new lint to use contains() instead of iter().any() for u8 and i8 slices

Author: lapla-cogito

CHANGELOG.md

@@ -5455,6 +5455,7 @@ Released 2018-09-13
 [`comparison_to_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_to_empty
 [`const_is_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#const_is_empty
 [`const_static_lifetime`]: https://rust-lang.github.io/rust-clippy/master/index.html#const_static_lifetime
+[`contains_for_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#contains_for_slice
 [`copy_iterator`]: https://rust-lang.github.io/rust-clippy/master/index.html#copy_iterator
 [`crate_in_macro_def`]: https://rust-lang.github.io/rust-clippy/master/index.html#crate_in_macro_def
 [`create_dir`]: https://rust-lang.github.io/rust-clippy/master/index.html#create_dir

clippy_lints/src/contains_for_slice.rs

@@ -0,0 +1,65 @@
+use crate::methods::method_call;
+use clippy_utils::diagnostics::span_lint;
+use rustc_hir::Expr;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::{self};
+use rustc_session::declare_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `iter().any()` on slices of `u8` or `i8` and suggests using `contains()` instead.
+    ///
+    /// ### Why is this bad?
+    /// `iter().any()` on slices of `u8` or `i8` is optimized to use `memchr`.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// fn foo(values: &[u8]) -> bool {
+    ///    values.iter().any(|&v| v == 10)
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// fn foo(values: &[u8]) -> bool {
+    ///    values.contains(&10)
+    /// }
+    /// ```
+    #[clippy::version = "1.85.0"]
+    pub CONTAINS_FOR_SLICE,
+    perf,
+    "using `contains()` instead of `iter().any()` on u8/i8 slices is more efficient"
+}
+
+declare_lint_pass!(ContainsForSlice => [CONTAINS_FOR_SLICE]);
+
+impl LateLintPass<'_> for ContainsForSlice {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+        if !expr.span.from_expansion()
+            // any()
+            && let Some((name, recv, _, _, _)) = method_call(expr)
+            && name == "any"
+            // iter()
+            && let Some((name, recv, _, _, _)) = method_call(recv)
+            && name == "iter"
+        {
+            // check if the receiver is a u8/i8 slice
+            let ref_type = cx.typeck_results().expr_ty(recv);
+
+            match ref_type.kind() {
+                ty::Ref(_, inner_type, _) if inner_type.is_slice() => {
+                    if let ty::Slice(slice_type) = inner_type.kind()
+                        && (slice_type.to_string() == "u8" || slice_type.to_string() == "i8")
+                    {
+                        span_lint(
+                            cx,
+                            CONTAINS_FOR_SLICE,
+                            expr.span,
+                            "using `contains()` instead of `iter().any()` on u8/i8 slices is more efficient",
+                        );
+                    }
+                },
+                _ => {},
+            }
+        }
+    }
+}

clippy_lints/src/declared_lints.rs

@@ -107,6 +107,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::collapsible_if::COLLAPSIBLE_IF_INFO,
     crate::collection_is_never_read::COLLECTION_IS_NEVER_READ_INFO,
     crate::comparison_chain::COMPARISON_CHAIN_INFO,
+    crate::contains_for_slice::CONTAINS_FOR_SLICE_INFO,
     crate::copies::BRANCHES_SHARING_CODE_INFO,
     crate::copies::IFS_SAME_COND_INFO,
     crate::copies::IF_SAME_THEN_ELSE_INFO,

clippy_lints/src/lib.rs

@@ -100,6 +100,7 @@ mod cognitive_complexity;
 mod collapsible_if;
 mod collection_is_never_read;
 mod comparison_chain;
+mod contains_for_slice;
 mod copies;
 mod copy_iterator;
 mod crate_in_macro_def;
@@ -967,5 +968,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(manual_ignore_case_cmp::ManualIgnoreCaseCmp));
     store.register_late_pass(|_| Box::new(unnecessary_literal_bound::UnnecessaryLiteralBound));
     store.register_late_pass(move |_| Box::new(arbitrary_source_item_ordering::ArbitrarySourceItemOrdering::new(conf)));
+    store.register_late_pass(|_| Box::new(contains_for_slice::ContainsForSlice));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

tests/ui/contains_for_slice.rs

@@ -0,0 +1,32 @@
+#![warn(clippy::contains_for_slice)]
+
+fn main() {
+    let vec: Vec<u8> = vec![1, 2, 3, 4, 5, 6];
+    let values = &vec[..];
+    let _ = values.iter().any(|&v| v == 4);
+    //~^ ERROR: using `contains()` instead of `iter().any()` on u8/i8 slices is more efficient
+
+    let vec: Vec<u8> = vec![1, 2, 3, 4, 5, 6];
+    let values = &vec[..];
+    let _ = values.contains(&4);
+    // no error, because it uses `contains()`
+
+    let vec: Vec<u32> = vec![1, 2, 3, 4, 5, 6];
+    let values = &vec[..];
+    let _ = values.iter().any(|&v| v == 4);
+    // no error, because it's not a slice of u8/i8
+
+    let values: [u8; 6] = [3, 14, 15, 92, 6, 5];
+    let _ = values.iter().any(|&v| v == 10);
+    // no error, because it's an array
+}
+
+fn foo(values: &[u8]) -> bool {
+    values.iter().any(|&v| v == 10)
+    //~^ ERROR: using `contains()` instead of `iter().any()` on u8/i8 slices is more efficient
+}
+
+fn bar(values: [u8; 3]) -> bool {
+    values.iter().any(|&v| v == 10)
+    // no error, because it's an array
+}

tests/ui/contains_for_slice.stderr

@@ -0,0 +1,17 @@
+error: using `contains()` instead of `iter().any()` on u8/i8 slices is more efficient
+  --> tests/ui/contains_for_slice.rs:6:13
+   |
+LL |     let _ = values.iter().any(|&v| v == 4);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::contains-for-slice` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::contains_for_slice)]`
+
+error: using `contains()` instead of `iter().any()` on u8/i8 slices is more efficient
+  --> tests/ui/contains_for_slice.rs:25:5
+   |
+LL |     values.iter().any(|&v| v == 10)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+