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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::match_type;
use clippy_utils::visitors::is_local_used;
use clippy_utils::{path_to_local_id, paths, peel_blocks, peel_ref_operators, strip_pat_refs};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Closure, Expr, ExprKind, PatKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, UintTy};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for naive byte counts
///
/// ### Why is this bad?
/// The [`bytecount`](https://crates.io/crates/bytecount)
/// crate has methods to count your bytes faster, especially for large slices.
///
/// ### Known problems
/// If you have predominantly small slices, the
/// `bytecount::count(..)` method may actually be slower. However, if you can
/// ensure that less than 2³²-1 matches arise, the `naive_count_32(..)` can be
/// faster in those cases.
///
/// ### Example
/// ```rust
/// # let vec = vec![1_u8];
/// let count = vec.iter().filter(|x| **x == 0u8).count();
/// ```
///
/// Use instead:
/// ```rust,ignore
/// # let vec = vec![1_u8];
/// let count = bytecount::count(&vec, 0u8);
/// ```
#[clippy::version = "pre 1.29.0"]
pub NAIVE_BYTECOUNT,
pedantic,
"use of naive `<slice>.filter(|&x| x == y).count()` to count byte values"
}
declare_lint_pass!(ByteCount => [NAIVE_BYTECOUNT]);
impl<'tcx> LateLintPass<'tcx> for ByteCount {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::MethodCall(count, [count_recv], _) = expr.kind;
if count.ident.name == sym::count;
if let ExprKind::MethodCall(filter, [filter_recv, filter_arg], _) = count_recv.kind;
if filter.ident.name == sym!(filter);
if let ExprKind::Closure(&Closure { body, .. }) = filter_arg.kind;
let body = cx.tcx.hir().body(body);
if let [param] = body.params;
if let PatKind::Binding(_, arg_id, _, _) = strip_pat_refs(param.pat).kind;
if let ExprKind::Binary(ref op, l, r) = body.value.kind;
if op.node == BinOpKind::Eq;
if match_type(cx,
cx.typeck_results().expr_ty(filter_recv).peel_refs(),
&paths::SLICE_ITER);
let operand_is_arg = |expr| {
let expr = peel_ref_operators(cx, peel_blocks(expr));
path_to_local_id(expr, arg_id)
};
let needle = if operand_is_arg(l) {
r
} else if operand_is_arg(r) {
l
} else {
return;
};
if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(needle).peel_refs().kind();
if !is_local_used(cx, needle, arg_id);
then {
let haystack = if let ExprKind::MethodCall(path, args, _) =
filter_recv.kind {
let p = path.ident.name;
if (p == sym::iter || p == sym!(iter_mut)) && args.len() == 1 {
&args[0]
} 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,
);
}
};
}
}
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