feat: unnecessary_min_max lint

CHANGELOG.md

@@ -5799,6 +5799,7 @@ Released 2018-09-13
 [`unnecessary_lazy_evaluations`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_lazy_evaluations
 [`unnecessary_literal_unwrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_literal_unwrap
 [`unnecessary_map_on_constructor`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_map_on_constructor
+[`unnecessary_min_max`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_min_max
 [`unnecessary_mut_passed`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_mut_passed
 [`unnecessary_operation`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_operation
 [`unnecessary_owned_empty_strings`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_owned_empty_strings

clippy_lints/src/declared_lints.rs

@@ -466,6 +466,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::UNNECESSARY_JOIN_INFO,
     crate::methods::UNNECESSARY_LAZY_EVALUATIONS_INFO,
     crate::methods::UNNECESSARY_LITERAL_UNWRAP_INFO,
+    crate::methods::UNNECESSARY_MIN_MAX_INFO,
     crate::methods::UNNECESSARY_RESULT_MAP_OR_ELSE_INFO,
     crate::methods::UNNECESSARY_SORT_BY_INFO,
     crate::methods::UNNECESSARY_TO_OWNED_INFO,

clippy_lints/src/methods/mod.rs

@@ -116,6 +116,7 @@ mod unnecessary_iter_cloned;
 mod unnecessary_join;
 mod unnecessary_lazy_eval;
 mod unnecessary_literal_unwrap;
+mod unnecessary_min_max;
 mod unnecessary_result_map_or_else;
 mod unnecessary_sort_by;
 mod unnecessary_to_owned;
@@ -3961,6 +3962,27 @@ declare_clippy_lint! {
     "cloning an `Option` via `as_ref().cloned()`"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for unnecessary calls to `min()` or `max()`
+    ///
+    /// ### Why is this bad?
+    ///
+    /// In these cases it is not necessary to call `min()`
+    /// ### Example
+    /// ```no_run
+    /// let _ = 0.min(7_u32);
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let _ = 0;
+    /// ```
+    #[clippy::version = "1.78.0"]
+    pub UNNECESSARY_MIN_MAX,
+    complexity,
+    "using 'min()/max()' when there is no need for it"
+}
+
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for usage of `.map_or_else()` "map closure" for `Result` type.
@@ -4236,6 +4258,7 @@ impl_lint_pass!(Methods => [
     UNNECESSARY_RESULT_MAP_OR_ELSE,
     MANUAL_C_STR_LITERALS,
     UNNECESSARY_GET_THEN_CHECK,
+    UNNECESSARY_MIN_MAX,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -4526,6 +4549,7 @@ impl Methods {
                     Some(("bytes", recv2, [], _, _)) => bytes_count_to_len::check(cx, expr, recv, recv2),
                     _ => {},
                 },
+                ("min" | "max", [arg]) => unnecessary_min_max::check(cx, expr, name, recv, arg),
                 ("drain", ..) => {
                     if let Node::Stmt(Stmt { hir_id: _, kind, .. }) = cx.tcx.parent_hir_node(expr.hir_id)
                         && matches!(kind, StmtKind::Semi(_))

clippy_lints/src/methods/unnecessary_min_max.rs

@@ -0,0 +1,100 @@
+use std::cmp::Ordering;
+
+use super::UNNECESSARY_MIN_MAX;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+
+use clippy_utils::consts::{constant, Constant};
+use clippy_utils::source::snippet;
+use clippy_utils::{clip, int_bits, unsext};
+use hir::Expr;
+
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+
+use rustc_middle::ty;
+use rustc_span::Span;
+
+pub fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    name: &str,
+    recv: &'tcx Expr<'_>,
+    arg: &'tcx Expr<'_>,
+) {
+    let typeck_results = cx.typeck_results();
+    if let (Some(left), Some(right)) = (constant(cx, typeck_results, recv), constant(cx, typeck_results, arg)) {
+        let Some(ord) = Constant::partial_cmp(cx.tcx, typeck_results.expr_ty(recv), &left, &right) else {
+            return;
+        };
+
+        lint(cx, expr, name, recv.span, arg.span, ord);
+    } else if let Some(extrema) = detect_extrema(cx, recv) {
+        let ord = match extrema {
+            Extrema::Minimum => Ordering::Less,
+            Extrema::Maximum => Ordering::Greater,
+        };
+        lint(cx, expr, name, recv.span, arg.span, ord);
+    } else if let Some(extrema) = detect_extrema(cx, arg) {
+        let ord = match extrema {
+            Extrema::Minimum => Ordering::Greater,
+            Extrema::Maximum => Ordering::Less,
+        };
+        lint(cx, expr, name, recv.span, arg.span, ord);
+    }
+}
+
+fn lint(cx: &LateContext<'_>, expr: &Expr<'_>, name: &str, lhs: Span, rhs: Span, order: Ordering) {
+    let cmp_str = if (name == "min" && order.is_ge()) || (name == "max" && order.is_le()) {
+        "smaller"
+    } else {
+        "greater"
+    };
+
+    let suggested_value = if (name == "min" && order.is_ge()) || (name == "max" && order.is_le()) {
+        snippet(cx, rhs, "..")
+    } else {
+        snippet(cx, lhs, "..")
+    };
+
+    let msg = format!(
+        "`{}` is never {} than `{}` and has therefore no effect",
+        snippet(cx, lhs, ".."),
+        cmp_str,
+        snippet(cx, rhs, "..")
+    );
+    span_lint_and_sugg(
+        cx,
+        UNNECESSARY_MIN_MAX,
+        expr.span,
+        &msg,
+        "try",
+        suggested_value.to_string(),
+        Applicability::MachineApplicable,
+    );
+}
+
+#[derive(Debug)]
+enum Extrema {
+    Minimum,
+    Maximum,
+}
+fn detect_extrema<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<Extrema> {
+    let ty = cx.typeck_results().expr_ty(expr);
+
+    let cv = constant(cx, cx.typeck_results(), expr)?;
+
+    match (ty.kind(), cv) {
+        (&ty::Uint(_), Constant::Int(0)) => Some(Extrema::Minimum),
+        (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
+            Some(Extrema::Minimum)
+        },
+
+        (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
+            Some(Extrema::Maximum)
+        },
+        (&ty::Uint(uty), Constant::Int(i)) if i == clip(cx.tcx, u128::MAX, uty) => Some(Extrema::Maximum),
+
+        _ => None,
+    }
+}

tests/ui/cast.rs

@@ -12,6 +12,7 @@
 #![allow(
     clippy::cast_abs_to_unsigned,
     clippy::no_effect,
+    clippy::unnecessary_min_max,
     clippy::unnecessary_operation,
     clippy::unnecessary_literal_unwrap
 )]