2 contains_name, get_pat_name, match_type, paths, single_segment_path, snippet_with_applicability,
3 span_lint_and_sugg, walk_ptrs_ty,
5 use if_chain::if_chain;
6 use rustc_ast::ast::UintTy;
7 use rustc_errors::Applicability;
8 use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, UnOp};
9 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::Symbol;
14 declare_clippy_lint! {
15 /// **What it does:** Checks for naive byte counts
17 /// **Why is this bad?** The [`bytecount`](https://crates.io/crates/bytecount)
18 /// crate has methods to count your bytes faster, especially for large slices.
20 /// **Known problems:** If you have predominantly small slices, the
21 /// `bytecount::count(..)` method may actually be slower. However, if you can
22 /// ensure that less than 2³²-1 matches arise, the `naive_count_32(..)` can be
23 /// faster in those cases.
28 /// # let vec = vec![1_u8];
29 /// &vec.iter().filter(|x| **x == 0u8).count(); // use bytecount::count instead
33 "use of naive `<slice>.filter(|&x| x == y).count()` to count byte values"
36 declare_lint_pass!(ByteCount => [NAIVE_BYTECOUNT]);
38 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ByteCount {
39 fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
41 if let ExprKind::MethodCall(ref count, _, ref count_args, _) = expr.kind;
42 if count.ident.name == sym!(count);
43 if count_args.len() == 1;
44 if let ExprKind::MethodCall(ref filter, _, ref filter_args, _) = count_args[0].kind;
45 if filter.ident.name == sym!(filter);
46 if filter_args.len() == 2;
47 if let ExprKind::Closure(_, _, body_id, _, _) = filter_args[1].kind;
49 let body = cx.tcx.hir().body(body_id);
51 if body.params.len() == 1;
52 if let Some(argname) = get_pat_name(&body.params[0].pat);
53 if let ExprKind::Binary(ref op, ref l, ref r) = body.value.kind;
54 if op.node == BinOpKind::Eq;
56 walk_ptrs_ty(cx.tables.expr_ty(&filter_args[0])),
59 let needle = match get_path_name(l) {
60 Some(name) if check_arg(name, argname, r) => r,
61 _ => match get_path_name(r) {
62 Some(name) if check_arg(name, argname, l) => l,
66 if ty::Uint(UintTy::U8) != walk_ptrs_ty(cx.tables.expr_ty(needle)).kind {
69 let haystack = if let ExprKind::MethodCall(ref path, _, ref args, _) =
71 let p = path.ident.name;
72 if (p == sym!(iter) || p == sym!(iter_mut)) && args.len() == 1 {
80 let mut applicability = Applicability::MaybeIncorrect;
85 "You appear to be counting bytes the naive way",
86 "Consider using the bytecount crate",
87 format!("bytecount::count({}, {})",
88 snippet_with_applicability(cx, haystack.span, "..", &mut applicability),
89 snippet_with_applicability(cx, needle.span, "..", &mut applicability)),
99 fn check_arg(name: Symbol, arg: Symbol, needle: &Expr<'_>) -> bool {
100 name == arg && !contains_name(name, needle)
103 fn get_path_name(expr: &Expr<'_>) -> Option<Symbol> {
105 ExprKind::Box(ref e) | ExprKind::AddrOf(BorrowKind::Ref, _, ref e) | ExprKind::Unary(UnOp::UnDeref, ref e) => {
108 ExprKind::Block(ref b, _) => {
109 if b.stmts.is_empty() {
110 b.expr.as_ref().and_then(|p| get_path_name(p))
115 ExprKind::Path(ref qpath) => single_segment_path(qpath).map(|ps| ps.ident.name),