From bd31d9ee9c772e10fb256ba177b738170862ac9e Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 14 May 2023 23:22:27 +0000
Subject: [PATCH] Erase ReError properly

---
 compiler/rustc_middle/src/ty/sty.rs           |  4 +++-
 .../erase-error-in-mir-drop-tracking.rs       | 23 ++++++++++++++++++
 .../erase-error-in-mir-drop-tracking.stderr   | 24 +++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/borrowck/erase-error-in-mir-drop-tracking.rs
 create mode 100644 tests/ui/borrowck/erase-error-in-mir-drop-tracking.stderr

diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index d175cf72d672a..e6d51c4ec9770 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1708,7 +1708,9 @@ impl<'tcx> Region<'tcx> {
             ty::ReErased => {
                 flags = flags | TypeFlags::HAS_RE_ERASED;
             }
-            ty::ReError(_) => {}
+            ty::ReError(_) => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+            }
         }
 
         debug!("type_flags({:?}) = {:?}", self, flags);
diff --git a/tests/ui/borrowck/erase-error-in-mir-drop-tracking.rs b/tests/ui/borrowck/erase-error-in-mir-drop-tracking.rs
new file mode 100644
index 0000000000000..addbe5d658aee
--- /dev/null
+++ b/tests/ui/borrowck/erase-error-in-mir-drop-tracking.rs
@@ -0,0 +1,23 @@
+// compile-flags: -Zdrop-tracking-mir
+// edition:2021
+
+use std::future::Future;
+
+trait Client {
+    type Connecting<'a>: Future + Send
+    where
+        Self: 'a;
+
+    fn connect(&'_ self) -> Self::Connecting<'a>;
+    //~^ ERROR use of undeclared lifetime name `'a`
+}
+
+fn call_connect<C>(c: &'_ C) -> impl '_ + Future + Send
+where
+    C: Client + Send + Sync,
+{
+    async move { c.connect().await }
+    //~^ ERROR `C` does not live long enough
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/erase-error-in-mir-drop-tracking.stderr b/tests/ui/borrowck/erase-error-in-mir-drop-tracking.stderr
new file mode 100644
index 0000000000000..53abe3dc9521d
--- /dev/null
+++ b/tests/ui/borrowck/erase-error-in-mir-drop-tracking.stderr
@@ -0,0 +1,24 @@
+error[E0261]: use of undeclared lifetime name `'a`
+  --> $DIR/erase-error-in-mir-drop-tracking.rs:11:46
+   |
+LL |     fn connect(&'_ self) -> Self::Connecting<'a>;
+   |                                              ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL |     fn connect<'a>(&'_ self) -> Self::Connecting<'a>;
+   |               ++++
+help: consider introducing lifetime `'a` here
+   |
+LL | trait Client<'a> {
+   |             ++++
+
+error: `C` does not live long enough
+  --> $DIR/erase-error-in-mir-drop-tracking.rs:19:5
+   |
+LL |     async move { c.connect().await }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0261`.