Silence redundant clone suggestion

Author: estebank

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -787,6 +787,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         span: Span,
     ) {
         let tcx = self.infcx.tcx;
+        if let Some(_) = self.clone_on_reference(expr) {
+            // Avoid redundant clone suggestion already suggested in `explain_captures`.
+            // See `tests/ui/moves/needs-clone-through-deref.rs`
+            return;
+        }
         // Try to find predicates on *generic params* that would allow copying `ty`
         let suggestion =
             if let Some(symbol) = tcx.hir().maybe_get_struct_pattern_shorthand_field(expr) {

tests/ui/moves/needs-clone-through-deref.fixed

@@ -0,0 +1,18 @@
+//@ run-rustfix
+#![allow(dead_code, noop_method_call)]
+use std::ops::Deref;
+struct S(Vec<usize>);
+impl Deref for S {
+    type Target = Vec<usize>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl S {
+    fn foo(&self) {
+        // `self.clone()` returns `&S`, not `Vec`
+        for _ in <Vec<usize> as Clone>::clone(&self).into_iter() {} //~ ERROR cannot move out of dereference of `S`
+    }
+}
+fn main() {}

tests/ui/moves/needs-clone-through-deref.rs

@@ -1,3 +1,4 @@
+//@ run-rustfix
 #![allow(dead_code, noop_method_call)]
 use std::ops::Deref;
 struct S(Vec<usize>);

tests/ui/moves/needs-clone-through-deref.stderr

@@ -1,5 +1,5 @@
 error[E0507]: cannot move out of dereference of `S`
-  --> $DIR/needs-clone-through-deref.rs:14:18
+  --> $DIR/needs-clone-through-deref.rs:15:18
    |
 LL |         for _ in self.clone().into_iter() {}
    |                  ^^^^^^^^^^^^ ----------- value moved due to this method call
@@ -12,10 +12,6 @@ help: you can `clone` the value and consume it, but this might not be your desir
    |
 LL |         for _ in <Vec<usize> as Clone>::clone(&self).into_iter() {}
    |                  ++++++++++++++++++++++++++++++    ~
-help: consider cloning the value if the performance cost is acceptable
-   |
-LL |         for _ in self.clone().clone().into_iter() {}
-   |                              ++++++++
 
 error: aborting due to 1 previous error