Rollup merge of #144265 - compiler-errors:copy-ice, r=oli-obk

Dont ICE on copy error being suppressed due to overflow

See comment in test file.

Fixes #144165

Author: matthiaskrgr

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -303,10 +303,11 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     }
 
     fn has_ambiguous_copy(&mut self, ty: Ty<'tcx>) -> bool {
-        let Some(copy_trait_def) = self.infcx.tcx.lang_items().copy_trait() else { return false };
-        // This is only going to be ambiguous if there are incoherent impls, because otherwise
-        // ambiguity should never happen in MIR.
-        self.infcx.type_implements_trait(copy_trait_def, [ty], self.infcx.param_env).may_apply()
+        let Some(copy_def_id) = self.infcx.tcx.lang_items().copy_trait() else { return false };
+
+        // Avoid bogus move errors because of an incoherent `Copy` impl.
+        self.infcx.type_implements_trait(copy_def_id, [ty], self.infcx.param_env).may_apply()
+            && self.infcx.tcx.coherent_trait(copy_def_id).is_err()
     }
 
     fn report_cannot_move_from_static(&mut self, place: Place<'tcx>, span: Span) -> Diag<'infcx> {

tests/ui/borrowck/copy-overflow.rs

@@ -0,0 +1,16 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/144165>.
+
+// We were previously suppressing the copy error in the `Clone` impl because we assumed
+// that the only way we get `Copy` ambiguity errors was due to incoherent impls. This is
+// not true, since ambiguities can be encountered due to overflows (among other ways).
+
+struct S<T: 'static>(Option<&'static T>);
+
+impl<T: 'static> Copy for S<T> where S<T>: Copy + Clone {}
+impl<T: 'static> Clone for S<T> {
+    fn clone(&self) -> Self {
+        *self
+        //~^ ERROR cannot move out of `*self` which is behind a shared reference
+    }
+}
+fn main() {}

tests/ui/borrowck/copy-overflow.stderr

@@ -0,0 +1,15 @@
+error[E0507]: cannot move out of `*self` which is behind a shared reference
+  --> $DIR/copy-overflow.rs:12:9
+   |
+LL |         *self
+   |         ^^^^^ move occurs because `*self` has type `S<T>`, which does not implement the `Copy` trait
+   |
+help: consider cloning the value if the performance cost is acceptable
+   |
+LL -         *self
+LL +         self.clone()
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0507`.