diff --git a/CHANGELOG.md b/CHANGELOG.md
index 41a86e8ce510..c79345890df4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5621,6 +5621,7 @@ Released 2018-09-13
[`manual_find_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_find_map
[`manual_flatten`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_flatten
[`manual_hash_one`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_hash_one
+[`manual_ilog2`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_ilog2
[`manual_inspect`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect
[`manual_instant_elapsed`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_instant_elapsed
[`manual_is_ascii_check`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_ascii_check
diff --git a/clippy_config/src/msrvs.rs b/clippy_config/src/msrvs.rs
index e30df3d32341..8045e8919168 100644
--- a/clippy_config/src/msrvs.rs
+++ b/clippy_config/src/msrvs.rs
@@ -27,6 +27,7 @@ msrv_aliases! {
1,71,0 { TUPLE_ARRAY_CONVERSIONS, BUILD_HASHER_HASH_ONE }
1,70,0 { OPTION_RESULT_IS_VARIANT_AND, BINARY_HEAP_RETAIN }
1,68,0 { PATH_MAIN_SEPARATOR_STR }
+ 1,67,0 { MANUAL_ILOG2 }
1,65,0 { LET_ELSE, POINTER_CAST_CONSTNESS }
1,63,0 { CLONE_INTO }
1,62,0 { BOOL_THEN_SOME, DEFAULT_ENUM_ATTRIBUTE, CONST_EXTERN_C_FN }
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 2b229d2fe6ac..34a7fc572fcd 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -305,6 +305,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
crate::manual_float_methods::MANUAL_IS_FINITE_INFO,
crate::manual_float_methods::MANUAL_IS_INFINITE_INFO,
crate::manual_hash_one::MANUAL_HASH_ONE_INFO,
+ crate::manual_ilog2::MANUAL_ILOG2_INFO,
crate::manual_is_ascii_check::MANUAL_IS_ASCII_CHECK_INFO,
crate::manual_is_power_of_two::MANUAL_IS_POWER_OF_TWO_INFO,
crate::manual_let_else::MANUAL_LET_ELSE_INFO,
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 1d41f568f378..e9160d813767 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -206,6 +206,7 @@ mod manual_clamp;
mod manual_div_ceil;
mod manual_float_methods;
mod manual_hash_one;
+mod manual_ilog2;
mod manual_is_ascii_check;
mod manual_is_power_of_two;
mod manual_let_else;
@@ -944,5 +945,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
store.register_late_pass(|_| Box::new(manual_is_power_of_two::ManualIsPowerOfTwo));
store.register_late_pass(|_| Box::new(non_zero_suggestions::NonZeroSuggestions));
store.register_late_pass(move |_| Box::new(unused_trait_names::UnusedTraitNames::new(conf)));
+ store.register_late_pass(move |_| Box::new(manual_ilog2::ManualIlog2::new(conf)));
// add lints here, do not remove this comment, it's used in `new_lint`
}
diff --git a/clippy_lints/src/manual_ilog2.rs b/clippy_lints/src/manual_ilog2.rs
new file mode 100644
index 000000000000..1c57e462d62b
--- /dev/null
+++ b/clippy_lints/src/manual_ilog2.rs
@@ -0,0 +1,102 @@
+use clippy_config::msrvs::{self, Msrv};
+use clippy_config::Conf;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use rustc_ast::LitKind;
+use rustc_data_structures::packed::Pu128;
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::impl_lint_pass;
+
+declare_clippy_lint! {
+ /// ### What it does
+ /// Checks for expressions like `31 - x.leading_zeros()` or `x.ilog(2)` which are manual
+ /// reimplementations of `x.ilog2()`
+ /// ### Why is this bad?
+ /// Manual reimplementations of `ilog2` increase code complexity for little benefit.
+ /// ### Example
+ /// ```no_run
+ /// let x: u32 = 5;
+ /// let log = 31 - x.leading_zeros();
+ /// ```
+ /// Use instead:
+ /// ```no_run
+ /// let x: u32 = 5;
+ /// let log = x.ilog2();
+ /// ```
+ #[clippy::version = "1.82.0"]
+ pub MANUAL_ILOG2,
+ complexity,
+ "manually reimplementing `ilog2`"
+}
+
+pub struct ManualIlog2 {
+ msrv: Msrv,
+}
+
+impl ManualIlog2 {
+ #[must_use]
+ pub fn new(conf: &Conf) -> Self {
+ Self {
+ msrv: conf.msrv.clone(),
+ }
+ }
+}
+
+impl_lint_pass!(ManualIlog2 => [MANUAL_ILOG2]);
+
+impl LateLintPass<'_> for ManualIlog2 {
+ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+ if !self.msrv.meets(msrvs::MANUAL_ILOG2) {
+ return;
+ }
+ let mut applicability = Applicability::MachineApplicable;
+
+ if let ExprKind::Binary(op, left, right) = expr.kind
+ && BinOpKind::Sub == op.node
+ && let ExprKind::Lit(lit) = left.kind
+ && let LitKind::Int(Pu128(val), _) = lit.node
+ && let ExprKind::MethodCall(method_name, reciever, _, _) = right.kind
+ && method_name.ident.as_str() == "leading_zeros"
+ {
+ let type_ = cx.typeck_results().expr_ty(reciever);
+ let Some(bit_width) = (match type_.kind() {
+ ty::Int(itype) => itype.bit_width(),
+ ty::Uint(itype) => itype.bit_width(),
+ _ => return,
+ }) else {
+ return;
+ };
+ if val == u128::from(bit_width) - 1 {
+ suggest_change(cx, reciever, expr, &mut applicability);
+ }
+ }
+
+ if let ExprKind::MethodCall(method_name, reciever, args, _) = expr.kind
+ && method_name.ident.as_str() == "ilog"
+ && args.len() == 1
+ && let ExprKind::Lit(lit) = args[0].kind
+ && let LitKind::Int(Pu128(2), _) = lit.node
+ && cx.typeck_results().expr_ty(reciever).is_integral()
+ {
+ suggest_change(cx, reciever, expr, &mut applicability);
+ }
+ }
+
+ extract_msrv_attr!(LateContext);
+}
+
+fn suggest_change(cx: &LateContext<'_>, reciever: &Expr<'_>, full_expr: &Expr<'_>, applicability: &mut Applicability) {
+ let sugg = snippet_with_applicability(cx, reciever.span, "..", applicability);
+ span_lint_and_sugg(
+ cx,
+ MANUAL_ILOG2,
+ full_expr.span,
+ "manually reimplementing `ilog2`",
+ "consider using .ilog2()",
+ format!("{sugg}.ilog2()"),
+ *applicability,
+ );
+}
diff --git a/tests/ui/manual_ilog2.fixed b/tests/ui/manual_ilog2.fixed
new file mode 100644
index 000000000000..865009db8d79
--- /dev/null
+++ b/tests/ui/manual_ilog2.fixed
@@ -0,0 +1,12 @@
+#![warn(clippy::manual_ilog2)]
+
+fn main() {
+ let a: u32 = 5;
+ let _ = a.ilog2();
+ let _ = a.ilog2();
+
+ let b: u64 = 543534;
+ let _ = b.ilog2();
+
+ let _ = 64 - b.leading_zeros(); // No lint
+}
diff --git a/tests/ui/manual_ilog2.rs b/tests/ui/manual_ilog2.rs
new file mode 100644
index 000000000000..c72b1ba66f0b
--- /dev/null
+++ b/tests/ui/manual_ilog2.rs
@@ -0,0 +1,12 @@
+#![warn(clippy::manual_ilog2)]
+
+fn main() {
+ let a: u32 = 5;
+ let _ = 31 - a.leading_zeros();
+ let _ = a.ilog(2);
+
+ let b: u64 = 543534;
+ let _ = 63 - b.leading_zeros();
+
+ let _ = 64 - b.leading_zeros(); // No lint because manual ilog2 is BIT_WIDTH - 1 - x.leading_zeros()
+}
diff --git a/tests/ui/manual_ilog2.stderr b/tests/ui/manual_ilog2.stderr
new file mode 100644
index 000000000000..88abb3ce9efd
--- /dev/null
+++ b/tests/ui/manual_ilog2.stderr
@@ -0,0 +1,23 @@
+error: manually reimplementing `ilog2`
+ --> tests/ui/manual_ilog2.rs:5:13
+ |
+LL | let _ = 31 - a.leading_zeros();
+ | ^^^^^^^^^^^^^^^^^^^^^^ help: consider using .ilog2(): `a.ilog2()`
+ |
+ = note: `-D clippy::manual-ilog2` implied by `-D warnings`
+ = help: to override `-D warnings` add `#[allow(clippy::manual_ilog2)]`
+
+error: manually reimplementing `ilog2`
+ --> tests/ui/manual_ilog2.rs:6:13
+ |
+LL | let _ = a.ilog(2);
+ | ^^^^^^^^^ help: consider using .ilog2(): `a.ilog2()`
+
+error: manually reimplementing `ilog2`
+ --> tests/ui/manual_ilog2.rs:9:13
+ |
+LL | let _ = 63 - b.leading_zeros();
+ | ^^^^^^^^^^^^^^^^^^^^^^ help: consider using .ilog2(): `b.ilog2()`
+
+error: aborting due to 3 previous errors
+