Add erasing_op lint

For expressions that can be replaced by a zero.
This commit is contained in:
Yury Krivopalov 2017-09-30 20:14:00 +03:00
parent f68e408cb6
commit 033c99b1ba
5 changed files with 110 additions and 0 deletions

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@ -0,0 +1,62 @@
use consts::{constant_simple, Constant};
use rustc::hir::*;
use rustc::lint::*;
use syntax::codemap::Span;
use utils::{in_macro, span_lint};
/// **What it does:** Checks for erasing operations, e.g. `x * 0`.
///
/// **Why is this bad?** The whole expression can be replaced by zero.
/// Most likely mistake was made and code should be reviewed or simplified.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// 0 / x; 0 * x; x & 0
/// ```
declare_lint! {
pub ERASING_OP,
Warn,
"using erasing operations, e.g. `x * 0` or `y & 0`"
}
#[derive(Copy, Clone)]
pub struct ErasingOp;
impl LintPass for ErasingOp {
fn get_lints(&self) -> LintArray {
lint_array!(ERASING_OP)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ErasingOp {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if in_macro(e.span) {
return;
}
if let ExprBinary(ref cmp, ref left, ref right) = e.node {
match cmp.node {
BiMul | BiBitAnd => {
check(cx, left, e.span);
check(cx, right, e.span);
},
BiDiv => check(cx, left, e.span),
_ => (),
}
}
}
}
fn check(cx: &LateContext, e: &Expr, span: Span) {
if let Some(Constant::Int(v)) = constant_simple(cx, e) {
if v.to_u128_unchecked() == 0 {
span_lint(
cx,
ERASING_OP,
span,
"the operation is ineffective. Consider reducing it to `0`",
);
}
}
}

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@ -86,6 +86,7 @@ pub mod entry;
pub mod enum_clike;
pub mod enum_glob_use;
pub mod enum_variants;
pub mod erasing_op;
pub mod eq_op;
pub mod escape;
pub mod eta_reduction;
@ -246,6 +247,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
reg.register_early_lint_pass(box needless_continue::NeedlessContinue);
reg.register_late_lint_pass(box eta_reduction::EtaPass);
reg.register_late_lint_pass(box identity_op::IdentityOp);
reg.register_late_lint_pass(box erasing_op::ErasingOp);
reg.register_early_lint_pass(box items_after_statements::ItemsAfterStatements);
reg.register_late_lint_pass(box mut_mut::MutMut);
reg.register_late_lint_pass(box mut_reference::UnnecessaryMutPassed);

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@ -6,6 +6,14 @@ error: &-masking with zero
|
= note: `-D bad-bit-mask` implied by `-D warnings`
error: the operation is ineffective. Consider reducing it to `0`
--> $DIR/bit_masks.rs:12:5
|
12 | x & 0 == 0;
| ^^^^^
|
= note: `-D erasing-op` implied by `-D warnings`
error: incompatible bit mask: `_ & 2` can never be equal to `1`
--> $DIR/bit_masks.rs:15:5
|
@ -48,6 +56,12 @@ error: &-masking with zero
35 | 0 & x == 0;
| ^^^^^^^^^^
error: the operation is ineffective. Consider reducing it to `0`
--> $DIR/bit_masks.rs:35:5
|
35 | 0 & x == 0;
| ^^^^^
error: incompatible bit mask: `_ | 2` will always be higher than `1`
--> $DIR/bit_masks.rs:39:5
|

12
tests/ui/erasing_op.rs Normal file
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@ -0,0 +1,12 @@
#[allow(no_effect)]
#[warn(erasing_op)]
fn main() {
let x: u8 = 0;
x * 0;
0 & x;
0 / x;
}

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@ -0,0 +1,20 @@
error: the operation is ineffective. Consider reducing it to `0`
--> $DIR/erasing_op.rs:9:5
|
9 | x * 0;
| ^^^^^
|
= note: `-D erasing-op` implied by `-D warnings`
error: the operation is ineffective. Consider reducing it to `0`
--> $DIR/erasing_op.rs:10:5
|
10 | 0 & x;
| ^^^^^
error: the operation is ineffective. Consider reducing it to `0`
--> $DIR/erasing_op.rs:11:5
|
11 | 0 / x;
| ^^^^^