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 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};
  12
  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`
  17     ///
  18     /// **Why is this bad?** These functions expect a count
  19     /// of `T` and not a number of bytes
  20     ///
  21     /// **Known problems:** None.
  22     ///
  23     /// **Example:**
  24     /// ```rust,no_run
  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) };
  31     /// ```
  32     pub SIZE_OF_IN_ELEMENT_COUNT,
  33     correctness,
  34     "using `size_of::<T>` or `size_of_val::<T>` where a count of elements of `T` is expected"
  35 }
  36
  37 declare_lint_pass!(SizeOfInElementCount => [SIZE_OF_IN_ELEMENT_COUNT]);
  38
  39 fn get_size_of_ty(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, inverted: bool) -> Option<Ty<'tcx>> {
  40     match expr.kind {
  41         ExprKind::Call(count_func, _func_args) => {
  42             if_chain! {
  43                 if !inverted;
  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);
  48                 then {
  49                     cx.typeck_results().node_substs(count_func.hir_id).types().next()
  50                 } else {
  51                     None
  52                 }
  53             }
  54         },
  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))
  57         },
  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))
  60         },
  61         ExprKind::Cast(expr, _) => get_size_of_ty(cx, expr, inverted),
  62         _ => None,
  63     }
  64 }
  65
  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::COPY_NONOVERLAPPING,
  69         &paths::COPY,
  70         &paths::WRITE_BYTES,
  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,
  76     ];
  77     const METHODS: [&str; 11] = [
  78         "write_bytes",
  79         "copy_to",
  80         "copy_from",
  81         "copy_to_nonoverlapping",
  82         "copy_from_nonoverlapping",
  83         "add",
  84         "wrapping_add",
  85         "sub",
  86         "wrapping_sub",
  87         "offset",
  88         "wrapping_offset",
  89     ];
  90
  91     if_chain! {
  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));
  98
  99         // Get the pointee type
 100         if let Some(pointee_ty) = cx.typeck_results().node_substs(func.hir_id).types().next();
 101         then {
 102             return Some((pointee_ty, count));
 103         }
 104     };
 105     if_chain! {
 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);
 110
 111         // Get the pointee type
 112         if let ty::RawPtr(TypeAndMut { ty: pointee_ty, .. }) =
 113             cx.typeck_results().expr_ty(ptr_self).kind();
 114         then {
 115             return Some((pointee_ty, count));
 116         }
 117     };
 118     None
 119 }
 120
 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";
 125
 126         const LINT_MSG: &str = "found a count of bytes \
 127              instead of a count of elements of `T`";
 128
 129         if_chain! {
 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);
 133
 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);
 138             then {
 139                 span_lint_and_help(
 140                     cx,
 141                     SIZE_OF_IN_ELEMENT_COUNT,
 142                     count_expr.span,
 143                     LINT_MSG,
 144                     None,
 145                     HELP_MSG
 146                 );
 147             }
 148         };
 149     }
 150 }