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https://github.com/rust-lang/rust-clippy
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Lint manual swaps
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4 changed files with 139 additions and 38 deletions
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@ -8,11 +8,12 @@ A collection of lints to catch common mistakes and improve your Rust code.
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[Jump to usage instructions](#usage)
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##Lints
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There are 126 lints included in this crate:
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There are 127 lints included in this crate:
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name | default | meaning
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---------------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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[absurd_extreme_comparisons](https://github.com/Manishearth/rust-clippy/wiki#absurd_extreme_comparisons) | warn | a comparison involving a maximum or minimum value involves a case that is always true or always false
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[almost_swapped](https://github.com/Manishearth/rust-clippy/wiki#almost_swapped) | warn | `foo = bar; bar = foo` sequence
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[approx_constant](https://github.com/Manishearth/rust-clippy/wiki#approx_constant) | warn | the approximate of a known float constant (in `std::f64::consts` or `std::f32::consts`) is found; suggests to use the constant
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[bad_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask) | warn | expressions of the form `_ & mask == select` that will only ever return `true` or `false` (because in the example `select` containing bits that `mask` doesn't have)
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[block_in_if_condition_expr](https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_expr) | warn | braces can be eliminated in conditions that are expressions, e.g `if { true } ...`
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@ -62,6 +63,7 @@ name
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[let_and_return](https://github.com/Manishearth/rust-clippy/wiki#let_and_return) | warn | creating a let-binding and then immediately returning it like `let x = expr; x` at the end of a block
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[let_unit_value](https://github.com/Manishearth/rust-clippy/wiki#let_unit_value) | warn | creating a let binding to a value of unit type, which usually can't be used afterwards
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[linkedlist](https://github.com/Manishearth/rust-clippy/wiki#linkedlist) | warn | usage of LinkedList, usually a vector is faster, or a more specialized data structure like a VecDeque
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[manual_swap](https://github.com/Manishearth/rust-clippy/wiki#manual_swap) | warn | manual swap
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[map_clone](https://github.com/Manishearth/rust-clippy/wiki#map_clone) | warn | using `.map(|x| x.clone())` to clone an iterator or option's contents (recommends `.cloned()` instead)
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[map_entry](https://github.com/Manishearth/rust-clippy/wiki#map_entry) | warn | use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`
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[match_bool](https://github.com/Manishearth/rust-clippy/wiki#match_bool) | warn | a match on boolean expression; recommends `if..else` block instead
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@ -114,7 +116,6 @@ name
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[string_to_string](https://github.com/Manishearth/rust-clippy/wiki#string_to_string) | warn | calling `String::to_string` which is inefficient
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[suspicious_assignment_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_assignment_formatting) | warn | suspicious formatting of `*=`, `-=` or `!=`
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[suspicious_else_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_else_formatting) | warn | suspicious formatting of `else if`
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[suspicious_swap](https://github.com/Manishearth/rust-clippy/wiki#suspicious_swap) | warn | `foo = bar; bar = foo` sequence
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[temporary_assignment](https://github.com/Manishearth/rust-clippy/wiki#temporary_assignment) | warn | assignments to temporaries
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[toplevel_ref_arg](https://github.com/Manishearth/rust-clippy/wiki#toplevel_ref_arg) | warn | An entire binding was declared as `ref`, in a function argument (`fn foo(ref x: Bar)`), or a `let` statement (`let ref x = foo()`). In such cases, it is preferred to take references with `&`.
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[trivial_regex](https://github.com/Manishearth/rust-clippy/wiki#trivial_regex) | warn | finds trivial regular expressions in `Regex::new(_)` invocations
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@ -287,7 +287,8 @@ pub fn plugin_registrar(reg: &mut Registry) {
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returns::LET_AND_RETURN,
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returns::NEEDLESS_RETURN,
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strings::STRING_LIT_AS_BYTES,
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swap::SUSPICIOUS_SWAP,
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swap::ALMOST_SWAPPED,
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swap::MANUAL_SWAP,
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temporary_assignment::TEMPORARY_ASSIGNMENT,
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transmute::USELESS_TRANSMUTE,
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types::ABSURD_EXTREME_COMPARISONS,
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140
src/swap.rs
140
src/swap.rs
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@ -1,7 +1,26 @@
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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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use utils::{differing_macro_contexts, snippet_opt, span_lint_and_then, SpanlessEq};
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/// **What it does:** This lints manual swapping.
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///
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/// **Why is this bad?** The `std::mem::swap` function exposes the intent better without
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/// deinitializing or copying either variable.
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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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/// let t = b;
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/// b = a;
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/// a = t;
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/// ```
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declare_lint! {
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pub MANUAL_SWAP,
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Warn,
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"manual swap"
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}
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/// **What it does:** This lints `foo = bar; bar = foo` sequences.
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///
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@ -15,7 +34,7 @@ use syntax::codemap::mk_sp;
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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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pub ALMOST_SWAPPED,
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Warn,
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"`foo = bar; bar = foo` sequence"
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}
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@ -25,42 +44,95 @@ 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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lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
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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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check_manual_swap(cx, block);
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check_suspicious_swap(cx, block);
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}
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}
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/// Implementation of the `MANUAL_SWAP` lint.
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fn check_manual_swap(cx: &LateContext, block: &Block) {
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for w in block.stmts.windows(3) {
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if_let_chain!{[
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// let t = foo();
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let StmtDecl(ref tmp, _) = w[0].node,
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let DeclLocal(ref tmp) = tmp.node,
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let Some(ref tmp_init) = tmp.init,
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let PatKind::Ident(_, ref tmp_name, None) = tmp.pat.node,
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// foo() = bar();
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let StmtSemi(ref first, _) = w[1].node,
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let ExprAssign(ref lhs1, ref rhs1) = first.node,
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// bar() = t;
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let StmtSemi(ref second, _) = w[2].node,
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let ExprAssign(ref lhs2, ref rhs2) = second.node,
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let ExprPath(None, ref rhs2) = rhs2.node,
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rhs2.segments.len() == 1,
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tmp_name.node.name.as_str() == rhs2.segments[0].identifier.name.as_str(),
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SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1),
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SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2)
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], {
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let (what, lhs, rhs) = if let (Some(first), Some(second)) = (snippet_opt(cx, lhs1.span), snippet_opt(cx, rhs1.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(tmp.span.lo, second.span.hi);
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span_lint_and_then(cx,
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MANUAL_SWAP,
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span,
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&format!("this looks like you are swapping{} manually", 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(&mut {}, &mut {})", 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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/// Implementation of the `ALMOST_SWAPPED` lint.
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fn check_suspicious_swap(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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ALMOST_SWAPPED,
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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(&mut {}, &mut {})", 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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@ -4,6 +4,8 @@
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#![deny(clippy)]
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#![allow(unused_assignments)]
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struct Foo(u32);
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fn main() {
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let mut a = 42;
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let mut b = 1337;
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@ -12,6 +14,31 @@ fn main() {
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b = a;
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//~^^ ERROR this looks like you are trying to swap `a` and `b`
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//~| HELP try
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//~| SUGGESTION std::mem::swap(a, b);
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//~| SUGGESTION std::mem::swap(&mut a, &mut b);
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//~| NOTE or maybe you should use `std::mem::replace`?
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let t = a;
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a = b;
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b = t;
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//~^^^ ERROR this looks like you are swapping `a` and `b` manually
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//~| HELP try
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//~| SUGGESTION std::mem::swap(&mut a, &mut b);
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//~| NOTE or maybe you should use `std::mem::replace`?
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let mut c = Foo(42);
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c.0 = a;
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a = c.0;
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//~^^ ERROR this looks like you are trying to swap `c.0` and `a`
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//~| HELP try
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//~| SUGGESTION std::mem::swap(&mut c.0, &mut a);
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//~| NOTE or maybe you should use `std::mem::replace`?
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let t = c.0;
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c.0 = a;
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a = t;
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//~^^^ ERROR this looks like you are swapping `c.0` and `a` manually
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//~| HELP try
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//~| SUGGESTION std::mem::swap(&mut c.0, &mut a);
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//~| NOTE or maybe you should use `std::mem::replace`?
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}
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