fix(unnecessary_mut_passed): retain parens around the arguments (#15731)

Fixes #15722

changelog: [`unnecessary_mut_passed`]: retain parens around the
arguments

Author: Alexendoo

clippy_lints/src/declared_lints.rs

@@ -533,7 +533,6 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::multiple_unsafe_ops_per_block::MULTIPLE_UNSAFE_OPS_PER_BLOCK_INFO,
     crate::mut_key::MUTABLE_KEY_TYPE_INFO,
     crate::mut_mut::MUT_MUT_INFO,
-    crate::mut_reference::UNNECESSARY_MUT_PASSED_INFO,
     crate::mutable_debug_assertion::DEBUG_ASSERT_WITH_MUT_CALL_INFO,
     crate::mutex_atomic::MUTEX_ATOMIC_INFO,
     crate::mutex_atomic::MUTEX_INTEGER_INFO,
@@ -752,6 +751,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::unnecessary_box_returns::UNNECESSARY_BOX_RETURNS_INFO,
     crate::unnecessary_literal_bound::UNNECESSARY_LITERAL_BOUND_INFO,
     crate::unnecessary_map_on_constructor::UNNECESSARY_MAP_ON_CONSTRUCTOR_INFO,
+    crate::unnecessary_mut_passed::UNNECESSARY_MUT_PASSED_INFO,
     crate::unnecessary_owned_empty_strings::UNNECESSARY_OWNED_EMPTY_STRINGS_INFO,
     crate::unnecessary_self_imports::UNNECESSARY_SELF_IMPORTS_INFO,
     crate::unnecessary_semicolon::UNNECESSARY_SEMICOLON_INFO,

clippy_lints/src/lib.rs

@@ -252,7 +252,6 @@ mod multiple_bound_locations;
 mod multiple_unsafe_ops_per_block;
 mod mut_key;
 mod mut_mut;
-mod mut_reference;
 mod mutable_debug_assertion;
 mod mutex_atomic;
 mod needless_arbitrary_self_type;
@@ -375,6 +374,7 @@ mod unit_types;
 mod unnecessary_box_returns;
 mod unnecessary_literal_bound;
 mod unnecessary_map_on_constructor;
+mod unnecessary_mut_passed;
 mod unnecessary_owned_empty_strings;
 mod unnecessary_self_imports;
 mod unnecessary_semicolon;
@@ -483,7 +483,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
     store.register_late_pass(|_| Box::new(misc::LintPass));
     store.register_late_pass(|_| Box::new(eta_reduction::EtaReduction));
     store.register_late_pass(|_| Box::new(mut_mut::MutMut));
-    store.register_late_pass(|_| Box::new(mut_reference::UnnecessaryMutPassed));
+    store.register_late_pass(|_| Box::new(unnecessary_mut_passed::UnnecessaryMutPassed));
     store.register_late_pass(|_| Box::<significant_drop_tightening::SignificantDropTightening<'_>>::default());
     store.register_late_pass(|_| Box::new(len_zero::LenZero));
     store.register_late_pass(move |_| Box::new(attrs::Attributes::new(conf)));

clippy_lints/src/mut_reference.rs renamed to clippy_lints/src/unnecessary_mut_passed.rs

@@ -1,5 +1,5 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::sugg::Sugg;
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::source::SpanRangeExt;
 use rustc_errors::Applicability;
 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability};
 use rustc_lint::{LateContext, LateLintPass};
@@ -87,16 +87,33 @@ fn check_arguments<'tcx>(
             if let ty::Ref(_, _, Mutability::Not) | ty::RawPtr(_, Mutability::Not) = parameter.kind()
                 && let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, arg) = argument.kind
             {
-                let mut applicability = Applicability::MachineApplicable;
-                let sugg = Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).addr();
-                span_lint_and_sugg(
+                let applicability = Applicability::MachineApplicable;
+
+                let span_to_remove = {
+                    let span_until_arg = argument.span.until(arg.span);
+                    if let Some(Some(ref_pos)) = span_until_arg.with_source_text(cx, |src| {
+                        src
+                            // we don't use `strip_prefix` here, because `argument` might be enclosed in parens, in
+                            // which case `&` is no longer the prefix
+                            .find('&')
+                            // just a sanity check, in case some proc-macro messes up the spans
+                            .filter(|ref_pos| src[*ref_pos..].contains("mut"))
+                    }) && let Ok(lo) = u32::try_from(ref_pos + '&'.len_utf8())
+                    {
+                        span_until_arg.split_at(lo).1
+                    } else {
+                        return;
+                    }
+                };
+
+                span_lint_and_then(
                     cx,
                     UNNECESSARY_MUT_PASSED,
                     argument.span,
                     format!("the {fn_kind} `{name}` doesn't need a mutable reference"),
-                    "remove this `mut`",
-                    sugg.to_string(),
-                    applicability,
+                    |diag| {
+                        diag.span_suggestion_verbose(span_to_remove, "remove this `mut`", String::new(), applicability);
+                    },
                 );
             }
         }

tests/ui/mut_reference.stderr

@@ -40,6 +40,7 @@ mod issue11268 {
 struct MyStruct;
 
 impl MyStruct {
+    fn takes_nothing(&self) {}
     fn takes_ref(&self, a: &i32) {}
     fn takes_refmut(&self, a: &mut i32) {}
     fn takes_ref_ref(&self, a: &&i32) {}
@@ -168,3 +169,22 @@ fn raw_ptrs(my_struct: MyStruct) {
     my_struct.takes_raw_mut(&raw mut n);
     my_struct.takes_raw_const(a);
 }
+
+#[expect(clippy::needless_borrow)]
+fn issue15722(mut my_struct: MyStruct) {
+    (&my_struct).takes_nothing();
+    //~^ unnecessary_mut_passed
+    (&my_struct).takes_nothing();
+
+    // Only put parens around the argument that used to have it
+    (&my_struct).takes_ref(&42);
+    //~^ unnecessary_mut_passed
+    //~| unnecessary_mut_passed
+    #[expect(clippy::double_parens)]
+    (&my_struct).takes_ref((&42));
+    //~^ unnecessary_mut_passed
+    //~| unnecessary_mut_passed
+    #[expect(clippy::double_parens)]
+    my_struct.takes_ref((&42));
+    //~^ unnecessary_mut_passed
+}

tests/ui/mut_reference.fixed renamed to tests/ui/unnecessary_mut_passed.fixed

@@ -40,6 +40,7 @@ mod issue11268 {
 struct MyStruct;
 
 impl MyStruct {
+    fn takes_nothing(&self) {}
     fn takes_ref(&self, a: &i32) {}
     fn takes_refmut(&self, a: &mut i32) {}
     fn takes_ref_ref(&self, a: &&i32) {}
@@ -168,3 +169,22 @@ fn raw_ptrs(my_struct: MyStruct) {
     my_struct.takes_raw_mut(&raw mut n);
     my_struct.takes_raw_const(a);
 }
+
+#[expect(clippy::needless_borrow)]
+fn issue15722(mut my_struct: MyStruct) {
+    (&mut my_struct).takes_nothing();
+    //~^ unnecessary_mut_passed
+    (&my_struct).takes_nothing();
+
+    // Only put parens around the argument that used to have it
+    (&mut my_struct).takes_ref(&mut 42);
+    //~^ unnecessary_mut_passed
+    //~| unnecessary_mut_passed
+    #[expect(clippy::double_parens)]
+    (&mut my_struct).takes_ref((&mut 42));
+    //~^ unnecessary_mut_passed
+    //~| unnecessary_mut_passed
+    #[expect(clippy::double_parens)]
+    my_struct.takes_ref((&mut 42));
+    //~^ unnecessary_mut_passed
+}