71 lines
2.3 KiB
Rust
71 lines
2.3 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, Constant};
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use utils::{span_lint, snippet, in_macro};
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/// **What it does:** This lint checks for identity operations, e.g. `x + 0`. It is `Warn` by default.
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///
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/// **Why is this bad?** This code can be removed without changing the meaning. So it just obscures what's going on. Delete it mercilessly.
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///
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/// **Known problems:** None
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///
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/// **Example:** `x / 1 + 0 * 1 - 0 | 0`
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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) {
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return;
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}
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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 => 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 => 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(Constant::Int(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,
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IDENTITY_OP,
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span,
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&format!("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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