Move ByteCount into Methods lint pass

Author: Jarcho

clippy_lints/src/bytecount.rs

@@ -59,7 +59,6 @@ store.register_lints(&[
     booleans::NONMINIMAL_BOOL,
     booleans::OVERLY_COMPLEX_BOOL_EXPR,
     borrow_deref_ref::BORROW_DEREF_REF,
-    bytecount::NAIVE_BYTECOUNT,
     bytes_count_to_len::BYTES_COUNT_TO_LEN,
     cargo::CARGO_COMMON_METADATA,
     cargo::MULTIPLE_CRATE_VERSIONS,
@@ -330,6 +329,7 @@ store.register_lints(&[
     methods::MAP_FLATTEN,
     methods::MAP_IDENTITY,
     methods::MAP_UNWRAP_OR,
+    methods::NAIVE_BYTECOUNT,
     methods::NEEDLESS_OPTION_AS_DEREF,
     methods::NEEDLESS_OPTION_TAKE,
     methods::NEEDLESS_SPLITN,

clippy_lints/src/lib.register_lints.rs

@@ -4,7 +4,6 @@
 
 store.register_group(true, "clippy::pedantic", Some("clippy_pedantic"), vec![
     LintId::of(attrs::INLINE_ALWAYS),
-    LintId::of(bytecount::NAIVE_BYTECOUNT),
     LintId::of(case_sensitive_file_extension_comparisons::CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS),
     LintId::of(casts::BORROW_AS_PTR),
     LintId::of(casts::CAST_LOSSLESS),
@@ -64,6 +63,7 @@ store.register_group(true, "clippy::pedantic", Some("clippy_pedantic"), vec![
     LintId::of(methods::IMPLICIT_CLONE),
     LintId::of(methods::INEFFICIENT_TO_STRING),
     LintId::of(methods::MAP_UNWRAP_OR),
+    LintId::of(methods::NAIVE_BYTECOUNT),
     LintId::of(methods::UNNECESSARY_JOIN),
     LintId::of(misc::USED_UNDERSCORE_BINDING),
     LintId::of(mismatching_type_param_order::MISMATCHING_TYPE_PARAM_ORDER),

clippy_lints/src/lib.register_pedantic.rs

@@ -180,7 +180,6 @@ mod blocks_in_if_conditions;
 mod bool_assert_comparison;
 mod booleans;
 mod borrow_deref_ref;
-mod bytecount;
 mod bytes_count_to_len;
 mod cargo;
 mod case_sensitive_file_extension_comparisons;
@@ -718,7 +717,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     );
     store.register_late_pass(move || Box::new(pass_by_ref_or_value));
     store.register_late_pass(|| Box::new(ref_option_ref::RefOptionRef));
-    store.register_late_pass(|| Box::new(bytecount::ByteCount));
     store.register_late_pass(|| Box::new(infinite_iter::InfiniteIter));
     store.register_late_pass(|| Box::new(inline_fn_without_body::InlineFnWithoutBody));
     store.register_late_pass(|| Box::new(useless_conversion::UselessConversion::default()));

clippy_lints/src/lib.rs

@@ -0,0 +1,70 @@
+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;
+use rustc_middle::ty::{self, UintTy};
+use rustc_span::sym;
+
+use super::NAIVE_BYTECOUNT;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    filter_recv: &'tcx Expr<'_>,
+    filter_arg: &'tcx Expr<'_>,
+) {
+    if_chain! {
+        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,
+            );
+        }
+    };
+}

clippy_lints/src/methods/bytecount.rs

@@ -1,4 +1,5 @@
 mod bind_instead_of_map;
+mod bytecount;
 mod bytes_nth;
 mod chars_cmp;
 mod chars_cmp_with_unwrap;
@@ -82,7 +83,9 @@ use bind_instead_of_map::BindInsteadOfMap;
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
-use clippy_utils::{contains_return, get_trait_def_id, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
+use clippy_utils::{
+    contains_return, get_trait_def_id, is_trait_method, iter_input_pats, meets_msrv, msrvs, paths, return_ty,
+};
 use if_chain::if_chain;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
@@ -2368,6 +2371,37 @@ declare_clippy_lint! {
     "Iterator for empty array"
 }
 
+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"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2471,7 +2505,8 @@ impl_lint_pass!(Methods => [
     NO_EFFECT_REPLACE,
     OBFUSCATED_IF_ELSE,
     ITER_ON_SINGLE_ITEMS,
-    ITER_ON_EMPTY_COLLECTIONS
+    ITER_ON_EMPTY_COLLECTIONS,
+    NAIVE_BYTECOUNT,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -2726,12 +2761,13 @@ impl Methods {
                     },
                     _ => {},
                 },
-                ("count", []) => match method_call(recv) {
+                ("count", []) if is_trait_method(cx, expr, sym::Iterator) => match method_call(recv) {
                     Some(("cloned", [recv2], _)) => iter_overeager_cloned::check(cx, expr, recv, recv2, true, false),
                     Some((name2 @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
                         iter_count::check(cx, expr, recv2, name2);
                     },
                     Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
+                    Some(("filter", [recv2, arg], _)) => bytecount::check(cx, expr, recv2, arg),
                     _ => {},
                 },
                 ("drain", [arg]) => {