63 lines
1.9 KiB
Rust
63 lines
1.9 KiB
Rust
use rustc::lint::*;
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use rustc_front::hir::*;
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use syntax::codemap::Span;
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use consts::{constant_simple, is_negative};
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use consts::Constant::ConstantInt;
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use utils::{span_lint, snippet, in_macro};
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declare_lint! { pub IDENTITY_OP, Warn,
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"using identity operations, e.g. `x + 0` or `y / 1`" }
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#[derive(Copy,Clone)]
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pub struct IdentityOp;
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impl LintPass for IdentityOp {
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fn get_lints(&self) -> LintArray {
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lint_array!(IDENTITY_OP)
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}
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}
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impl LateLintPass for IdentityOp {
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fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
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if in_macro(cx, e.span) { return; }
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if let ExprBinary(ref cmp, ref left, ref right) = e.node {
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match cmp.node {
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BiAdd | BiBitOr | BiBitXor => {
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check(cx, left, 0, e.span, right.span);
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check(cx, right, 0, e.span, left.span);
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},
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BiShl | BiShr | BiSub =>
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check(cx, right, 0, e.span, left.span),
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BiMul => {
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check(cx, left, 1, e.span, right.span);
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check(cx, right, 1, e.span, left.span);
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},
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BiDiv =>
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check(cx, right, 1, e.span, left.span),
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BiBitAnd => {
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check(cx, left, -1, e.span, right.span);
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check(cx, right, -1, e.span, left.span);
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},
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_ => ()
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}
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}
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}
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}
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fn check(cx: &LateContext, e: &Expr, m: i8, span: Span, arg: Span) {
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if let Some(ConstantInt(v, ty)) = constant_simple(e) {
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if match m {
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0 => v == 0,
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-1 => is_negative(ty) && v == 1,
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1 => !is_negative(ty) && v == 1,
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_ => unreachable!(),
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} {
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span_lint(cx, IDENTITY_OP, span, &format!(
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"the operation is ineffective. Consider reducing it to `{}`",
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snippet(cx, arg, "..")));
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}
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}
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}
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