Add usize cast to clippy::manual_bits suggestion

clippy_lints/src/manual_bits.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::source::snippet_opt;
-use clippy_utils::{meets_msrv, msrvs};
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::{get_parent_expr, meets_msrv, msrvs};
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind, GenericArg, QPath};
@@ -59,16 +59,19 @@ impl<'tcx> LateLintPass<'tcx> for ManualBits {
             if matches!(resolved_ty.kind(), ty::Int(_) | ty::Uint(_));
             if let ExprKind::Lit(lit) = &other_expr.kind;
             if let LitKind::Int(8, _) = lit.node;
-
             then {
+                let mut app = Applicability::MachineApplicable;
+                let ty_snip = snippet_with_applicability(cx, real_ty.span, "..", &mut app);
+                let sugg = create_sugg(cx, expr, format!("{ty_snip}::BITS"));
+
                 span_lint_and_sugg(
                     cx,
                     MANUAL_BITS,
                     expr.span,
                     "usage of `mem::size_of::<T>()` to obtain the size of `T` in bits",
                     "consider using",
-                    format!("{}::BITS", snippet_opt(cx, real_ty.span).unwrap()),
-                    Applicability::MachineApplicable,
+                    sugg,
+                    app,
                 );
             }
         }
@@ -108,3 +111,36 @@ fn get_size_of_ty<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<
         }
     }
 }
+
+fn create_sugg(cx: &LateContext<'_>, expr: &Expr<'_>, base_sugg: String) -> String {
+    if let Some(parent_expr) = get_parent_expr(cx, expr) {
+        if is_ty_conversion(parent_expr) {
+            return base_sugg;
+        }
+
+        // These expressions have precedence over casts, the suggestion therefore
+        // needs to be wrapped into parentheses
+        match parent_expr.kind {
+            ExprKind::Unary(..) | ExprKind::AddrOf(..) | ExprKind::MethodCall(..) => {
+                return format!("({base_sugg} as usize)");
+            },
+            _ => {},
+        }
+    }
+
+    format!("{base_sugg} as usize")
+}
+
+fn is_ty_conversion(expr: &Expr<'_>) -> bool {
+    if let ExprKind::Cast(..) = expr.kind {
+        true
+    } else if let ExprKind::MethodCall(path, [_], _) = expr.kind
+        && path.ident.name == rustc_span::sym::try_into
+    {
+        // This is only called for `usize` which implements `TryInto`. Therefore,
+        // we don't have to check here if `self` implements the `TryInto` trait.
+        true
+    } else {
+        false
+    }
+}

tests/ui/manual_bits.fixed

@@ -1,38 +1,44 @@
 // run-rustfix
 
 #![warn(clippy::manual_bits)]
-#![allow(clippy::no_effect, path_statements, unused_must_use, clippy::unnecessary_operation)]
+#![allow(
+    clippy::no_effect,
+    clippy::useless_conversion,
+    path_statements,
+    unused_must_use,
+    clippy::unnecessary_operation
+)]
 
 use std::mem::{size_of, size_of_val};
 
 fn main() {
-    i8::BITS;
-    i16::BITS;
-    i32::BITS;
-    i64::BITS;
-    i128::BITS;
-    isize::BITS;
-
-    u8::BITS;
-    u16::BITS;
-    u32::BITS;
-    u64::BITS;
-    u128::BITS;
-    usize::BITS;
-
-    i8::BITS;
-    i16::BITS;
-    i32::BITS;
-    i64::BITS;
-    i128::BITS;
-    isize::BITS;
-
-    u8::BITS;
-    u16::BITS;
-    u32::BITS;
-    u64::BITS;
-    u128::BITS;
-    usize::BITS;
+    i8::BITS as usize;
+    i16::BITS as usize;
+    i32::BITS as usize;
+    i64::BITS as usize;
+    i128::BITS as usize;
+    isize::BITS as usize;
+
+    u8::BITS as usize;
+    u16::BITS as usize;
+    u32::BITS as usize;
+    u64::BITS as usize;
+    u128::BITS as usize;
+    usize::BITS as usize;
+
+    i8::BITS as usize;
+    i16::BITS as usize;
+    i32::BITS as usize;
+    i64::BITS as usize;
+    i128::BITS as usize;
+    isize::BITS as usize;
+
+    u8::BITS as usize;
+    u16::BITS as usize;
+    u32::BITS as usize;
+    u64::BITS as usize;
+    u128::BITS as usize;
+    usize::BITS as usize;
 
     size_of::<usize>() * 4;
     4 * size_of::<usize>();
@@ -42,7 +48,12 @@ fn main() {
     size_of_val(&0u32) * 8;
 
     type Word = u32;
-    Word::BITS;
+    Word::BITS as usize;
     type Bool = bool;
     size_of::<Bool>() * 8;
+
+    let _: u32 = u128::BITS as u32;
+    let _: u32 = u128::BITS.try_into().unwrap();
+    let _ = (u128::BITS as usize).pow(5);
+    let _ = &(u128::BITS as usize);
 }

tests/ui/manual_bits.rs

@@ -1,7 +1,13 @@
 // run-rustfix
 
 #![warn(clippy::manual_bits)]
-#![allow(clippy::no_effect, path_statements, unused_must_use, clippy::unnecessary_operation)]
+#![allow(
+    clippy::no_effect,
+    clippy::useless_conversion,
+    path_statements,
+    unused_must_use,
+    clippy::unnecessary_operation
+)]
 
 use std::mem::{size_of, size_of_val};
 
@@ -45,4 +51,9 @@ fn main() {
     size_of::<Word>() * 8;
     type Bool = bool;
     size_of::<Bool>() * 8;
+
+    let _: u32 = (size_of::<u128>() * 8) as u32;
+    let _: u32 = (size_of::<u128>() * 8).try_into().unwrap();
+    let _ = (size_of::<u128>() * 8).pow(5);
+    let _ = &(size_of::<u128>() * 8);
 }