Make NEEDLESS_PASS_BY_REF_MUT not emitted if `avoid-breaking-exported…

…-api` option is enabled

clippy_lints/src/lib.rs

@@ -1058,7 +1058,11 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     let stack_size_threshold = conf.stack_size_threshold;
     store.register_late_pass(move |_| Box::new(large_stack_frames::LargeStackFrames::new(stack_size_threshold)));
     store.register_late_pass(|_| Box::new(single_range_in_vec_init::SingleRangeInVecInit));
-    store.register_late_pass(|_| Box::new(needless_pass_by_ref_mut::NeedlessPassByRefMut));
+    store.register_late_pass(move |_| {
+        Box::new(needless_pass_by_ref_mut::NeedlessPassByRefMut::new(
+            avoid_breaking_exported_api,
+        ))
+    });
     store.register_late_pass(|_| Box::new(incorrect_impls::IncorrectImpls));
     store.register_late_pass(move |_| {
         Box::new(single_call_fn::SingleCallFn {

clippy_lints/src/needless_pass_by_ref_mut.rs

@@ -12,7 +12,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::mir::FakeReadCause;
 use rustc_middle::ty::{self, Ty};
-use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::symbol::kw;
 use rustc_span::Span;
@@ -43,7 +43,21 @@ declare_clippy_lint! {
     suspicious,
     "using a `&mut` argument when it's not mutated"
 }
-declare_lint_pass!(NeedlessPassByRefMut => [NEEDLESS_PASS_BY_REF_MUT]);
+
+#[derive(Copy, Clone)]
+pub struct NeedlessPassByRefMut {
+    avoid_breaking_exported_api: bool,
+}
+
+impl NeedlessPassByRefMut {
+    pub fn new(avoid_breaking_exported_api: bool) -> Self {
+        Self {
+            avoid_breaking_exported_api,
+        }
+    }
+}
+
+impl_lint_pass!(NeedlessPassByRefMut => [NEEDLESS_PASS_BY_REF_MUT]);
 
 fn should_skip<'tcx>(
     cx: &LateContext<'tcx>,
@@ -81,6 +95,10 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessPassByRefMut {
         span: Span,
         fn_def_id: LocalDefId,
     ) {
+        if self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(fn_def_id) {
+            return;
+        }
+
         if span.from_expansion() {
             return;
         }

tests/ui/should_impl_trait/method_list_2.stderr

@@ -39,14 +39,6 @@ LL | |     }
    |
    = help: consider implementing the trait `std::hash::Hash` or choosing a less ambiguous method name
 
-error: this argument is a mutable reference, but not used mutably
-  --> $DIR/method_list_2.rs:38:31
-   |
-LL |     pub fn hash(&self, state: &mut T) {
-   |                               ^^^^^^ help: consider changing to: `&T`
-   |
-   = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
-
 error: method `index` can be confused for the standard trait method `std::ops::Index::index`
   --> $DIR/method_list_2.rs:42:5
    |
@@ -157,5 +149,5 @@ LL | |     }
    |
    = help: consider implementing the trait `std::ops::Sub` or choosing a less ambiguous method name
 
-error: aborting due to 16 previous errors
+error: aborting due to 15 previous errors