sugg on expr 1

Author: ada4a

clippy_lints/src/mut_mut.rs

@@ -1,5 +1,7 @@
-use clippy_utils::diagnostics::{span_lint, span_lint_hir};
+use clippy_utils::diagnostics::{span_lint, span_lint_hir, span_lint_hir_and_then};
 use clippy_utils::higher;
+use clippy_utils::sugg::Sugg;
+use rustc_errors::Applicability;
 use rustc_hir::{self as hir, AmbigArg, intravisit};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty;
@@ -80,12 +82,17 @@ impl<'tcx> intravisit::Visitor<'tcx> for MutVisitor<'_, 'tcx> {
             } else if let ty::Ref(_, ty, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind()
                 && ty.peel_refs().is_sized(self.cx.tcx, self.cx.typing_env())
             {
-                span_lint_hir(
+                let mut applicability = Applicability::MaybeIncorrect;
+                let sugg = Sugg::hir_with_applicability(self.cx, e, "..", &mut applicability).mut_addr_deref();
+                span_lint_hir_and_then(
                     self.cx,
                     MUT_MUT,
                     expr.hir_id,
                     expr.span,
-                    "this expression mutably borrows a mutable reference. Consider reborrowing",
+                    "this expression mutably borrows a mutable reference",
+                    |diag| {
+                        diag.span_suggestion(expr.span, "reborrow instead", sugg, applicability);
+                    },
                 );
             }
         }

tests/ui/mut_mut.fixed

@@ -0,0 +1,94 @@
+//@aux-build:proc_macros.rs
+
+#![warn(clippy::mut_mut)]
+#![allow(unused)]
+#![allow(
+    clippy::no_effect,
+    clippy::uninlined_format_args,
+    clippy::unnecessary_operation,
+    clippy::needless_pass_by_ref_mut
+)]
+
+extern crate proc_macros;
+use proc_macros::{external, inline_macros};
+
+fn fun(x: &mut &mut u32) {
+    //~^ mut_mut
+}
+
+fn less_fun(x: *mut *mut u32) {
+    let y = x;
+}
+
+macro_rules! mut_ptr {
+    ($p:expr) => {
+        &mut $p
+    };
+}
+
+#[allow(unused_mut, unused_variables)]
+#[inline_macros]
+fn main() {
+    let mut x = &mut &mut 1u32;
+    //~^ mut_mut
+    {
+        let mut y = &mut *x;
+        //~^ mut_mut
+    }
+
+    {
+        let y: &mut &mut u32 = &mut &mut 2;
+        //~^ mut_mut
+        //~| mut_mut
+    }
+
+    {
+        let y: &mut &mut &mut u32 = &mut &mut &mut 2;
+        //~^ mut_mut
+        //~| mut_mut
+        //~| mut_mut
+    }
+
+    let mut z = inline!(&mut $(&mut 3u32));
+    //~^ mut_mut
+}
+
+fn issue939() {
+    let array = [5, 6, 7, 8, 9];
+    let mut args = array.iter().skip(2);
+    for &arg in &mut args {
+        println!("{}", arg);
+    }
+
+    let args = &mut args;
+    for arg in args {
+        println!(":{}", arg);
+    }
+}
+
+fn issue6922() {
+    // do not lint from an external macro
+    external!(let mut_mut_ty: &mut &mut u32 = &mut &mut 1u32;);
+}
+
+mod issue9035 {
+    use std::fmt::Display;
+
+    struct Foo<'a> {
+        inner: &'a mut dyn Display,
+    }
+
+    impl Foo<'_> {
+        fn foo(&mut self) {
+            let hlp = &mut self.inner;
+            bar(hlp);
+        }
+    }
+
+    fn bar(_: &mut impl Display) {}
+}
+
+fn allow_works() {
+    #[allow(clippy::mut_mut)]
+    let _ = &mut &mut 1;
+}

tests/ui/mut_mut.stderr

@@ -21,11 +21,11 @@ LL |     let mut z = inline!(&mut $(&mut 3u32));
    |
    = note: this error originates in the macro `__inline_mac_fn_main` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: this expression mutably borrows a mutable reference. Consider reborrowing
+error: this expression mutably borrows a mutable reference
   --> tests/ui/mut_mut.rs:35:21
    |
 LL |         let mut y = &mut x;
-   |                     ^^^^^^
+   |                     ^^^^^^ help: reborrow instead: `&mut *x`
 
 error: generally you want to avoid `&mut &mut _` if possible
   --> tests/ui/mut_mut.rs:40:32

tests/ui/mut_mut_unfixable.stderr

@@ -13,11 +13,11 @@ error: generally you want to avoid `&mut &mut _` if possible
 LL |     let mut x = &mut &mut 1u32;
    |                 ^^^^^^^^^^^^^^
 
-error: this expression mutably borrows a mutable reference. Consider reborrowing
+error: this expression mutably borrows a mutable reference
   --> tests/ui/mut_mut_unfixable.rs:18:21
    |
 LL |         let mut y = &mut x;
-   |                     ^^^^^^
+   |                     ^^^^^^ help: reborrow instead: `&mut *x`
 
 error: generally you want to avoid `&mut &mut _` if possible
   --> tests/ui/mut_mut_unfixable.rs:24:17