| use crate::utils::{ |
| contains_name, get_pat_name, match_type, paths, single_segment_path, snippet_with_applicability, |
| span_lint_and_sugg, walk_ptrs_ty, |
| }; |
| use if_chain::if_chain; |
| use rustc::hir::*; |
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| use rustc::ty; |
| use rustc::{declare_lint_pass, declare_tool_lint}; |
| use rustc_errors::Applicability; |
| use syntax::ast::{Name, UintTy}; |
| |
| 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]; |
| /// &vec.iter().filter(|x| **x == 0u8).count(); // use bytecount::count instead |
| /// ``` |
| pub NAIVE_BYTECOUNT, |
| perf, |
| "use of naive `<slice>.filter(|&x| x == y).count()` to count byte values" |
| } |
| |
| declare_lint_pass!(ByteCount => [NAIVE_BYTECOUNT]); |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ByteCount { |
| fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr) { |
| if_chain! { |
| if let ExprKind::MethodCall(ref count, _, ref count_args) = expr.kind; |
| if count.ident.name == sym!(count); |
| if count_args.len() == 1; |
| if let ExprKind::MethodCall(ref filter, _, ref filter_args) = count_args[0].kind; |
| if filter.ident.name == sym!(filter); |
| if filter_args.len() == 2; |
| if let ExprKind::Closure(_, _, body_id, _, _) = filter_args[1].kind; |
| then { |
| let body = cx.tcx.hir().body(body_id); |
| if_chain! { |
| if body.params.len() == 1; |
| if let Some(argname) = get_pat_name(&body.params[0].pat); |
| if let ExprKind::Binary(ref op, ref l, ref r) = body.value.kind; |
| if op.node == BinOpKind::Eq; |
| if match_type(cx, |
| walk_ptrs_ty(cx.tables.expr_ty(&filter_args[0])), |
| &paths::SLICE_ITER); |
| then { |
| let needle = match get_path_name(l) { |
| Some(name) if check_arg(name, argname, r) => r, |
| _ => match get_path_name(r) { |
| Some(name) if check_arg(name, argname, l) => l, |
| _ => { return; } |
| } |
| }; |
| if ty::Uint(UintTy::U8) != walk_ptrs_ty(cx.tables.expr_ty(needle)).kind { |
| return; |
| } |
| let haystack = if let ExprKind::MethodCall(ref path, _, ref args) = |
| filter_args[0].kind { |
| let p = path.ident.name; |
| if (p == sym!(iter) || p == sym!(iter_mut)) && args.len() == 1 { |
| &args[0] |
| } else { |
| &filter_args[0] |
| } |
| } else { |
| &filter_args[0] |
| }; |
| 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, |
| ); |
| } |
| }; |
| } |
| }; |
| } |
| } |
| |
| fn check_arg(name: Name, arg: Name, needle: &Expr) -> bool { |
| name == arg && !contains_name(name, needle) |
| } |
| |
| fn get_path_name(expr: &Expr) -> Option<Name> { |
| match expr.kind { |
| ExprKind::Box(ref e) | ExprKind::AddrOf(_, ref e) | ExprKind::Unary(UnOp::UnDeref, ref e) => get_path_name(e), |
| ExprKind::Block(ref b, _) => { |
| if b.stmts.is_empty() { |
| b.expr.as_ref().and_then(|p| get_path_name(p)) |
| } else { |
| None |
| } |
| }, |
| ExprKind::Path(ref qpath) => single_segment_path(qpath).map(|ps| ps.ident.name), |
| _ => None, |
| } |
| } |