81 lines
2.7 KiB
Rust
81 lines
2.7 KiB
Rust
use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::ty;
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use rustc::{declare_lint_pass, declare_tool_lint};
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use syntax::source_map::Span;
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use crate::consts::{constant_simple, Constant};
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use crate::utils::{clip, in_macro, snippet, span_lint, unsext};
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declare_clippy_lint! {
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/// **What it does:** Checks for identity operations, e.g., `x + 0`.
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///
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/// **Why is this bad?** This code can be removed without changing the
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/// 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:**
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/// ```rust
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/// x / 1 + 0 * 1 - 0 | 0
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/// ```
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pub IDENTITY_OP,
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complexity,
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"using identity operations, e.g., `x + 0` or `y / 1`"
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}
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declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
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if in_macro(e.span) {
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return;
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}
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if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
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match cmp.node {
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BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
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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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BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
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BinOpKind::Mul => {
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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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BinOpKind::Div => check(cx, right, 1, e.span, left.span),
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BinOpKind::BitAnd => {
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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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#[allow(clippy::cast_possible_wrap)]
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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)) = constant_simple(cx, cx.tables, e) {
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let check = match cx.tables.expr_ty(e).sty {
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ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
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ty::Uint(uty) => clip(cx.tcx, !0, uty),
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_ => return,
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};
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if match m {
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0 => v == 0,
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-1 => v == check,
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1 => v == 1,
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_ => unreachable!(),
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} {
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span_lint(
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cx,
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IDENTITY_OP,
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span,
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&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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}
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}
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