mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-21 02:23:19 +00:00
110 lines
4.4 KiB
Rust
110 lines
4.4 KiB
Rust
use rustc::hir::*;
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use rustc::lint::*;
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use rustc::ty;
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use syntax::ast::{Name, UintTy};
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use utils::{contains_name, get_pat_name, match_type, paths, single_segment_path, snippet, span_lint_and_sugg,
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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_chain! {
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if let ExprMethodCall(ref count, _, ref count_args) = expr.node;
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if count.name == "count";
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if count_args.len() == 1;
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if let ExprMethodCall(ref filter, _, ref filter_args) = count_args[0].node;
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if filter.name == "filter";
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if filter_args.len() == 2;
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if let ExprClosure(_, _, body_id, _, _) = filter_args[1].node;
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then {
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let body = cx.tcx.hir.body(body_id);
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if_chain! {
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if body.arguments.len() == 1;
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if let Some(argname) = get_pat_name(&body.arguments[0].pat);
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if let ExprBinary(ref op, ref l, ref r) = body.value.node;
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if op.node == BiEq;
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if 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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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::TyUint(UintTy::U8) != walk_ptrs_ty(cx.tables.expr_ty(needle)).sty {
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return;
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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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snippet(cx, needle.span, "..")));
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}
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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: Name, arg: Name, 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<Name> {
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match expr.node {
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ExprBox(ref e) | ExprAddrOf(_, ref e) | ExprUnary(UnOp::UnDeref, ref e) => get_path_name(e),
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ExprBlock(ref b) => 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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ExprPath(ref qpath) => single_segment_path(qpath).map(|ps| ps.name),
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_ => None,
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}
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}
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