Rollup merge of #158430 - TaKO8Ki:fix-clone-suggestion-empty-obligations, r=Kivooeo

Guard clone suggestion against empty obligation errors

Fixes #148631

Author: JonathanBrouwer

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1461,15 +1461,19 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             let cause = ObligationCause::misc(expr.span, self.mir_def_id());
             ocx.register_bound(cause, self.infcx.param_env, ty, clone_trait);
             let errors = ocx.evaluate_obligations_error_on_ambiguity();
-            if errors.iter().all(|error| {
-                match error.obligation.predicate.as_clause().and_then(|c| c.as_trait_clause()) {
-                    Some(clause) => match clause.self_ty().skip_binder().kind() {
-                        ty::Adt(def, _) => def.did().is_local() && clause.def_id() == clone_trait,
-                        _ => false,
-                    },
-                    None => false,
-                }
-            }) {
+            if !errors.is_empty()
+                && errors.iter().all(|error| {
+                    match error.obligation.predicate.as_clause().and_then(|c| c.as_trait_clause()) {
+                        Some(clause) => match clause.self_ty().skip_binder().kind() {
+                            ty::Adt(def, _) => {
+                                def.did().is_local() && clause.def_id() == clone_trait
+                            }
+                            _ => false,
+                        },
+                        None => false,
+                    }
+                })
+            {
                 let mut type_spans = vec![];
                 let mut types = FxIndexSet::default();
                 for clause in errors

tests/ui/moves/unconstrained-impl-param-clone-suggestion.rs

@@ -0,0 +1,20 @@
+// Regression test for https://github.com/rust-lang/rust/issues/148631
+
+struct C;
+
+struct S<T>(T);
+
+trait Tr {}
+
+impl<T> Clone for S<C>
+//~^ ERROR the type parameter `T` is not constrained
+where
+    S<T>: Tr,
+{
+    fn clone(&self) -> Self {
+        *self
+        //~^ ERROR cannot move out of `*self`
+    }
+}
+
+fn main() {}

tests/ui/moves/unconstrained-impl-param-clone-suggestion.stderr

@@ -0,0 +1,19 @@
+error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/unconstrained-impl-param-clone-suggestion.rs:9:6
+   |
+LL | impl<T> Clone for S<C>
+   |     -^-
+   |     ||
+   |     |unconstrained type parameter
+   |     help: remove the unused type parameter `T`
+
+error[E0507]: cannot move out of `*self` which is behind a shared reference
+  --> $DIR/unconstrained-impl-param-clone-suggestion.rs:15:9
+   |
+LL |         *self
+   |         ^^^^^ move occurs because `*self` has type `S<C>`, which does not implement the `Copy` trait
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0207, E0507.
+For more information about an error, try `rustc --explain E0207`.