new lint: identity_op, refactored bit_masks a bit

This commit is contained in:
llogiq 2015-05-15 18:46:43 +02:00
parent 6f527ea810
commit edf747ab76
6 changed files with 112 additions and 1 deletions

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@ -21,6 +21,7 @@ Lints included in this crate:
- `float_cmp`: Warns on `==` or `!=` comparisons of floaty typed values. As floating-point operations usually involve rounding errors, it is always better to check for approximate equality within some small bounds
- `precedence`: Warns on expressions where precedence may trip up the unwary reader of the source and suggests adding parenthesis, e.g. `x << 2 + y` will be parsed as `x << (2 + y)`
- `redundant_closure`: Warns on usage of eta-reducible closures like `|a| foo(a)` (which can be written as just `foo`)
- `identity_op`: Warns on identity operations like `x + 0` or `y / 1` (which can be reduced to `x` and `y`, respectively)
To use, add the following lines to your Cargo.toml:

82
src/identity_op.rs Normal file
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@ -0,0 +1,82 @@
use rustc::plugin::Registry;
use rustc::lint::*;
use rustc::middle::const_eval::lookup_const_by_id;
use rustc::middle::def::*;
use syntax::ast::*;
use syntax::ast_util::{is_comparison_binop, binop_to_string};
use syntax::ptr::P;
use syntax::codemap::Span;
declare_lint! { pub IDENTITY_OP, Warn,
"Warn on identity operations, e.g. '_ + 0'"}
#[derive(Copy,Clone)]
pub struct IdentityOp;
impl LintPass for IdentityOp {
fn get_lints(&self) -> LintArray {
lint_array!(IDENTITY_OP)
}
fn check_expr(&mut self, cx: &Context, e: &Expr) {
if let ExprBinary(ref cmp, ref left, ref right) = e.node {
match cmp.node {
BiAdd | BiBitOr | BiBitXor => {
check(cx, left, 0, e.span, right.span);
check(cx, right, 0, e.span, left.span);
},
BiShl | BiShr | BiSub =>
check(cx, right, 0, e.span, left.span),
BiMul => {
check(cx, left, 1, e.span, right.span);
check(cx, right, 1, e.span, left.span);
},
BiDiv =>
check(cx, right, 1, e.span, left.span),
BiBitAnd => {
check(cx, left, -1, e.span, right.span);
check(cx, right, -1, e.span, left.span);
},
_ => ()
}
}
}
}
fn check(cx: &Context, e: &Expr, m: i8, span: Span, arg: Span) {
if have_lit(cx, e, m) {
let map = cx.sess().codemap();
cx.span_lint(IDENTITY_OP, span, &format!(
"The operation is ineffective. Consider reducing it to '{}'",
&*map.span_to_snippet(arg).unwrap_or("..".to_string())));
}
}
fn have_lit(cx: &Context, e : &Expr, m: i8) -> bool {
match &e.node {
&ExprUnary(UnNeg, ref litexp) => have_lit(cx, litexp, -m),
&ExprLit(ref lit) => {
match (&lit.node, m) {
(&LitInt(0, _), 0) => true,
(&LitInt(1, SignedIntLit(_, Plus)), 1) => true,
(&LitInt(1, UnsuffixedIntLit(Plus)), 1) => true,
(&LitInt(1, SignedIntLit(_, Minus)), -1) => true,
(&LitInt(1, UnsuffixedIntLit(Minus)), -1) => true,
_ => false
}
},
&ExprParen(ref p) => have_lit(cx, p, m),
&ExprPath(_, _) => {
match cx.tcx.def_map.borrow().get(&e.id) {
Some(&PathResolution { base_def: DefConst(def_id), ..}) =>
match lookup_const_by_id(cx.tcx, def_id, Option::None) {
Some(l) => have_lit(cx, l, m),
None => false
},
_ => false
}
}
_ => false
}
}

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@ -22,6 +22,7 @@ pub mod ptr_arg;
pub mod needless_bool;
pub mod approx_const;
pub mod eta_reduction;
pub mod identity_op;
#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
@ -38,6 +39,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
reg.register_lint_pass(box misc::FloatCmp as LintPassObject);
reg.register_lint_pass(box misc::Precedence as LintPassObject);
reg.register_lint_pass(box eta_reduction::EtaPass as LintPassObject);
reg.register_lint_pass(box identity_op::IdentityOp as LintPassObject);
reg.register_lint_group("clippy", vec![types::BOX_VEC, types::LINKEDLIST,
misc::SINGLE_MATCH, misc::STR_TO_STRING,
@ -50,5 +52,6 @@ pub fn plugin_registrar(reg: &mut Registry) {
misc::CMP_NAN, misc::FLOAT_CMP,
misc::PRECEDENCE,
eta_reduction::REDUNDANT_CLOSURE,
identity_op::IDENTITY_OP,
]);
}

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@ -5,7 +5,7 @@ const THREE_BITS : i64 = 7;
const EVEN_MORE_REDIRECTION : i64 = THREE_BITS;
#[deny(bad_bit_mask)]
#[allow(ineffective_bit_mask)]
#[allow(ineffective_bit_mask, identity_op)]
fn main() {
let x = 5;

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@ -6,6 +6,7 @@ fn id<X>(x: X) -> X {
}
#[deny(eq_op)]
#[allow(identity_op)]
fn main() {
// simple values and comparisons
1 == 1; //~ERROR

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@ -0,0 +1,24 @@
#![feature(plugin)]
#![plugin(clippy)]
const ONE : i64 = 1;
const NEG_ONE : i64 = -1;
const ZERO : i64 = 0;
#[deny(identity_op)]
fn main() {
let x = 0;
x + 0; //~ERROR
0 + x; //~ERROR
x - ZERO; //~ERROR
x | (0); //~ERROR
((ZERO)) | x; //~ERROR
x * 1; //~ERROR
1 * x; //~ERROR
x / ONE; //~ERROR
x & NEG_ONE; //~ERROR
-1 & x; //~ERROR
}