Rollup merge of #88525 - notriddle:notriddle/coherence-dyn-auto-trait, r=petrochenkov

fix(rustc_typeck): produce better errors for dyn auto trait

Fixes #85026

2 files changed, 29 insertions, 0 deletions

diff --git a/src/test/ui/coherence/issue-85026.rs b/src/test/ui/coherence/issue-85026.rs
new file mode 100644
index 00000000000..8b116545aa6
--- /dev/null
+++ b/src/test/ui/coherence/issue-85026.rs
@@ -0,0 +1,10 @@
+#![feature(auto_traits)]
+auto trait AutoTrait {}
+
+// You cannot impl your own `dyn AutoTrait`.
+impl dyn AutoTrait {} //~ERROR E0785
+
+// You cannot impl someone else's `dyn AutoTrait`
+impl dyn Unpin {} //~ERROR E0785
+
+fn main() {}
diff --git a/src/test/ui/coherence/issue-85026.stderr b/src/test/ui/coherence/issue-85026.stderr
new file mode 100644
index 00000000000..a5da19bbfaa
--- /dev/null
+++ b/src/test/ui/coherence/issue-85026.stderr
@@ -0,0 +1,19 @@
+error[E0785]: cannot define inherent `impl` for a dyn auto trait
+  --> $DIR/issue-85026.rs:5:6
+   |
+LL | impl dyn AutoTrait {}
+   |      ^^^^^^^^^^^^^ impl requires at least one non-auto trait
+   |
+   = note: define and implement a new trait or type instead
+
+error[E0785]: cannot define inherent `impl` for a dyn auto trait
+  --> $DIR/issue-85026.rs:8:6
+   |
+LL | impl dyn Unpin {}
+   |      ^^^^^^^^^ impl requires at least one non-auto trait
+   |
+   = note: define and implement a new trait or type instead
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0785`.