67 lines
2.3 KiB
Rust
67 lines
2.3 KiB
Rust
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use rustc::lint::*;
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use rustc_front::hir::*;
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use utils::{differing_macro_contexts, snippet_opt, span_lint_and_then, SpanlessEq};
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use syntax::codemap::mk_sp;
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/// **What it does:** This lints `foo = bar; bar = foo` sequences.
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///
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/// **Why is this bad?** This looks like a failed attempt to swap.
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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,ignore
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/// a = b;
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/// b = a;
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/// ```
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declare_lint! {
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pub SUSPICIOUS_SWAP,
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Warn,
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"`foo = bar; bar = foo` sequence"
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}
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#[derive(Copy,Clone)]
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pub struct Swap;
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impl LintPass for Swap {
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fn get_lints(&self) -> LintArray {
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lint_array![SUSPICIOUS_SWAP]
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}
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}
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impl LateLintPass for Swap {
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fn check_block(&mut self, cx: &LateContext, block: &Block) {
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for w in block.stmts.windows(2) {
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if_let_chain!{[
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let StmtSemi(ref first, _) = w[0].node,
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let StmtSemi(ref second, _) = w[1].node,
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!differing_macro_contexts(first.span, second.span),
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let ExprAssign(ref lhs0, ref rhs0) = first.node,
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let ExprAssign(ref lhs1, ref rhs1) = second.node,
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SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1),
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SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0)
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], {
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let (what, lhs, rhs) = if let (Some(first), Some(second)) = (snippet_opt(cx, lhs0.span), snippet_opt(cx, rhs0.span)) {
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(format!(" `{}` and `{}`", first, second), first, second)
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} else {
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("".to_owned(), "".to_owned(), "".to_owned())
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};
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let span = mk_sp(first.span.lo, second.span.hi);
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span_lint_and_then(cx,
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SUSPICIOUS_SWAP,
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span,
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&format!("this looks like you are trying to swap{}", what),
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|db| {
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if !what.is_empty() {
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db.span_suggestion(span, "try",
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format!("std::mem::swap({}, {})", lhs, rhs));
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db.fileline_note(span, "or maybe you should use `std::mem::replace`?");
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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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