3 contains_name, get_pat_name, match_type, paths, single_segment_path, snippet_with_applicability,
4 span_lint_and_sugg, walk_ptrs_ty,
6 use if_chain::if_chain;
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 use rustc_errors::Applicability;
12 use syntax::ast::{Name, UintTy};
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 /// &my_data.filter(|&x| x == 0u8).count() // use bytecount::count instead
32 "use of naive `<slice>.filter(|&x| x == y).count()` to count byte values"
35 declare_lint_pass!(ByteCount => [NAIVE_BYTECOUNT]);
37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ByteCount {
38 fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr) {
40 if let ExprKind::MethodCall(ref count, _, ref count_args) = expr.node;
41 if count.ident.name == *sym::count;
42 if count_args.len() == 1;
43 if let ExprKind::MethodCall(ref filter, _, ref filter_args) = count_args[0].node;
44 if filter.ident.name == *sym::filter;
45 if filter_args.len() == 2;
46 if let ExprKind::Closure(_, _, body_id, _, _) = filter_args[1].node;
48 let body = cx.tcx.hir().body(body_id);
50 if body.arguments.len() == 1;
51 if let Some(argname) = get_pat_name(&body.arguments[0].pat);
52 if let ExprKind::Binary(ref op, ref l, ref r) = body.value.node;
53 if op.node == BinOpKind::Eq;
55 walk_ptrs_ty(cx.tables.expr_ty(&filter_args[0])),
58 let needle = match get_path_name(l) {
59 Some(name) if check_arg(name, argname, r) => r,
60 _ => match get_path_name(r) {
61 Some(name) if check_arg(name, argname, l) => l,
65 if ty::Uint(UintTy::U8) != walk_ptrs_ty(cx.tables.expr_ty(needle)).sty {
68 let haystack = if let ExprKind::MethodCall(ref path, _, ref args) =
70 let p = path.ident.name;
71 if (p == *sym::iter || p == *sym::iter_mut) && args.len() == 1 {
79 let mut applicability = Applicability::MaybeIncorrect;
84 "You appear to be counting bytes the naive way",
85 "Consider using the bytecount crate",
86 format!("bytecount::count({}, {})",
87 snippet_with_applicability(cx, haystack.span, "..", &mut applicability),
88 snippet_with_applicability(cx, needle.span, "..", &mut applicability)),
98 fn check_arg(name: Name, arg: Name, needle: &Expr) -> bool {
99 name == arg && !contains_name(name, needle)
102 fn get_path_name(expr: &Expr) -> Option<Name> {
104 ExprKind::Box(ref e) | ExprKind::AddrOf(_, ref e) | ExprKind::Unary(UnOp::UnDeref, ref e) => get_path_name(e),
105 ExprKind::Block(ref b, _) => {
106 if b.stmts.is_empty() {
107 b.expr.as_ref().and_then(|p| get_path_name(p))
112 ExprKind::Path(ref qpath) => single_segment_path(qpath).map(|ps| ps.ident.name),