Fall back when relating two opaques by substs in MIR typeck

4 files changed, 65 insertions, 0 deletions

diff --git a/src/test/ui/impl-trait/issue-100075-2.rs b/src/test/ui/impl-trait/issue-100075-2.rs
new file mode 100644
index 00000000000..cf059af1925
--- /dev/null
+++ b/src/test/ui/impl-trait/issue-100075-2.rs
@@ -0,0 +1,8 @@
+fn opaque<T>(t: T) -> impl Sized {
+    //~^ ERROR cannot resolve opaque type
+    //~| WARNING function cannot return without recursing
+    opaque(Some(t))
+}
+
+#[allow(dead_code)]
+fn main() {}
diff --git a/src/test/ui/impl-trait/issue-100075-2.stderr b/src/test/ui/impl-trait/issue-100075-2.stderr
new file mode 100644
index 00000000000..5a1f1a97d04
--- /dev/null
+++ b/src/test/ui/impl-trait/issue-100075-2.stderr
@@ -0,0 +1,24 @@
+warning: function cannot return without recursing
+  --> $DIR/issue-100075-2.rs:1:1
+   |
+LL | fn opaque<T>(t: T) -> impl Sized {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+...
+LL |     opaque(Some(t))
+   |     --------------- recursive call site
+   |
+   = note: `#[warn(unconditional_recursion)]` on by default
+   = help: a `loop` may express intention better if this is on purpose
+
+error[E0720]: cannot resolve opaque type
+  --> $DIR/issue-100075-2.rs:1:23
+   |
+LL | fn opaque<T>(t: T) -> impl Sized {
+   |                       ^^^^^^^^^^ recursive opaque type
+...
+LL |     opaque(Some(t))
+   |     --------------- returning here with type `impl Sized`
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0720`.
diff --git a/src/test/ui/impl-trait/issue-100075.rs b/src/test/ui/impl-trait/issue-100075.rs
new file mode 100644
index 00000000000..ea30abb4855
--- /dev/null
+++ b/src/test/ui/impl-trait/issue-100075.rs
@@ -0,0 +1,21 @@
+trait Marker {}
+impl<T> Marker for T {}
+
+fn maybe<T>(
+    _t: T,
+) -> Option<
+    //removing the line below makes it compile
+    &'static T,
+> {
+    None
+}
+
+fn _g<T>(t: &'static T) -> &'static impl Marker {
+    //~^ ERROR cannot resolve opaque type
+    if let Some(t) = maybe(t) {
+        return _g(t);
+    }
+    todo!()
+}
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/issue-100075.stderr b/src/test/ui/impl-trait/issue-100075.stderr
new file mode 100644
index 00000000000..267ecfdaed1
--- /dev/null
+++ b/src/test/ui/impl-trait/issue-100075.stderr
@@ -0,0 +1,12 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/issue-100075.rs:13:37
+   |
+LL | fn _g<T>(t: &'static T) -> &'static impl Marker {
+   |                                     ^^^^^^^^^^^ recursive opaque type
+...
+LL |         return _g(t);
+   |                ----- returning here with type `&impl Marker`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0720`.