Tweak output in for loops

Do not suggest `.clone()` as we already suggest borrowing the iterated
value.

Author: estebank

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -7,6 +7,7 @@ use rustc_errors::{
 };
 use rustc_hir as hir;
 use rustc_hir::intravisit::{walk_block, walk_expr, Visitor};
+// use rustc_hir::{AsyncGeneratorKind, GeneratorKind, LoopSource::ForLoop};
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::ObligationCause;
@@ -397,8 +398,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         && let Some(node) = hir.find(hir.local_def_id_to_hir_id(def_id))
                         && let Some(fn_sig) = node.fn_sig()
                         && let Some(ident) = node.ident()
-                        && let Some(pos) = args.iter()
-                            .position(|arg| arg.hir_id == expr.hir_id)
+                        && let Some(pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id)
                         && let Some(arg) = fn_sig.decl.inputs.get(pos + offset)
                     {
                         let mut span: MultiSpan = arg.span.into();
@@ -425,7 +425,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     }
                     let place = &self.move_data.move_paths[mpi].place;
                     let ty = place.ty(self.body, self.infcx.tcx).ty;
-                    self.suggest_cloning(err, ty, move_span);
+                    if let hir::Node::Expr(parent_expr) = parent
+                        && let hir::ExprKind::Call(call_expr, _) = parent_expr.kind
+                        && let hir::ExprKind::Path(
+                            hir::QPath::LangItem(hir::LangItem::IntoIterIntoIter, _, _)
+                        ) = call_expr.kind
+                    {
+                        // Do not suggest `.clone()` in a `for` loop, we already suggest borrowing.
+                    } else {
+                        self.suggest_cloning(err, ty, move_span);
+                    }
                 }
             }
             if let Some(pat) = finder.pat && !seen_spans.contains(&pat.span) {

src/test/ui/issues/issue-61108.stderr

@@ -14,10 +14,6 @@ note: this function takes ownership of the receiver `self`, which moves `bad_let
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |                  ^^^^
-help: consider cloning the value if the performance cost is acceptable
-   |
-LL |     for l in bad_letters.clone() {
-   |                         ++++++++
 help: consider iterating over a slice of the `Vec<char>`'s content to avoid moving into the `for` loop
    |
 LL |     for l in &bad_letters {

src/test/ui/issues/issue-64559.stderr

@@ -15,10 +15,6 @@ note: this function takes ownership of the receiver `self`, which moves `orig`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |                  ^^^^
-help: consider cloning the value if the performance cost is acceptable
-   |
-LL |     for _val in orig.clone() {}
-   |                     ++++++++
 help: consider iterating over a slice of the `Vec<bool>`'s content to avoid moving into the `for` loop
    |
 LL |     for _val in &orig {}

src/test/ui/moves/move-fn-self-receiver.stderr

@@ -127,10 +127,6 @@ LL |     for _val in implicit_into_iter {}
 LL |     implicit_into_iter;
    |     ^^^^^^^^^^^^^^^^^^ value used here after move
    |
-help: consider cloning the value if the performance cost is acceptable
-   |
-LL |     for _val in implicit_into_iter.clone() {}
-   |                                   ++++++++
 help: consider iterating over a slice of the `Vec<bool>`'s content to avoid moving into the `for` loop
    |
 LL |     for _val in &implicit_into_iter {}

src/test/ui/suggestions/borrow-for-loop-head.stderr

@@ -21,10 +21,6 @@ note: this function takes ownership of the receiver `self`, which moves `a`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |                  ^^^^
-help: consider cloning the value if the performance cost is acceptable
-   |
-LL |         for j in a.clone() {
-   |                   ++++++++
 help: consider iterating over a slice of the `Vec<i32>`'s content to avoid moving into the `for` loop
    |
 LL |         for j in &a {