overhaul mutex_{atomic,integer} (#15632)

- only lint on definitions of offending mutexes, not all their uses
(fixes rust-lang/rust-clippy#13378)
- give more orderly help messages
- stop linting on `Mutex<*const T>` (see the corresponding commit for
context)
- offer (partial) suggestions

The last change might be deemed a bit too much for the feature freeze,
but it can be easily extracted out into a separate PR.

changelog: [`mutex_atomic`]: only lint the definitions, not uses
changelog: [`mutex_atomic`]: better help messages, and suggestions
changelog: [`mutex_atomic`]: don't lint `Mutex<*const T>`
changelog: [`mutex_integer`]: only lint the definitions, not uses
changelog: [`mutex_integer`]: better help messages, and suggestions

Author: llogiq

clippy_lints/src/mutex_atomic.rs

@@ -1,7 +1,12 @@
-use clippy_utils::diagnostics::span_lint;
+use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::res::MaybeDef;
-use rustc_hir::Expr;
-use rustc_lint::{LateContext, LateLintPass};
+use clippy_utils::source::{IntoSpan, SpanRangeExt};
+use clippy_utils::sugg::Sugg;
+use clippy_utils::ty::ty_from_hir_ty;
+use rustc_errors::{Applicability, Diag};
+use rustc_hir::{self as hir, Expr, ExprKind, Item, ItemKind, LetStmt, QPath};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::mir::Mutability;
 use rustc_middle::ty::{self, IntTy, Ty, UintTy};
 use rustc_session::declare_lint_pass;
 use rustc_span::sym;
@@ -88,24 +93,83 @@ declare_clippy_lint! {
 
 declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]);
 
+// NOTE: we don't use `check_expr` because that would make us lint every _use_ of such mutexes, not
+// just their definitions
 impl<'tcx> LateLintPass<'tcx> for Mutex {
-    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        let ty = cx.typeck_results().expr_ty(expr);
-        if let ty::Adt(_, subst) = ty.kind()
-            && ty.is_diag_item(cx, sym::Mutex)
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
+        if !item.span.from_expansion()
+            && let ItemKind::Static(_, _, ty, body_id) = item.kind
         {
-            let mutex_param = subst.type_at(0);
-            if let Some(atomic_name) = get_atomic_name(mutex_param) {
-                let msg = format!(
-                    "consider using an `{atomic_name}` instead of a `Mutex` here; if you just want the locking \
-                         behavior and not the internal type, consider using `Mutex<()>`"
-                );
-                match *mutex_param.kind() {
-                    ty::Uint(t) if t != UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, msg),
-                    ty::Int(t) if t != IntTy::Isize => span_lint(cx, MUTEX_INTEGER, expr.span, msg),
-                    _ => span_lint(cx, MUTEX_ATOMIC, expr.span, msg),
+            let body = cx.tcx.hir_body(body_id);
+            let mid_ty = ty_from_hir_ty(cx, ty);
+            check_expr(cx, body.value.peel_blocks(), &TypeAscriptionKind::Required(ty), mid_ty);
+        }
+    }
+    fn check_local(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx LetStmt<'_>) {
+        if !stmt.span.from_expansion()
+            && let Some(init) = stmt.init
+        {
+            let mid_ty = cx.typeck_results().expr_ty(init);
+            check_expr(cx, init.peel_blocks(), &TypeAscriptionKind::Optional(stmt.ty), mid_ty);
+        }
+    }
+}
+
+/// Whether the type ascription `: Mutex<X>` (which we'll suggest replacing with `AtomicX`) is
+/// required
+enum TypeAscriptionKind<'tcx> {
+    /// Yes; for us, this is the case for statics
+    Required(&'tcx hir::Ty<'tcx>),
+    /// No; the ascription might've been necessary in an expression like:
+    /// ```ignore
+    /// let mutex: Mutex<u64> = Mutex::new(0);
+    /// ```
+    /// to specify the type of `0`, but since `AtomicX` already refers to a concrete type, we won't
+    /// need this ascription anymore.
+    Optional(Option<&'tcx hir::Ty<'tcx>>),
+}
+
+fn check_expr<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>, ty_ascription: &TypeAscriptionKind<'tcx>, ty: Ty<'tcx>) {
+    if let ty::Adt(_, subst) = ty.kind()
+        && ty.is_diag_item(cx, sym::Mutex)
+        && let mutex_param = subst.type_at(0)
+        && let Some(atomic_name) = get_atomic_name(mutex_param)
+    {
+        let msg = "using a `Mutex` where an atomic would do";
+        let diag = |diag: &mut Diag<'_, _>| {
+            // if `expr = Mutex::new(arg)`, we can try emitting a suggestion
+            if let ExprKind::Call(qpath, [arg]) = expr.kind
+                && let ExprKind::Path(QPath::TypeRelative(_mutex, new)) = qpath.kind
+                && new.ident.name == sym::new
+            {
+                let mut applicability = Applicability::MaybeIncorrect;
+                let arg = Sugg::hir_with_applicability(cx, arg, "_", &mut applicability);
+                let mut suggs = vec![(expr.span, format!("std::sync::atomic::{atomic_name}::new({arg})"))];
+                match ty_ascription {
+                    TypeAscriptionKind::Required(ty_ascription) => {
+                        suggs.push((ty_ascription.span, format!("std::sync::atomic::{atomic_name}")));
+                    },
+                    TypeAscriptionKind::Optional(Some(ty_ascription)) => {
+                        // See https://github.com/rust-lang/rust-clippy/pull/15386 for why this is
+                        // required
+                        let colon_ascription = (cx.sess().source_map())
+                            .span_extend_to_prev_char_before(ty_ascription.span, ':', true)
+                            .with_leading_whitespace(cx)
+                            .into_span();
+                        suggs.push((colon_ascription, String::new()));
+                    },
+                    TypeAscriptionKind::Optional(None) => {}, // nothing to remove/replace
                 }
+                diag.multipart_suggestion("try", suggs, applicability);
+            } else {
+                diag.help(format!("consider using an `{atomic_name}` instead"));
             }
+            diag.help("if you just want the locking behavior and not the internal type, consider using `Mutex<()>`");
+        };
+        match *mutex_param.kind() {
+            ty::Uint(t) if t != UintTy::Usize => span_lint_and_then(cx, MUTEX_INTEGER, expr.span, msg, diag),
+            ty::Int(t) if t != IntTy::Isize => span_lint_and_then(cx, MUTEX_INTEGER, expr.span, msg, diag),
+            _ => span_lint_and_then(cx, MUTEX_ATOMIC, expr.span, msg, diag),
         }
     }
 }
@@ -135,7 +199,8 @@ fn get_atomic_name(ty: Ty<'_>) -> Option<&'static str> {
                 IntTy::I128 => None,
             }
         },
-        ty::RawPtr(_, _) => Some("AtomicPtr"),
+        // `AtomicPtr` only accepts `*mut T`
+        ty::RawPtr(_, Mutability::Mut) => Some("AtomicPtr"),
         _ => None,
     }
 }

tests/ui/mutex_atomic.fixed

@@ -0,0 +1,67 @@
+#![warn(clippy::mutex_integer)]
+#![warn(clippy::mutex_atomic)]
+#![allow(clippy::borrow_as_ptr)]
+
+use std::sync::Mutex;
+
+fn main() {
+    let _ = std::sync::atomic::AtomicBool::new(true);
+    //~^ mutex_atomic
+
+    let _ = std::sync::atomic::AtomicUsize::new(5usize);
+    //~^ mutex_atomic
+
+    let _ = std::sync::atomic::AtomicIsize::new(9isize);
+    //~^ mutex_atomic
+
+    let mut x = 4u32;
+    // `AtomicPtr` only accepts `*mut T`, so this should not lint
+    let _ = Mutex::new(&x as *const u32);
+
+    let _ = std::sync::atomic::AtomicPtr::new(&mut x as *mut u32);
+    //~^ mutex_atomic
+
+    let _ = std::sync::atomic::AtomicU32::new(0u32);
+    //~^ mutex_integer
+
+    let _ = std::sync::atomic::AtomicI32::new(0i32);
+    //~^ mutex_integer
+
+    let _ = Mutex::new(0f32); // there are no float atomics, so this should not lint
+    let _ = std::sync::atomic::AtomicU8::new(0u8);
+    //~^ mutex_integer
+
+    let _ = std::sync::atomic::AtomicI16::new(0i16);
+    //~^ mutex_integer
+
+    let _x = std::sync::atomic::AtomicI8::new(0);
+    //~^ mutex_integer
+
+    const X: i64 = 0;
+    let _ = std::sync::atomic::AtomicI64::new(X);
+    //~^ mutex_integer
+
+    // there are no 128 atomics, so these two should not lint
+    {
+        let _ = Mutex::new(0u128);
+        let _x: Mutex<i128> = Mutex::new(0);
+    }
+}
+
+// don't lint on _use_, only declaration
+fn issue13378() {
+    static MTX: std::sync::atomic::AtomicU32 = std::sync::atomic::AtomicU32::new(0);
+    //~^ mutex_integer
+
+    let mtx = std::sync::atomic::AtomicI32::new(0);
+    //~^ mutex_integer
+    // This will still lint, since we're reassigning the mutex to a variable -- oh well.
+    // But realistically something like this won't really come up.
+    let reassigned = mtx;
+    //~^ mutex_integer
+
+    // don't eat the `)` when removing the type ascription -- see
+    // https://github.com/rust-lang/rust-clippy/issues/15377
+    let (funky_mtx) = std::sync::atomic::AtomicU64::new(0);
+    //~^ mutex_integer
+}

tests/ui/mutex_atomic.rs

@@ -2,47 +2,66 @@
 #![warn(clippy::mutex_atomic)]
 #![allow(clippy::borrow_as_ptr)]
 
+use std::sync::Mutex;
+
 fn main() {
-    use std::sync::Mutex;
-    Mutex::new(true);
+    let _ = Mutex::new(true);
     //~^ mutex_atomic
 
-    Mutex::new(5usize);
+    let _ = Mutex::new(5usize);
     //~^ mutex_atomic
 
-    Mutex::new(9isize);
+    let _ = Mutex::new(9isize);
     //~^ mutex_atomic
 
     let mut x = 4u32;
-    Mutex::new(&x as *const u32);
-    //~^ mutex_atomic
+    // `AtomicPtr` only accepts `*mut T`, so this should not lint
+    let _ = Mutex::new(&x as *const u32);
 
-    Mutex::new(&mut x as *mut u32);
+    let _ = Mutex::new(&mut x as *mut u32);
     //~^ mutex_atomic
 
-    Mutex::new(0u32);
+    let _ = Mutex::new(0u32);
     //~^ mutex_integer
 
-    Mutex::new(0i32);
+    let _ = Mutex::new(0i32);
     //~^ mutex_integer
 
-    Mutex::new(0f32); // there are no float atomics, so this should not lint
-    Mutex::new(0u8);
+    let _ = Mutex::new(0f32); // there are no float atomics, so this should not lint
+    let _ = Mutex::new(0u8);
     //~^ mutex_integer
 
-    Mutex::new(0i16);
+    let _ = Mutex::new(0i16);
     //~^ mutex_integer
 
     let _x: Mutex<i8> = Mutex::new(0);
     //~^ mutex_integer
 
     const X: i64 = 0;
-    Mutex::new(X);
+    let _ = Mutex::new(X);
     //~^ mutex_integer
 
     // there are no 128 atomics, so these two should not lint
     {
-        Mutex::new(0u128);
+        let _ = Mutex::new(0u128);
         let _x: Mutex<i128> = Mutex::new(0);
     }
 }
+
+// don't lint on _use_, only declaration
+fn issue13378() {
+    static MTX: Mutex<u32> = Mutex::new(0);
+    //~^ mutex_integer
+
+    let mtx = Mutex::new(0);
+    //~^ mutex_integer
+    // This will still lint, since we're reassigning the mutex to a variable -- oh well.
+    // But realistically something like this won't really come up.
+    let reassigned = mtx;
+    //~^ mutex_integer
+
+    // don't eat the `)` when removing the type ascription -- see
+    // https://github.com/rust-lang/rust-clippy/issues/15377
+    let (funky_mtx): Mutex<u64> = Mutex::new(0);
+    //~^ mutex_integer
+}