `impl Fn()` may not live long enough
   --> $DIR/missing-static-bound-from-impl.rs:11:9
    |
 LL |         Box::new(<T as Original>::f())
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |         |
-   |         the associated type `<T as Original>::{synthetic#0}` must be valid for the static lifetime...
+   |         the associated type `impl Fn()` must be valid for the static lifetime...
    |         ...so that the type `impl Fn()` will meet its required lifetime bounds
 
 error: aborting due to 1 previous error