clippy_lints/src/size_of_in_element_count.rs

   1 //! Lint on use of `size_of` or `size_of_val` of T in an expression
   2 //! expecting a count of T
   3
   4 use crate::utils::{match_def_path, paths, span_lint_and_help};
   5 use if_chain::if_chain;
   6 use rustc_hir::BinOpKind;
   7 use rustc_hir::{Expr, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_middle::ty::{self, Ty, TyS, TypeAndMut};
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Detects expressions where
  14     /// `size_of::<T>` or `size_of_val::<T>` is used as a
  15     /// count of elements of type `T`
  16     ///
  17     /// **Why is this bad?** These functions expect a count
  18     /// of `T` and not a number of bytes
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Example:**
  23     /// ```rust,no_run
  24     /// # use std::ptr::copy_nonoverlapping;
  25     /// # use std::mem::size_of;
  26     /// const SIZE: usize = 128;
  27     /// let x = [2u8; SIZE];
  28     /// let mut y = [2u8; SIZE];
  29     /// unsafe { copy_nonoverlapping(x.as_ptr(), y.as_mut_ptr(), size_of::<u8>() * SIZE) };
  30     /// ```
  31     pub SIZE_OF_IN_ELEMENT_COUNT,
  32     correctness,
  33     "using `size_of::<T>` or `size_of_val::<T>` where a count of elements of `T` is expected"
  34 }
  35
  36 declare_lint_pass!(SizeOfInElementCount => [SIZE_OF_IN_ELEMENT_COUNT]);
  37
  38 fn get_size_of_ty(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<Ty<'tcx>> {
  39     match expr.kind {
  40         ExprKind::Call(count_func, _func_args) => {
  41             if_chain! {
  42                 if let ExprKind::Path(ref count_func_qpath) = count_func.kind;
  43                 if let Some(def_id) = cx.qpath_res(count_func_qpath, count_func.hir_id).opt_def_id();
  44                 if match_def_path(cx, def_id, &paths::MEM_SIZE_OF)
  45                     || match_def_path(cx, def_id, &paths::MEM_SIZE_OF_VAL);
  46                 then {
  47                     cx.typeck_results().node_substs(count_func.hir_id).types().next()
  48                 } else {
  49                     None
  50                 }
  51             }
  52         },
  53         ExprKind::Binary(op, left, right) if BinOpKind::Mul == op.node || BinOpKind::Div == op.node => {
  54             get_size_of_ty(cx, left).or_else(|| get_size_of_ty(cx, right))
  55         },
  56         ExprKind::Cast(expr, _) => get_size_of_ty(cx, expr),
  57         _ => None,
  58     }
  59 }
  60
  61 fn get_pointee_ty_and_count_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<(Ty<'tcx>, &'tcx Expr<'tcx>)> {
  62     const FUNCTIONS: [&[&str]; 8] = [
  63         &paths::COPY_NONOVERLAPPING,
  64         &paths::COPY,
  65         &paths::WRITE_BYTES,
  66         &paths::PTR_SWAP_NONOVERLAPPING,
  67         &paths::PTR_SLICE_FROM_RAW_PARTS,
  68         &paths::PTR_SLICE_FROM_RAW_PARTS_MUT,
  69         &paths::SLICE_FROM_RAW_PARTS,
  70         &paths::SLICE_FROM_RAW_PARTS_MUT,
  71     ];
  72     const METHODS: [&str; 11] = [
  73         "write_bytes",
  74         "copy_to",
  75         "copy_from",
  76         "copy_to_nonoverlapping",
  77         "copy_from_nonoverlapping",
  78         "add",
  79         "wrapping_add",
  80         "sub",
  81         "wrapping_sub",
  82         "offset",
  83         "wrapping_offset",
  84     ];
  85
  86     if_chain! {
  87         // Find calls to ptr::{copy, copy_nonoverlapping}
  88         // and ptr::{swap_nonoverlapping, write_bytes},
  89         if let ExprKind::Call(func, [.., count]) = expr.kind;
  90         if let ExprKind::Path(ref func_qpath) = func.kind;
  91         if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
  92         if FUNCTIONS.iter().any(|func_path| match_def_path(cx, def_id, func_path));
  93
  94         // Get the pointee type
  95         if let Some(pointee_ty) = cx.typeck_results().node_substs(func.hir_id).types().next();
  96         then {
  97             return Some((pointee_ty, count));
  98         }
  99     };
 100     if_chain! {
 101         // Find calls to copy_{from,to}{,_nonoverlapping} and write_bytes methods
 102         if let ExprKind::MethodCall(method_path, _, [ptr_self, .., count], _) = expr.kind;
 103         let method_ident = method_path.ident.as_str();
 104         if METHODS.iter().any(|m| *m == &*method_ident);
 105
 106         // Get the pointee type
 107         if let ty::RawPtr(TypeAndMut { ty: pointee_ty, .. }) =
 108             cx.typeck_results().expr_ty(ptr_self).kind();
 109         then {
 110             return Some((pointee_ty, count));
 111         }
 112     };
 113     None
 114 }
 115
 116 impl<'tcx> LateLintPass<'tcx> for SizeOfInElementCount {
 117     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 118         const HELP_MSG: &str = "use a count of elements instead of a count of bytes\
 119             , it already gets multiplied by the size of the type";
 120
 121         const LINT_MSG: &str = "found a count of bytes \
 122              instead of a count of elements of `T`";
 123
 124         if_chain! {
 125             // Find calls to functions with an element count parameter and get
 126             // the pointee type and count parameter expression
 127             if let Some((pointee_ty, count_expr)) = get_pointee_ty_and_count_expr(cx, expr);
 128
 129             // Find a size_of call in the count parameter expression and
 130             // check that it's the same type
 131             if let Some(ty_used_for_size_of) = get_size_of_ty(cx, count_expr);
 132             if TyS::same_type(pointee_ty, ty_used_for_size_of);
 133             then {
 134                 span_lint_and_help(
 135                     cx,
 136                     SIZE_OF_IN_ELEMENT_COUNT,
 137                     count_expr.span,
 138                     LINT_MSG,
 139                     None,
 140                     HELP_MSG
 141                 );
 142             }
 143         };
 144     }
 145 }