115 lines
4.6 KiB
Rust
115 lines
4.6 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::ty::match_type;
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use clippy_utils::{contains_name, get_pat_name, paths, single_segment_path};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, UintTy};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::sym;
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use rustc_span::Symbol;
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declare_clippy_lint! {
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/// **What it does:** Checks for naive byte counts
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///
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/// **Why is this bad?** The [`bytecount`](https://crates.io/crates/bytecount)
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/// crate has methods to count your bytes faster, especially for large slices.
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///
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/// **Known problems:** If you have predominantly small slices, the
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/// `bytecount::count(..)` method may actually be slower. However, if you can
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/// ensure that less than 2³²-1 matches arise, the `naive_count_32(..)` can be
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/// faster in those cases.
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///
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/// **Example:**
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///
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/// ```rust
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/// # let vec = vec![1_u8];
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/// &vec.iter().filter(|x| **x == 0u8).count(); // use bytecount::count instead
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/// ```
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pub NAIVE_BYTECOUNT,
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pedantic,
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"use of naive `<slice>.filter(|&x| x == y).count()` to count byte values"
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}
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declare_lint_pass!(ByteCount => [NAIVE_BYTECOUNT]);
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impl<'tcx> LateLintPass<'tcx> for ByteCount {
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fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
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if_chain! {
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if let ExprKind::MethodCall(count, _, count_args, _) = expr.kind;
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if count.ident.name == sym!(count);
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if count_args.len() == 1;
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if let ExprKind::MethodCall(filter, _, filter_args, _) = count_args[0].kind;
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if filter.ident.name == sym!(filter);
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if filter_args.len() == 2;
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if let ExprKind::Closure(_, _, body_id, _, _) = filter_args[1].kind;
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let body = cx.tcx.hir().body(body_id);
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if body.params.len() == 1;
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if let Some(argname) = get_pat_name(body.params[0].pat);
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if let ExprKind::Binary(ref op, l, r) = body.value.kind;
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if op.node == BinOpKind::Eq;
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if match_type(cx,
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cx.typeck_results().expr_ty(&filter_args[0]).peel_refs(),
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&paths::SLICE_ITER);
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then {
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let needle = match get_path_name(l) {
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Some(name) if check_arg(name, argname, r) => r,
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_ => match get_path_name(r) {
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Some(name) if check_arg(name, argname, l) => l,
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_ => { return; }
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}
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};
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if ty::Uint(UintTy::U8) != *cx.typeck_results().expr_ty(needle).peel_refs().kind() {
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return;
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}
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let haystack = if let ExprKind::MethodCall(path, _, args, _) =
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filter_args[0].kind {
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let p = path.ident.name;
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if (p == sym::iter || p == sym!(iter_mut)) && args.len() == 1 {
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&args[0]
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} else {
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&filter_args[0]
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}
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} else {
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&filter_args[0]
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};
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let mut applicability = Applicability::MaybeIncorrect;
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span_lint_and_sugg(
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cx,
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NAIVE_BYTECOUNT,
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expr.span,
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"you appear to be counting bytes the naive way",
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"consider using the bytecount crate",
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format!("bytecount::count({}, {})",
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snippet_with_applicability(cx, haystack.span, "..", &mut applicability),
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snippet_with_applicability(cx, needle.span, "..", &mut applicability)),
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applicability,
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);
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}
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};
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}
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}
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fn check_arg(name: Symbol, arg: Symbol, needle: &Expr<'_>) -> bool {
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name == arg && !contains_name(name, needle)
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}
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fn get_path_name(expr: &Expr<'_>) -> Option<Symbol> {
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match expr.kind {
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ExprKind::Box(e) | ExprKind::AddrOf(BorrowKind::Ref, _, e) | ExprKind::Unary(UnOp::Deref, e) => {
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get_path_name(e)
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},
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ExprKind::Block(b, _) => {
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if b.stmts.is_empty() {
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b.expr.as_ref().and_then(|p| get_path_name(p))
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} else {
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None
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}
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},
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ExprKind::Path(ref qpath) => single_segment_path(qpath).map(|ps| ps.ident.name),
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_ => None,
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}
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}
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