diff --git a/clippy_lints/src/misc.rs b/clippy_lints/src/misc.rs index 308e92057..f16feb9b1 100644 --- a/clippy_lints/src/misc.rs +++ b/clippy_lints/src/misc.rs @@ -18,7 +18,7 @@ use crate::utils::sugg::Sugg; use crate::utils::{ get_item_name, get_parent_expr, higher, implements_trait, in_constant, is_integer_const, iter_input_pats, last_path_segment, match_qpath, match_trait_method, paths, snippet, snippet_opt, span_lint, span_lint_and_sugg, - span_lint_and_then, span_lint_hir_and_then, SpanlessEq, + span_lint_and_then, span_lint_hir_and_then, SpanlessEq, unsext, }; declare_clippy_lint! { @@ -139,12 +139,14 @@ declare_clippy_lint! { } declare_clippy_lint! { - /// **What it does:** Checks for getting the remainder of a division by one. + /// **What it does:** Checks for getting the remainder of a division by one or minus + /// one. /// - /// **Why is this bad?** The result can only ever be zero. No one will write - /// such code deliberately, unless trying to win an Underhanded Rust - /// Contest. Even for that contest, it's probably a bad idea. Use something more - /// underhanded. + /// **Why is this bad?** The result for a divisor of one can only ever be zero; for + /// minus one it can cause panic/overflow (if the left operand is the minimal value of + /// the respective integer type) or results in zero. No one will write such code + /// deliberately, unless trying to win an Underhanded Rust Contest. Even for that + /// contest, it's probably a bad idea. Use something more underhanded. /// /// **Known problems:** None. /// @@ -152,10 +154,11 @@ declare_clippy_lint! { /// ```rust /// # let x = 1; /// let a = x % 1; + /// let a = x % -1; /// ``` pub MODULO_ONE, correctness, - "taking a number modulo 1, which always returns 0" + "taking a number modulo +/-1, which can either panic/overflow or always returns 0" } declare_clippy_lint! { @@ -429,8 +432,17 @@ impl<'tcx> LateLintPass<'tcx> for MiscLints { } diag.note("`f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`"); }); - } else if op == BinOpKind::Rem && is_integer_const(cx, right, 1) { - span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0"); + } else if op == BinOpKind::Rem { + if is_integer_const(cx, right, 1) { + span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0"); + } + + if let ty::Int(ity) = cx.typeck_results().expr_ty(right).kind() { + if is_integer_const(cx, right, unsext(cx.tcx, -1, *ity)) { + span_lint(cx, MODULO_ONE, expr.span, + "any number modulo -1 will panic/overflow or result in 0"); + } + }; } }, _ => {}, diff --git a/tests/ui/modulo_one.rs b/tests/ui/modulo_one.rs index cc8c8e7cd..678a312f6 100644 --- a/tests/ui/modulo_one.rs +++ b/tests/ui/modulo_one.rs @@ -2,13 +2,22 @@ #![allow(clippy::no_effect, clippy::unnecessary_operation)] static STATIC_ONE: usize = 2 - 1; +static STATIC_NEG_ONE: i64 = 1 - 2; fn main() { 10 % 1; + 10 % -1; 10 % 2; + i32::MIN % (-1); // also caught by rustc const ONE: u32 = 1 * 1; + const NEG_ONE: i64 = 1 - 2; + const INT_MIN: i64 = i64::MIN; 2 % ONE; - 5 % STATIC_ONE; + 5 % STATIC_ONE; // NOT caught by lint + 2 % NEG_ONE; + 5 % STATIC_NEG_ONE; // NOT caught by lint + INT_MIN % NEG_ONE; // also caught by rustc + INT_MIN % STATIC_NEG_ONE; // ONLY caught by rustc } diff --git a/tests/ui/modulo_one.stderr b/tests/ui/modulo_one.stderr index 6bee68360..2b2c69973 100644 --- a/tests/ui/modulo_one.stderr +++ b/tests/ui/modulo_one.stderr @@ -1,13 +1,45 @@ +error: this arithmetic operation will overflow + --> $DIR/modulo_one.rs:11:5 + | +LL | i32::MIN % (-1); // also caught by rustc + | ^^^^^^^^^^^^^^^ attempt to compute the remainder of `i32::MIN % -1_i32`, which would overflow + | + = note: `#[deny(arithmetic_overflow)]` on by default + +error: this arithmetic operation will overflow + --> $DIR/modulo_one.rs:21:5 + | +LL | INT_MIN % NEG_ONE; // also caught by rustc + | ^^^^^^^^^^^^^^^^^ attempt to compute the remainder of `i64::MIN % -1_i64`, which would overflow + +error: this arithmetic operation will overflow + --> $DIR/modulo_one.rs:22:5 + | +LL | INT_MIN % STATIC_NEG_ONE; // ONLY caught by rustc + | ^^^^^^^^^^^^^^^^^^^^^^^^ attempt to compute the remainder of `i64::MIN % -1_i64`, which would overflow + error: any number modulo 1 will be 0 - --> $DIR/modulo_one.rs:7:5 + --> $DIR/modulo_one.rs:8:5 | LL | 10 % 1; | ^^^^^^ | = note: `-D clippy::modulo-one` implied by `-D warnings` +error: any number modulo -1 will panic/overflow or result in 0 + --> $DIR/modulo_one.rs:9:5 + | +LL | 10 % -1; + | ^^^^^^^ + +error: any number modulo -1 will panic/overflow or result in 0 + --> $DIR/modulo_one.rs:11:5 + | +LL | i32::MIN % (-1); // also caught by rustc + | ^^^^^^^^^^^^^^^ + error: the operation is ineffective. Consider reducing it to `1` - --> $DIR/modulo_one.rs:10:22 + --> $DIR/modulo_one.rs:13:22 | LL | const ONE: u32 = 1 * 1; | ^^^^^ @@ -15,16 +47,28 @@ LL | const ONE: u32 = 1 * 1; = note: `-D clippy::identity-op` implied by `-D warnings` error: the operation is ineffective. Consider reducing it to `1` - --> $DIR/modulo_one.rs:10:22 + --> $DIR/modulo_one.rs:13:22 | LL | const ONE: u32 = 1 * 1; | ^^^^^ error: any number modulo 1 will be 0 - --> $DIR/modulo_one.rs:12:5 + --> $DIR/modulo_one.rs:17:5 | LL | 2 % ONE; | ^^^^^^^ -error: aborting due to 4 previous errors +error: any number modulo -1 will panic/overflow or result in 0 + --> $DIR/modulo_one.rs:19:5 + | +LL | 2 % NEG_ONE; + | ^^^^^^^^^^^ + +error: any number modulo -1 will panic/overflow or result in 0 + --> $DIR/modulo_one.rs:21:5 + | +LL | INT_MIN % NEG_ONE; // also caught by rustc + | ^^^^^^^^^^^^^^^^^ + +error: aborting due to 11 previous errors