1 //! Lint on use of `size_of` or `size_of_val` of T in an expression
2 //! expecting a count of T
4 use clippy_utils::diagnostics::span_lint_and_help;
5 use clippy_utils::{match_def_path, paths};
6 use if_chain::if_chain;
7 use rustc_hir::BinOpKind;
8 use rustc_hir::{Expr, ExprKind};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_middle::ty::{self, Ty, TyS, TypeAndMut};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 declare_clippy_lint! {
14 /// **What it does:** Detects expressions where
15 /// `size_of::<T>` or `size_of_val::<T>` is used as a
16 /// count of elements of type `T`
18 /// **Why is this bad?** These functions expect a count
19 /// of `T` and not a number of bytes
21 /// **Known problems:** None.
25 /// # use std::ptr::copy_nonoverlapping;
26 /// # use std::mem::size_of;
27 /// const SIZE: usize = 128;
28 /// let x = [2u8; SIZE];
29 /// let mut y = [2u8; SIZE];
30 /// unsafe { copy_nonoverlapping(x.as_ptr(), y.as_mut_ptr(), size_of::<u8>() * SIZE) };
32 pub SIZE_OF_IN_ELEMENT_COUNT,
34 "using `size_of::<T>` or `size_of_val::<T>` where a count of elements of `T` is expected"
37 declare_lint_pass!(SizeOfInElementCount => [SIZE_OF_IN_ELEMENT_COUNT]);
39 fn get_size_of_ty(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, inverted: bool) -> Option<Ty<'tcx>> {
41 ExprKind::Call(count_func, _func_args) => {
44 if let ExprKind::Path(ref count_func_qpath) = count_func.kind;
45 if let Some(def_id) = cx.qpath_res(count_func_qpath, count_func.hir_id).opt_def_id();
46 if match_def_path(cx, def_id, &paths::MEM_SIZE_OF)
47 || match_def_path(cx, def_id, &paths::MEM_SIZE_OF_VAL);
49 cx.typeck_results().node_substs(count_func.hir_id).types().next()
55 ExprKind::Binary(op, left, right) if BinOpKind::Mul == op.node => {
56 get_size_of_ty(cx, left, inverted).or_else(|| get_size_of_ty(cx, right, inverted))
58 ExprKind::Binary(op, left, right) if BinOpKind::Div == op.node => {
59 get_size_of_ty(cx, left, inverted).or_else(|| get_size_of_ty(cx, right, !inverted))
61 ExprKind::Cast(expr, _) => get_size_of_ty(cx, expr, inverted),
66 fn get_pointee_ty_and_count_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<(Ty<'tcx>, &'tcx Expr<'tcx>)> {
67 const FUNCTIONS: [&[&str]; 8] = [
68 &paths::PTR_COPY_NONOVERLAPPING,
71 &paths::PTR_SWAP_NONOVERLAPPING,
72 &paths::PTR_SLICE_FROM_RAW_PARTS,
73 &paths::PTR_SLICE_FROM_RAW_PARTS_MUT,
74 &paths::SLICE_FROM_RAW_PARTS,
75 &paths::SLICE_FROM_RAW_PARTS_MUT,
77 const METHODS: [&str; 11] = [
81 "copy_to_nonoverlapping",
82 "copy_from_nonoverlapping",
92 // Find calls to ptr::{copy, copy_nonoverlapping}
93 // and ptr::{swap_nonoverlapping, write_bytes},
94 if let ExprKind::Call(func, [.., count]) = expr.kind;
95 if let ExprKind::Path(ref func_qpath) = func.kind;
96 if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
97 if FUNCTIONS.iter().any(|func_path| match_def_path(cx, def_id, func_path));
99 // Get the pointee type
100 if let Some(pointee_ty) = cx.typeck_results().node_substs(func.hir_id).types().next();
102 return Some((pointee_ty, count));
106 // Find calls to copy_{from,to}{,_nonoverlapping} and write_bytes methods
107 if let ExprKind::MethodCall(method_path, _, [ptr_self, .., count], _) = expr.kind;
108 let method_ident = method_path.ident.as_str();
109 if METHODS.iter().any(|m| *m == &*method_ident);
111 // Get the pointee type
112 if let ty::RawPtr(TypeAndMut { ty: pointee_ty, .. }) =
113 cx.typeck_results().expr_ty(ptr_self).kind();
115 return Some((pointee_ty, count));
121 impl<'tcx> LateLintPass<'tcx> for SizeOfInElementCount {
122 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
123 const HELP_MSG: &str = "use a count of elements instead of a count of bytes\
124 , it already gets multiplied by the size of the type";
126 const LINT_MSG: &str = "found a count of bytes \
127 instead of a count of elements of `T`";
130 // Find calls to functions with an element count parameter and get
131 // the pointee type and count parameter expression
132 if let Some((pointee_ty, count_expr)) = get_pointee_ty_and_count_expr(cx, expr);
134 // Find a size_of call in the count parameter expression and
135 // check that it's the same type
136 if let Some(ty_used_for_size_of) = get_size_of_ty(cx, count_expr, false);
137 if TyS::same_type(pointee_ty, ty_used_for_size_of);
141 SIZE_OF_IN_ELEMENT_COUNT,