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Trigger modulo_one lint also on -1.

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Markus Legner 2020-11-21 12:28:53 +01:00
parent 7a7399076a
commit 82a7068007
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3 changed files with 80 additions and 15 deletions
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30
clippy_lints/src/misc.rs
View file

@ -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");
}
};
}
},
_ => {},

11
tests/ui/modulo_one.rs
View file

@ -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
}

54
tests/ui/modulo_one.stderr
View file

@ -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