clippy_lints/src/methods/bytecount.rs

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::res::{MaybeDef as _, MaybeResPath as _};
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::visitors::is_local_used;
use clippy_utils::{peel_blocks, peel_ref_operators, strip_pat_refs, sym};
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Closure, Expr, ExprKind, PatKind};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, UintTy};

use super::NAIVE_BYTECOUNT;

pub(super) fn check<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &'tcx Expr<'_>,
    filter_recv: &'tcx Expr<'_>,
    filter_arg: &'tcx Expr<'_>,
) {
    if let ExprKind::Closure(&Closure { body, .. }) = filter_arg.kind
        && let body = cx.tcx.hir_body(body)
        && let [param] = body.params
        && let PatKind::Binding(_, arg_id, _, _) = strip_pat_refs(param.pat).kind
        && let ExprKind::Binary(ref op, l, r) = body.value.kind
        && op.node == BinOpKind::Eq
        && cx
            .typeck_results()
            .expr_ty(filter_recv)
            .peel_refs()
            .is_diag_item(cx, sym::SliceIter)
        && let operand_is_arg = (|expr| {
            let expr = peel_ref_operators(cx, peel_blocks(expr));
            expr.res_local_id() == Some(arg_id)
        })
        && let needle = if operand_is_arg(l) {
            r
        } else if operand_is_arg(r) {
            l
        } else {
            return;
        }
        && ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(needle).peel_refs().kind()
        && !is_local_used(cx, needle, arg_id)
    {
        let haystack = if let ExprKind::MethodCall(path, receiver, [], _) = filter_recv.kind {
            let p = path.ident.name;
            if p == sym::iter || p == sym::iter_mut {
                receiver
            } else {
                filter_recv
            }
        } else {
            filter_recv
        };
        let mut applicability = Applicability::MaybeIncorrect;
        span_lint_and_sugg(
            cx,
            NAIVE_BYTECOUNT,
            expr.span,
            "you appear to be counting bytes the naive way",
            "consider using the bytecount crate",
            format!(
                "bytecount::count({}, {})",
                snippet_with_applicability(cx, haystack.span, "..", &mut applicability),
                snippet_with_applicability(cx, needle.span, "..", &mut applicability)
            ),
            applicability,
        );
    }
}