implemented unnecessary min

Author: FelixMaetzler

CHANGELOG.md

@@ -5671,6 +5671,7 @@ 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`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_min
 [`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

@@ -450,6 +450,7 @@ 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_INFO,
     crate::methods::UNNECESSARY_SORT_BY_INFO,
     crate::methods::UNNECESSARY_TO_OWNED_INFO,
     crate::methods::UNWRAP_OR_DEFAULT_INFO,

clippy_lints/src/methods/mod.rs

@@ -112,6 +112,7 @@ mod unnecessary_iter_cloned;
 mod unnecessary_join;
 mod unnecessary_lazy_eval;
 mod unnecessary_literal_unwrap;
+mod unnecessary_min;
 mod unnecessary_sort_by;
 mod unnecessary_to_owned;
 mod unwrap_expect_used;
@@ -3887,6 +3888,27 @@ declare_clippy_lint! {
     "splitting a trimmed string at hard-coded newlines"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for unnecessary calls to `min()`
+    ///
+    /// ### 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 _ = 7;
+    /// ```
+    #[clippy::version = "1.77.0"]
+    pub UNNECESSARY_MIN,
+    complexity,
+    "using 'min()' when there is no need for it"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Msrv,
@@ -4043,6 +4065,7 @@ impl_lint_pass!(Methods => [
     ITER_FILTER_IS_OK,
     MANUAL_IS_VARIANT_AND,
     STR_SPLIT_AT_NEWLINE,
+    UNNECESSARY_MIN,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -4324,6 +4347,7 @@ impl Methods {
                     Some(("bytes", recv2, [], _, _)) => bytes_count_to_len::check(cx, expr, recv, recv2),
                     _ => {},
                 },
+                ("min", [arg]) => unnecessary_min::check(cx, expr, recv, arg),
                 ("drain", ..) => {
                     if let Node::Stmt(Stmt { hir_id: _, kind, .. }) = cx.tcx.hir().get_parent(expr.hir_id)
                         && matches!(kind, StmtKind::Semi(_))

clippy_lints/src/methods/unnecessary_min.rs

@@ -0,0 +1,111 @@
+use std::cmp::Ordering;
+
+use super::UNNECESSARY_MIN;
+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<'_>, recv: &'tcx Expr<'_>, arg: &'tcx Expr<'_>) {
+    if both_are_constant(cx, expr, recv, arg) {
+        return;
+    }
+    one_extrema(cx, expr, recv, arg);
+}
+fn lint(cx: &LateContext<'_>, expr: &Expr<'_>, sugg: Span, other: Span) {
+    let msg = format!(
+        "`{}` is never greater than `{}` and has therefore no effect",
+        snippet(cx, sugg, "Not yet implemented"),
+        snippet(cx, other, "Not yet implemented")
+    );
+    span_lint_and_sugg(
+        cx,
+        UNNECESSARY_MIN,
+        expr.span,
+        &msg,
+        "try",
+        snippet(cx, sugg, "Not yet implemented").to_string(),
+        Applicability::MachineApplicable,
+    );
+}
+
+fn try_to_eval<'tcx>(
+    cx: &LateContext<'tcx>,
+    recv: &'tcx Expr<'_>,
+    arg: &'tcx Expr<'_>,
+) -> (Option<Constant<'tcx>>, Option<Constant<'tcx>>) {
+    (
+        (constant(cx, cx.typeck_results(), recv)),
+        (constant(cx, cx.typeck_results(), arg)),
+    )
+}
+#[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,
+    }
+}
+fn both_are_constant<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    recv: &'tcx Expr<'_>,
+    arg: &'tcx Expr<'_>,
+) -> bool {
+    let ty = cx.typeck_results().expr_ty(recv);
+    if let (Some(left), Some(right)) = try_to_eval(cx, recv, arg)
+        && let Some(ord) = Constant::partial_cmp(cx.tcx, ty, &left, &right)
+    {
+        let (sugg, other) = match ord {
+            Ordering::Less => (recv.span, arg.span),
+            Ordering::Equal | Ordering::Greater => (arg.span, recv.span),
+        };
+
+        lint(cx, expr, sugg, other);
+        return true;
+    }
+    false
+}
+fn one_extrema<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, recv: &'tcx Expr<'_>, arg: &'tcx Expr<'_>) -> bool {
+    if let Some(extrema) = detect_extrema(cx, recv) {
+        match extrema {
+            Extrema::Minimum => lint(cx, expr, recv.span, arg.span),
+            Extrema::Maximum => lint(cx, expr, arg.span, recv.span),
+        }
+        return true;
+    } else if let Some(extrema) = detect_extrema(cx, arg) {
+        match extrema {
+            Extrema::Minimum => lint(cx, expr, arg.span, recv.span),
+            Extrema::Maximum => lint(cx, expr, recv.span, arg.span),
+        }
+        return true;
+    }
+
+    false
+}

tests/ui/cast.stderr

@@ -333,6 +333,15 @@ help: ... or use `try_from` and handle the error accordingly
 LL |     i8::try_from((-99999999999i64).min(1));
    |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+error: `(-99999999999i64)` is never greater than `1` and has therefore no effect
+  --> $DIR/cast.rs:179:5
+   |
+LL |     (-99999999999i64).min(1) as i8;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(-99999999999i64)`
+   |
+   = note: `-D clippy::unnecessary-min` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::unnecessary_min)]`
+
 error: casting `u64` to `u8` may truncate the value
   --> $DIR/cast.rs:193:5
    |
@@ -444,5 +453,5 @@ help: ... or use `try_from` and handle the error accordingly
 LL |     let c = u8::try_from(q / 1000);
    |             ~~~~~~~~~~~~~~~~~~~~~~
 
-error: aborting due to 51 previous errors
+error: aborting due to 52 previous errors
 

tests/ui/unnecessary_min.fixed

@@ -0,0 +1,45 @@
+#![allow(unused)]
+#![warn(clippy::unnecessary_min)]
+
+fn main() {
+    const A: i64 = 45;
+    const B: i64 = -1;
+    const C: i64 = const_fn(B);
+    let _ = (A * B); // Both are constants
+    let _ = B; // Both are constants
+    let _ = B; // Both are constants
+
+    let _ = (-6_i32); // Both are Literals
+    let _ = 6; // Both are Literals
+
+    let _ = 6; // Both are Literals
+
+    let _ = 0; // unsigned with zero
+    let _ = 0_u32; // unsigned with zero
+
+    let _ = i32::MIN; // singed MIN
+    let _ = i32::MIN; // singed MIN
+
+    let _ = 42; // singed MAX
+    let _ = 42; // singed MAX
+
+    let _ = 0; // unsigned with zero and function
+
+    let _ = 0; // unsigned with zero and function
+
+    let _ = i64::MIN; // signed with MIN and function
+
+    let _ = i64::MIN; // signed with MIN and function
+
+    let _ = test_i64(); // signed with MAX and function
+    let _ = test_i64(); // signed with MAX and function
+}
+fn test_usize() -> usize {
+    42
+}
+fn test_i64() -> i64 {
+    42
+}
+const fn const_fn(input: i64) -> i64 {
+    -2 * input
+}

tests/ui/unnecessary_min.rs

@@ -0,0 +1,45 @@
+#![allow(unused)]
+#![warn(clippy::unnecessary_min)]
+
+fn main() {
+    const A: i64 = 45;
+    const B: i64 = -1;
+    const C: i64 = const_fn(B);
+    let _ = (A * B).min(B); // Both are constants
+    let _ = C.min(B); // Both are constants
+    let _ = B.min(C); // Both are constants
+
+    let _ = (-6_i32).min(9); // Both are Literals
+    let _ = 9_u32.min(6); // Both are Literals
+
+    let _ = 6.min(7_u8); // Both are Literals
+
+    let _ = 0.min(7_u8); // unsigned with zero
+    let _ = 7.min(0_u32); // unsigned with zero
+
+    let _ = i32::MIN.min(42); // singed MIN
+    let _ = 42.min(i32::MIN); // singed MIN
+
+    let _ = i32::MAX.min(42); // singed MAX
+    let _ = 42.min(i32::MAX); // singed MAX
+
+    let _ = 0.min(test_usize()); // unsigned with zero and function
+
+    let _ = test_usize().min(0); // unsigned with zero and function
+
+    let _ = i64::MIN.min(test_i64()); // signed with MIN and function
+
+    let _ = test_i64().min(i64::MIN); // signed with MIN and function
+
+    let _ = i64::MAX.min(test_i64()); // signed with MAX and function
+    let _ = test_i64().min(i64::MAX); // signed with MAX and function
+}
+fn test_usize() -> usize {
+    42
+}
+fn test_i64() -> i64 {
+    42
+}
+const fn const_fn(input: i64) -> i64 {
+    -2 * input
+}