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<'_>, inverted: bool) -> Option<Ty<'tcx>> {
  39     match expr.kind {
  40         ExprKind::Call(count_func, _func_args) => {
  41             if_chain! {
  42                 if !inverted;
  43                 if let ExprKind::Path(ref count_func_qpath) = count_func.kind;
  44                 if let Some(def_id) = cx.qpath_res(count_func_qpath, count_func.hir_id).opt_def_id();
  45                 if match_def_path(cx, def_id, &paths::MEM_SIZE_OF)
  46                     || match_def_path(cx, def_id, &paths::MEM_SIZE_OF_VAL);
  47                 then {
  48                     cx.typeck_results().node_substs(count_func.hir_id).types().next()
  49                 } else {
  50                     None
  51                 }
  52             }
  53         },
  54         ExprKind::Binary(op, left, right) if BinOpKind::Mul == op.node => {
  55             get_size_of_ty(cx, left, inverted).or_else(|| get_size_of_ty(cx, right, inverted))
  56         },
  57         ExprKind::Binary(op, left, right) if BinOpKind::Div == op.node => {
  58             get_size_of_ty(cx, left, inverted).or_else(|| get_size_of_ty(cx, right, !inverted))
  59         },
  60         ExprKind::Cast(expr, _) => get_size_of_ty(cx, expr, inverted),
  61         _ => None,
  62     }
  63 }
  64
  65 fn get_pointee_ty_and_count_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<(Ty<'tcx>, &'tcx Expr<'tcx>)> {
  66     const FUNCTIONS: [&[&str]; 8] = [
  67         &paths::COPY_NONOVERLAPPING,
  68         &paths::COPY,
  69         &paths::WRITE_BYTES,
  70         &paths::PTR_SWAP_NONOVERLAPPING,
  71         &paths::PTR_SLICE_FROM_RAW_PARTS,
  72         &paths::PTR_SLICE_FROM_RAW_PARTS_MUT,
  73         &paths::SLICE_FROM_RAW_PARTS,
  74         &paths::SLICE_FROM_RAW_PARTS_MUT,
  75     ];
  76     const METHODS: [&str; 11] = [
  77         "write_bytes",
  78         "copy_to",
  79         "copy_from",
  80         "copy_to_nonoverlapping",
  81         "copy_from_nonoverlapping",
  82         "add",
  83         "wrapping_add",
  84         "sub",
  85         "wrapping_sub",
  86         "offset",
  87         "wrapping_offset",
  88     ];
  89
  90     if_chain! {
  91         // Find calls to ptr::{copy, copy_nonoverlapping}
  92         // and ptr::{swap_nonoverlapping, write_bytes},
  93         if let ExprKind::Call(func, [.., count]) = expr.kind;
  94         if let ExprKind::Path(ref func_qpath) = func.kind;
  95         if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
  96         if FUNCTIONS.iter().any(|func_path| match_def_path(cx, def_id, func_path));
  97
  98         // Get the pointee type
  99         if let Some(pointee_ty) = cx.typeck_results().node_substs(func.hir_id).types().next();
 100         then {
 101             return Some((pointee_ty, count));
 102         }
 103     };
 104     if_chain! {
 105         // Find calls to copy_{from,to}{,_nonoverlapping} and write_bytes methods
 106         if let ExprKind::MethodCall(method_path, _, [ptr_self, .., count], _) = expr.kind;
 107         let method_ident = method_path.ident.as_str();
 108         if METHODS.iter().any(|m| *m == &*method_ident);
 109
 110         // Get the pointee type
 111         if let ty::RawPtr(TypeAndMut { ty: pointee_ty, .. }) =
 112             cx.typeck_results().expr_ty(ptr_self).kind();
 113         then {
 114             return Some((pointee_ty, count));
 115         }
 116     };
 117     None
 118 }
 119
 120 impl<'tcx> LateLintPass<'tcx> for SizeOfInElementCount {
 121     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 122         const HELP_MSG: &str = "use a count of elements instead of a count of bytes\
 123             , it already gets multiplied by the size of the type";
 124
 125         const LINT_MSG: &str = "found a count of bytes \
 126              instead of a count of elements of `T`";
 127
 128         if_chain! {
 129             // Find calls to functions with an element count parameter and get
 130             // the pointee type and count parameter expression
 131             if let Some((pointee_ty, count_expr)) = get_pointee_ty_and_count_expr(cx, expr);
 132
 133             // Find a size_of call in the count parameter expression and
 134             // check that it's the same type
 135             if let Some(ty_used_for_size_of) = get_size_of_ty(cx, count_expr, false);
 136             if TyS::same_type(pointee_ty, ty_used_for_size_of);
 137             then {
 138                 span_lint_and_help(
 139                     cx,
 140                     SIZE_OF_IN_ELEMENT_COUNT,
 141                     count_expr.span,
 142                     LINT_MSG,
 143                     None,
 144                     HELP_MSG
 145                 );
 146             }
 147         };
 148     }
 149 }