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//! Lint on use of `size_of` or `size_of_val` of T in an expression
//! expecting a count of T
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::{match_def_path, paths};
use if_chain::if_chain;
use rustc_hir::BinOpKind;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, Ty, TypeAndMut};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Detects expressions where
/// `size_of::<T>` or `size_of_val::<T>` is used as a
/// count of elements of type `T`
///
/// ### Why is this bad?
/// These functions expect a count
/// of `T` and not a number of bytes
///
/// ### Example
/// ```rust,no_run
/// # use std::ptr::copy_nonoverlapping;
/// # use std::mem::size_of;
/// const SIZE: usize = 128;
/// let x = [2u8; SIZE];
/// let mut y = [2u8; SIZE];
/// unsafe { copy_nonoverlapping(x.as_ptr(), y.as_mut_ptr(), size_of::<u8>() * SIZE) };
/// ```
#[clippy::version = "1.50.0"]
pub SIZE_OF_IN_ELEMENT_COUNT,
correctness,
"using `size_of::<T>` or `size_of_val::<T>` where a count of elements of `T` is expected"
}
declare_lint_pass!(SizeOfInElementCount => [SIZE_OF_IN_ELEMENT_COUNT]);
fn get_size_of_ty<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, inverted: bool) -> Option<Ty<'tcx>> {
match expr.kind {
ExprKind::Call(count_func, _func_args) => {
if_chain! {
if !inverted;
if let ExprKind::Path(ref count_func_qpath) = count_func.kind;
if let Some(def_id) = cx.qpath_res(count_func_qpath, count_func.hir_id).opt_def_id();
if matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::mem_size_of | sym::mem_size_of_val));
then {
cx.typeck_results().node_substs(count_func.hir_id).types().next()
} else {
None
}
}
},
ExprKind::Binary(op, left, right) if BinOpKind::Mul == op.node => {
get_size_of_ty(cx, left, inverted).or_else(|| get_size_of_ty(cx, right, inverted))
},
ExprKind::Binary(op, left, right) if BinOpKind::Div == op.node => {
get_size_of_ty(cx, left, inverted).or_else(|| get_size_of_ty(cx, right, !inverted))
},
ExprKind::Cast(expr, _) => get_size_of_ty(cx, expr, inverted),
_ => None,
}
}
fn get_pointee_ty_and_count_expr<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'_>,
) -> Option<(Ty<'tcx>, &'tcx Expr<'tcx>)> {
const FUNCTIONS: [&[&str]; 8] = [
&paths::PTR_COPY_NONOVERLAPPING,
&paths::PTR_COPY,
&paths::PTR_WRITE_BYTES,
&paths::PTR_SWAP_NONOVERLAPPING,
&paths::PTR_SLICE_FROM_RAW_PARTS,
&paths::PTR_SLICE_FROM_RAW_PARTS_MUT,
&paths::SLICE_FROM_RAW_PARTS,
&paths::SLICE_FROM_RAW_PARTS_MUT,
];
const METHODS: [&str; 11] = [
"write_bytes",
"copy_to",
"copy_from",
"copy_to_nonoverlapping",
"copy_from_nonoverlapping",
"add",
"wrapping_add",
"sub",
"wrapping_sub",
"offset",
"wrapping_offset",
];
if_chain! {
// Find calls to ptr::{copy, copy_nonoverlapping}
// and ptr::{swap_nonoverlapping, write_bytes},
if let ExprKind::Call(func, [.., count]) = expr.kind;
if let ExprKind::Path(ref func_qpath) = func.kind;
if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
if FUNCTIONS.iter().any(|func_path| match_def_path(cx, def_id, func_path));
// Get the pointee type
if let Some(pointee_ty) = cx.typeck_results().node_substs(func.hir_id).types().next();
then {
return Some((pointee_ty, count));
}
};
if_chain! {
// Find calls to copy_{from,to}{,_nonoverlapping} and write_bytes methods
if let ExprKind::MethodCall(method_path, ptr_self, [.., count], _) = expr.kind;
let method_ident = method_path.ident.as_str();
if METHODS.iter().any(|m| *m == method_ident);
// Get the pointee type
if let ty::RawPtr(TypeAndMut { ty: pointee_ty, .. }) =
cx.typeck_results().expr_ty(ptr_self).kind();
then {
return Some((*pointee_ty, count));
}
};
None
}
impl<'tcx> LateLintPass<'tcx> for SizeOfInElementCount {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
const HELP_MSG: &str = "use a count of elements instead of a count of bytes\
, it already gets multiplied by the size of the type";
const LINT_MSG: &str = "found a count of bytes \
instead of a count of elements of `T`";
if_chain! {
// Find calls to functions with an element count parameter and get
// the pointee type and count parameter expression
if let Some((pointee_ty, count_expr)) = get_pointee_ty_and_count_expr(cx, expr);
// Find a size_of call in the count parameter expression and
// check that it's the same type
if let Some(ty_used_for_size_of) = get_size_of_ty(cx, count_expr, false);
if pointee_ty == ty_used_for_size_of;
then {
span_lint_and_help(
cx,
SIZE_OF_IN_ELEMENT_COUNT,
count_expr.span,
LINT_MSG,
None,
HELP_MSG
);
}
};
}
}
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