81 lines
3.0 KiB
Rust
81 lines
3.0 KiB
Rust
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use consts::{constant, Constant};
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use rustc_const_math::ConstInt;
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use rustc::hir::*;
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use rustc::lint::*;
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use utils::{match_type, paths, snippet, span_lint_and_sugg, walk_ptrs_ty};
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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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/// &my_data.filter(|&x| x == 0u8).count() // use bytecount::count instead
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/// ```
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declare_lint! {
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pub NAIVE_BYTECOUNT,
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Warn,
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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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#[derive(Copy, Clone)]
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pub struct ByteCount;
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impl LintPass for ByteCount {
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fn get_lints(&self) -> LintArray {
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lint_array!(NAIVE_BYTECOUNT)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ByteCount {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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if_let_chain!([
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let ExprMethodCall(ref count, _, ref count_args) = expr.node,
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count.name == "count",
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count_args.len() == 1,
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let ExprMethodCall(ref filter, _, ref filter_args) = count_args[0].node,
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filter.name == "filter",
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filter_args.len() == 2,
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let ExprClosure(_, _, body_id, _) = filter_args[1].node,
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], {
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let body = cx.tcx.hir.body(body_id);
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if_let_chain!([
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let ExprBinary(ref op, ref l, ref r) = body.value.node,
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op.node == BiEq,
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match_type(cx,
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walk_ptrs_ty(cx.tables.expr_ty(&filter_args[0])),
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&paths::SLICE_ITER),
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let Some((Constant::Int(ConstInt::U8(needle)), _)) =
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constant(cx, l).or_else(|| constant(cx, r))
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], {
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let haystack = if let ExprMethodCall(ref path, _, ref args) =
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filter_args[0].node {
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let p = path.name;
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if (p == "iter" || p == "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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span_lint_and_sugg(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(cx, haystack.span, ".."),
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needle));
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});
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});
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}
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}
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