From b19b5be58c30156f22aca3e6c519984651750451 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Fri, 23 Jun 2023 19:17:32 +0000
Subject: [PATCH] In `<&NotClone as Clone>::clone()` call, account for bindings

Address #112857:

```
error[E0308]: mismatched types
  --> $DIR/explain_clone_autoref.rs:28:5
   |
LL | fn clone_thing3(nc: &NotClone) -> NotClone {
   |                                   -------- expected `NotClone` because of return type
...
LL |     nc
   |     ^^ expected `NotClone`, found `&NotClone`
   |
note: `NotClone` does not implement `Clone`, so `&NotClone` was cloned instead
  --> $DIR/explain_clone_autoref.rs:26:14
   |
LL |     let nc = nc.clone();
   |              ^^
help: consider annotating `NotClone` with `#[derive(Clone)]`
   |
LL + #[derive(Clone)]
LL | struct NotClone;
   |
```
---
 .../src/fn_ctxt/suggestions.rs                | 27 +++++++++++-
 tests/ui/typeck/explain_clone_autoref.rs      | 18 ++++++++
 tests/ui/typeck/explain_clone_autoref.stderr  | 41 ++++++++++++++++++-
 3 files changed, 84 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 3a4fe334f888a..c3dc68a160b80 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -1494,7 +1494,32 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         found_ty: Ty<'tcx>,
         expr: &hir::Expr<'_>,
     ) {
-        let hir::ExprKind::MethodCall(segment, callee_expr, &[], _) = expr.kind else { return; };
+        let (segment, callee_expr, expr) = match expr.kind {
+            // When `expr` is `foo.clone()`, get `foo` and `clone`.
+            hir::ExprKind::MethodCall(segment, callee_expr, &[], _) => (segment, callee_expr, expr),
+            // When `expr` is `x` in `let x = foo.clone(); x`, get `foo` and `clone`.
+            hir::ExprKind::Path(hir::QPath::Resolved(
+                None,
+                hir::Path { segments: [_], res: crate::Res::Local(binding), .. },
+            )) => {
+                let Some(hir::Node::Pat(
+                    hir::Pat { hir_id, kind: hir::PatKind::Binding(_, _, _, _), .. }
+                )) = self.tcx.hir().find(*binding) else {
+                    return;
+                };
+                let parent = self.tcx.hir().parent_id(*hir_id);
+                let Some(hir::Node::Local(
+                    hir::Local { init: Some(init), .. }
+                )) = self.tcx.hir().find(parent) else {
+                    return;
+                };
+                let hir::ExprKind::MethodCall(segment, callee_expr, &[], _) = init.kind else {
+                    return;
+                };
+                (segment, callee_expr, *init)
+            }
+            _ => return,
+        };
         let Some(clone_trait_did) = self.tcx.lang_items().clone_trait() else { return; };
         let ty::Ref(_, pointee_ty, _) = found_ty.kind() else { return };
         let results = self.typeck_results.borrow();
diff --git a/tests/ui/typeck/explain_clone_autoref.rs b/tests/ui/typeck/explain_clone_autoref.rs
index 4d21574700ad9..84ef4eb154cc5 100644
--- a/tests/ui/typeck/explain_clone_autoref.rs
+++ b/tests/ui/typeck/explain_clone_autoref.rs
@@ -11,3 +11,21 @@ fn clone_thing(nc: &NotClone) -> NotClone {
     //~| NOTE `NotClone` does not implement `Clone`, so `&NotClone` was cloned instead
     //~| NOTE expected `NotClone`, found `&NotClone`
 }
+
+fn clone_thing2(nc: &NotClone) -> NotClone {
+    let nc: NotClone = nc.clone();
+    //~^ ERROR mismatched type
+    //~| NOTE expected due to this
+    //~| NOTE `NotClone` does not implement `Clone`, so `&NotClone` was cloned instead
+    //~| NOTE expected `NotClone`, found `&NotClone`
+    nc
+}
+
+fn clone_thing3(nc: &NotClone) -> NotClone {
+    //~^ NOTE expected `NotClone` because of return type
+    let nc = nc.clone();
+    //~^ NOTE `NotClone` does not implement `Clone`, so `&NotClone` was cloned instead
+    nc
+    //~^ ERROR mismatched type
+    //~| NOTE expected `NotClone`, found `&NotClone`
+}
\ No newline at end of file
diff --git a/tests/ui/typeck/explain_clone_autoref.stderr b/tests/ui/typeck/explain_clone_autoref.stderr
index 38cb7fe551841..22b5c27134c8c 100644
--- a/tests/ui/typeck/explain_clone_autoref.stderr
+++ b/tests/ui/typeck/explain_clone_autoref.stderr
@@ -18,6 +18,45 @@ LL + #[derive(Clone)]
 LL | struct NotClone;
    |
 
-error: aborting due to previous error
+error[E0308]: mismatched types
+  --> $DIR/explain_clone_autoref.rs:16:24
+   |
+LL |     let nc: NotClone = nc.clone();
+   |             --------   ^^^^^^^^^^ expected `NotClone`, found `&NotClone`
+   |             |
+   |             expected due to this
+   |
+note: `NotClone` does not implement `Clone`, so `&NotClone` was cloned instead
+  --> $DIR/explain_clone_autoref.rs:16:24
+   |
+LL |     let nc: NotClone = nc.clone();
+   |                        ^^
+help: consider annotating `NotClone` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct NotClone;
+   |
+
+error[E0308]: mismatched types
+  --> $DIR/explain_clone_autoref.rs:28:5
+   |
+LL | fn clone_thing3(nc: &NotClone) -> NotClone {
+   |                                   -------- expected `NotClone` because of return type
+...
+LL |     nc
+   |     ^^ expected `NotClone`, found `&NotClone`
+   |
+note: `NotClone` does not implement `Clone`, so `&NotClone` was cloned instead
+  --> $DIR/explain_clone_autoref.rs:26:14
+   |
+LL |     let nc = nc.clone();
+   |              ^^
+help: consider annotating `NotClone` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct NotClone;
+   |
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.