Rollup merge of rust-lang#121471 - estebank:lint-clone, r=TaKO8Ki

When encountering `<&T as Clone>::clone(x)` because `T: Clone`, suggest `#[derive(Clone)]`

CC rust-lang#40699.

```
warning: call to `.clone()` on a reference in this situation does nothing
  --> $DIR/noop-method-call.rs:23:71
   |
LL |     let non_clone_type_ref_clone: &PlainType<u32> = non_clone_type_ref.clone();
   |                                                                       ^^^^^^^^
   |
   = note: the type `PlainType<u32>` does not implement `Clone`, so calling `clone` on `&PlainType<u32>` copies the reference, which does not do anything and can be removed
help: remove this redundant call
   |
LL -     let non_clone_type_ref_clone: &PlainType<u32> = non_clone_type_ref.clone();
LL +     let non_clone_type_ref_clone: &PlainType<u32> = non_clone_type_ref;
   |
help: if you meant to clone `PlainType<u32>`, implement `Clone` for it
   |
LL + #[derive(Clone)]
LL | struct PlainType<T>(T);
   |
```

compiler/rustc_lint/messages.ftl

@@ -429,6 +429,7 @@ lint_non_upper_case_global = {$sort} `{$name}` should have an upper case name
 lint_noop_method_call = call to `.{$method}()` on a reference in this situation does nothing
     .suggestion = remove this redundant call
     .note = the type `{$orig_ty}` does not implement `{$trait_}`, so calling `{$method}` on `&{$orig_ty}` copies the reference, which does not do anything and can be removed
+    .derive_suggestion = if you meant to clone `{$orig_ty}`, implement `Clone` for it
 
 lint_only_cast_u8_to_char = only `u8` can be cast into `char`
     .suggestion = use a `char` literal instead

compiler/rustc_lint/src/lints.rs

@@ -1314,6 +1314,12 @@ pub struct NoopMethodCallDiag<'a> {
     pub trait_: Symbol,
     #[suggestion(code = "", applicability = "machine-applicable")]
     pub label: Span,
+    #[suggestion(
+        lint_derive_suggestion,
+        code = "#[derive(Clone)]\n",
+        applicability = "maybe-incorrect"
+    )]
+    pub suggest_derive: Option<Span>,
 }
 
 #[derive(LintDiagnostic)]

compiler/rustc_lint/src/noop_method_call.rs

@@ -121,10 +121,20 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
         let orig_ty = expr_ty.peel_refs();
 
         if receiver_ty == expr_ty {
+            let suggest_derive = match orig_ty.kind() {
+                ty::Adt(def, _) => Some(cx.tcx.def_span(def.did()).shrink_to_lo()),
+                _ => None,
+            };
             cx.emit_span_lint(
                 NOOP_METHOD_CALL,
                 span,
-                NoopMethodCallDiag { method: call.ident.name, orig_ty, trait_, label: span },
+                NoopMethodCallDiag {
+                    method: call.ident.name,
+                    orig_ty,
+                    trait_,
+                    label: span,
+                    suggest_derive,
+                },
             );
         } else {
             match name {

tests/ui/lint/noop-method-call.rs

@@ -1,5 +1,4 @@
 //@ check-pass
-//@ run-rustfix
 
 #![feature(rustc_attrs)]
 #![allow(unused)]

tests/ui/lint/noop-method-call.stderr

@@ -1,5 +1,5 @@
 warning: call to `.clone()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:16:25
+  --> $DIR/noop-method-call.rs:15:25
    |
 LL |     let _ = &mut encoded.clone();
    |                         ^^^^^^^^ help: remove this redundant call
@@ -8,52 +8,102 @@ LL |     let _ = &mut encoded.clone();
    = note: `#[warn(noop_method_call)]` on by default
 
 warning: call to `.clone()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:18:21
+  --> $DIR/noop-method-call.rs:17:21
    |
 LL |     let _ = &encoded.clone();
    |                     ^^^^^^^^ help: remove this redundant call
    |
    = note: the type `[u8]` does not implement `Clone`, so calling `clone` on `&[u8]` copies the reference, which does not do anything and can be removed
 
 warning: call to `.clone()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:24:71
+  --> $DIR/noop-method-call.rs:23:71
    |
 LL |     let non_clone_type_ref_clone: &PlainType<u32> = non_clone_type_ref.clone();
-   |                                                                       ^^^^^^^^ help: remove this redundant call
+   |                                                                       ^^^^^^^^
    |
    = note: the type `PlainType<u32>` does not implement `Clone`, so calling `clone` on `&PlainType<u32>` copies the reference, which does not do anything and can be removed
+help: remove this redundant call
+   |
+LL -     let non_clone_type_ref_clone: &PlainType<u32> = non_clone_type_ref.clone();
+LL +     let non_clone_type_ref_clone: &PlainType<u32> = non_clone_type_ref;
+   |
+help: if you meant to clone `PlainType<u32>`, implement `Clone` for it
+   |
+LL + #[derive(Clone)]
+LL | struct PlainType<T>(T);
+   |
 
 warning: call to `.deref()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:32:63
+  --> $DIR/noop-method-call.rs:31:63
    |
 LL |     let non_deref_type_deref: &PlainType<u32> = non_deref_type.deref();
-   |                                                               ^^^^^^^^ help: remove this redundant call
+   |                                                               ^^^^^^^^
    |
    = note: the type `PlainType<u32>` does not implement `Deref`, so calling `deref` on `&PlainType<u32>` copies the reference, which does not do anything and can be removed
+help: remove this redundant call
+   |
+LL -     let non_deref_type_deref: &PlainType<u32> = non_deref_type.deref();
+LL +     let non_deref_type_deref: &PlainType<u32> = non_deref_type;
+   |
+help: if you meant to clone `PlainType<u32>`, implement `Clone` for it
+   |
+LL + #[derive(Clone)]
+LL | struct PlainType<T>(T);
+   |
 
 warning: call to `.borrow()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:36:66
+  --> $DIR/noop-method-call.rs:35:66
    |
 LL |     let non_borrow_type_borrow: &PlainType<u32> = non_borrow_type.borrow();
-   |                                                                  ^^^^^^^^^ help: remove this redundant call
+   |                                                                  ^^^^^^^^^
    |
    = note: the type `PlainType<u32>` does not implement `Borrow`, so calling `borrow` on `&PlainType<u32>` copies the reference, which does not do anything and can be removed
+help: remove this redundant call
+   |
+LL -     let non_borrow_type_borrow: &PlainType<u32> = non_borrow_type.borrow();
+LL +     let non_borrow_type_borrow: &PlainType<u32> = non_borrow_type;
+   |
+help: if you meant to clone `PlainType<u32>`, implement `Clone` for it
+   |
+LL + #[derive(Clone)]
+LL | struct PlainType<T>(T);
+   |
 
 warning: call to `.clone()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:45:19
+  --> $DIR/noop-method-call.rs:44:19
    |
 LL |     non_clone_type.clone();
-   |                   ^^^^^^^^ help: remove this redundant call
+   |                   ^^^^^^^^
    |
    = note: the type `PlainType<T>` does not implement `Clone`, so calling `clone` on `&PlainType<T>` copies the reference, which does not do anything and can be removed
+help: remove this redundant call
+   |
+LL -     non_clone_type.clone();
+LL +     non_clone_type;
+   |
+help: if you meant to clone `PlainType<T>`, implement `Clone` for it
+   |
+LL + #[derive(Clone)]
+LL | struct PlainType<T>(T);
+   |
 
 warning: call to `.clone()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:50:19
+  --> $DIR/noop-method-call.rs:49:19
    |
 LL |     non_clone_type.clone();
-   |                   ^^^^^^^^ help: remove this redundant call
+   |                   ^^^^^^^^
    |
    = note: the type `PlainType<u32>` does not implement `Clone`, so calling `clone` on `&PlainType<u32>` copies the reference, which does not do anything and can be removed
+help: remove this redundant call
+   |
+LL -     non_clone_type.clone();
+LL +     non_clone_type;
+   |
+help: if you meant to clone `PlainType<u32>`, implement `Clone` for it
+   |
+LL + #[derive(Clone)]
+LL | struct PlainType<T>(T);
+   |
 
 warning: 7 warnings emitted