fix: don't suggest .into_iter() for .cloned()/.copied() on non-reference Option

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -917,6 +917,30 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     "`count` is defined on `{iterator_trait}`, which `{rcvr_ty}` does not implement"
                 ));
             }
+        } else if matches!(item_ident.name.as_str(), "cloned" | "copied")
+            && let ty::Adt(adt_def, args) = rcvr_ty.kind()
+            && tcx.is_diagnostic_item(sym::Option, adt_def.did())
+            && let inner_ty = args.type_at(0)
+            // Skip refs (`Option<&T>.into_iter().cloned()` is valid, let the default branch
+            // handle it), and params/infer where we can't statically rule out a reference.
+            && !matches!(inner_ty.kind(), ty::Ref(..) | ty::Param(_) | ty::Infer(_))
+        {
+            // The default branch below would suggest `.into_iter()`, but that still
+            // fails: `Option<T>` yields `T` by value, not `&T`, so `.cloned()`/`.copied()`
+            // can't resolve. Give a targeted diagnostic instead.
+            err.span_label(span, format!("this method is only available on `Option<&_>`"));
+            if let SelfSource::MethodCall(rcvr_expr) = source
+                && !span.in_external_macro(tcx.sess.source_map())
+            {
+                let call_expr = self.tcx.hir_expect_expr(self.tcx.parent_hir_id(rcvr_expr.hir_id));
+                err.span_suggestion(
+                    rcvr_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi()),
+                    format!("consider removing the `.{}()` call", item_ident.name),
+                    "",
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            return Err(());
         } else if self.impl_into_iterator_should_be_iterator(rcvr_ty, span, unsatisfied_predicates)
         {
             err.span_label(span, format!("`{rcvr_ty}` is not an iterator"));

tests/ui/methods/option-cloned-copied-non-ref-excluded.rs

@@ -0,0 +1,27 @@
+// Tests that the guard for `.cloned()`/`.copied()` on `Option<T>` correctly
+// excludes inner types where the targeted diagnostic would be wrong:
+//
+// - `Option<&T>`: `Option<&T>` has inherent `cloned()`/`copied()` methods,
+//   so these compile successfully and the guard must not fire.
+// - `Option<T>` (generic param): falls through to the standard "not an
+//   iterator / call .into_iter() first" diagnostic.
+//
+// See https://github.com/rust-lang/rust/issues/151147
+
+// Reference inner type: these should compile without error.
+pub fn cloned_on_ref(x: Option<&i32>) -> Option<i32> {
+    x.cloned()
+}
+
+pub fn copied_on_ref(x: Option<&i32>) -> Option<i32> {
+    x.copied()
+}
+
+// Generic param inner type: falls through to the standard diagnostic.
+pub fn cloned_on_param<T: Clone>(x: Option<T>) {
+    x.cloned();
+    //~^ ERROR no method named `cloned` found for enum `Option<T>` in the current scope
+    //~| HELP call `.into_iter()` first
+}
+
+fn main() {}

tests/ui/methods/option-cloned-copied-non-ref-excluded.stderr

@@ -0,0 +1,14 @@
+error[E0599]: no method named `cloned` found for enum `Option<T>` in the current scope
+  --> $DIR/option-cloned-copied-non-ref-excluded.rs:22:7
+   |
+LL |     x.cloned();
+   |       ^^^^^^ `Option<T>` is not an iterator
+   |
+help: call `.into_iter()` first
+   |
+LL |     x.into_iter().cloned();
+   |       ++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0599`.

tests/ui/methods/option-cloned-copied-non-ref.fixed

@@ -0,0 +1,26 @@
+// Tests that calling `.cloned()` or `.copied()` on `Option<T>` where `T` is an
+// owned (non-reference) type gives a targeted diagnostic instead of the
+// misleading "not an iterator / call .into_iter() first" suggestion.
+// See https://github.com/rust-lang/rust/issues/151147
+
+//@ run-rustfix
+
+pub fn cloned_on_owned(x: Option<i32>) -> i32 {
+    x.unwrap()
+    //~^ ERROR no method named `cloned` found for enum `Option<i32>` in the current scope
+    //~| HELP consider removing the `.cloned()` call
+}
+
+pub fn copied_on_owned(x: Option<i32>) -> i32 {
+    x.unwrap()
+    //~^ ERROR no method named `copied` found for enum `Option<i32>` in the current scope
+    //~| HELP consider removing the `.copied()` call
+}
+
+pub fn cloned_on_string(x: Option<String>) -> String {
+    x.unwrap()
+    //~^ ERROR no method named `cloned` found for enum `Option<String>` in the current scope
+    //~| HELP consider removing the `.cloned()` call
+}
+
+fn main() {}

tests/ui/methods/option-cloned-copied-non-ref.rs

@@ -0,0 +1,26 @@
+// Tests that calling `.cloned()` or `.copied()` on `Option<T>` where `T` is an
+// owned (non-reference) type gives a targeted diagnostic instead of the
+// misleading "not an iterator / call .into_iter() first" suggestion.
+// See https://github.com/rust-lang/rust/issues/151147
+
+//@ run-rustfix
+
+pub fn cloned_on_owned(x: Option<i32>) -> i32 {
+    x.cloned().unwrap()
+    //~^ ERROR no method named `cloned` found for enum `Option<i32>` in the current scope
+    //~| HELP consider removing the `.cloned()` call
+}
+
+pub fn copied_on_owned(x: Option<i32>) -> i32 {
+    x.copied().unwrap()
+    //~^ ERROR no method named `copied` found for enum `Option<i32>` in the current scope
+    //~| HELP consider removing the `.copied()` call
+}
+
+pub fn cloned_on_string(x: Option<String>) -> String {
+    x.cloned().unwrap()
+    //~^ ERROR no method named `cloned` found for enum `Option<String>` in the current scope
+    //~| HELP consider removing the `.cloned()` call
+}
+
+fn main() {}

tests/ui/methods/option-cloned-copied-non-ref.stderr

@@ -0,0 +1,30 @@
+error[E0599]: no method named `cloned` found for enum `Option<i32>` in the current scope
+  --> $DIR/option-cloned-copied-non-ref.rs:9:7
+   |
+LL |     x.cloned().unwrap()
+   |      -^^^^^^--
+   |      ||
+   |      |this method is only available on `Option<&_>`
+   |      help: consider removing the `.cloned()` call
+
+error[E0599]: no method named `copied` found for enum `Option<i32>` in the current scope
+  --> $DIR/option-cloned-copied-non-ref.rs:15:7
+   |
+LL |     x.copied().unwrap()
+   |      -^^^^^^--
+   |      ||
+   |      |this method is only available on `Option<&_>`
+   |      help: consider removing the `.copied()` call
+
+error[E0599]: no method named `cloned` found for enum `Option<String>` in the current scope
+  --> $DIR/option-cloned-copied-non-ref.rs:21:7
+   |
+LL |     x.cloned().unwrap()
+   |      -^^^^^^--
+   |      ||
+   |      |this method is only available on `Option<&_>`
+   |      help: consider removing the `.cloned()` call
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0599`.